299
Variations in Stride Length and Running Economy in Male Novice Runners Subsequent to a Seven-Week Training Program S. P. Bailey, S. P. Messier J. B. Snow Biomechanics Laboratory, Wake Forest University
Introduction
S. P. Bailey and S. P. Messier, Variations in Stride Length and Running Economy in Male Novice Runners Subsequent to a Seven-Week Training Program. mt j Sports Med, Vol l2,No 3,pp299—304, 1991.
There are many intrinsic biomechanical factors that are thought to influence running economy; however, empirical study supports the existence of only one factor as being of prime importance (8). Specifically, Hogberg (9) observed that alterations in stride length resulted in an increase in submaxirnal oxygen consumption. More recently, Cavanagh
Accepted: July 23, 1990
and Williams (4) have replicated Hogberg's study using a
The purposes of this investigation were to
ting techniques. They determined that experienced runners possessed a freely chosen stride length that minimized submaximal oxygen consumption.
document the changes in stride length of college-age male novice runners (n 13) who were allowed of freely choose
their stride length throughout a 7-week training period (FCSL), and to compare subsequent changes in running economy to those observed in a similar group of runners (n = 13) that ran for 7 weeks with constant stride lengths equivalent to their initially chosen stride lengths (CSL). Subjects trained 3 days per week for approximately 7 weeks
(22 training bouts). Each training bout consisted of a minute warmup (60% VO2max) and a 15-minute run at a speed equivalent to 80% of the subjects' initial VO2max. Absolute stride length (ASL), heart rate (HR), and ratings of perceived exertion (RPE) were measured during the 12th and 20th minute of exercise. Relative and absolute submaximal V02 were measured during the 4th and 22nd training bout. No significant differences in percent change in ASL were found between the groups or across the weeks of training at the 12th or 20th minute of exercise; however, there was a significant difference (p .05) between the groups during the 4th week of training. No significant differences were found between the groups in relative or absolute submaximal V02. Relative submaximal V02 at the 12th minute of exercise decreased significantly following the training period in both the FCSL (—3.38%) and CSL (—4.32%) groups. Absolute submaximal V02 did not change significantly following the training period. Significant reductions in HR and local and general RPEs were observed across the training period; however, no significant difference in any of these variables were found between the groups. These results indicate that the variability in stride length inherent in male novice runners has no significant effect on running economy during the intial 7 weeks of training. Key words
Stride length, running economy, perceived exertion mt. J. SportsMed. 12(1991)299—304 Georg Thieme Verlag StuttgartNew York
larger sample size (n = 10) and non-linear regression curve fit-
Alterations in stride length also appear to have a significant effect on the perceived effort of experienced run-
ners. Messier, Franke, and Rejeski (12) revealed that both local (legs) and general ratings of perceived exertion (RPE) were significantly greater during runs in which the stride length of experienced runners was 14% longer than their freely chosen stride length. Significant increases in local RPEs were
also observed during runs where these same subjects were asked to overstride by 7% or understride by 14%.
Dillman (6), in a review of the running literature, concluded that more experienced runners are likely to possess greater relative stride lengths than less experienced or novice runners. Cavanagh, Pollock, and Landa (3) found, however, that good runners possess greater relative stride lengths than elite runners. Although somewhat contradictory, both studies suggest that experienced runners possess relative stride lengths that differ from those of less experienced runners.
The results of previous studies concerning stride length variations in runners suggest that experienced runners will choose a near optimal stride length and that experienced runners possess stride lengths that differ from novice runners. The process by which an experienced runner chooses this stride length is unknown. It has been suggested that experienced runners obtain a near optimal stride length by either altering their stride length and stride frequency in an effort to minimize perceived exertion, or randomly select a stride length and stride frequency combination that becomes physiologically the most optimal through conditioning or repetition
(4). Documentation of the concurrent changes that occur in stride length, perceived effort, and running economy as a result of training may provide avenues that could possibly be used to hasten the process by which running economy and performance are improved in novice runners. Consequently, the purpose of our investigation was to document the changes in
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Abstract
mt. J. Sports Med. 12(1991)
freely chosen stride length in male novice runners during a
S. P. Bailey, S. P. Messier Table 1
Descriptive (M SE) Subject Data
seven-week training program and to compare any correspond-
ing change in running economy to that of a similar group of runners who trained at a constant stride length.
Methods
Subjects Twenty-eight male college students, randomly selected from a pooi of volunteers from undergraduate health and fitness courses, served as subjects for this investigation. All subjects were in good physical health and had never participated in an aerobic running program. Height, mass, age, leg length (distance from the anterior superior iliac spine to the medial malleolus), and three skin fold measurements (chest, abdomen, and thigh) were recorded for each subject prior to
Age (yrs)
18.23
18.92
(0.12)
(0.43)
Height (cm)
179.0 (1.00)
179.0
True Leg Length (cm)
94.00
94.00 (1.00)
(1.00)
(1.00)
other training bouts, exercise intensity during the 4th and 22nd training bout was equal to 80% of initial VO2max.
the pretraining maximal exercise test. Mass and skinfold measurements were repeated for all subjects prior to the post training maximal exercise test. All skinfold measurements were performed by the same investigator. Descriptive data for
During respiratory gas analyses, subjects breathed through a low resistance breathing valve (Hans
the two groups are presented in Table 1.
