A NOVEL RUNNING MECHANIC’S CLASS CHANGES KINEMATICS BUT NOT RUNNING ECONOMY DANIEL H. CRAIGHEAD,1 NICK LEHECKA,2

AND

DEBORAH L. KING1

1

Department of Exercise and Sport Sciences, Ithaca College, Ithaca, New York; and 2Finger Lakes Running and Triathlon Company, Ithaca, New York ABSTRACT

Craighead, DH, Lehecka, N, and King, DL. A novel running mechanic’s class changes kinematics but not running economy. J Strength Cond Res 28(11): 3137–3145, 2014—A novel method of running technique instruction, Midstance to Midstance Running (MMR), was studied to determine how MMR affected kinematics and running economy (RE) of recreational runners. An experimental pre-post randomized groups design was used. Participants (n = 18) were recreational runners who ran at least 3 days a week and 5 km per run. All testing was performed on a treadmill at 2.8 m$s21. The intervention group (n = 9) completed 8 weeks of instruction in MMR; the control group (n = 9) continued running without instruction. The MMR group showed significant decreases in stride length (SL) (p = 0.02) and maximum knee flexion velocity in stance (p = 0.01), and a significant increase in stride rate (SR) (p = 0.02) after 8 weeks. No significant changes were found in heart rate, rating of perceived exertion, or RE. Midstance to Midstance Running was effective in changing SR and SL, but was not effective in changing other kinematic variables such as foot contact position and maximum knee flexion during swing. Midstance to Midstance Running did not affect RE. Evidence suggests that MMR may be an appropriate instructional method for recreational runners trying to decrease SL and increase SR.

KEY WORDS biomechanics, physiology, movement, oxygen consumption, stride rate, stride length INTRODUCTION

R

unning is one of the most popular forms of exercise, and with the numerous health benefits of running, its popularity is increasing. According to the 2013 National Runner Survey, over 15.5 million people finished running events in 2012, and these numbers increased over threefold since 1990 (31). Most of the runners participating in running events are core, or recreational, Address correspondence to Deborah L. King, [email protected]. 28(11)/3137–3145 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association

runners. Core runners are defined as active adult runners who run throughout the year. These individuals primarily run for exercise or health benefits, but also participate in 7–8 running events per year depending on gender (31). Given this popularity of running, it is no surprise that continued focus has been placed on optimizing running technique to improve performance and reduce injury rates in runners. The relationship between running technique and running injuries is complex; although, decreases in ground reaction force (GRF) magnitude and loading rate (LR) may reduce the risk of running-related injuries (2,18,28). Common running techniques promoted to reduced GRFs are shorter stride lengths (SLs), increased stride rates (SRs), and mid or forefoot strike patterns at initial contact (IC) (18). Stride rate and SL have also been linked to running performance along with decreased vertical oscillation of the center of mass (COM), increased knee flexion angle during swing, lower GRFs, and effective use of elastic energy (1,21,27,30,32,37). One of the most valuable and common predictors of distance running performance is running economy (RE) (32). Runners with better RE have a lower energy cost for running a given speed than runners with poor RE. Running economy is influenced by training, environmental, physiological, and anthropometric factors in addition to biomechanical factors (32); running well requires skill and correct timing of movements (1). Thus, in addition to optimizing training regimens to maximize physiological responses to improve performance, runners strive to optimize running form. Changing running technique is not trivial. Motor skill acquisition relies on instruction, demonstration, understanding of mechanical principles, and feedback (34). Running technique modifications have been successfully implemented in healthy and injured runners through gait re-training programs that involved 8 treadmill running sessions over 2 weeks of treadmill running with real-time kinematic feedback (6,7,29). Mirror training and verbal feedback have also successfully been used over an 8-session training program to alter running mechanics in runners with patellofemoral pain (38). However, these intense gait re-training regimens, 8 days of training over 2 weeks, may not be sufficiently time or cost-effective for the recreational runner trying to improve running form. Pose and Chi running are 2 popular techniques that are purported to improve running performance and are available VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |

