Research Quarterly for Exercise and Sport, 86, 63–70, 2015 Copyright q SHAPE America ISSN 0270-1367 print/ISSN 2168-3824 online DOI: 10.1080/02701367.2014.977432
Cardiorespiratory and Biomechanical Responses to Simulated Recreational Horseback Riding in Healthy Children Brandon R. Rigby, Zacharias Papadakis, Annie A. Bane, Jin K. Park, and Peter W. Grandjean Baylor University
Purpose: The purpose of this study was to determine the reliability of cardiorespiratory and pelvic kinematic responses to simulated horseback riding (SHBR) and to characterize responses to SHBR relative to walking in apparently healthy children. Method: Fifteen healthy children (Mage ¼ 9.5 ^ 2.6 years) completed SHBR on a commercially available simulator at low intensity (0.27 Hz) and high intensity (0.65 Hz) during 3 sessions on different occasions. Heart rate (HR), blood pressure, and respiratory gases were measured at rest and during steadystate exercise at both intensities. Pelvic displacement was measured during steady-state exercise. Rate of energy expenditure, mean arterial pressure, and rate pressure product (RPP) were calculated. Participants also walked on a treadmill for 26.8 m/min to 80.5 m/min in 13.4m/min increments at 0% grade during 1 session to compare cardiorespiratory responses with those of SHBR. Results: Physiological variables across all 3 SHBR sessions were similar at both intensities ( p . .05 for all). Intraclass correlation coefficients (ICCs) and coefficients of variation indicate good to modest reliability of cardiorespiratory measures during SHBR (ICCs ¼ .542 – .996 for oxygen consumption, energy expenditure, and RPP). Cardiorespiratory variables, except for HR, were 2% to 19% greater, and pelvic displacement was up to 37% greater with high-intensity riding. Treadmill walking at all speeds elicited greater physiological responses compared with SHBR ( p , .05). Conclusion: Cardiorespiratory responses and pelvic kinematics are reproducible with SHBR in young children, and these responses were lower than those elicited by slow treadmill walking. Keywords: cardiovascular responses, horseback riding simulator, kinematics, youth
Many young people experience horseback riding (HBR) as outdoor recreation, and some forms of HBR are gaining widespread acceptance as therapeutic interventions for children and youth (Millhouse-Flourie, 2004). Results from a growing body of evidence support the efficacy of HBR in special populations with improvements reported for gross motor function (Casady & Nichols-Larsen, 2004; McGibbon, Andrade, Widener, & Cintas, 1998; Sterba, Rogers, France, & Vokes, 2002), posture (Bertoti, 1988; Haehl, Giuliani, & Submitted September 18, 2013; accepted May 20, 2014. Correspondence should be addressed to Peter W. Grandjean, Baylor Laboratories for Exercise Science and Technology, Center for Healthy Living, Baylor University, One Bear Place #97313, Waco, TX 76798-7313. E-mail: [email protected]
Lewis, 1999; Shurtleff & Engsberg, 2012), balance (Hammer et al., 2005; Silkwood-Sherer, Killian, Long, & Martin, 2012; Silkwood-Sherer & Warmbier, 2007), spasticity (Hammer et al., 2005; Lechner et al., 2003; Lechner, Kakebeeke, Hegemann, & Baumberger, 2007), muscle asymmetry (Benda, McGibbon, & Grant, 2003; McGibbon, Benda, Duncan, & Silkwood-Sherer, 2009), energy expenditure (Bongers & Takken, 2012; McGibbon et al., 1998), and mental health (Davis et al., 2009; McGibbon et al., 2009; MillhouseFlourie, 2004). The benefits attributed to HBR are interesting because it is a physical activity that has largely gone uncharacterized, particularly with respect to cardiorespiratory and kinematic responses. Indeed, we know very little about the physical responses and training adaptations to HBR or how these
64
B. R. RIGBY ET AL.
compare to common physical activities, such as walking, which are part of current recommendations and position statements for improving and maintaining health and fitness (e.g., Centers for Disease Control and Prevention, 2011; Morris, 2009). Limited information exists on the cardiorespiratory and biomechanical responses to HBR, due in part to a host of factors that confound measurement precision. Obtaining reproducible movements from the horse is probably the most obvious among confounding factors (Devienne & Guezennec, 2000). Movements of the rider in response to the horse augment the variability. Environmental conditions, such as temperature and humidity, and the logistics of collecting respiratory and kinematic data as the horse and rider move throughout a large space add to the difficulties in characterizing the physical responses to HBR. Moreover, even if most of these factors are controlled or accounted for during a single measurement session, reproducing the same conditions becomes virtually impossible when attempting to obtain preand post-HBR intervention measurements that are often separated by many HBR sessions and several weeks. One way to address the variability in measuring the riders’ cardiorespiratory and biomechanical responses during HBR is to simulate movements commonly made by the horse with a stationary HBR simulator in an environmentally controlled setting. Indeed, commercially available HBR simulators are increasingly being used to supplement HBR and to study physical responses that may occur during recreational HBR (Dhindsa, Barnes, DeVan, Nualnim, & Tanaka, 2008; Shimomura et al., 2009). The use of a simulator eliminates physiologic influences that may be due to the affect between the rider and the horse. In addition, the use of an HBR simulator may enable investigators to quantify changes in physiological responses that are thought to occur with habitual HBR. Determining the reliability of such measurements and comparing the physiological responses to those of common physical activities may be particularly useful for quantifying the benefits of HBR. Our primary research objective was to determine the variation in cardiorespiratory and pelvic kinematic responses during simulated horseback riding (SHBR) in children. We employed simulator settings that approximate a horse’s movement at a slow-to-moderate walk (i.e., below a trot). A second objective was to compare the cardiovascular responses to SHBR relative to those measured during walking—one of the most common and well-characterized physical activities.
METHODS Participants This research was approved by our university’s Institutional Review Board for Research with Human Participants
(Approved Protocol #278898-1). We recruited apparently healthy children aged 6 to 14 years old with little or no previous HBR experience. Enrollment was open to boys and girls of all ethnicities. Flyers were sent to schools and various organizations, such as the YMCA, with information to parents including a brief explanation of the study and contact information. Recruitment was completed via e-mail or personal contact with a parent/guardian. On the first visit, designed as a screening and familiarization session, parents answered questions concerning their child’s medical history. Both the child and parent were familiarized with the study protocol through a verbal and written explanation outlining the study design and were introduced to and familiarized with all of the equipment used in the study (e.g., allowed to walk on the treadmill and ride on the simulator). All details of the study were reviewed again and parents were given a consent document and children were given an age-appropriate assent document to read, review, and sign. Volunteer children were screened to include those: without a diagnosed congenital heart condition or cardiovascular condition that would preclude them from vigorous exercise; without orthopedic problems that could be exacerbated by exercise; who were not currently taking medications that would interfere with heart rate (HR), blood pressure (BP), or respiration during exercise (e.g., Ritalin, Adderall, insulin, etc.); and who were free from any condition that would prevent them from participating safely in this study. Of the 16 children who responded via their parent, 15 met requirements (8 girls and 7 boys) and completed all aspects of the study. One child dropped out of the study because he found the equipment we used to measure primary variables of interest (e.g., HR monitor, mask for ventilation [VE] and respiratory gas collection) to be too unpleasant. Preliminary Procedures On the second lab visit, the participants’ height, weight, and body composition were measured. Weight was assessed using a digital scale and height was assessed using a stadiometer attached to the scale. Body composition was determined by dual X-ray absorptiometry (Hologic 4500W, Hologic Inc., Bedford, MA). Participants were fitted with an HR monitor (Polar Electro Inc., Lake Success, NY), and HR, VE, and respiratory gases (e.g., rates of oxygen consumption [VO2] and carbon dioxide production) were measured continuously during 5 min of seated rest. BP was measured once during the rest period and was assessed manually using an aneroid sphygmomanometer and stethoscope. Respiratory gases were measured using an integrated metabolic system (ParvoMedics, Sandy, UT). Just after resting measurements, participants underwent a graded exercise test on a motorized treadmill (Trackmaster, Full Vision Inc., Newton, KS). Participants began by walking at
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
26.8 m/min and progressed to 80.5 m/min in 13.4-m/min increments while maintaining 0% grade. Each stage lasted for 5 min to achieve a steady state at each walking speed. HR, BP, and respiratory gases were measured throughout exercise, and mean arterial pressure (MAP), rate pressure product (RPP), and kilocalorie (kcal) expenditure were calculated from these direct measures. Walking is one of the most common activities of daily living (Ridley, Ainsworth, & Olds, 2008). Physical responses to other activities are frequently compared to walking (Harrell et al., 2005; Ridley et al., 2008). Therefore, we compared the cardiorespiratory responses obtained during the treadmill walking session to the magnitude of responses obtained during the SHBR sessions. Simulated Horseback Riding Testing Sessions We collected all SHBR data during three testing sessions. The protocol for each of the three testing sessions was identical. Sessions were scheduled so that there was a minimum of 2 days and a maximum of 7 days between sessions. Participants were fitted with an HR monitor. A motion capture system (PhaseSpace Inc., San Leandro, CA) was used to quantify anteroposterior, medial-lateral, and vertical pelvic displacement during steady-state SHBR. An aluminum bar affixed with two markers, emitting infrared light, on each end of the bar was placed on the superior aspect of the participant’s posterior pelvis. Another aluminum bar, with a similar configuration, was placed on the superior aspect of the participant’s anterior pelvis. Within each session, HR, VE, and respiratory gases were measured continuously during 5 min of seated rest. BP was measured once during the rest period. Participants rode on an HBR simulator (Core Trainerw, Panasonic Inc., Secaucus, NJ) at two intensity levels. The lower-intensity level (0.27 Hz) corresponded to a very slow-paced walk for a horse. The higher-intensity level (0.65 Hz) corresponded to a fast-paced walk. Participants rode at each intensity level for 5 min to achieve a steady state. HR, BP, and respiratory gases were measured after the participants achieved steady state at each exercise intensity, and MAP, RPP, and kcal expenditure were calculated from these direct measures. Pelvic kinematics were measured during several gait cycles once the participant reached a steady state. Statistical Analysis A sample size of nine was calculated based on an average paired difference to be detected in absolute VO2 in healthy children of 0.5 mL/kg/min, standard deviation of 0.4 mL/kg/ min, alpha error probability of .05, and statistical power of 90%. The cardiorespiratory dependent variables were VE, VO 2 absolute, VO 2 relative to body weight, kcal
65
expenditure, HR, systolic blood pressure (SBP), diastolic blood pressure, MAP, and RPP. The dependent kinematic data were pelvic displacements along the anteroposterior, vertical, and medial-lateral axes. Independent variables were the sessions (Sessions 1, 2, and 3) and simulator intensity (low ¼ 0.27 Hz; high ¼ 0.65 Hz). Treadmill intensities of 26.8 m/min, 40.2 m/min, 53.6 m/min, 67.1 m/min, and 80.5 m/min were included as independent levels when SHBR was compared with walking intensities. To address our first objective, 2 (intensity) £ 3 (session) repeated-measure analyses of variances (ANOVAs) were used to determine reliability of cardiorespiratory and kinematic variables. Intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) were calculated for measured and calculated dependent variables. Our second objective was addressed using 1 £ 7 (intensities: SHBR at low and high intensity and treadmill walking at 26.8 m/min, 40.2 m/min, 53.6 m/min, 67.1 m/ min, and 80.5 m/min) ANOVAs to compare cardiorespiratory data between SHBR and walking. Duncan’s multiple range tests were used to follow up significant intensity differences. A comparison error rate was set at p , .05. All statistical procedures were performed using Statistical Analysis Software (SAS) Version 9.2 (SAS, Cary, NC). Effect sizes were calculated according to methods previously described by Cohen (1988) and more recently by Rhea (Rhea, 2004) for repeated measurements.