measured on a breath-by-breath basis using a Medical
Participation in this investigation required that each subject completed two pretraining treadmill acclimation
runs, pre- and post- training maximal exercise tests, and twenty-two 20-minute training bouts. Each subject assigned himself to one of two groups by selecting a specific training schedule (i.e., M-W-F or T-Th-Sat), with the only restriction
being that there was an equal number of subjects in each group. One group, termed the Freely Chosen Stride Length (FCSL) group, was allowed to freely vary their stride length throughout the training program. The other group, termed the Constant Stride Length (CSL) group, maintained a constant stride length throughout the training period. Each subject read and signed an informed consent document prior to participation. One subject from each group failed to complete the training program. Treadmill Acclimation Runs
Two acclimation runs were used to habituate the subjects to treadmill running, oxygen consumption equip-
ment, and Borg's RPE scale (2). Each acclimation run consisted of four 2-minute stages. During the first two stages, the
subject walked at 0.89 ms and 1.56 ms respectively. The third stage consisted of a slow jog at 2.24 m s —1and the final stage was a run at a velocity of 2.68 m
Respiratory Gas Analysis
Respiratory gas analyses were performed for each subject during pre- and post-training maximal exercise tests and during the 4th and 22nd training bout. The maximal exercise tests were used to describe improvements in cardiorespiratory fitness resulting from the training program and to provide criteria for determining training intensity. Respiratory gas analyses performed during the training bouts were used as measures of running economy. While respiratory gas analyses were peformed throughout the 4th and 22nd training bout, only those values obtained during the 12th and 20th minute of exercise were used for statistical analyses. As in all
Graphics, System 2001. Expiratory airflow was measured with a heated linear pneumotach (Validyne, D250). Calibration of the pneumotach was performed by injecting a known volume of gas at different flow rates and profiles. Expired air
was sampled at the mouth-piece at a rate of 200 ni}min Fractions of 02 and CO2 were determined using rapid response analyzers (Medical Graphics), which were calibrated using precision analyzed gas mixtures. Response times for both analyzers were between 350 and 450 ms. Analog outputs
from these devices were sampled at 100 Hz and underwent analog-to-digital conversion using a flow-waveform analyzer (Medical Graphics). On-line computer analysis for determination of oxygen consumption (VO2), carbon dioxide produc-
tion (VCO2), and RER was subsequently performed by the host computer system (CAD/NET) and displayed breath-bybreath. Maximal Exercise Test
Preceeding and at the conclusion of the training program, each subject completed a graded maximal exercise test, using a low-fit run protocol in which exercise intensity started at three METS and increased approximately one MET
each minute until the subject reached a state of voluntary exhaustion. All tests were conducted using a Quinton 65 treadmill interfaced with a Q 3000 Stress Test Monitor. Throughout the test, heart rates were monitored each minute using a 12 lead Quinton electrocardiograph. Each subject met the criteria for maximal oxygen uptake as described by Astrand and Rodahl (1): (1) a plateau or decline in oxygen uptake despite a further
increase in workload, (2) a respiratory exchange ratio of 1.10, and (3) a maximal heart rate of I SD of age predicted maximal values.
Training All subjects trained on a Quinton 18—60 treadmill 20 minutes per day, 3 days per week for approximately 7 weeks (22 training bouts). Each exercise bout consisted of a 5minute warm-up at a treadmill speed which elicited a heart rate response equivalent to 60% of pretraining VO2max. Grade of
the treadmill was 0% during all training bouts. Heart rate,
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Procedures
Rudolph, 2700). Ventilatory and gas exchange responses were
mt. J. Sports Med. 12 (1991) 301
Stride Length Variations
general and local RPE, and absolute stride length were
2.0 a
measured during the 12th and 20th mm of each training bout. A single lead ECG monitored by a Physio-Control Lifepack 5
was used to determine heart rate. Stride lengths were determined using the protocol of Cavanagh and Williams (4). Mean stride length (SL) is the product of mean stride time (ST) and mean treadmill velocity (V): determining the latter two par-
and averaging the results.
Each footfall by a runner results in a decreased treadmill belt speed and attenuated voltage to the treadmill. This voltage change is easily observed in visible speedometer needle fluctuations. To obtain a permanent copy of the voltage fluctuations, the signal was amplified and subsequently recorded on a single channel chart recorder. The number of footfalls made in the final 12s of the 12th and 20th mm of exercise
-1.0
•
C)
-J C)
3.0
;2.0
.
Stride Length Manipulation The freely chosen stride length group (FCSL) was allowed to freely vary their stride length throughout the
training period. Conversely, in the constant stride length group (CSL), an attempt was made to maintain stride length throughout the training period. More specifically, each CSL subject was allowed to freely vary his stride length during the first training run. During all subsequent runs, stride length was held constant by having the subject run to the sound of a Franz electronic metronome set to tick at a speed equivalent to each
subject's initial freely chosen stride frequency. Initial frequency values were obtained during the 12th and 20th mm of exercise in the first training bout.
Parenthetically, prior to any stride length manipulation, each subject had accumulated at least 45 mm of treadmill running. Scheib (13) determined that there was no statistical difference in kinematic and temporal variables related to the stride length of novice treadmill runners following 45 mm of treadmill running.
Statistical Analysis Mean weekly values were determined for heart rate, local and general RPEs, and percent changes in absolute
stride length. Two factor ANOVAs repeated across the 7 weeks of training were performed separately for the 12th and 20th mm of exercise for each of the above mentioned variables. In addition, two factor ANOVAs repeated across preand post-training values were performed separately for the 12th and 20th minute of exercise on realtive and absolute sub-
max V02 data collected during the 4th and 22nd training bouts. Moreover, two factor ANOVAs repeated across preand post-training values were performed on VO2max values.