3137

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

Running Mechanics Classes to runners through clinics, videos, books, software applications, or virtual training programs. Both Pose and Chi running emphasize a mid or forefoot strike with reduced SLs. Pose running stresses a forward lean of the trunk, such that the shoulder, hip, and heel of the stance leg are vertically aligned at contact (2). This IC position is the “Pose.” Chi running also stresses proper postural alignment and a slight forward lean but further emphasizes a relaxed body posture (8). To create these running adaptations, both Pose and Chi training programs use running drills with instruction, demonstrations, and feedback. In addition to focusing on IC postures and foot contact position, both techniques incorporate vertical removal of the foot from the ground during stance emphasizing lifting the foot from ground instead of pushing down against the ground. Specific kinematic adaptations, as compared with traditional heel strike running, are increased knee flexion at IC and TO (2,9), increased ankle plantarflexion at IC (2), reduced foot contact distance (17), and increased knee flexion and ankle dorsiflexion in stance (2). In general, the fore or midfoot striking emphasized in Pose and Chi running is characterized by decreased SLs (increased SRs), lowered impact forces, and improved use of stored elastic energy in comparison to a rearfoot strike (14,23,24,26,30,35). In Pose running, the kinematic adaptations have been associated with reduced power absorption and generation at the knee, increased power absorption at the ankle (2), and reduced vertical oscillation (2,9,17). Pose running also has decreased GRFs (19). Chi runners perform less eccentric work at the knee and have lower LR than traditional heel strikers (19). However, the effectiveness of Pose and Chi running on decreasing running-related injuries and improving running performance is equivocal (20). For the Pose method, the observed alterations in running biomechanics have not been associated with improvements in RE. Inconsistent and even detrimental effects on RE have been reported (2,9,17). No scientific evidence was found on Chi running’s effect on running performance. A new running instructional method called Midstance to Midstance Running (MMR) has similar biomechanical goals as Pose and Chi running including midfoot striking, vertical removal of the foot after contact, decreased vertical oscillation, and decreased SL. However, MMR has different teaching methods than Pose or Chi running. The overarching aim of MMR is to simplify the process for runners trying to achieve a midfoot strike pattern. Midstance to Midstance Running classes teach runners to focus on the primary instruction of lifting the foot from the ground immediately after IC and bringing it straight toward the buttocks. This instruction is combined with basic video feedback. The MMR’s instruction is grounded in the antiphase interlimb coordination of bipedal locomotion in humans (12). The hip and knee flexion used to vertically lift the foot from the ground is hoped to create hip extension of the opposing leg. Earlier hip extension is aimed at creating

3138

the

an IC more underneath the body on a slightly flexed knee with a slightly plantarflexed ankle. Quickly lifting the foot from the ground, as opposed to emphasizing a push back and down against the ground, is also hoped to reduce vertical oscillation. These kinematic adaptations ideally will create a mid or forefoot strike with reduced SL and improved RE. Emphasizing 1 primary technique as the focal point of instruction is hoped to improve motor learning (22) and enable runners to more easily change their running technique. Video feedback is provided to supplement learning (22). Additional analogies and mental images that augment the main cue are used as needed. With growing evidence to suggest that running at a higher SR with a mid or forefoot strike pattern benefits some runners, strength and conditioning practitioners, runners, and coaches need to know which running technique programs are effective. Accordingly, the purpose of this study was to determine whether MMR classes would change SR, SL, lower extremity kinematics, and RE in recreational runners. It was hypothesized that 8 weeks of MMR training would (a) increase SR and decrease SL, (b) increase knee flexion and ankle plantarflexion and decrease hip flexion and horizontal position of ankle at IC, (c) increase maximum knee flexion and maximum knee flexion velocity during stance, (d) increase maximum knee flexion and maximum knee flexion velocity during swing, (e) reduce vertical oscillation, and (f ) improve RE.

METHODS Experimental Approach to the Problem

This study aimed to establish the effects of MMR on running biomechanics and RE. An 8-week intervention was selected to provide sufficient time for adaptations to occur (2,6,7,9,17,29,38). During the 8-week training period, runners were required to attend five 1-h running classes totaling 5 hours of MMR class instruction. Other running technique programs have provided instructional time ranging from 2.5 to 15 hours (2,6,7,9,17,29,38). Requiring only 5 hours of supervised practice for this study was an intentional choice. The intervention time frame represented a realistic time commitment for recreational runners and provided instructional hours and practice time in a range that has been successfully used for running re-training (2,6,7,9,17,29,38). An experimental pre-post randomized group design was used. Independent variables for the study were group (MMR and control) and time (pre and post). Runners were pair matched first on gender, then age, weekly mileage, and pace. Both the control (no running classes) and MMR (5 running classes) groups were instructed to continue their regular running and training programs over the 8-week period. To test the effect of the MMR classes on running biomechanics and RE, SR, SL, 9 lower extremity kinematic variables, heart rate (HR), rating of perceived exertion (RPE), and RE were measured pre (at week 0) and post (at week 9) the 8-week training period. These variables comprised the dependent variables for the study. Sagittal plane lower extremity kinematics have high reliability (0.93–1.00) when

TM

Journal of Strength and Conditioning Research

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

the

TM

Journal of Strength and Conditioning Research multiple trials are averaged together (13). Running economy has good reliability and improves at workloads under lactate threshold and when controlling for time of day, day of week, diet, and footwear (32). In particular, energy cost, SR, HR, and respiratory parameters are stable measures for runners with SR being the most stable (4). Intraclass correlation coefficients for running HR, RPE, and V_ O2 are reported to range from 0.84 to 0.96 for HR, 0.82 to 89 for RPE, and 0.93 to 0.96 for relative V_ O2 (15). Subjects

Using data from the literature (2,9,17), a sample size estimation revealed that 10 runners per group were needed to detect a 5% difference in means at a power level of 0.8 for an alpha value of 0.05 for the kinematic variables. Twentyone healthy adult recreational runners volunteered to participate in this study. Inclusion criteria included being 18 years or older, no injuries limiting running in the past 6 months, and running a minimum of 3 days per week at least 5 km per day at a self-reported speed between 2.7 and 3.0 m$s21 for the past 6 months. All participants had a history of participating in road races ranging in distance from 5 km to marathons and had been running for a minimum of 2 years. Over the course of the study, 2 participants dropped out between sessions 1 and 2 and 1 participant dropped out during the 8-week intervention period, all due to injury. The oldest participant in the MMR group was one of the participants who dropped out due to injury. A total of 18 runners completed the study, 9 in the MMR group and 9 in the control group (Table 1). All participants who finished the study were free of injury during the entire study. The study was approved by the Ithaca College All-College Review Board for Human Subjects Research, and all participants gave their written informed consent before participating. Procedures