RESULTS The participant characteristics can be found in Table 1. The maximum and minimum values and ranges for each characteristic are given for the cohort. Our primary objective was to determine reliability in cardiorespiratory and pelvic kinematic responses to SHBR. Cardiorespiratory responses among sessions during SHBR are presented in Table 2a (for rest) and in Tables 2b and 2c (for low and high intensity). Dependent-variable responses were similar across all testing sessions ( p . .05 for all), and
TABLE 1 Characteristics of All Participants Variable
Mean ^ SD
Max
Min
Range
Age (years) Height (cm) Weight (kg) BMI (kg/m2) % Body Fat
9.5 ^ 2.6 142.1 ^ 15.8 41.5 ^ 18.6 19.6 ^ 4.9 27 ^ 8
14.2 170.2 86.3 29.8 42
6.7 120.7 20.8 13.6 14
7.5 49.5 65.5 16.2 28
Note. Data were obtained from 15 healthy children (8 girls and 7 boys). All values are presented as means ^ standard deviation. BMI ¼ body mass index; % Body Fat ¼ body fat expressed as a percentage of body weight; Max ¼ maximum value; Min ¼ minimum value.
66
B. R. RIGBY ET AL. TABLE 2 Variation of Cardiorespiratory Variables at Rest and at Both Intensities
Variable a. Rest VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP b. Low Intensity VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP c. High Intensity VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Session 1
Session 2
Session 3
ANOVA p Value
ICC
CV
7.7 ^ 0.4 5.6 ^ 0.3 0.22 ^ 0.02 1.1 ^ 0.1 94 ^ 2 77.8 ^ 2.9 97 ^ 3
7.6 ^ 0.3 5.7 ^ 0.4 0.22 ^ 0.01 1.1 ^ 0.1 93 ^ 1 74.1 ^ 2.6 94 ^ 3
7.9 ^ 0.4 5.8 ^ 0.3 0.22 ^ 0.02 1.1 ^ 0.3 98 ^ 3 73.6 ^ 3.4 97 ^ 3
.5876 .9642 .7734 .8575 .0730 .6030 .4939
.731 .988 .938 .961 .019 .381 .542
9.3 9.6 10.0 9.9 5.7 12.6 8.9
8.4 ^ 0.4 6.2 ^ 0.4 0.24 ^ 0.02 1.2 ^ 0.1 94 ^ 2 77.2 ^ 2.7 97 ^ 3
8.3 ^ 0.5 6.1 ^ 0.3 0.24 ^ 0.02 1.2 ^ 0.1 95 ^ 2 75.3 ^ 2.9 97 ^ 3
8.3 ^ 0.4 6.0 ^ 0.3 0.23 ^ 0.02 1.1 ^ 0.1 97 ^ 2 74.7 ^ 3.3 97 ^ 3
.9698 .2247 .4132 .4812 .4933 .9088 .9941
.994 .659 .898 .924 .328 .851 .996
6.8 8.3 8.6 7.5 5.1 11.4 7.8
9.9 ^ 0.7 7.1 ^ 0.3 0.29 ^ 0.03 1.4 ^ 0.2 96 ^ 2 79.3 ^ 2.6 103 ^ 4
9.8 ^ 0.8 7.0 ^ 0.3 0.28 ^ 0.03 1.4 ^ 0.2 97 ^ 2 77.3 ^ 3.0 103 ^ 3
10.1 ^ 0.8 7.1 ^ 0.3 0.28 ^ 0.03 1.3 ^ 0.2 100 ^ 2 75.7 ^ 3.2 102 ^ 3
.6688 .5314 .5123 .2703 .1319 .7255 .9295
.960 .781 .971 .872 .081 .547 .933
9.5 8.2 8.1 10.9 5.0 11.7 9.9
Note. Data were obtained from 15 participants (8 girls and 7 boys). Variables are presented as means ^ standard error. VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/ min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100); ANOVA ¼ analysis of variance; ICC ¼ intraclass correlation coefficient; CV ¼ coefficient of variation (standard deviation/mean £ 100).
with the exception of HR, repeated variable responses demonstrated high ICCs. The range of ICCs from rest to high-intensity exercise was as follows: .731 to .994 for VE; .898 to .971 for absolute VO2; .872 to .961 for kcal expenditure; and .542 to .996 for RPP. Pelvic displacements along each axis between sessions for both intensities during SHBR are presented in Table 3. There were no significant differences in kinematic responses between the three sessions ( p . .05 for all), but
repeat measurements at similar SHBR intensities demonstrated low ICCs and high CVs. Cardiorespiratory and pelvic kinematic responses are presented for rest and both intensities during SHBR in Table 4. Absolute and relative VO2 ( p , .0001 for both), VE ( p , .0001), MAP ( p ¼ .0002), RPP ( p , .0001), and kcal expenditure ( p ¼ .0004) were greater with high-intensity riding compared with rest and low-intensity riding. HR was not different across intensities ( p ¼ .0831). Pelvic displace-
TABLE 3 Variation of Pelvic Kinematics at Rest and at Both Intensities Variable a. Low Intensity A-P axis V axis M-L axis b. High Intensity A-P axis V axis M-L axis
Session 1
Session 2
Session 3
ANOVA p Value
ICC
CV
10.7 ^ 0.2 2.1 ^ 0.2 8.0 ^ 0.2
10.8 ^ 0.2 1.8 ^ 0.1 8.5 ^ 0.2
10.6 ^ 0.4 1.9 ^ 0.2 8.0 ^ 0.3
.8838 .5982 .1298
.874 .200 .014
7.5 25.3 8.5
13.3 ^ 1.0 3.1 ^ 0.5 9.6 ^ 0.6
11.5 ^ 0.3 2.2 ^ 0.2 8.6 ^ 0.3
12.2 ^ 0.5 2.4 ^ 0.2 9.4 ^ 0.6
.0976 .0561 .2502
.026 .187 .455
12.0 30.5 12.6
Note. Data were obtained from 15 participants (8 girls and 7 boys). All displacements are in centimeters. Displacements are reported as means ^ standard error. A-P ¼ anterior-posterior; V ¼ vertical; M-L ¼ medial-lateral; ANOVA ¼ analysis of variance; ICC ¼ intraclass correlation coefficient; CV ¼ coefficient of variation (standard deviation/mean £ 100).
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
67
TABLE 4 Cardiorespiratory and Kinematic Variables at Rest and During Simulated HBR for All Participants Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP A-P axis V axis M-L axis
Rest
Low Intensity
High Intensity
ANOVA p Value
7.7 ^ 0.2a 5.7 ^ 0.2a 0.22 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.2 ^ 1.5a 96 ^ 2a n/a n/a n/a
8.3 ^ 0.3a 6.1 ^ 0.2a 0.24 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.8 ^ 1.7a 97 ^ 2a 10.7 ^ 0.2a 1.9 ^ 0.1a 8.2 ^ 0.1a
9.9 ^ 0.4b 7.0 ^ 0.2b 0.28 ^ 0.02b 1.4 ^ 0.1b 98 ^ 1a 77.5 ^ 1.7b 103 ^ 2b 12.3 ^ 0.4b 2.6 ^ 0.2b 9.2 ^ 0.3b
,.0001 ,.0001 ,.0001 .0004 .0831 .0002 ,.0001 .0045 .0013 .0383
Note. Data were obtained from 15 participants (8 girls and 7 boys). All variables are presented as means ^ standard error; means with the same superscript are statistically similar ( p . .05). HBR ¼ horseback riding; ANOVA ¼ analysis of variance; VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100); A-P ¼ anterior-posterior; V ¼ vertical; M-L ¼ medial-lateral. No kinematic data were collected at rest.