2
3
4
5
6
7
Week of Training
of each training bout were counted and estimated to the nearest tenth of a stride. Mean stride time was calculated using the formula, ST(s) = l/(number of strides/12s). Subsequently, mean stride length was calculated using the formula, SL(m) = ST(s) x V (ms 1) Stride length was defined as the distance between successive foot contacts.
2 CSL
b.
p
.05; FCSL > CSL.
Fig. 1 Percent change (± SE) in absolute stride length during the 7-week training program at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
If a significant interaction was found, a simple effects procedure was used to determine the exact nature of the difference (10). In the absence of a significant interaction, a NewmanKeuls post hoc procedure was used to compare differences in overall main effects. The alpha level for each analysis was set at 0.05.
Results
Stride Length Variability Manipulation Check No significant differences in stride length existed across the 7 weeks of training at either the 12th or 20th mm of exercise in the CSL group (p = 1.00; Fig. 1). The small changes in stride length attest to the efficacy of the manipulation procedure. Percent Change in Stride Length Significant differences in percent change in ab-
solute stride length between the groups were only found during the 4th week of training at the 20th minute of exercise (p = .03). When compared to the first week of training, stride length in the FCSL group at minute 20 were 2.21 % greater during the 4th week (Fig. ib). Subsequently, stride lengths in the FCSL group decreased through the 7th week of training until they were only 0.63% greater than the subjects' initial stride length (Fig. ib). Mean weekly values of absolute stride for the FCSL and CSL groups are provided in Table 2.
Physiological Variables VO2max
Relative maximal oxygen consumption (V02 max) increased 3.56% in the FCSL group and 5.05% in the
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ameters enabled the former to be calculated. Treadmill belt velocity was determined using the formula, V = (number of belt revolutions x belt length)/time. Mean treadmill velocity was subsequently determined by monitoring and calibrating the treadmill belt speed at least twice during each training run
mt J. Sports Med. 12(1991)
C E
35
E
32.5
S. P. Bailey, S. P. Messier
C C
0
•
E
D CSL
C
0
ci,
C
0
2750
E E 2250
•
E
0 C 0
35
C)
C)
C
a,
6)
C
0
0)6
CSL 2750
a)
Cl
>, 2250
30
pre
*p
post
.05; Post-test
Pre-test.
pre
Fig. 2 Relative submaximal oxygen consumption (± SE) values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
a.
175
Fig. 3 Absolute submaximal oxygen consumption (± SE) values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
FCSL and CSL groups across the seven-week traini ng period.
*
*
170
C
E 165
•
a) cc
post
FCSL Group
CSL Group
(n=13)
(n=13)
12th
20th
12th
20th
Week
mm
mm
mm
mm
1
100.4
99.5 (3.9)
99.5 (3.5)
99.5 (3.5)
99.8 (4.0)
99.7
99.6 (3.6)
99.7
(3.8)
3
101.2 (3.9)
101.0 (4.5)
99.6 (3.6)
99.5 (3.6)
4
101.6 (4.3)
101.8
(4.3)
99.5 (3.6)
99.6 (3.6) 99.5 (3.6)
(3.8) cSL
2
1
2
3
4
5
6
7
5
Week of Training * significantly (p s .05> dIfferent from week 1.
6
102.0 (4.4)
(3.6)
101.4
99.6
(4.3)
(3.6)
101.4 (4.2)
99.6
(4.2)
(3.6)
99.7 (3.6)
101.2 (4.3)
100.2 (4.3)
99.6 (3.6)
99.7 (3.6)
100.8
Fig. 4 Mean (± SE) heart rate values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
7
CSL group during the 7-week trainin1g period. Post-training min 1 and 44.52 ml VO2max values were 44.82 ml . kg kg — 1min 'in the FCSL and CSL groups, respectively. Body
the training period (p = .03) (Fig. 2a). Relative submax V02 decreased 3.38% in the FCSL group and 4.32% in the CSL group (Fig. 2a). No significant differences were found in relative submax V02 between the FCSL and the CSL groups across the training period at the 12th and 20th minute of exercise. Relative submax V02 values at the 20th minute of exer-
mass increased from 76.7 kg to 77.8 kg in the FCSL group and from 76.7 to 77.3 kg in the CSL group. The sum of three skinfolds (ESF) increased from 60.08 to 69.66 in the FCSL group and from 54.00 to 55.62 in the CSL group.
Running Economy Relative submax V02 values decreased significantly in both groups at the 12th minute of exercise following
cise decreased .8% and 1.7% in the FCSL and CSL groups, respectively (Fig. 2b).
Absolute submax V02 did not change significandy in either group following the training period (Fig. 3). Furthermore, no significant differences were found in abso-
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302
mt. .J. Sports Med. 12 (1991) 303
Stride Length Variations
In
a.
12.0
w11.0
:: 13.0
2
3
4
5
6
7
Week of Training .05) less than week 1. significantly (p
E
1
2
3
4
5
6
7
Week of Training
* significantly (p c .05) less than week 1.
Fig. 5 Mean (± SE) general ratings of perceived exertion at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
Fig. 6 Mean (± SE) local ratings of perceived exertion at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
lute submax V02 between the FCSL and the CSL groups
sequently, we hypothesized that a training period of a slightly
across the training period at the 12th and 20th minute of exercise.
Heart Rate
No significant differences in heart rate were found between the groups across the training period at the 12th or 20th minute of exercise. Heart rates, however, were found to change significantly across the weeks of training at both time intervals (Fig. 4).