Each participant completed 3 treadmill (model C954; Precor USA, Woodinville, WA, USA) running sessions at 2.8 m$s21, the median self-reported running speed of the participants, which was chosen to elicit RPE values between 12 and 14,

| www.nsca.com

“somewhat hard,” on the Borg scale. The treadmill grade was set to zero. Session 1 was a treadmill familiarization session designed to allow treadmill running kinematics to become reliable (25,33) and consisted of two 15-minute back to back treadmill runs with participants allowed up to 5-minute rest between the 2 runs. Session 2, pretesting at week 0, consisted of a 15-minute treadmill run with sagittal kinematic video collected during minutes 5 and 10. Submaximal V_ O2, HR, and RPE were collected during the last 5 minutes. After session 2, participants were pair matched into MMR and control groups first based on gender, followed by age, weekly mileage, and finally by pace. After being matched, one of each pair was randomly assigned to the MMR group and the control group. The MMR group was required to attend 5 MMR classes over the next 8 weeks. The MMR classes were administered at a local running specialty store in Ithaca, NY. Each class was 1-hour long. Session 3, posttesting, was identical to session 2 but occurred during week 9 after the 8-week training program. Sessions 2 and 3 were scheduled for the same time of the day, within 1 hour, and same day of the week if possible. If the same day of week could not be scheduled, testing was scheduled on a similar day of week (workday schedule vs. weekend). Participants were instructed not to engage in vigorous physical activity the day of or before testing and to follow the same daily schedule each testing day. Participants wore the same running shoes for both testing sessions. Testing was completed in a temperature-controlled room (728–748), and the participants completed identical selfselected warm-ups before testing for both sessions 2 and 3. Kinematics

Kinematic data were obtained with a high-speed video camera (Fastcam PCI R2; Photron USA, Inc., San Diego; CA, USA) recording at 250 Hz, placed on a tripod perpendicular to the sagittal plane of the runner 4.6 m from the center of the treadmill and 1.2 m high. A light was attached to the camera in line with the camera’s optical axis to illuminate reflective markers placed on the participant.

TABLE 1. Participant characteristics.*† MMR

Age (y) Height (m) Mass (kg) Running volume (km$wk21)

Control

Mean 6 SD

Range

6 6 6 6

23–66 1.57–1.78 55.9–79.5 14.1–62.5

43.1 1.72 70.9 29.6

15.8 7.9 13.1 16.6

Mean 6 SD

Range

p

6 6 6 6

22–47 1.55–1.80 55.2–87.3 15.6–46.9

0.391 0.992 0.645 0.596

37.6 1.68 68.1 26.1

10.0 8.9 12.2 10.1

*MMR = Midstance to Midstance Running. †p-values are for independent t-tests between the 2 groups (MMR and control) for each variable.

VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |

3139

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

Running Mechanics Classes A 0.7 3 0.4 m rectangular calibration frame was held at waist level over the belt of the treadmill parallel to the sagittal plane to perform a 2-dimensional calibration before each testing session. Eight retroreflective markers were placed on the right side of the participant over the shoulder joint center, greater trochanter, lateral femoral condyle, lateral malleolus, lateral fifth metatarsal head, and lateral posterior calcaneus to define trunk, thigh, leg, and foot segments. Five strides from the fifth minute of running were automatically digitized and filtered with a fourth order Butterworth filter using automatic cutoffs as determined with the Jackson knee point method using Vicon Motus software (version 8.4; Vicon, Centennial, CO, USA). A stride was defined from right foot IC to the subsequent right foot IC. Initial contact was visually determined from the video as the first frame where the foot was in contact with the treadmill. From the 2D coordinates, 9 kinematic variables were calculated (Table 2). Two spatiotemporal variables, SR and SL, were calculated directly from the video data. Stride rate was calculated based on the frame numbers of each IC. Stride length was calculated using the formula velocity = SR 3 SL in m$s21. All kinematic and spatiotemporal variables were averaged across the 5 strides for subsequent analysis. Finally, foot strike pattern was categorized as rearfoot strike, midfoot strike, or forefoot strike by using foot angle at IC and visual inspection based on the methods of Daoud et al. (10). The researcher who categorized the foot strike pattern was blinded to the participant’s intervention group.