ments along all three axes were greater with high-intensity riding compared with low-intensity riding (anteroposterior axis, p ¼ .0045; vertical axis, p ¼ .0013; medial-lateral axis, p ¼ .0383). A second objective was to compare physiological responses to SHBR to those measured during slow-tobrisk walking. Cardiorespiratory measurements at rest and responses during SHBR and at different submaximal treadmill walking intensities are presented in Table 5. All cardiorespiratory variables measured at steady state during low-intensity SHBR (0.27 Hz) were not different from resting values. With the exception of HR, cardiorespiratory values were greater during SHBR at the higher intensity (0.65 Hz) compared with those obtained at rest or during low-intensity SHBR. All cardiorespiratory responses to treadmill walking at speeds up to 80.5 m/min were of greater magnitude than what was observed at high-intensity SHBR. In fact,
treadmill walking at 26.8 m/min elicited greater cardiorespiratory responses than high-intensity SHBR for all variables but MAP. Effect sizes for cardiorespiratory responses to SHBR and a treadmill are presented in Table 6. DISCUSSION The purpose of this study was to characterize cardiorespiratory and pelvic kinematic responses to SHBR and the variation in these responses in apparently healthy children. Our protocol enabled us to determine cardiovascular responses, energy expenditure, and pelvic movement in a controlled environment. The HBR simulator allowed us to specifically quantify the work rate at low (0.27 Hz) and high (0.65 Hz) intensities, approximating HBR at slow and brisk walking paces. Our results show that in a controlled setting, the pulmonary responses and cardiovascular responses— with the exception of HR—are reproducible. The HR and
TABLE 5 Cardiorespiratory Variables at Rest and During SHBR and Treadmill Walking SHBR Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Treadmill Walking
Rest
Low Intensity
High Intensity
26.8 m/min
40.2 m/min
53.6 m/min
67.1 m/min
80.5 m/min
7.7 ^ 0.2a 5.7 ^ 0.2a 0.22 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.2 ^ 1.5a 96 ^ 2a
8.3 ^ 0.3a 6.1 ^ 0.2a 0.24 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.8 ^ 1.7a 97 ^ 2a
9.9 ^ 0.4b 7.0 ^ 0.2b 0.28 ^ 0.02b 1.4 ^ 0.1b 98 ^ 1a 77.5 ^ 1.7b 103 ^ 2b
12.0 ^ 0.8c 9.8 ^ 0.7c 0.39 ^ 0.04c 1.9 ^ 0.2c 106 ^ 3b 80.8 ^ 3.2bc 116 ^ 5c
13.1 ^ 0.9cd 10.7 ^ 0.8c 0.43 ^ 0.04cd 2.1 ^ 0.2cd 108 ^ 2b 83.9 ^ 3.0cd 127 ^ 5d
14.4 ^ 0.9d 11.9 ^ 0.7d 0.48 ^ 0.05de 2.3 ^ 0.2de 114 ^ 2c 85.5 ^ 2.9cde 142 ^ 5e
16.0 ^ 1.2e 13.1 ^ 0.6e 0.54 ^ 0.05e 2.6 ^ 0.3e 117 ^ 2c 87.4 ^ 2.9de 150 ^ 5f
18.7 ^ 1.4f 15.5 ^ 0.6f 0.63 ^ 0.06f 3.1 ^ 0.3f 125 ^ 2d 89.5 ^ 2.9e 168 ^ 6g
Note. Data were obtained from 15 participants (8 girls and 7 boys). All variables are presented as means ^ standard error; means with the same superscript are statistically similar ( p . .05). SHBR ¼ simulated horseback riding; VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100).
68
B. R. RIGBY ET AL. TABLE 6 Effect Sizes for Cardiorespiratory Responses During SHBR and Treadmill Walking SHBR
Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Treadmill Walking
Rest-Low
Rest-High
Rest-27 m/min
Rest-54 m/min
Rest-81 m/min
0.44 0.32 0.26 0.26 0.03 0.05 0.06
1.59 1.11 1.02 0.95 0.32 0.20 0.57
1.69 2.66 1.92 1.93 0.86 0.18 1.03
2.72 3.93 2.87 2.95 1.71 0.56 2.78
4.63 6.14 4.55 4.71 2.82 0.88 4.55
Note. Data were obtained from 15 participants (8 girls and 7 boys). SHBR ¼ simulated horseback riding; VE (L/min) ¼ ventilation; absolute VO2 (L/ min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100).
pelvic kinematic responses, although not statistically different between sessions, demonstrate a substantial degree of variability. HRs were found to be of higher variability at rest and high-intensity SHBR while pelvic kinematic data became less reliable with the higher-intensity SHBR. Although HR is used to monitor exercise intensity, the greatest HR variability occurs at rest and during lightintensity activities in children (Winsley, Armstrong, Bywater, & Fawkner, 2003). The variation in HR at rest and during light activity is thought to be due to a predominating influence of the parasympathetic versus sympathetic autonomic control (Winsley et al., 2003). We attempted to control for outside influences on HR and other cardiovascular measurements by testing under standardized conditions and at the same time of day. However, it appears that many outside factors—even under controlled conditions—can add to the parasympathetic modulation and cause substantial variation in resting HR and the HR responses to SHBR. Absolute variation in the kinematic data were very small (i.e., less than 1 cm), and the displacement in each plane is small. This puts a premium on measurement precision. The largest source of variation appears to be among participants, indicating different strategies for maintaining erect postures during riding. However, the low ICCs (.100 to .378) and relatively high CVs (10% –28%) indicate that a considerable amount of individual variation also exists. Our results indicate that pelvic displacement measures can be reproduced. However, care should be taken to properly place anatomical markers and calibrate the motion capture system. Moreover, our results support the importance of specific riding instructions and protocol familiarization when measuring pelvic displacement responses during HBR. The reliability of cardiorespiratory responses and gait kinematics has been investigated in children while walking and running on a treadmill at submaximal intensities. In one study, the coefficient of reliability for VO2 was 68% in healthy boys who completed two trials of submaximal treadmill running at 120.7 m/min, 134.1 m/min, and 147.5 m/min
(Unnithan, Murray, Timmons, Buchanan, & Paton, 1995). The coefficient of reliability for VE was 50% and coefficient of reliability for HR was 94%, indicating no training (i.e., learning) effect on the cardiovascular system (Unnithan et al., 1995). In another study, 41 healthy children aged 6 years completed three 10-min walking trials on a treadmill at 80.5 m/min at 0% grade, which was preceded by a familiarization session in which the children walked for 5 min at 80.5 m/min (Tseh et al., 2000). The CV and the ICC for VO2 across the three trials was 2.0 ^ 1.5% and .96, respectively, indicating good reliability during level treadmill walking in children (Tseh et al., 2000). VO2 results from our present study appear to be consistent with the reliability estimates reported for treadmill walking in children. The reliability of VO2, HR, stride length, and vertical displacement of the hip joint was investigated in 24 children ages 7 to 11 years old (Frost, Bar-Or, Dowling, & White, 1995). The children were randomized into four groups, with one group (Group A) instructed to walk at a comfortable walking speed (ranging from 69.7 m/min to 99.2 m/min) on a treadmill. Other groups walked on the treadmill at faster speeds (Group B, þ 15% of the speed of Group A; Group C, þ 50.9 m/min of the speed of Group B; Group D, þ 15% of the speed of Group C). Each group completed two sessions, with each session consisting of six 6-min trials for each group. No statistically significant differences were reported in mean VO2, mean HR, stride length, or vertical displacement of the hip between sessions or between trials for all groups. Stride length tended to increase from Trial 1 to Trial 6 in Session 1 for all groups, while vertical displacement tended to increase from Trial 1 to Trial 6 in both sessions for Groups A through C (Frost et al., 1995). These results indicate good reliability in the cardiorespiratory variables and moderate reliability in the kinematic variables. Our present findings for SHBR indicate reliability that is consistent with what is reported in the literature for treadmill walking. That is, we demonstrate a greater degree of precision and less variation in respiratory responses than we do for pelvic displacement. However, all of the
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
physiologic and kinematic measures can be reproduced under standard conditions with reasonable reliability. A second objective of this investigation was to compare cardiorespiratory responses during SHBR to responses measured during treadmill walking. We chose walking because it is one of the most common physical activities of daily living (Centers for Disease Control and Prevention, 2011). Our results show that cardiorespiratory responses were significantly greater with treadmill walking than those measured at any intensity on the HBR simulator. Indeed, treadmill walking induced much larger effects on cardiorespiratory markers than did those observed with SHBR. In accordance with effect size interpretation proposed by Rhea (2004), the magnitude of cardiorespiratory response to SHBR might be interpreted as moderate, whereas responses to treadmill walking at slow-to-moderate speeds are large. To our knowledge, this is the first study to compare these cardiorespiratory responses between an HBR simulator and walking on a treadmill in healthy children. Our results suggest that at best, HBR may only supplement the recommended daily activity requirements for healthy children. Because of the lower cardiorespiratory requirements of SHBR and HBR, this form of physical activity may be a suitable means of transitioning children of low cardiorespiratory fitness and those with physical impairments to a more physically active lifestyle (Morris, 2009). Shimomura et al. (2009) described cardiorespiratory responses to walking and SHBR in 14 male adults. Participants rode on an HBR simulator at 0.8 Hz, 1.2 Hz, and 1.4 Hz for 3 min each with a 5-min rest period between intensities. While riding at 0.8 Hz on the simulator, the participants had a mean HR of 73 ^ 5 bpm, a mean SBP of 131 ^ 3 mmHg, and a mean VO2 of 5.1 ^ 0.3 mL/kg/min. Participants also walked on a treadmill at 2 km/h, 3 km/h, 4 km/h, 5 km/h, and 6 km/h under the same time constraints. While walking at 2 km/h, participants had a mean HR of 79 ^ 4 bpm, a mean SBP of 135 ^ 5 mmHg, and a mean VO2 of 9.6 ^ 0.3 mL/kg/min (Shimomura et al., 2009). Although no statistical comparisons were made between exercise modes, these results indicate that walking at 2 km/h elicits a greater exercise response when compared with SHBR at 0.8 Hz. These results appear to be consistent with our own data. The average relative VO2 for all participants during lowintensity riding was 6.1 mL/kg/min. This intensity is comparable to that when children (8 – 12 years old) are reading or older children (13 –15 years old) are playing a video game while standing (Harrell et al., 2005). According to the compendium of physical activities, HBR at a walking pace elicits a metabolic equivalent level of 2.5 from a child while riding (Ridley et al., 2008). This average response is similar to the intensity we observed for children riding at a high-intensity (0.65 Hz) on the HBR simulator. The slightly higher average VO2 observed by Ridley et al. (2008) may include environmental conditions or responses to riding an actual horse versus a machine. The steady-state VO2 that we
69
observed at 0.65 Hz on the simulator is comparable to children performing light activities such as brushing their teeth (Ridley et al., 2008). The average VO2 while walking at 26.8 m/min on the treadmill (9.8 mL/kg/min) is comparable to children playing with animals (light effort) or lifting weights at moderate effort (Ridley et al., 2008). One limitation of this study was that we chose not to measure maximum exercise effort and maximal oxygen consumption (VO2max). As such, we are not able to report exercise intensities in terms of a percentage of maximal HR or VO2max or expressed as a percentage of HR or VO2 reserve. Another limitation was that we did not power the study to examine variations in cardiorespiratory responses that may be, at least partially, explained by gender, physical maturity, and body composition.