Ratings of Perceived Exertion General RPEs significantly decreased in both groups across the training period at the 20th mm of exercise (p < .00 1; Fig. 5b). No significant differences, however, were
found between the groups at either the 12th or 20th minute of exercise (Fig. 5). In addition, there were no significant differences between the groups in local RPEs at the 12th or 20th minute of exercise. Furthermore, the interactions between the weeks of training and groups at the 12th and 20th minute of exercise were found to be nonsignificant for both general and
local RPEs. Local RPEs, however, significantly decreased across the training period (p < .001; Fig. 6). Discussion
Changes in Stride Length It has been concluded by Dillman (6) that more experienced runners are likely to possess greater relative stride lengths than less experienced or novice runners. Furthermore, pilot data from our laboratory found that the stride lengths of novice female runners increased throughout a five-week treadmill training program. During the five-week training period, however, increases in stride length gradually decreased. Sub-
greater duration (7 weeks) would be sufficient to document both an initial increase in stride length and a subsequent leveling-off of stride length in the later weeks. The results of the present investigation indicate a consistent increase in stride lengths through four weeks of training, followed by decreases in stride lengths through the remaining three weeks (Fig. 1).
Moreover, observation of the weekly variations in stride length appear to indicate no consistent trend throughout the training period (Fig. 1). It is entirely possible that any significant changes in stride length may be a result of several months if not years of run training and that a training program of the
duration employed in this investigation was not sufficient to document any significant trend in stride length alterations.
VO2max and Descriptive Variables As expected, relative VO2max increased as a result of the training program: 3.56% in the FCSL group and 5.05% in the CSL group. The magnitudes of the increase in VO2max observed in this study are not as great as the approximate 10% increase in VO2max described by other investigators utilizing training programs of similar duration and intensity (5, 7). The attenuated increase in VO2max observed in our investigation is probably a result of the unexpected increases in body mass and skinfold thickness following the training program. While it was not the purpose of this investigation to improve cardiovascular fitness or reduce body mass and skinfold thickness, these awkward results complicate interpretation of the running economy data.
Stride Length and Running Economy Several investigations have demonstrated that alterations from a freely chosen stride length results in reductions in running economy in experienced runners (4, 9). These
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1
304 mt. J. Sports Med. 12(1991)
During the 7th week of training, there was no significant difference between the groups in stride length. The only time point where significant differences in stride length existed between the groups was during the 4th week of training. During this time point, the mean stride length of the FCSL group was 2.21 % greater than the mean stride length of the CSL group. Heart rates and ratings of perceived exertion were, however, not significantly different between the groups during the 4th week of training. Therefore, it is unlikey that running economy differed significantly between the groups during the 4th week of training. Subsequently, we conclude that stride length variations of the magnitude observed in this study had no significant effect on alterations in running economy.
Stride Length and Heart Rate
existed. Stride length alteration has been documented to have a significant effect on RPE when stride length was increased by 3.5% (12). Apparently, the 2.19% difference in stride length between the groups at week 4 was not sufficient to elicit significant differences in RPE.
Conclusions The results of our study indicate that the stride lengths of novice runners remain variable following seven weeks of treadmill training. It was also apparent that stride
length variations had no significant effect on running economy. Stride length manipulation during the first seven weeks of treadmill training, therefore, would most likely not hasten improvements in running economy. Observation of the alterations of mechanical variables other than stride length
during the initial weeks of training may provide avenues through which mechanical manipulation could hasten improvements in running economy. References Astrand P. 0., Rodahl K.: Textbook of work physiology. New York, N.Y.: McGraw Hill Book Company, 1986. Borg G. A. V.: Perceived exertion: A note on "history" and methods.MedSciSportsExerc 5: 90—93, 1973. Cavanagh P. R., Pollock M. L., Landa J.: A biomechanical comparison of elite and good distance runners. Ann NYAcad Sci 301: " 328—345,1977. Cavanagh P. R., Williams K. R.: The effect of stride length vari2
Knuttgen (11) has shown that changes in stride length significantly affect heart rate. It was surprising, therefore, that no between group differences in heart rate were observed during week 4, the interval in which between group dif-
ferences in stride length were present. It appears that the 2.21 % increase in stride length experienced by the FCSL
ation on oxygen uptake during distance running. Med Sci Sports Exercl4:30—35, 1982. Clausen J. P., Larsen, 0. A., Trap-Jensen J.: Physical training in the management of coronary artery disease. Circulation 40: 143—154,
6
group was not sufficient to elicit significant changes in heart rate. 8
Following the 5th week of training, there was a
non-significant increase in heart rate in both groups. If this change had occurred only in the FCSL group, the small increase could have been attributed to the decline in stride length
that was observed during the final three weeks of training. Since heart rate increased in both groups after week 5, the increases may be attributable to within subject variability or to the alteration of mechanical variables other than stride length.
Stride Length and Ratings of Perceived Exertion Local and general ratings of perceived exertion have been shown to increase when stride length is altered from that which is freely chosen (12). Thus, it was hypothesized that
a significant difference in stride length between the groups would produce similar differences in RPE. Since significant differences in percent changes in absolute stride length between the groups existed only during the 4th week of training at the 20th mm of exercise, it is here that differences in RPE would be most apparent. No significant differences, however,
1969. Dillman C. J.: Kinematic analyses of running. Exerc Sport Sci Rev 3:193—218,1975. Ekblom B., Astrand P. 0., Saltin B., Stenberg J., Wallstrom B.: Effect of training on circulatory response to exercise. J Appi Physiol 24:518—528,1968. Frederick F. C.: Synthesis, experimentation, and the biomechanics of economical movement. Med Sci Sport Exerc 17:44—47, 1985. Hogberg P.: How do stride length and stride frequency influence the energy-output during running? Arbeitsphysiologie 14:437—441, 1952.