Running Economy

Physiological data were measured during the last 5 minutes of the run allowing sufficient time for the participants to achieve steady state (27). Heart rate data were measured with a HR monitor (Polar Electro, Inc., Lake Success, NY, USA) secured around the participant’s chest, and RPE was obtained every minute using Borg’s 6–20 scale (3). Both HR and RPE were recorded every minute. Expired air samples were analyzed with a Parvo Medics metabolic cart (TrueOne 2400 Metabolic Measurement System; Parvo Medics, Sandy, UT, USA) connected to a 2-way non-rebreathing valve (model 2700 large 2-way NRBV; Hans Rudolph, Inc., Kansas City, MO, USA) through which the participants breathed atmospheric air. A nose clip was placed on the participant’s nose. Before each testing session, the flow meter was calibrated with a 3-L calibration syringe (series 5530 3-L; Hans Rudolph, Inc.), and a reference air calibration of the system was performed using a certified gas mixture containing 16% O2 and 4% CO2. Data were measured breath-by-breath, and the respiratory values were averaged every 30 seconds. The HR, RPE, and V_ O2 measurements were averaged over the last 5 minutes for further analysis. Running economy was calculated and expressed as ml$kg21$km21 (16). Training Protocol

For the MMR classes, each MMR participant was videotaped with a standard digital camcorder from the sagittal plane for several running strides at the beginning of the first class. After videoing, all participants were given the same

TABLE 2. Treatment and control groups’ biomechanical variables pre and post (means 6 SD) with ES.*† MMR group Variable SR (strides$s21) SL (m$stride21) Ankle to GT (m) DyGT (m) uThigh_IC (8) uKnee_IC (8) uAnkle_IC (8) uKnee_MSt (8) vKnee_Max_ST (8$s21) uKnee_MSw (8) vKnee_ Max_SW (8$s21)

Pre 1.38 2.02 0.20 0.12 20.4 11.5 20.9 43.8 530.5 87.0 487.3

6 6 6 6 6 6 6 6 6 6 6

0.06 0.09 0.03 0.03 4.2 6.2 6.5 4.9 72.7 8.8 46.7

Control group

Post

ES

6 6 6 6 6 6 6 6 6 6 6

0.94 0.67 0.67 0.00 0.11 0.85 0.52 0.27 0.98 0.51 0.35

1.42 1.96 0.18 0.12 20.8 15.7 23.8 44.9 469.6 91.7 504.7

0.06z 0.09z 0.03 0.02 2.2 3.2 4.6 3.2 49.5z 9.6 52.4

Pre 1.40 2.00 0.18 0.13 17.3 8.3 21.3 42.3 510.6 87.6 525.2

6 6 6 6 6 6 6 6 6 6 6

Post 0.07 0.11 0.04 0.02 4.8 5.5 6.3 4.5 37.3 13.8 92.2

1.41 1.99 0.19 0.13 19.5 11.4 21.5 47.4 513.9 88.4 497.1

6 6 6 6 6 6 6 6 6 6 6

ES 0.08 0.12 0.03 0.02 3.6 6.6 5.2 5.5§ 63.2 10.5 52.2

0.13 0.09 0.28 0.00 0.52 0.51 0.03 1.0 0.06 0.07 0.38

*MMR = Midstance to Midstance Running; ES = effect sizes; SR = stride rates; SL = stride lengths; GT = greater trochanter; IC = initial contact; TO = toe-off. †Ankle to GT = horizontal distance of the ankle to the GT at IC. DyGT = maximum vertical displacement of the GT during 1 stride. uThigh_IC = absolute angle of the thigh to vertical at IC, + = flexion. uKnee_IC = knee angle at IC, + = flexion. uAnkle_IC = ankle angle at IC, = is dorsiflexion. uKnee_MSt = maximum knee flexion during stance. vKnee_Max_ST = maximum knee angular velocity during stance. uKnee_MSw = maximum knee flexion during swing. vKnee_ Max_SW = maximum knee angular velocity during swing. Stance was defined from IC to TO and swing from TO to the subsequent IC of the same leg. zSignificant interaction: post MMR significantly different from pre (p , 0.025). §Significant interaction: post control significantly different from pre (p , 0.025).

3140

the

TM

Journal of Strength and Conditioning Research

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

the

TM

Journal of Strength and Conditioning Research

| www.nsca.com

TABLE 3. MMR and control groups’ physiological variables means and SD.* MMR group

Control group

Variable

Pre

Post

ES

Pre

Post

ES

RE (ml$kg21$km21) HR (b$min21) RPE

206.5 6 18.5 140.8 6 23.7 12.1 6 2.24

203.0 6 15.0 150.1 6 18.9 11.6 6 1.95

0.20 0.43 0.24

199.3 6 19.5 146.7 6 17.10 11.5 6 2.37

200.5 6 11.3 150.6 6 13.1 10.9 6 2.18

0.08 0.26 0.26

*MMR = Midstance to Midstance Running; RE = running economy; HR = heart rate; RPE = rating of perceived exertion.

30-minute introduction to MMR running covering the differences of running with decreased SL and a mid or forefoot strike pattern as compared with a typical rearfoot strike running pattern. Following the introduction, the participants viewed their running as a group and then took turns treadmill running for 5 minutes at a time while being

videoed and receiving verbal cues and feedback. Specifically, participants were told to focus on lifting the stance leg from the ground early, just after contact, and to bring the foot straight up to the buttocks. As needed, analogies were provided for the participant such as imagining a wall directly behind them prohibiting backward movement of the foot. This process was repeated until each participant ran and received personal feedback 3 times for a total of 15 minutes of running. Throughout the process, the participants watched and learned from other participants. The participants were told to focus on the MMR technique during every run throughout the next 8 weeks. During subsequent visits, the MMR participants received both individual and group instruction by 2 MMR trained instructors. Participants were again videoed running on a treadmill for 5 minutes while receiving individual feedback and watching and learning from other runners. Each participant completed 3 rotations totaling 15 minutes of running with instruction and feedback. After each session, participants were again reminded to focus continually on bringing the foot quickly toward the buttocks immediately after IC during all their runs. All sessions were 1 hour in length. During the 8-week training program, the control group Figure 1. The effect of Midstance to Midstance Running (MMR) instruction compared with no instruction received weekly educational on stride length (A) and stride rate (B). *Statistically significant change from pre to post for the MMR group (p # 0.025). materials on running training; these materials did not relate VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |

3141

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

Running Mechanics Classes to the topic of the study. Examples of topics addressed in the materials included running in the heat, cross-training, and common running injuries. After the 8-week period, all participants returned for session 3 which was identical to session 2. After the completion of the study, MMR group participants were given the educational materials originally provided to the control group, and control group participants were offered 2 free MMR classes. Statistical Analyses

Data analyses were completed using IBM SPSS Statistics version 19 (SPSS, Inc., Chicago, IL, USA) with alpha set to 0.05. Means and SDs were computed for all variables. Independent t-tests were performed for age, height, mass, and running volume to compare basic demographics between the 2 groups. Effect sizes were calculated for each dependent variable from pre- to post-training by group. Two-way repeated-measures analysis of variance tests with 1 between-factor (group) and 1 within-factor (time) were used to identify differences in the dependent variables between the 2 groups of participants. Shapiro-Wilk’s and Mauchly’s tests were conducted to verify the assumptions of normality and sphericity. Post hoc analyses were performed using paired t-tests to compare means for each significant groupby-time interaction to determine pre- to post-training differences for the MMR and control groups with the alpha level adjusted to 0.025 using the Bonferroni correction for multiple comparisons. Fischer’s exact test was used to identify differences in foot strike pattern for the MMR and control group from pre- to post-training.

RESULTS Means, SDs, and effect sizes of all kinematic variables are provided in Table 3. The data followed a normal distribution and did not violate the assumption of sphericity. There were no significant differences between groups for age, height, mass, or running volume (Table 1). There were significant group-by-time interactions for SR and SL. Stride rate increased 4% (p = 0.016) after intervention with an accompanying decrease in SL (p = 0.016) in the MMR group (Figure 1). The effect sizes for SL and SR were moderate to large for the MMR group (Table 2). There were no significant changes in SR or SL in the control group. There were significant group-by-time interactions for knee angle at midstance (uKnee_MSt) and maximum knee flexion velocity in stance (vKnee_Max_ST). After the 8-week training period, uKnee_MSt increased 48 (p = 0.002) in the control group with no change in uKnee_MSt in the MMR group. Maximum knee flexion velocity in stance decreased of 618$s21 (p = 0.013) in the MMR group pre to post with no change in the control group. Both of these effect sizes were large (Table 2). The effect size for maximum knee flexion during swing (uKnee_MSw) was moderate for the MMR group (Table 2), but there were no significant differences in uKnee_MSw. During pretesting, 8 of the 9 MMR participants and all of the control participants

3142

the

exhibited a rearfoot strike pattern. During posttesting, the number of rearfoot strikers decreased to 6 in the MMR group and 9 in the control group. These changes were not significant. Foot strike, quantified by ankle angle at IC (uAnkle_IC), showed no significant changes from pre to post; although, the effect size for the MMR group was moderate (Table 2). Average RPE values were slightly lower than the target 12 to 14 “somewhat hard” zone; however, all but 2 participants, 1 in the MMR group and 1 in the control group, were between 11 and 14 for during pre- and posttesting. There were no significant interactions or main effects for submaximal HR, RE, or RPE (Table 3).

DISCUSSION Midstance to Midstance Running participants had significant changes in running form; although, only one of the hypotheses was supported. Specifically, there was a decrease in SL and an increase SR. Although the effect sizes were moderate to large, the 3–4% changes in SR and SL were smaller than the 14–15% reported after 7 consecutive days of Pose instruction (17) and the 6% change observed after Pose instruction once a week for 12 weeks (9). The smaller changes in this study may be because of the reduced volume of training used in the MMR intervention. However, it is also possible that the smaller changes could be because of the instructional technique used in MMR or the recreational level of runners. Midstance to Midstance Running relies less heavily on drills and modeling as compared with Pose instruction. Instead, MMR relies primarily on video feedback and verbal instruction. Though running re-training has successfully been accomplished without drills through real-time kinematic feedback and mirror training, these studies provided more intense practice, scheduling training session 4 times a week for 2 weeks, as compared with the MMR instruction (6,7,29,38). A decrease in maximum knee flexion velocity during stance was observed in the MMR group, in contrast to the hypothesized increase. Fletcher et al. (16) also reported a significant decrease in maximum knee flexion velocity during stance after Pose training. They postulated that Pose running caused a more aligned body posture at contact that reduced knee flexion and lowered knee flexion velocity during stance (17). Knee flexion velocity during stance is related to loading and thus has implications for injury risk. A higher knee flexion velocity is usually associated with a decrease in impact loading by effectively reducing the mass of the contacting leg (11). Thus, lower knee flexion velocities could increase LR in MMR. However, an increased in SR, which was also observed in MMR, is associated with smaller LRs which could counteract the effects of the decrease in knee flexion velocity during stance in MMR (26). In comparison, impact forces and LR have been found to be lower in Pose runners as compared with rearfoot running (2); although, Pose running involves a midfoot strike which was not consistently observed in the MMR participants. Fletcher et al. (17), however, did not find a decrease in impact forces with Pose