CONCLUSION Our findings support the use of SHBR to quantify cardiorespiratory and biomechanical responses during HBR at a walking pace. Our results show that cardiorespiratory responses are reproducible with SHBR in young children, while pelvic kinematics are more variable. Consistent placement of markers at anatomically defined locations, specific riding instructions for participants, and familiarization of the protocol can help reduce the variation observed in the kinematic data. Physiological responses to SHBR are lower than those elicited by treadmill walking at 26.8 m/min in healthy, able-bodied children. Our findings may be interpreted in a more practical sense to mean that recreational HBR at a walking pace may not be sufficient to provide an adequate exercise response in healthy children. Instead, HBR at a walking pace might be used as a supplement to the recommended daily activity requirements in this population.
WHAT DOES THIS ARTICLE ADD? We demonstrated that the ability to quantify cardiorespiratory and pelvic kinematic variables in children is reproducible during SHBR in a controlled setting. Our results support our premise—that SHBR may be a viable means of quantifying physiological responses to HBR and changes that may result from regularly practiced HBR. These findings may be of practical significance for those utilizing HBR as a recreational activity or as a therapeutic modality. We were able to demonstrate reproducible measurements of cardiorespiratory variables and pelvic kinematics during physiologic responses that were of lower intensity than slow-paced walking. While one study characterized the effects of walking and riding an HBR simulator on HR, SBP, and VO2 in young adults (Shimomura et al., 2009), this was not the main purpose of the study, which was to compare the exercise intensity of
70
B. R. RIGBY ET AL.
a novel machine to different modes of exercise. To our knowledge, this is the first study to characterize the cardiorespiratory and pelvic kinematic responses to SHBR and to characterize the cardiorespiratory responses to SHBR relative to those measured during walking. Other studies have investigated the reliability of cardiorespiratory responses and pelvic kinematics during submaximal running and walking in children (Frost et al., 1995; Tseh et al., 2000). Ours is the first study to determine the reliability of cardiorespiratory and pelvic kinematic responses to SHBR in children. REFERENCES Benda, W., McGibbon, N. H., & Grant, K. L. (2003). Improvements in muscle symmetry in children with cerebral palsy after equine-assisted therapy (hippotherapy). Journal of Alternative and Complementary Medicine, 9, 817 –825. doi:10.1089/107555303771952163 Bertoti, D. B. (1988). Effect of therapeutic horseback riding on posture in children with cerebral palsy. Physical Therapy, 68, 1505 – 1512. Retrieved from http://ptjournal.apta.org/ Bongers, B. C., & Takken, T. (2012). Physiological demands of therapeutic horseback riding in children with moderate to severe motor impairments: An exploratory study. Pediatric Physical Therapy, 24, 252–257. doi:10. 1097/PEP.0b013e31825c1a7d Casady, R. L., & Nichols-Larsen, D. S. (2004). The effect of hippotherapy on ten children with cerebral palsy. Pediatric Physical Therapy, 16, 165–172. doi:10.1097/01.PEP.0000136003.15233.0C Centers for Disease Control and Prevention. (2011). How much physical activity do children need? Retrieved from http://www.cdc.gov/ physicalactivity/everyone/guidelines/children.html Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum. Davis, E., Davies, B., Wolfe, R., Raadsveld, R., Heine, B., Thomason, P., . . . Graham, H. K. (2009). A randomized controlled trial of the impact of therapeutic horse riding on the quality of life, health, and function of children with cerebral palsy. Developmental Medicine & Child Neurology, 51, 111–119. doi:10.1111/j.1469-8749.2008.03245.x Devienne, M.-F., & Guezennec, C.-Y. (2000). Energy expenditure of horse riding. European Journal of Applied Physiology, 82, 499 –503. doi:10. 1007/s004210000207 Dhindsa, M., Barnes, J. N., DeVan, A. E., Nualnim, N., & Tanaka, H. (2008). Innovative exercise device that simulates horseback riding: Cardiovascular and metabolic responses. Comparative Exercise Physiology, 5, 1 –5. doi:10.1017/S1478061508914481 Frost, G., Bar-Or, O., Dowling, J., & White, C. (1995). Habituation of children to treadmill walking and running: Metabolic and kinematic criteria. Pediatric Exercise Science, 7, 162–175. Retrieved from http:// journals.humankinetics.com/pes Haehl, V., Giuliani, C., & Lewis, C. (1999). Influence of hippotherapy on the kinematics and functional performance of two children with cerebral palsy. Pediatric Physical Therapy, 11, 89–101. doi:10.1097/00001577199901120-00006 Hammer, A., Nilsagard, Y., Forsberg, A., Pepa, H., Skargren, E., & Oberg, B. (2005). Evaluation of therapeutic riding (Sweden)/hippotherapy (United States): A single-subject experimental design study replicated in eleven patients with multiple sclerosis. Physiotherapy Theory and Practice, 21, 51 –77. doi:10.1080/09593980590911525 Harrell, J. S., McMurray, R. G., Baggett, C. D., Pennell, M. L., Pearce, P. F., & Bangdiwala, S. I. (2005). Energy costs of physical activities in children and adolescents. Medicine & Science in Sports & Exercise, 37, 329–336. doi:10.1249/01.MSS.0000153115.33762.3F
Lechner, H. E., Feldhaus, S., Gudmundsen, L., Hegemann, D., Michel, D., Zach, G. A., & Knecht, H. (2003). The short-term effect of hippotherapy on spasticity in patients with spinal cord injury. Spinal Cord, 41, 502–505. doi:10.1038/sj.sc.3101492 Lechner, H. E., Kakebeeke, T. H., Hegemann, D., & Baumberger, M. (2007). The effect of hippotherapy on spasticity and on mental well-being of persons with spinal cord injury. Archives of Physical Medicine and Rehabilitation, 88, 1241 – 1248. doi:10.1016/j.apmr.2007.07.015 McGibbon, N. H., Andrade, C.-K., Widener, G., & Cintas, H. L. (1998). Effect of an equine-movement therapy on gait, energy expenditure, and motor function in children with spastic cerebral palsy: A pilot study. Developmental Medicine & Child Neurology, 40, 754–762. doi:10.1111/ j.1469-8749.1998.tb12344.x McGibbon, N. H., Benda, W., Duncan, B. R., & Silkwood-Sherer, D. (2009). Immediate and long-term effects of hippotherapy on symmetry of adductor muscle activity and functional ability in children with spastic cerebral palsy. Archives of Physical Medicine and Rehabilitation, 90, 966–974. doi:10.1016/j.apmr.2009.01.011 Millhouse-Flourie, T. (2004). Physical, occupational, respiratory, speech, equine and pet therapies for mitochondrial disease. Mitochondrion, 4, 549–558. doi:10.1016/j.mito.2004.07.013 Morris, P. J. (2009). Physical activity recommendations for children and adolescents with chronic diseases. Current Sports Medicine Reports, 7, 353–358. doi:10.1249/JSR.0b013e31818f0795 Rhea, M. R. (2004). Determining the magnitude of treatment effects in strength training research through the use of effect size. Journal of Strength and Conditioning Research, 18, 918 – 920. doi:10.1519/ 14403.1 Ridley, K., Ainsworth, B. E., & Olds, T. S. (2008). Development of a compendium of energy expenditures for youth. International Journal of Behavioral Nutrition and Physical Activity, 5, 45, doi:10.1186/14795868-5-45 Shimomura, K., Murase, N., Osada, T., Kime, R., Anjo, M., Esaki, K., . . . Katsumura, T. (2009). A study of passive weight-bearing lower limb exercise effects on local muscles and whole body oxidative metabolism: A comparison with simulated horse riding, bicycle, and walking exercise. Dynamic Medicine, 8, 4, doi:10.1186/1476-5918-8-4 Shurtleff, T., & Engsberg, J. (2012). Long-term effects of hippotherapy on one child with cerebral palsy: A research case study. British Journal of Occupational Therapy, 75, 359 – 366. doi:10.4276/ 030802212X13433105374279 Silkwood-Sherer, D. J., Killian, C. B., Long, T. M., & Martin, K. S. (2012). Hippotherapy—an intervention to habilitate balance deficits in children with movement disorders: A clinical trial. Physical Therapy, 92, 707–717. doi:10.2522/ptj.20110081 Silkwood-Sherer, D., & Warmbier, H. (2007). Effects of hippotherapy on postural stability in persons with multiple sclerosis: A pilot study. Journal of Neurologic Physical Therapy, 31, 77–84. doi:10.1097/NPT. 0b013e31806769f7 Sterba, J. A., Rogers, B. T., France, A. P., & Vokes, D. A. (2002). Horseback riding in children with cerebral palsy: Effect on gross motor function. Developmental Medicine & Child Neurology, 44, 301– 308. doi:10.1111/j.1469-8749.2002.tb00815.x Tseh, W., Caputo, J. L., Craig, I. S., Keefer, D. J., Martin, P. E., & Morgan, D. W. (2000). Metabolic accommodation of young children to treadmill walking. Gait and Posture, 12, 139–142. doi:10.1016/S0966-6362(00) 00063-1 Unnithan, V. B., Murray, L. A., Timmons, J. A., Buchanan, D., & Paton, J. Y. (1995). Reproducibility of cardiorespiratory measurements during submaximal and maximal running in children. British Journal of Sports Medicine, 29, 66–71. doi:10.1136/bjsm.29.1.66 Winsley, R. J., Armstrong, N., Bywater, K., & Fawkner, S. G. (2003). Reliability of heart rate variability measures at rest and during light exercise in children. British Journal of Sports Medicine, 37, 550– 552. doi:10.1136/bjsm.37.6.550
Copyright of Research Quarterly for Exercise & Sport is the property of Routledge and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Cardiorespiratory and Biomechanical Responses to Simulated Recreational Horseback Riding in Healthy Children Brandon R. Rigby, Zacharias Papadakis, Annie A. Bane, Jin K. Park, and Peter W. Grandjean Baylor University
Purpose: The purpose of this study was to determine the reliability of cardiorespiratory and pelvic kinematic responses to simulated horseback riding (SHBR) and to characterize responses to SHBR relative to walking in apparently healthy children. Method: Fifteen healthy children (Mage ¼ 9.5 ^ 2.6 years) completed SHBR on a commercially available simulator at low intensity (0.27 Hz) and high intensity (0.65 Hz) during 3 sessions on different occasions. Heart rate (HR), blood pressure, and respiratory gases were measured at rest and during steadystate exercise at both intensities. Pelvic displacement was measured during steady-state exercise. Rate of energy expenditure, mean arterial pressure, and rate pressure product (RPP) were calculated. Participants also walked on a treadmill for 26.8 m/min to 80.5 m/min in 13.4m/min increments at 0% grade during 1 session to compare cardiorespiratory responses with those of SHBR. Results: Physiological variables across all 3 SHBR sessions were similar at both intensities ( p . .05 for all). Intraclass correlation coefficients (ICCs) and coefficients of variation indicate good to modest reliability of cardiorespiratory measures during SHBR (ICCs ¼ .542 – .996 for oxygen consumption, energy expenditure, and RPP). Cardiorespiratory variables, except for HR, were 2% to 19% greater, and pelvic displacement was up to 37% greater with high-intensity riding. Treadmill walking at all speeds elicited greater physiological responses compared with SHBR ( p , .05). Conclusion: Cardiorespiratory responses and pelvic kinematics are reproducible with SHBR in young children, and these responses were lower than those elicited by slow treadmill walking. Keywords: cardiovascular responses, horseback riding simulator, kinematics, youth