Kirk R. E.: Experimental design. Procedures for the behavioral sciences. Belmont, CA: Brooks/Cole Publishing. pp 365—379, 1982.
Knuttgen H. G.: Oxygen uptake and pulse rate while running with undetermined and determined stride lengths at different speeds. 12 ActaPhysiolScands2: 366—371,1961. Messier S. P., Franke W. D., Rejeski W. J.: Effects of altered stride lengths on ratings of perceived exertion during running. Research 13 QuarterlyforExerciseana'Sport57 (4): 273—279, 1986. Schieb D. A.: Kinematic accommodation of novice treadmill runners. Research QuarterlyforExercise andSport 57: 1—7, 1986. Stephen P. Bailey Dept. of Exercise Science Blatt P. E. Center
University of South Carolina Columbia, SC 29208 (803)777—8421
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investigations have also indicated that the freely chosen stride length of experienced runners is physiologically near optimal (4, 9). The results of our investigation found relative submax V02 to be reduced significantly in both groups following the training period at the 12th minute of exercise and a trend for a reduction in relative submax V02 in both groups at the 20th minute of exercise (Fig. 2). It is entirely possible that the reductions in relative submax V02 across the training period are a resuit of the concurrent increases in body mass in both groups. This possibility is substantiated by the nonsignificant changes in absolute submax V02 observed in both groups, at both time intervals, across the training period (Fig. 3).
S. P. Bailey, S. P. Messier
Variations in Stride Length and Running Economy in Male Novice Runners Subsequent to a Seven-Week Training Program S. P. Bailey, S. P. Messier J. B. Snow Biomechanics Laboratory, Wake Forest University
Introduction
S. P. Bailey and S. P. Messier, Variations in Stride Length and Running Economy in Male Novice Runners Subsequent to a Seven-Week Training Program. mt j Sports Med, Vol l2,No 3,pp299—304, 1991.
There are many intrinsic biomechanical factors that are thought to influence running economy; however, empirical study supports the existence of only one factor as being of prime importance (8). Specifically, Hogberg (9) observed that alterations in stride length resulted in an increase in submaxirnal oxygen consumption. More recently, Cavanagh
Accepted: July 23, 1990
and Williams (4) have replicated Hogberg's study using a
The purposes of this investigation were to
ting techniques. They determined that experienced runners possessed a freely chosen stride length that minimized submaximal oxygen consumption.
document the changes in stride length of college-age male novice runners (n 13) who were allowed of freely choose
their stride length throughout a 7-week training period (FCSL), and to compare subsequent changes in running economy to those observed in a similar group of runners (n = 13) that ran for 7 weeks with constant stride lengths equivalent to their initially chosen stride lengths (CSL). Subjects trained 3 days per week for approximately 7 weeks
(22 training bouts). Each training bout consisted of a minute warmup (60% VO2max) and a 15-minute run at a speed equivalent to 80% of the subjects' initial VO2max. Absolute stride length (ASL), heart rate (HR), and ratings of perceived exertion (RPE) were measured during the 12th and 20th minute of exercise. Relative and absolute submaximal V02 were measured during the 4th and 22nd training bout. No significant differences in percent change in ASL were found between the groups or across the weeks of training at the 12th or 20th minute of exercise; however, there was a significant difference (p .05) between the groups during the 4th week of training. No significant differences were found between the groups in relative or absolute submaximal V02. Relative submaximal V02 at the 12th minute of exercise decreased significantly following the training period in both the FCSL (—3.38%) and CSL (—4.32%) groups. Absolute submaximal V02 did not change significantly following the training period. Significant reductions in HR and local and general RPEs were observed across the training period; however, no significant difference in any of these variables were found between the groups. These results indicate that the variability in stride length inherent in male novice runners has no significant effect on running economy during the intial 7 weeks of training. Key words
Stride length, running economy, perceived exertion mt. J. SportsMed. 12(1991)299—304 Georg Thieme Verlag StuttgartNew York
larger sample size (n = 10) and non-linear regression curve fit-
Alterations in stride length also appear to have a significant effect on the perceived effort of experienced run-
ners. Messier, Franke, and Rejeski (12) revealed that both local (legs) and general ratings of perceived exertion (RPE) were significantly greater during runs in which the stride length of experienced runners was 14% longer than their freely chosen stride length. Significant increases in local RPEs were
also observed during runs where these same subjects were asked to overstride by 7% or understride by 14%.
Dillman (6), in a review of the running literature, concluded that more experienced runners are likely to possess greater relative stride lengths than less experienced or novice runners. Cavanagh, Pollock, and Landa (3) found, however, that good runners possess greater relative stride lengths than elite runners. Although somewhat contradictory, both studies suggest that experienced runners possess relative stride lengths that differ from those of less experienced runners.
The results of previous studies concerning stride length variations in runners suggest that experienced runners will choose a near optimal stride length and that experienced runners possess stride lengths that differ from novice runners. The process by which an experienced runner chooses this stride length is unknown. It has been suggested that experienced runners obtain a near optimal stride length by either altering their stride length and stride frequency in an effort to minimize perceived exertion, or randomly select a stride length and stride frequency combination that becomes physiologically the most optimal through conditioning or repetition
(4). Documentation of the concurrent changes that occur in stride length, perceived effort, and running economy as a result of training may provide avenues that could possibly be used to hasten the process by which running economy and performance are improved in novice runners. Consequently, the purpose of our investigation was to document the changes in
Downloaded by: Universite Laval. Copyrighted material.