TM

Journal of Strength and Conditioning Research

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

the

TM

Journal of Strength and Conditioning Research running, though their runners also exhibited a decrease in maximum knee flexion velocity during stance. With the decreased knee flexion velocity during stance combined with increased SR and absence of a midfoot strike pattern in the MMR runners, it is difficult to postulate the effects of MMR on impact forces. Previous studies focusing on Pose running have found changes in foot and knee angles at IC as well as a decreased horizontal distance between the foot and the COM at IC that were not observed in this study (2,9,17). It is possible that the significant knee and ankle angle changes observed with Pose running were not found in MMR because Pose running focuses on specific kinematic events with drills and cues designed for each event. In particular, Pose running places emphasis on achieving the shoulder over hip over ankle pose at IC with a midfoot strike (2). The instructional method for MMR, after a general introduction to desired running changes such as landing under the COM and limiting COM vertical oscillation, relies primarily on the cue to lift the foot vertically from the ground immediately after IC. Midstance to Midstance Running participants may have found multiple kinematic solutions to accomplish this 1 instruction. If different adjustments took place between the participants, no consistent biomechanical changes would be observed at IC. Conversely, in Pose running, the multiple drills focusing on IC foot and body position may allow runners to attain more consistent IC kinematics. Although the hypotheses that the knee would be more flexed, the ankle more plantarflexed, and the foot more underneath the body at IC were not supported, there were moderate to large effect sizes for these variables in the MMR group. In contrast, a moderate effect size was found only for knee flexion at IC for the control group. Particularly interesting was the large effect size for ankle plantarflexion at IC for the MMR group; though, the 38 increase in ankle plantarflexion was not significant. Moreover, only 2 people in the MMR group changed from a rearfoot to forefoot or midfoot strike pattern. Interestingly, although both Pose and Chi running are characterized by mid of forefoot strikes, only 1 study has reported significant changes in ankle angle at IC (2). Moreover, Goss (19) reported that 11 of the 23 Chi runners and 5 of the 7 Pose runners recruited for a study had a rearfoot strike. Further research is needed to determine whether changing IC kinematics with MMR instruction is possible with increased volume of instruction or alterations in instructional technique. Even though lifting the foot from the ground immediately after IC is the foundational instruction of MMR, there were no significant changes in maximum knee flexion or maximum knee flexion velocity during swing. However, there was a moderate effect size in maximum knee flexion during swing for the MMR group. Similarly, recreational runners who underwent 7.5 hours of Pose training did not exhibit changes in knee flexion during swing (2). The Pose training included instruction on lifting the foot toward the buttocks

| www.nsca.com

as one of several instructions that included aligning the shoulder, hip, and ankle in stance, leaning forward to allow the body to fall forward, contacting with the midfoot, and maintaining a flexed knee throughout the gait cycle (2). In comparison, the MMR runners’ focus of attention was simply on lifting the foot quickly and vertically from the ground. It is possible that more intense or longer training is required to elicit significant changes in swing phase knee kinematics or that only small subtle changes in swing phase kinematics are required to elicit the main goal of shorter strides and faster SRs in MMR. There was no change in vertical oscillation following MMR instruction. Vertical oscillation has been shown to decrease in Pose running; although, these studies used a higher volume and density of training than in this study (2,9). Decreased vertical oscillation is related to improved RE (37) and thus, along with decreased SL and increased SR, decreased vertical oscillation, is a main goal of MMR running. However, Dallam et al. (9) reported an increase in submaximal oxygen consumption after Pose training even though the Pose runners had a decreased vertical oscillation after training. There was no significant change in RE after MMR training as was hypothesized in this study. These results corroborate findings of the Pose method, which report either no change in RE (17) or an increase in oxygen cost indicating a decreased RE (9). Importantly, RE did not decrease in the MMR group and RPE did not increase. The MMR participants did not have an increase in oxygen cost and did not perceive an increase in exertion using the novel MMR running style. Even though there were no significant changes in RE in this study, it is not possible to make conclusions about running performance after MMR training. Paradoxically, runners trained in the Pose method realized a nonsignificant average increase of 25 seconds in a 2.4-km time trial post-training with no change in RE (17). Running economy has been linked to optimal SL (1), although the changes in SL observed in this study were not accompanied by changes in RE. Dallam et al. (9) postulated that experienced runners may already run with optimized SL and SR in support of work by Cavanagh and Williams (5) who reported that shod recreational distance runners (40–110 miles per week) naturally adopted an optimal SL. In contrast, Morgan et al. (27) reported that 20% of distance runners ran with a stride that was too long and were able to improve their RE by training for 3 weeks with a reduced SL. Further research is needed to determine if the decreased SL and increased SR of MMR improve RE or performance in runners who over stride. Despite the running technique changes observed in MMR and the growing body of literature documenting kinematic and kinetic changes with minimalist (34), barefoot (11,14,23,26,30,36), Pose (2,9,17), and Chi (19) running, the effects of these running styles on RE, running performance, VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |

3143

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

Running Mechanics Classes and injury are still inclusive. It would be worthwhile to examine the effects of MMR on runners identified as overstriders as the literature suggests that decreasing SL can be beneficial in this group of runners (30). Further research is also warranted to understand the long-term adaptations to MMR and to measure effects on running performance and injury.