Many young people experience horseback riding (HBR) as outdoor recreation, and some forms of HBR are gaining widespread acceptance as therapeutic interventions for children and youth (Millhouse-Flourie, 2004). Results from a growing body of evidence support the efficacy of HBR in special populations with improvements reported for gross motor function (Casady & Nichols-Larsen, 2004; McGibbon, Andrade, Widener, & Cintas, 1998; Sterba, Rogers, France, & Vokes, 2002), posture (Bertoti, 1988; Haehl, Giuliani, & Submitted September 18, 2013; accepted May 20, 2014. Correspondence should be addressed to Peter W. Grandjean, Baylor Laboratories for Exercise Science and Technology, Center for Healthy Living, Baylor University, One Bear Place #97313, Waco, TX 76798-7313. E-mail: [email protected]
Lewis, 1999; Shurtleff & Engsberg, 2012), balance (Hammer et al., 2005; Silkwood-Sherer, Killian, Long, & Martin, 2012; Silkwood-Sherer & Warmbier, 2007), spasticity (Hammer et al., 2005; Lechner et al., 2003; Lechner, Kakebeeke, Hegemann, & Baumberger, 2007), muscle asymmetry (Benda, McGibbon, & Grant, 2003; McGibbon, Benda, Duncan, & Silkwood-Sherer, 2009), energy expenditure (Bongers & Takken, 2012; McGibbon et al., 1998), and mental health (Davis et al., 2009; McGibbon et al., 2009; MillhouseFlourie, 2004). The benefits attributed to HBR are interesting because it is a physical activity that has largely gone uncharacterized, particularly with respect to cardiorespiratory and kinematic responses. Indeed, we know very little about the physical responses and training adaptations to HBR or how these
64
B. R. RIGBY ET AL.
compare to common physical activities, such as walking, which are part of current recommendations and position statements for improving and maintaining health and fitness (e.g., Centers for Disease Control and Prevention, 2011; Morris, 2009). Limited information exists on the cardiorespiratory and biomechanical responses to HBR, due in part to a host of factors that confound measurement precision. Obtaining reproducible movements from the horse is probably the most obvious among confounding factors (Devienne & Guezennec, 2000). Movements of the rider in response to the horse augment the variability. Environmental conditions, such as temperature and humidity, and the logistics of collecting respiratory and kinematic data as the horse and rider move throughout a large space add to the difficulties in characterizing the physical responses to HBR. Moreover, even if most of these factors are controlled or accounted for during a single measurement session, reproducing the same conditions becomes virtually impossible when attempting to obtain preand post-HBR intervention measurements that are often separated by many HBR sessions and several weeks. One way to address the variability in measuring the riders’ cardiorespiratory and biomechanical responses during HBR is to simulate movements commonly made by the horse with a stationary HBR simulator in an environmentally controlled setting. Indeed, commercially available HBR simulators are increasingly being used to supplement HBR and to study physical responses that may occur during recreational HBR (Dhindsa, Barnes, DeVan, Nualnim, & Tanaka, 2008; Shimomura et al., 2009). The use of a simulator eliminates physiologic influences that may be due to the affect between the rider and the horse. In addition, the use of an HBR simulator may enable investigators to quantify changes in physiological responses that are thought to occur with habitual HBR. Determining the reliability of such measurements and comparing the physiological responses to those of common physical activities may be particularly useful for quantifying the benefits of HBR. Our primary research objective was to determine the variation in cardiorespiratory and pelvic kinematic responses during simulated horseback riding (SHBR) in children. We employed simulator settings that approximate a horse’s movement at a slow-to-moderate walk (i.e., below a trot). A second objective was to compare the cardiovascular responses to SHBR relative to those measured during walking—one of the most common and well-characterized physical activities.
METHODS Participants This research was approved by our university’s Institutional Review Board for Research with Human Participants
(Approved Protocol #278898-1). We recruited apparently healthy children aged 6 to 14 years old with little or no previous HBR experience. Enrollment was open to boys and girls of all ethnicities. Flyers were sent to schools and various organizations, such as the YMCA, with information to parents including a brief explanation of the study and contact information. Recruitment was completed via e-mail or personal contact with a parent/guardian. On the first visit, designed as a screening and familiarization session, parents answered questions concerning their child’s medical history. Both the child and parent were familiarized with the study protocol through a verbal and written explanation outlining the study design and were introduced to and familiarized with all of the equipment used in the study (e.g., allowed to walk on the treadmill and ride on the simulator). All details of the study were reviewed again and parents were given a consent document and children were given an age-appropriate assent document to read, review, and sign. Volunteer children were screened to include those: without a diagnosed congenital heart condition or cardiovascular condition that would preclude them from vigorous exercise; without orthopedic problems that could be exacerbated by exercise; who were not currently taking medications that would interfere with heart rate (HR), blood pressure (BP), or respiration during exercise (e.g., Ritalin, Adderall, insulin, etc.); and who were free from any condition that would prevent them from participating safely in this study. Of the 16 children who responded via their parent, 15 met requirements (8 girls and 7 boys) and completed all aspects of the study. One child dropped out of the study because he found the equipment we used to measure primary variables of interest (e.g., HR monitor, mask for ventilation [VE] and respiratory gas collection) to be too unpleasant. Preliminary Procedures On the second lab visit, the participants’ height, weight, and body composition were measured. Weight was assessed using a digital scale and height was assessed using a stadiometer attached to the scale. Body composition was determined by dual X-ray absorptiometry (Hologic 4500W, Hologic Inc., Bedford, MA). Participants were fitted with an HR monitor (Polar Electro Inc., Lake Success, NY), and HR, VE, and respiratory gases (e.g., rates of oxygen consumption [VO2] and carbon dioxide production) were measured continuously during 5 min of seated rest. BP was measured once during the rest period and was assessed manually using an aneroid sphygmomanometer and stethoscope. Respiratory gases were measured using an integrated metabolic system (ParvoMedics, Sandy, UT). Just after resting measurements, participants underwent a graded exercise test on a motorized treadmill (Trackmaster, Full Vision Inc., Newton, KS). Participants began by walking at
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
26.8 m/min and progressed to 80.5 m/min in 13.4-m/min increments while maintaining 0% grade. Each stage lasted for 5 min to achieve a steady state at each walking speed. HR, BP, and respiratory gases were measured throughout exercise, and mean arterial pressure (MAP), rate pressure product (RPP), and kilocalorie (kcal) expenditure were calculated from these direct measures. Walking is one of the most common activities of daily living (Ridley, Ainsworth, & Olds, 2008). Physical responses to other activities are frequently compared to walking (Harrell et al., 2005; Ridley et al., 2008). Therefore, we compared the cardiorespiratory responses obtained during the treadmill walking session to the magnitude of responses obtained during the SHBR sessions. Simulated Horseback Riding Testing Sessions We collected all SHBR data during three testing sessions. The protocol for each of the three testing sessions was identical. Sessions were scheduled so that there was a minimum of 2 days and a maximum of 7 days between sessions. Participants were fitted with an HR monitor. A motion capture system (PhaseSpace Inc., San Leandro, CA) was used to quantify anteroposterior, medial-lateral, and vertical pelvic displacement during steady-state SHBR. An aluminum bar affixed with two markers, emitting infrared light, on each end of the bar was placed on the superior aspect of the participant’s posterior pelvis. Another aluminum bar, with a similar configuration, was placed on the superior aspect of the participant’s anterior pelvis. Within each session, HR, VE, and respiratory gases were measured continuously during 5 min of seated rest. BP was measured once during the rest period. Participants rode on an HBR simulator (Core Trainerw, Panasonic Inc., Secaucus, NJ) at two intensity levels. The lower-intensity level (0.27 Hz) corresponded to a very slow-paced walk for a horse. The higher-intensity level (0.65 Hz) corresponded to a fast-paced walk. Participants rode at each intensity level for 5 min to achieve a steady state. HR, BP, and respiratory gases were measured after the participants achieved steady state at each exercise intensity, and MAP, RPP, and kcal expenditure were calculated from these direct measures. Pelvic kinematics were measured during several gait cycles once the participant reached a steady state. Statistical Analysis A sample size of nine was calculated based on an average paired difference to be detected in absolute VO2 in healthy children of 0.5 mL/kg/min, standard deviation of 0.4 mL/kg/ min, alpha error probability of .05, and statistical power of 90%. The cardiorespiratory dependent variables were VE, VO 2 absolute, VO 2 relative to body weight, kcal
65
expenditure, HR, systolic blood pressure (SBP), diastolic blood pressure, MAP, and RPP. The dependent kinematic data were pelvic displacements along the anteroposterior, vertical, and medial-lateral axes. Independent variables were the sessions (Sessions 1, 2, and 3) and simulator intensity (low ¼ 0.27 Hz; high ¼ 0.65 Hz). Treadmill intensities of 26.8 m/min, 40.2 m/min, 53.6 m/min, 67.1 m/min, and 80.5 m/min were included as independent levels when SHBR was compared with walking intensities. To address our first objective, 2 (intensity) £ 3 (session) repeated-measure analyses of variances (ANOVAs) were used to determine reliability of cardiorespiratory and kinematic variables. Intraclass correlation coefficients (ICCs) and coefficients of variation (CVs) were calculated for measured and calculated dependent variables. Our second objective was addressed using 1 £ 7 (intensities: SHBR at low and high intensity and treadmill walking at 26.8 m/min, 40.2 m/min, 53.6 m/min, 67.1 m/ min, and 80.5 m/min) ANOVAs to compare cardiorespiratory data between SHBR and walking. Duncan’s multiple range tests were used to follow up significant intensity differences. A comparison error rate was set at p , .05. All statistical procedures were performed using Statistical Analysis Software (SAS) Version 9.2 (SAS, Cary, NC). Effect sizes were calculated according to methods previously described by Cohen (1988) and more recently by Rhea (Rhea, 2004) for repeated measurements.