Abstract
mt. J. Sports Med. 12(1991)
freely chosen stride length in male novice runners during a
S. P. Bailey, S. P. Messier Table 1
Descriptive (M SE) Subject Data
seven-week training program and to compare any correspond-
ing change in running economy to that of a similar group of runners who trained at a constant stride length.
Methods
Subjects Twenty-eight male college students, randomly selected from a pooi of volunteers from undergraduate health and fitness courses, served as subjects for this investigation. All subjects were in good physical health and had never participated in an aerobic running program. Height, mass, age, leg length (distance from the anterior superior iliac spine to the medial malleolus), and three skin fold measurements (chest, abdomen, and thigh) were recorded for each subject prior to
Age (yrs)
18.23
18.92
(0.12)
(0.43)
Height (cm)
179.0 (1.00)
179.0
True Leg Length (cm)
94.00
94.00 (1.00)
(1.00)
(1.00)
other training bouts, exercise intensity during the 4th and 22nd training bout was equal to 80% of initial VO2max.
the pretraining maximal exercise test. Mass and skinfold measurements were repeated for all subjects prior to the post training maximal exercise test. All skinfold measurements were performed by the same investigator. Descriptive data for
During respiratory gas analyses, subjects breathed through a low resistance breathing valve (Hans
the two groups are presented in Table 1.
measured on a breath-by-breath basis using a Medical
Participation in this investigation required that each subject completed two pretraining treadmill acclimation
runs, pre- and post- training maximal exercise tests, and twenty-two 20-minute training bouts. Each subject assigned himself to one of two groups by selecting a specific training schedule (i.e., M-W-F or T-Th-Sat), with the only restriction
being that there was an equal number of subjects in each group. One group, termed the Freely Chosen Stride Length (FCSL) group, was allowed to freely vary their stride length throughout the training program. The other group, termed the Constant Stride Length (CSL) group, maintained a constant stride length throughout the training period. Each subject read and signed an informed consent document prior to participation. One subject from each group failed to complete the training program. Treadmill Acclimation Runs
Two acclimation runs were used to habituate the subjects to treadmill running, oxygen consumption equip-
ment, and Borg's RPE scale (2). Each acclimation run consisted of four 2-minute stages. During the first two stages, the
subject walked at 0.89 ms and 1.56 ms respectively. The third stage consisted of a slow jog at 2.24 m s —1and the final stage was a run at a velocity of 2.68 m
Respiratory Gas Analysis
Respiratory gas analyses were performed for each subject during pre- and post-training maximal exercise tests and during the 4th and 22nd training bout. The maximal exercise tests were used to describe improvements in cardiorespiratory fitness resulting from the training program and to provide criteria for determining training intensity. Respiratory gas analyses performed during the training bouts were used as measures of running economy. While respiratory gas analyses were peformed throughout the 4th and 22nd training bout, only those values obtained during the 12th and 20th minute of exercise were used for statistical analyses. As in all
Graphics, System 2001. Expiratory airflow was measured with a heated linear pneumotach (Validyne, D250). Calibration of the pneumotach was performed by injecting a known volume of gas at different flow rates and profiles. Expired air
was sampled at the mouth-piece at a rate of 200 ni}min Fractions of 02 and CO2 were determined using rapid response analyzers (Medical Graphics), which were calibrated using precision analyzed gas mixtures. Response times for both analyzers were between 350 and 450 ms. Analog outputs
from these devices were sampled at 100 Hz and underwent analog-to-digital conversion using a flow-waveform analyzer (Medical Graphics). On-line computer analysis for determination of oxygen consumption (VO2), carbon dioxide produc-
tion (VCO2), and RER was subsequently performed by the host computer system (CAD/NET) and displayed breath-bybreath. Maximal Exercise Test
Preceeding and at the conclusion of the training program, each subject completed a graded maximal exercise test, using a low-fit run protocol in which exercise intensity started at three METS and increased approximately one MET
each minute until the subject reached a state of voluntary exhaustion. All tests were conducted using a Quinton 65 treadmill interfaced with a Q 3000 Stress Test Monitor. Throughout the test, heart rates were monitored each minute using a 12 lead Quinton electrocardiograph. Each subject met the criteria for maximal oxygen uptake as described by Astrand and Rodahl (1): (1) a plateau or decline in oxygen uptake despite a further
increase in workload, (2) a respiratory exchange ratio of 1.10, and (3) a maximal heart rate of I SD of age predicted maximal values.
Training All subjects trained on a Quinton 18—60 treadmill 20 minutes per day, 3 days per week for approximately 7 weeks (22 training bouts). Each exercise bout consisted of a 5minute warm-up at a treadmill speed which elicited a heart rate response equivalent to 60% of pretraining VO2max. Grade of
the treadmill was 0% during all training bouts. Heart rate,
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Procedures
Rudolph, 2700). Ventilatory and gas exchange responses were
mt. J. Sports Med. 12 (1991) 301
Stride Length Variations
general and local RPE, and absolute stride length were
2.0 a
measured during the 12th and 20th mm of each training bout. A single lead ECG monitored by a Physio-Control Lifepack 5
was used to determine heart rate. Stride lengths were determined using the protocol of Cavanagh and Williams (4). Mean stride length (SL) is the product of mean stride time (ST) and mean treadmill velocity (V): determining the latter two par-
and averaging the results.