PRACTICAL APPLICATIONS Recreational, or core, runners are increasing in number and constitute an important component of runners in the United States. These runners are running for health and fitness benefits yet still participate in running events, such as 5 km, 10 km, half marathon, and marathons at a rate of more than 1 every 2 months. These runners are committed and motivated; however, relatively few evidence-based running technique programs are available for these runners. Because running technique is linked to injury risk and RE, strength and conditioning specialists working with runners will benefit from knowing which running techniques or programs are effective. The results of this study suggest that MMR as an instructional method to improve running technique can be effective at decreasing SL and increasing SR in recreational runners. However, the specific kinematic adaptations that cause the change in SR and SL may vary across runners. Midstance to Midstance Running was not effective in eliciting a mid or forefoot strike pattern or in improving RE in these recreational runners. Even though 2 runners in the MMR group did change to a midfoot strike pattern posttraining, there is no evidence supporting the use of MMR as a technique to illicit a mid or forefoot strike pattern. Thus, strength and conditioning practitioners using MMR with runners should not expect a change in foot strike pattern using MMR running. Importantly, however, RE did not decrease nor were there changes in perceived difficulty in MMR running. Runners using MMR did not incur negative performance effects as measured by HR, RE, or RPE. Running performance, however, was not directly measured in this study. Because of the possible benefits of increasing SR for runners who over stride, MMR instruction is a technique that strength and conditioning practitioners could try with these runners. For MMR to be implemented, the strength and conditioning professional needs an understanding of the fundamental concepts and key cues of MMR and a camcorder or mobile device camera. The underpinning concept to MMR is the cyclical out of phase pattern of the legs during running. Runners can focus on lifting their foot vertically from the ground after contact to achieve a shorter faster stride. Cue phrases can include variations of: “lift your foot from the ground early,” “lift your foot vertically off the ground, don’t push down,” and “pull your foot to your buttocks right after contact.” Strength and conditioning practitioners can add instructions such as “avoid pushing off the

3144

the

ground” and “imagine a wall directly behind you limiting a backwards push.” The strength and conditioning practitioner can use any type of video camera oriented to provide a side view of the runner. The camera can be handheld. Video is provided of the runner’s initial running form, and then following introduction of MMR and instruction, video is taken over a minimum of 15 minutes of running with viewing and feedback opportunities provided within these 15 minutes. It is important when providing feedback to be specific and to focus on the exact technique component that needs to be changed or improved (22). For example, the strength and conditioning practitioner should visually draw attention to the path of the heel or ankle on the video as it comes off the ground and give a specific comparison to the desired motion. Midstance to Midstance Running instruction with video feedback is repeated every 1–2 weeks over the course of 8 weeks. MMR taught in this manner seems to be effective in increasing SR and decreasing SL in adult recreational runners who train regularly. Thus, MMR is an instructional technique that strength and conditioning practitioners can try with runners who are striving to decrease SL and increase SR.

ACKNOWLEDGMENTS The authors acknowledge the Finger Lakes Running and Triathlon Company for donating running classes for this study and discounts for participants. Additionally, the authors thank the second author, the originator of the MMR instructional method, for initiating this project. The authors also acknowledge all the individuals who assisted with data collection and MMR class instruction and participated in this project. The results of this study do not constitute endorsement of MMR by the authors.

REFERENCES 1. Anderson, T. Biomechanics and running economy. Sports Med 22: 76–89, 1996. 2. Arendse, RE, Noakes, TD, Azevedo, LB, Romanov, N, Schwellnus, MP, and Fletcher, G. Reduced eccentric loading of the knee with the pose running method. Med Sci Sports Exerc 36: 272–277, 2004. 3. Borg, G. Perceived exertion as an indicator of somatic stress. Scand J Rehabil Med 2: 92–98, 1970. 4. Brisswalter, J and Legros, P. Daily stability in energy cost of running, respiratory parameters and stride rate among well-trained middle distance runners. Int J Sports Med 15: 238–241, 1994. 5. Cavanagh, PR and Williams, KR. The effect of stride length variation on oxygen uptake during distance running. Med Sci Sports Exerc 14: 30–35, 1982. 6. Cheung, RTH and Davis, IS. Landing pattern modification to improve patellofemoral pain in runners: A case series. J Orthop Sports Phys Ther 41: 914–919, 2011. 7. Crowell, HP and Davis, IS. Gait retraining to reduce lower extremity loading in runners. Clin Biomech (Bristol, Avon) 26: 78–83, 2011. 8. Cucuzella, M. Training runners in ChiRunning, can it minimize injury and make running more comfortable? Fam Med 41(Suppl.1): 529, 2009.