RESULTS The participant characteristics can be found in Table 1. The maximum and minimum values and ranges for each characteristic are given for the cohort. Our primary objective was to determine reliability in cardiorespiratory and pelvic kinematic responses to SHBR. Cardiorespiratory responses among sessions during SHBR are presented in Table 2a (for rest) and in Tables 2b and 2c (for low and high intensity). Dependent-variable responses were similar across all testing sessions ( p . .05 for all), and
TABLE 1 Characteristics of All Participants Variable
Mean ^ SD
Max
Min
Range
Age (years) Height (cm) Weight (kg) BMI (kg/m2) % Body Fat
9.5 ^ 2.6 142.1 ^ 15.8 41.5 ^ 18.6 19.6 ^ 4.9 27 ^ 8
14.2 170.2 86.3 29.8 42
6.7 120.7 20.8 13.6 14
7.5 49.5 65.5 16.2 28
Note. Data were obtained from 15 healthy children (8 girls and 7 boys). All values are presented as means ^ standard deviation. BMI ¼ body mass index; % Body Fat ¼ body fat expressed as a percentage of body weight; Max ¼ maximum value; Min ¼ minimum value.
66
B. R. RIGBY ET AL. TABLE 2 Variation of Cardiorespiratory Variables at Rest and at Both Intensities
Variable a. Rest VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP b. Low Intensity VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP c. High Intensity VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Session 1
Session 2
Session 3
ANOVA p Value
ICC
CV
7.7 ^ 0.4 5.6 ^ 0.3 0.22 ^ 0.02 1.1 ^ 0.1 94 ^ 2 77.8 ^ 2.9 97 ^ 3
7.6 ^ 0.3 5.7 ^ 0.4 0.22 ^ 0.01 1.1 ^ 0.1 93 ^ 1 74.1 ^ 2.6 94 ^ 3
7.9 ^ 0.4 5.8 ^ 0.3 0.22 ^ 0.02 1.1 ^ 0.3 98 ^ 3 73.6 ^ 3.4 97 ^ 3
.5876 .9642 .7734 .8575 .0730 .6030 .4939
.731 .988 .938 .961 .019 .381 .542
9.3 9.6 10.0 9.9 5.7 12.6 8.9
8.4 ^ 0.4 6.2 ^ 0.4 0.24 ^ 0.02 1.2 ^ 0.1 94 ^ 2 77.2 ^ 2.7 97 ^ 3
8.3 ^ 0.5 6.1 ^ 0.3 0.24 ^ 0.02 1.2 ^ 0.1 95 ^ 2 75.3 ^ 2.9 97 ^ 3
8.3 ^ 0.4 6.0 ^ 0.3 0.23 ^ 0.02 1.1 ^ 0.1 97 ^ 2 74.7 ^ 3.3 97 ^ 3
.9698 .2247 .4132 .4812 .4933 .9088 .9941
.994 .659 .898 .924 .328 .851 .996
6.8 8.3 8.6 7.5 5.1 11.4 7.8
9.9 ^ 0.7 7.1 ^ 0.3 0.29 ^ 0.03 1.4 ^ 0.2 96 ^ 2 79.3 ^ 2.6 103 ^ 4
9.8 ^ 0.8 7.0 ^ 0.3 0.28 ^ 0.03 1.4 ^ 0.2 97 ^ 2 77.3 ^ 3.0 103 ^ 3
10.1 ^ 0.8 7.1 ^ 0.3 0.28 ^ 0.03 1.3 ^ 0.2 100 ^ 2 75.7 ^ 3.2 102 ^ 3
.6688 .5314 .5123 .2703 .1319 .7255 .9295
.960 .781 .971 .872 .081 .547 .933
9.5 8.2 8.1 10.9 5.0 11.7 9.9
Note. Data were obtained from 15 participants (8 girls and 7 boys). Variables are presented as means ^ standard error. VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/ min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100); ANOVA ¼ analysis of variance; ICC ¼ intraclass correlation coefficient; CV ¼ coefficient of variation (standard deviation/mean £ 100).
with the exception of HR, repeated variable responses demonstrated high ICCs. The range of ICCs from rest to high-intensity exercise was as follows: .731 to .994 for VE; .898 to .971 for absolute VO2; .872 to .961 for kcal expenditure; and .542 to .996 for RPP. Pelvic displacements along each axis between sessions for both intensities during SHBR are presented in Table 3. There were no significant differences in kinematic responses between the three sessions ( p . .05 for all), but
repeat measurements at similar SHBR intensities demonstrated low ICCs and high CVs. Cardiorespiratory and pelvic kinematic responses are presented for rest and both intensities during SHBR in Table 4. Absolute and relative VO2 ( p , .0001 for both), VE ( p , .0001), MAP ( p ¼ .0002), RPP ( p , .0001), and kcal expenditure ( p ¼ .0004) were greater with high-intensity riding compared with rest and low-intensity riding. HR was not different across intensities ( p ¼ .0831). Pelvic displace-
TABLE 3 Variation of Pelvic Kinematics at Rest and at Both Intensities Variable a. Low Intensity A-P axis V axis M-L axis b. High Intensity A-P axis V axis M-L axis
Session 1
Session 2
Session 3
ANOVA p Value
ICC
CV
10.7 ^ 0.2 2.1 ^ 0.2 8.0 ^ 0.2
10.8 ^ 0.2 1.8 ^ 0.1 8.5 ^ 0.2
10.6 ^ 0.4 1.9 ^ 0.2 8.0 ^ 0.3
.8838 .5982 .1298
.874 .200 .014
7.5 25.3 8.5
13.3 ^ 1.0 3.1 ^ 0.5 9.6 ^ 0.6
11.5 ^ 0.3 2.2 ^ 0.2 8.6 ^ 0.3
12.2 ^ 0.5 2.4 ^ 0.2 9.4 ^ 0.6
.0976 .0561 .2502
.026 .187 .455
12.0 30.5 12.6
Note. Data were obtained from 15 participants (8 girls and 7 boys). All displacements are in centimeters. Displacements are reported as means ^ standard error. A-P ¼ anterior-posterior; V ¼ vertical; M-L ¼ medial-lateral; ANOVA ¼ analysis of variance; ICC ¼ intraclass correlation coefficient; CV ¼ coefficient of variation (standard deviation/mean £ 100).
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
67
TABLE 4 Cardiorespiratory and Kinematic Variables at Rest and During Simulated HBR for All Participants Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP A-P axis V axis M-L axis
Rest
Low Intensity
High Intensity
ANOVA p Value
7.7 ^ 0.2a 5.7 ^ 0.2a 0.22 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.2 ^ 1.5a 96 ^ 2a n/a n/a n/a
8.3 ^ 0.3a 6.1 ^ 0.2a 0.24 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.8 ^ 1.7a 97 ^ 2a 10.7 ^ 0.2a 1.9 ^ 0.1a 8.2 ^ 0.1a
9.9 ^ 0.4b 7.0 ^ 0.2b 0.28 ^ 0.02b 1.4 ^ 0.1b 98 ^ 1a 77.5 ^ 1.7b 103 ^ 2b 12.3 ^ 0.4b 2.6 ^ 0.2b 9.2 ^ 0.3b
,.0001 ,.0001 ,.0001 .0004 .0831 .0002 ,.0001 .0045 .0013 .0383
Note. Data were obtained from 15 participants (8 girls and 7 boys). All variables are presented as means ^ standard error; means with the same superscript are statistically similar ( p . .05). HBR ¼ horseback riding; ANOVA ¼ analysis of variance; VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100); A-P ¼ anterior-posterior; V ¼ vertical; M-L ¼ medial-lateral. No kinematic data were collected at rest.