Each footfall by a runner results in a decreased treadmill belt speed and attenuated voltage to the treadmill. This voltage change is easily observed in visible speedometer needle fluctuations. To obtain a permanent copy of the voltage fluctuations, the signal was amplified and subsequently recorded on a single channel chart recorder. The number of footfalls made in the final 12s of the 12th and 20th mm of exercise
-1.0
•
C)
-J C)
3.0
;2.0
.
Stride Length Manipulation The freely chosen stride length group (FCSL) was allowed to freely vary their stride length throughout the
training period. Conversely, in the constant stride length group (CSL), an attempt was made to maintain stride length throughout the training period. More specifically, each CSL subject was allowed to freely vary his stride length during the first training run. During all subsequent runs, stride length was held constant by having the subject run to the sound of a Franz electronic metronome set to tick at a speed equivalent to each
subject's initial freely chosen stride frequency. Initial frequency values were obtained during the 12th and 20th mm of exercise in the first training bout.
Parenthetically, prior to any stride length manipulation, each subject had accumulated at least 45 mm of treadmill running. Scheib (13) determined that there was no statistical difference in kinematic and temporal variables related to the stride length of novice treadmill runners following 45 mm of treadmill running.
Statistical Analysis Mean weekly values were determined for heart rate, local and general RPEs, and percent changes in absolute
stride length. Two factor ANOVAs repeated across the 7 weeks of training were performed separately for the 12th and 20th mm of exercise for each of the above mentioned variables. In addition, two factor ANOVAs repeated across preand post-training values were performed separately for the 12th and 20th minute of exercise on realtive and absolute sub-
max V02 data collected during the 4th and 22nd training bouts. Moreover, two factor ANOVAs repeated across preand post-training values were performed on VO2max values.
2
3
4
5
6
7
Week of Training
of each training bout were counted and estimated to the nearest tenth of a stride. Mean stride time was calculated using the formula, ST(s) = l/(number of strides/12s). Subsequently, mean stride length was calculated using the formula, SL(m) = ST(s) x V (ms 1) Stride length was defined as the distance between successive foot contacts.
2 CSL
b.
p
.05; FCSL > CSL.
Fig. 1 Percent change (± SE) in absolute stride length during the 7-week training program at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
If a significant interaction was found, a simple effects procedure was used to determine the exact nature of the difference (10). In the absence of a significant interaction, a NewmanKeuls post hoc procedure was used to compare differences in overall main effects. The alpha level for each analysis was set at 0.05.
Results
Stride Length Variability Manipulation Check No significant differences in stride length existed across the 7 weeks of training at either the 12th or 20th mm of exercise in the CSL group (p = 1.00; Fig. 1). The small changes in stride length attest to the efficacy of the manipulation procedure. Percent Change in Stride Length Significant differences in percent change in ab-
solute stride length between the groups were only found during the 4th week of training at the 20th minute of exercise (p = .03). When compared to the first week of training, stride length in the FCSL group at minute 20 were 2.21 % greater during the 4th week (Fig. ib). Subsequently, stride lengths in the FCSL group decreased through the 7th week of training until they were only 0.63% greater than the subjects' initial stride length (Fig. ib). Mean weekly values of absolute stride for the FCSL and CSL groups are provided in Table 2.
Physiological Variables VO2max
Relative maximal oxygen consumption (V02 max) increased 3.56% in the FCSL group and 5.05% in the
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ameters enabled the former to be calculated. Treadmill belt velocity was determined using the formula, V = (number of belt revolutions x belt length)/time. Mean treadmill velocity was subsequently determined by monitoring and calibrating the treadmill belt speed at least twice during each training run
mt J. Sports Med. 12(1991)
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S. P. Bailey, S. P. Messier
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6)
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Pre-test.
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Fig. 2 Relative submaximal oxygen consumption (± SE) values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
a.
175
Fig. 3 Absolute submaximal oxygen consumption (± SE) values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
FCSL and CSL groups across the seven-week traini ng period.
*
*
170
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a) cc
post
FCSL Group
CSL Group
(n=13)
(n=13)
12th
20th
12th
20th
Week
mm
mm
mm
mm
1
100.4
99.5 (3.9)
99.5 (3.5)
99.5 (3.5)
99.8 (4.0)
99.7
99.6 (3.6)
99.7
(3.8)
3
101.2 (3.9)
101.0 (4.5)
99.6 (3.6)
99.5 (3.6)
4
101.6 (4.3)
101.8
(4.3)
99.5 (3.6)
99.6 (3.6) 99.5 (3.6)
(3.8) cSL
2
1
2
3
4
5
6
7
5
Week of Training * significantly (p s .05> dIfferent from week 1.
6
102.0 (4.4)
(3.6)
101.4
99.6
(4.3)
(3.6)
101.4 (4.2)
99.6
(4.2)
(3.6)
99.7 (3.6)
101.2 (4.3)
100.2 (4.3)
99.6 (3.6)
99.7 (3.6)
100.8
Fig. 4 Mean (± SE) heart rate values at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
7
CSL group during the 7-week trainin1g period. Post-training min 1 and 44.52 ml VO2max values were 44.82 ml . kg kg — 1min 'in the FCSL and CSL groups, respectively. Body
the training period (p = .03) (Fig. 2a). Relative submax V02 decreased 3.38% in the FCSL group and 4.32% in the CSL group (Fig. 2a). No significant differences were found in relative submax V02 between the FCSL and the CSL groups across the training period at the 12th and 20th minute of exercise. Relative submax V02 values at the 20th minute of exer-
mass increased from 76.7 kg to 77.8 kg in the FCSL group and from 76.7 to 77.3 kg in the CSL group. The sum of three skinfolds (ESF) increased from 60.08 to 69.66 in the FCSL group and from 54.00 to 55.62 in the CSL group.