TM

Journal of Strength and Conditioning Research

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.

the

TM

Journal of Strength and Conditioning Research 9. Dallam, GM, Wilber, RL, Jadelis, K, Fletcher, G, and Romanov, N. Effect of a global alteration of running technique on kinematics and economy. J Sports Sci 23: 757–764, 2008. 10. Daoud, AI, Geissler, GJ, Wang, F, Saretsky, J, Daoud, YA, and Lieberman, DE. Foot strike and injury rates in endurance runners: A retrospective study. Med Sci Sports Exerc 44: 1325–1334, 2012. 11. De Wit, B, De Clercq, D, and Aerts, P. Biomechanical analysis of the stance phase during barefoot and shod running. J Biomech 33: 269–278, 2000. 12. Dietz, V. Spinal cord pattern generators for locomotion. Clin Neurophysiol 114: 1379–1389, 2003. 13. Diss, CE. The reliability of kinetic and kinematic variables used to analyse normal running gait. Gait Posture 14: 98–103, 2001. 14. Divert, C, Mornieux, G, Freychat, P, Baly, L, Mayer, F, and Belli, A. Barefoot-shod running differences: Shoe or mass effect? Int J Sports Med 29: 512–518, 2008. 15. Doma, KG and Blass, RM. The reliability of running economy among trained distance runners and field-based players. J Exerc Sci Fit 10: 90–96, 2012. 16. Fletcher, B, Esau, JR, and Macintosh, SP. Economy of running: Beyond the measurement of oxygen uptake. J Appl Physiol (1985) 107: 1918–1922, 2009. 17. Fletcher, G, Romanov, N, and Bartlett, R. PoseÒ method technique improves running performance without economy changes. Int J Sports Sci Coaching 3: 365–380, 2008. 18. Giandolini, M, Arnal, PJ, Millet, GY, Peyrot, N, Samozino, P, Dubois, B, and Morin, JB. Impact reduction during running: Efficiency of simple acute interventions in recreational runners. Eur J Appl Physiol 113: 599–609, 2013. 19. Goss, DL. A comparison of lower extremity joint work and initial loading rates among four different running styles. Dissertation, University of North Carolina, Chapel Hill, 2012. 20. Goss, DL and Gross, MT. A review of mechanics and injury trends among various running styles. US Army Med Dep J 62–71, 2012. 21. Halvorsen, K, Eriksson, M, and Gullstrand, L. Acute effects of reducing vertical displacement and step frequency on running economy. J Strength Cond Res 26: 2065–2070, 2012. 22. Knudsen, D and Morrison, C. Qualitative Analysis of Human Movement. Champaign, IL: Human Kinetics, 2002. pp. 108–120. 23. Kurz, MJ and Stergiou, N. Does footwear affect ankle coordination strategies? J Am Podiatr Med Assoc 94: 53–58, 2004.

| www.nsca.com

24. Larson, P, Higgins, E, Kaminski, J, Decker, T, Preble, J, Lyons, D, McIntyre, K, and Normile, A. Foot strike patterns of recreational and sub-elite runners in a long-distance road race. J Sports Sci 29: 1665–1673, 2011. 25. Lavcanska, V, Taylor, NF, and Schache, AG. Familiarization to treadmill running in young unimpaired adults. Hum Mov Sci 24: 544–557, 2005. 26. Lieberman, DE, Venkadesan, M, Werbel, WA, Daoud, AL, D’Andrea, S, Davis, IS, Mang’eni, RO, and Pitsiladis, Y. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 463: 531–535, 2010. 27. Morgan, D, Martin, P, Craib, M, Caruso, C, Clifton, R, and Hopewell, R. Effect of step length optimization on the aerobic demand of running. J Appl Physiol (1985) 77: 245–251, 1994. 28. Nigg, BN. Impact forces in running. Curr Opin Orthop 8: 43–47, 1997. 29. Noehren, B, Scholz, J, and Davis, I. The effect of real-time gait retraining on hip kinematics, pain and function in subjects with patellofemoral pain syndrome. Br J Sports Med 45: 691–696, 2011. 30. Perl, DP, Daoud, AI, and Lieberman, DE. Effects of footwear and strike type on running economy. Med Sci Sports Exerc 44: 1335–1343, 2012. 31. Running USA 2013 national runner survey. 2013 state of the Sport—Part I: “Core Runner” Profiles 2013. Available at: http://www.runningusa.org/ index.cfm?fuseaction=news.details&ArticleId=1539&returnTo=annualreports. Accessed August 30, 2013. 32. Saunders, PU, Pyne, DB, Telford, RD, and Hawley, JA. Factors affecting running economy in trained distance runners. Sports Med 34: 465–485, 2004. 33. Schieb, DA. Kinematic accommodation of novice treadmill runners. Res Q Exerc Sport 57: 1–7, 1986. 34. Schmidt, RA. Motor control and learning: A Behavioral emphasis. Champaign, IL: Human Kinetics, 1988. pp. 345–346–377–466. 35. Squadrone, R and Gallozzi, C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness 49: 6–13, 2009. 36. Utz-Meagher, C, Nulty, J, and Holt, L. Comparative analysis of barefoot and shod running. Sport Sci Rev 20: 113–130, 2011. 37. Williams, KR and Cavanagh, PR. Relationship between distance running mechanics, running economy, and performance. J Appl Physiol (1985) 63: 1236–1245, 1987. 38. Willy, RW, Scolz, JP, and Davis, IS. Mirror gait retraining for the treatment of patellofemoral pain in female runners. Clin Biomech (Bristol, Avon) 27: 1045–1051, 2012.

VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |

3145

Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.