ments along all three axes were greater with high-intensity riding compared with low-intensity riding (anteroposterior axis, p ¼ .0045; vertical axis, p ¼ .0013; medial-lateral axis, p ¼ .0383). A second objective was to compare physiological responses to SHBR to those measured during slow-tobrisk walking. Cardiorespiratory measurements at rest and responses during SHBR and at different submaximal treadmill walking intensities are presented in Table 5. All cardiorespiratory variables measured at steady state during low-intensity SHBR (0.27 Hz) were not different from resting values. With the exception of HR, cardiorespiratory values were greater during SHBR at the higher intensity (0.65 Hz) compared with those obtained at rest or during low-intensity SHBR. All cardiorespiratory responses to treadmill walking at speeds up to 80.5 m/min were of greater magnitude than what was observed at high-intensity SHBR. In fact,
treadmill walking at 26.8 m/min elicited greater cardiorespiratory responses than high-intensity SHBR for all variables but MAP. Effect sizes for cardiorespiratory responses to SHBR and a treadmill are presented in Table 6. DISCUSSION The purpose of this study was to characterize cardiorespiratory and pelvic kinematic responses to SHBR and the variation in these responses in apparently healthy children. Our protocol enabled us to determine cardiovascular responses, energy expenditure, and pelvic movement in a controlled environment. The HBR simulator allowed us to specifically quantify the work rate at low (0.27 Hz) and high (0.65 Hz) intensities, approximating HBR at slow and brisk walking paces. Our results show that in a controlled setting, the pulmonary responses and cardiovascular responses— with the exception of HR—are reproducible. The HR and
TABLE 5 Cardiorespiratory Variables at Rest and During SHBR and Treadmill Walking SHBR Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Treadmill Walking
Rest
Low Intensity
High Intensity
26.8 m/min
40.2 m/min
53.6 m/min
67.1 m/min
80.5 m/min
7.7 ^ 0.2a 5.7 ^ 0.2a 0.22 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.2 ^ 1.5a 96 ^ 2a
8.3 ^ 0.3a 6.1 ^ 0.2a 0.24 ^ 0.01a 1.1 ^ 0.1a 95 ^ 1a 75.8 ^ 1.7a 97 ^ 2a
9.9 ^ 0.4b 7.0 ^ 0.2b 0.28 ^ 0.02b 1.4 ^ 0.1b 98 ^ 1a 77.5 ^ 1.7b 103 ^ 2b
12.0 ^ 0.8c 9.8 ^ 0.7c 0.39 ^ 0.04c 1.9 ^ 0.2c 106 ^ 3b 80.8 ^ 3.2bc 116 ^ 5c
13.1 ^ 0.9cd 10.7 ^ 0.8c 0.43 ^ 0.04cd 2.1 ^ 0.2cd 108 ^ 2b 83.9 ^ 3.0cd 127 ^ 5d
14.4 ^ 0.9d 11.9 ^ 0.7d 0.48 ^ 0.05de 2.3 ^ 0.2de 114 ^ 2c 85.5 ^ 2.9cde 142 ^ 5e
16.0 ^ 1.2e 13.1 ^ 0.6e 0.54 ^ 0.05e 2.6 ^ 0.3e 117 ^ 2c 87.4 ^ 2.9de 150 ^ 5f
18.7 ^ 1.4f 15.5 ^ 0.6f 0.63 ^ 0.06f 3.1 ^ 0.3f 125 ^ 2d 89.5 ^ 2.9e 168 ^ 6g
Note. Data were obtained from 15 participants (8 girls and 7 boys). All variables are presented as means ^ standard error; means with the same superscript are statistically similar ( p . .05). SHBR ¼ simulated horseback riding; VE (L/min) ¼ ventilation; absolute VO2 (L/min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100).
68
B. R. RIGBY ET AL. TABLE 6 Effect Sizes for Cardiorespiratory Responses During SHBR and Treadmill Walking SHBR
Variable VE Relative VO2 Absolute VO2 Rate of EE HR MAP RPP
Treadmill Walking
Rest-Low
Rest-High
Rest-27 m/min
Rest-54 m/min
Rest-81 m/min
0.44 0.32 0.26 0.26 0.03 0.05 0.06
1.59 1.11 1.02 0.95 0.32 0.20 0.57
1.69 2.66 1.92 1.93 0.86 0.18 1.03
2.72 3.93 2.87 2.95 1.71 0.56 2.78
4.63 6.14 4.55 4.71 2.82 0.88 4.55
Note. Data were obtained from 15 participants (8 girls and 7 boys). SHBR ¼ simulated horseback riding; VE (L/min) ¼ ventilation; absolute VO2 (L/ min) ¼ absolute oxygen consumption; relative VO2 (mL/kg/min) ¼ relative oxygen consumption; rate of EE ¼ rate of energy expenditure (kcals/min); HR (bpm) ¼ heart rate; MAP ¼ mean arterial pressure ([SBP 2 DBP]/3 þ DBP) in mmHg; SBP ¼ systemic blood pressure; DBP ¼ diastolic blood pressure; RPP ¼ rate pressure product (SBP £ HR/100).
pelvic kinematic responses, although not statistically different between sessions, demonstrate a substantial degree of variability. HRs were found to be of higher variability at rest and high-intensity SHBR while pelvic kinematic data became less reliable with the higher-intensity SHBR. Although HR is used to monitor exercise intensity, the greatest HR variability occurs at rest and during lightintensity activities in children (Winsley, Armstrong, Bywater, & Fawkner, 2003). The variation in HR at rest and during light activity is thought to be due to a predominating influence of the parasympathetic versus sympathetic autonomic control (Winsley et al., 2003). We attempted to control for outside influences on HR and other cardiovascular measurements by testing under standardized conditions and at the same time of day. However, it appears that many outside factors—even under controlled conditions—can add to the parasympathetic modulation and cause substantial variation in resting HR and the HR responses to SHBR. Absolute variation in the kinematic data were very small (i.e., less than 1 cm), and the displacement in each plane is small. This puts a premium on measurement precision. The largest source of variation appears to be among participants, indicating different strategies for maintaining erect postures during riding. However, the low ICCs (.100 to .378) and relatively high CVs (10% –28%) indicate that a considerable amount of individual variation also exists. Our results indicate that pelvic displacement measures can be reproduced. However, care should be taken to properly place anatomical markers and calibrate the motion capture system. Moreover, our results support the importance of specific riding instructions and protocol familiarization when measuring pelvic displacement responses during HBR. The reliability of cardiorespiratory responses and gait kinematics has been investigated in children while walking and running on a treadmill at submaximal intensities. In one study, the coefficient of reliability for VO2 was 68% in healthy boys who completed two trials of submaximal treadmill running at 120.7 m/min, 134.1 m/min, and 147.5 m/min
(Unnithan, Murray, Timmons, Buchanan, & Paton, 1995). The coefficient of reliability for VE was 50% and coefficient of reliability for HR was 94%, indicating no training (i.e., learning) effect on the cardiovascular system (Unnithan et al., 1995). In another study, 41 healthy children aged 6 years completed three 10-min walking trials on a treadmill at 80.5 m/min at 0% grade, which was preceded by a familiarization session in which the children walked for 5 min at 80.5 m/min (Tseh et al., 2000). The CV and the ICC for VO2 across the three trials was 2.0 ^ 1.5% and .96, respectively, indicating good reliability during level treadmill walking in children (Tseh et al., 2000). VO2 results from our present study appear to be consistent with the reliability estimates reported for treadmill walking in children. The reliability of VO2, HR, stride length, and vertical displacement of the hip joint was investigated in 24 children ages 7 to 11 years old (Frost, Bar-Or, Dowling, & White, 1995). The children were randomized into four groups, with one group (Group A) instructed to walk at a comfortable walking speed (ranging from 69.7 m/min to 99.2 m/min) on a treadmill. Other groups walked on the treadmill at faster speeds (Group B, þ 15% of the speed of Group A; Group C, þ 50.9 m/min of the speed of Group B; Group D, þ 15% of the speed of Group C). Each group completed two sessions, with each session consisting of six 6-min trials for each group. No statistically significant differences were reported in mean VO2, mean HR, stride length, or vertical displacement of the hip between sessions or between trials for all groups. Stride length tended to increase from Trial 1 to Trial 6 in Session 1 for all groups, while vertical displacement tended to increase from Trial 1 to Trial 6 in both sessions for Groups A through C (Frost et al., 1995). These results indicate good reliability in the cardiorespiratory variables and moderate reliability in the kinematic variables. Our present findings for SHBR indicate reliability that is consistent with what is reported in the literature for treadmill walking. That is, we demonstrate a greater degree of precision and less variation in respiratory responses than we do for pelvic displacement. However, all of the
CARDIORESPIRATORY AND KINEMATIC RESPONSES TO SHBR
physiologic and kinematic measures can be reproduced under standard conditions with reasonable reliability. A second objective of this investigation was to compare cardiorespiratory responses during SHBR to responses measured during treadmill walking. We chose walking because it is one of the most common physical activities of daily living (Centers for Disease Control and Prevention, 2011). Our results show that cardiorespiratory responses were significantly greater with treadmill walking than those measured at any intensity on the HBR simulator. Indeed, treadmill walking induced much larger effects on cardiorespiratory markers than did those observed with SHBR. In accordance with effect size interpretation proposed by Rhea (2004), the magnitude of cardiorespiratory response to SHBR might be interpreted as moderate, whereas responses to treadmill walking at slow-to-moderate speeds are large. To our knowledge, this is the first study to compare these cardiorespiratory responses between an HBR simulator and walking on a treadmill in healthy children. Our results suggest that at best, HBR may only supplement the recommended daily activity requirements for healthy children. Because of the lower cardiorespiratory requirements of SHBR and HBR, this form of physical activity may be a suitable means of transitioning children of low cardiorespiratory fitness and those with physical impairments to a more physically active lifestyle (Morris, 2009). Shimomura et al. (2009) described cardiorespiratory responses to walking and SHBR in 14 male adults. Participants rode on an HBR simulator at 0.8 Hz, 1.2 Hz, and 1.4 Hz for 3 min each with a 5-min rest period between intensities. While riding at 0.8 Hz on the simulator, the participants had a mean HR of 73 ^ 5 bpm, a mean SBP of 131 ^ 3 mmHg, and a mean VO2 of 5.1 ^ 0.3 mL/kg/min. Participants also walked on a treadmill at 2 km/h, 3 km/h, 4 km/h, 5 km/h, and 6 km/h under the same time constraints. While walking at 2 km/h, participants had a mean HR of 79 ^ 4 bpm, a mean SBP of 135 ^ 5 mmHg, and a mean VO2 of 9.6 ^ 0.3 mL/kg/min (Shimomura et al., 2009). Although no statistical comparisons were made between exercise modes, these results indicate that walking at 2 km/h elicits a greater exercise response when compared with SHBR at 0.8 Hz. These results appear to be consistent with our own data. The average relative VO2 for all participants during lowintensity riding was 6.1 mL/kg/min. This intensity is comparable to that when children (8 – 12 years old) are reading or older children (13 –15 years old) are playing a video game while standing (Harrell et al., 2005). According to the compendium of physical activities, HBR at a walking pace elicits a metabolic equivalent level of 2.5 from a child while riding (Ridley et al., 2008). This average response is similar to the intensity we observed for children riding at a high-intensity (0.65 Hz) on the HBR simulator. The slightly higher average VO2 observed by Ridley et al. (2008) may include environmental conditions or responses to riding an actual horse versus a machine. The steady-state VO2 that we
69
observed at 0.65 Hz on the simulator is comparable to children performing light activities such as brushing their teeth (Ridley et al., 2008). The average VO2 while walking at 26.8 m/min on the treadmill (9.8 mL/kg/min) is comparable to children playing with animals (light effort) or lifting weights at moderate effort (Ridley et al., 2008). One limitation of this study was that we chose not to measure maximum exercise effort and maximal oxygen consumption (VO2max). As such, we are not able to report exercise intensities in terms of a percentage of maximal HR or VO2max or expressed as a percentage of HR or VO2 reserve. Another limitation was that we did not power the study to examine variations in cardiorespiratory responses that may be, at least partially, explained by gender, physical maturity, and body composition.
CONCLUSION Our findings support the use of SHBR to quantify cardiorespiratory and biomechanical responses during HBR at a walking pace. Our results show that cardiorespiratory responses are reproducible with SHBR in young children, while pelvic kinematics are more variable. Consistent placement of markers at anatomically defined locations, specific riding instructions for participants, and familiarization of the protocol can help reduce the variation observed in the kinematic data. Physiological responses to SHBR are lower than those elicited by treadmill walking at 26.8 m/min in healthy, able-bodied children. Our findings may be interpreted in a more practical sense to mean that recreational HBR at a walking pace may not be sufficient to provide an adequate exercise response in healthy children. Instead, HBR at a walking pace might be used as a supplement to the recommended daily activity requirements in this population.
WHAT DOES THIS ARTICLE ADD? We demonstrated that the ability to quantify cardiorespiratory and pelvic kinematic variables in children is reproducible during SHBR in a controlled setting. Our results support our premise—that SHBR may be a viable means of quantifying physiological responses to HBR and changes that may result from regularly practiced HBR. These findings may be of practical significance for those utilizing HBR as a recreational activity or as a therapeutic modality. We were able to demonstrate reproducible measurements of cardiorespiratory variables and pelvic kinematics during physiologic responses that were of lower intensity than slow-paced walking. While one study characterized the effects of walking and riding an HBR simulator on HR, SBP, and VO2 in young adults (Shimomura et al., 2009), this was not the main purpose of the study, which was to compare the exercise intensity of
70
B. R. RIGBY ET AL.
a novel machine to different modes of exercise. To our knowledge, this is the first study to characterize the cardiorespiratory and pelvic kinematic responses to SHBR and to characterize the cardiorespiratory responses to SHBR relative to those measured during walking. Other studies have investigated the reliability of cardiorespiratory responses and pelvic kinematics during submaximal running and walking in children (Frost et al., 1995; Tseh et al., 2000). Ours is the first study to determine the reliability of cardiorespiratory and pelvic kinematic responses to SHBR in children. REFERENCES Benda, W., McGibbon, N. H., & Grant, K. L. (2003). Improvements in muscle symmetry in children with cerebral palsy after equine-assisted therapy (hippotherapy). Journal of Alternative and Complementary Medicine, 9, 817 –825. doi:10.1089/107555303771952163 Bertoti, D. B. (1988). Effect of therapeutic horseback riding on posture in children with cerebral palsy. Physical Therapy, 68, 1505 – 1512. Retrieved from http://ptjournal.apta.org/ Bongers, B. C., & Takken, T. (2012). Physiological demands of therapeutic horseback riding in children with moderate to severe motor impairments: An exploratory study. Pediatric Physical Therapy, 24, 252–257. doi:10. 1097/PEP.0b013e31825c1a7d Casady, R. L., & Nichols-Larsen, D. S. (2004). The effect of hippotherapy on ten children with cerebral palsy. Pediatric Physical Therapy, 16, 165–172. doi:10.1097/01.PEP.0000136003.15233.0C Centers for Disease Control and Prevention. (2011). How much physical activity do children need? Retrieved from http://www.cdc.gov/ physicalactivity/everyone/guidelines/children.html Cohen, J. (1988). Statistical power analysis for the behavioral sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum. Davis, E., Davies, B., Wolfe, R., Raadsveld, R., Heine, B., Thomason, P., . . . Graham, H. K. (2009). A randomized controlled trial of the impact of therapeutic horse riding on the quality of life, health, and function of children with cerebral palsy. Developmental Medicine & Child Neurology, 51, 111–119. doi:10.1111/j.1469-8749.2008.03245.x Devienne, M.-F., & Guezennec, C.-Y. (2000). Energy expenditure of horse riding. European Journal of Applied Physiology, 82, 499 –503. doi:10. 1007/s004210000207 Dhindsa, M., Barnes, J. N., DeVan, A. E., Nualnim, N., & Tanaka, H. (2008). Innovative exercise device that simulates horseback riding: Cardiovascular and metabolic responses. Comparative Exercise Physiology, 5, 1 –5. doi:10.1017/S1478061508914481 Frost, G., Bar-Or, O., Dowling, J., & White, C. (1995). Habituation of children to treadmill walking and running: Metabolic and kinematic criteria. Pediatric Exercise Science, 7, 162–175. Retrieved from http:// journals.humankinetics.com/pes Haehl, V., Giuliani, C., & Lewis, C. (1999). Influence of hippotherapy on the kinematics and functional performance of two children with cerebral palsy. Pediatric Physical Therapy, 11, 89–101. doi:10.1097/00001577199901120-00006 Hammer, A., Nilsagard, Y., Forsberg, A., Pepa, H., Skargren, E., & Oberg, B. (2005). Evaluation of therapeutic riding (Sweden)/hippotherapy (United States): A single-subject experimental design study replicated in eleven patients with multiple sclerosis. Physiotherapy Theory and Practice, 21, 51 –77. doi:10.1080/09593980590911525 Harrell, J. S., McMurray, R. G., Baggett, C. D., Pennell, M. L., Pearce, P. F., & Bangdiwala, S. I. (2005). Energy costs of physical activities in children and adolescents. Medicine & Science in Sports & Exercise, 37, 329–336. doi:10.1249/01.MSS.0000153115.33762.3F
Lechner, H. E., Feldhaus, S., Gudmundsen, L., Hegemann, D., Michel, D., Zach, G. A., & Knecht, H. (2003). The short-term effect of hippotherapy on spasticity in patients with spinal cord injury. Spinal Cord, 41, 502–505. doi:10.1038/sj.sc.3101492 Lechner, H. E., Kakebeeke, T. H., Hegemann, D., & Baumberger, M. (2007). The effect of hippotherapy on spasticity and on mental well-being of persons with spinal cord injury. Archives of Physical Medicine and Rehabilitation, 88, 1241 – 1248. doi:10.1016/j.apmr.2007.07.015 McGibbon, N. H., Andrade, C.-K., Widener, G., & Cintas, H. L. (1998). Effect of an equine-movement therapy on gait, energy expenditure, and motor function in children with spastic cerebral palsy: A pilot study. Developmental Medicine & Child Neurology, 40, 754–762. doi:10.1111/ j.1469-8749.1998.tb12344.x McGibbon, N. H., Benda, W., Duncan, B. R., & Silkwood-Sherer, D. (2009). Immediate and long-term effects of hippotherapy on symmetry of adductor muscle activity and functional ability in children with spastic cerebral palsy. Archives of Physical Medicine and Rehabilitation, 90, 966–974. doi:10.1016/j.apmr.2009.01.011 Millhouse-Flourie, T. (2004). Physical, occupational, respiratory, speech, equine and pet therapies for mitochondrial disease. Mitochondrion, 4, 549–558. doi:10.1016/j.mito.2004.07.013 Morris, P. J. (2009). Physical activity recommendations for children and adolescents with chronic diseases. Current Sports Medicine Reports, 7, 353–358. doi:10.1249/JSR.0b013e31818f0795 Rhea, M. R. (2004). Determining the magnitude of treatment effects in strength training research through the use of effect size. Journal of Strength and Conditioning Research, 18, 918 – 920. doi:10.1519/ 14403.1 Ridley, K., Ainsworth, B. E., & Olds, T. S. (2008). Development of a compendium of energy expenditures for youth. International Journal of Behavioral Nutrition and Physical Activity, 5, 45, doi:10.1186/14795868-5-45 Shimomura, K., Murase, N., Osada, T., Kime, R., Anjo, M., Esaki, K., . . . Katsumura, T. (2009). A study of passive weight-bearing lower limb exercise effects on local muscles and whole body oxidative metabolism: A comparison with simulated horse riding, bicycle, and walking exercise. Dynamic Medicine, 8, 4, doi:10.1186/1476-5918-8-4 Shurtleff, T., & Engsberg, J. (2012). Long-term effects of hippotherapy on one child with cerebral palsy: A research case study. British Journal of Occupational Therapy, 75, 359 – 366. doi:10.4276/ 030802212X13433105374279 Silkwood-Sherer, D. J., Killian, C. B., Long, T. M., & Martin, K. S. (2012). Hippotherapy—an intervention to habilitate balance deficits in children with movement disorders: A clinical trial. Physical Therapy, 92, 707–717. doi:10.2522/ptj.20110081 Silkwood-Sherer, D., & Warmbier, H. (2007). Effects of hippotherapy on postural stability in persons with multiple sclerosis: A pilot study. Journal of Neurologic Physical Therapy, 31, 77–84. doi:10.1097/NPT. 0b013e31806769f7 Sterba, J. A., Rogers, B. T., France, A. P., & Vokes, D. A. (2002). Horseback riding in children with cerebral palsy: Effect on gross motor function. Developmental Medicine & Child Neurology, 44, 301– 308. doi:10.1111/j.1469-8749.2002.tb00815.x Tseh, W., Caputo, J. L., Craig, I. S., Keefer, D. J., Martin, P. E., & Morgan, D. W. (2000). Metabolic accommodation of young children to treadmill walking. Gait and Posture, 12, 139–142. doi:10.1016/S0966-6362(00) 00063-1 Unnithan, V. B., Murray, L. A., Timmons, J. A., Buchanan, D., & Paton, J. Y. (1995). Reproducibility of cardiorespiratory measurements during submaximal and maximal running in children. British Journal of Sports Medicine, 29, 66–71. doi:10.1136/bjsm.29.1.66 Winsley, R. J., Armstrong, N., Bywater, K., & Fawkner, S. G. (2003). Reliability of heart rate variability measures at rest and during light exercise in children. British Journal of Sports Medicine, 37, 550– 552. doi:10.1136/bjsm.37.6.550
Copyright of Research Quarterly for Exercise & Sport is the property of Routledge and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