Running Economy Relative submax V02 values decreased significantly in both groups at the 12th minute of exercise following
cise decreased .8% and 1.7% in the FCSL and CSL groups, respectively (Fig. 2b).
Absolute submax V02 did not change significandy in either group following the training period (Fig. 3). Furthermore, no significant differences were found in abso-
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302
mt. .J. Sports Med. 12 (1991) 303
Stride Length Variations
In
a.
12.0
w11.0
:: 13.0
2
3
4
5
6
7
Week of Training .05) less than week 1. significantly (p
E
1
2
3
4
5
6
7
Week of Training
* significantly (p c .05) less than week 1.
Fig. 5 Mean (± SE) general ratings of perceived exertion at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
Fig. 6 Mean (± SE) local ratings of perceived exertion at the (a) 12th and (b) 20th minute of exercise for the Freely Chosen Stride Length (FCSL) and Constant Stride Length (CSL) groups.
lute submax V02 between the FCSL and the CSL groups
sequently, we hypothesized that a training period of a slightly
across the training period at the 12th and 20th minute of exercise.
Heart Rate
No significant differences in heart rate were found between the groups across the training period at the 12th or 20th minute of exercise. Heart rates, however, were found to change significantly across the weeks of training at both time intervals (Fig. 4).
Ratings of Perceived Exertion General RPEs significantly decreased in both groups across the training period at the 20th mm of exercise (p < .00 1; Fig. 5b). No significant differences, however, were
found between the groups at either the 12th or 20th minute of exercise (Fig. 5). In addition, there were no significant differences between the groups in local RPEs at the 12th or 20th minute of exercise. Furthermore, the interactions between the weeks of training and groups at the 12th and 20th minute of exercise were found to be nonsignificant for both general and
local RPEs. Local RPEs, however, significantly decreased across the training period (p < .001; Fig. 6). Discussion
Changes in Stride Length It has been concluded by Dillman (6) that more experienced runners are likely to possess greater relative stride lengths than less experienced or novice runners. Furthermore, pilot data from our laboratory found that the stride lengths of novice female runners increased throughout a five-week treadmill training program. During the five-week training period, however, increases in stride length gradually decreased. Sub-
greater duration (7 weeks) would be sufficient to document both an initial increase in stride length and a subsequent leveling-off of stride length in the later weeks. The results of the present investigation indicate a consistent increase in stride lengths through four weeks of training, followed by decreases in stride lengths through the remaining three weeks (Fig. 1).
Moreover, observation of the weekly variations in stride length appear to indicate no consistent trend throughout the training period (Fig. 1). It is entirely possible that any significant changes in stride length may be a result of several months if not years of run training and that a training program of the
duration employed in this investigation was not sufficient to document any significant trend in stride length alterations.
VO2max and Descriptive Variables As expected, relative VO2max increased as a result of the training program: 3.56% in the FCSL group and 5.05% in the CSL group. The magnitudes of the increase in VO2max observed in this study are not as great as the approximate 10% increase in VO2max described by other investigators utilizing training programs of similar duration and intensity (5, 7). The attenuated increase in VO2max observed in our investigation is probably a result of the unexpected increases in body mass and skinfold thickness following the training program. While it was not the purpose of this investigation to improve cardiovascular fitness or reduce body mass and skinfold thickness, these awkward results complicate interpretation of the running economy data.
Stride Length and Running Economy Several investigations have demonstrated that alterations from a freely chosen stride length results in reductions in running economy in experienced runners (4, 9). These
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1
304 mt. J. Sports Med. 12(1991)
During the 7th week of training, there was no significant difference between the groups in stride length. The only time point where significant differences in stride length existed between the groups was during the 4th week of training. During this time point, the mean stride length of the FCSL group was 2.21 % greater than the mean stride length of the CSL group. Heart rates and ratings of perceived exertion were, however, not significantly different between the groups during the 4th week of training. Therefore, it is unlikey that running economy differed significantly between the groups during the 4th week of training. Subsequently, we conclude that stride length variations of the magnitude observed in this study had no significant effect on alterations in running economy.
Stride Length and Heart Rate
existed. Stride length alteration has been documented to have a significant effect on RPE when stride length was increased by 3.5% (12). Apparently, the 2.19% difference in stride length between the groups at week 4 was not sufficient to elicit significant differences in RPE.
Conclusions The results of our study indicate that the stride lengths of novice runners remain variable following seven weeks of treadmill training. It was also apparent that stride
length variations had no significant effect on running economy. Stride length manipulation during the first seven weeks of treadmill training, therefore, would most likely not hasten improvements in running economy. Observation of the alterations of mechanical variables other than stride length
during the initial weeks of training may provide avenues through which mechanical manipulation could hasten improvements in running economy. References Astrand P. 0., Rodahl K.: Textbook of work physiology. New York, N.Y.: McGraw Hill Book Company, 1986. Borg G. A. V.: Perceived exertion: A note on "history" and methods.MedSciSportsExerc 5: 90—93, 1973. Cavanagh P. R., Pollock M. L., Landa J.: A biomechanical comparison of elite and good distance runners. Ann NYAcad Sci 301: " 328—345,1977. Cavanagh P. R., Williams K. R.: The effect of stride length vari2
Knuttgen (11) has shown that changes in stride length significantly affect heart rate. It was surprising, therefore, that no between group differences in heart rate were observed during week 4, the interval in which between group dif-
ferences in stride length were present. It appears that the 2.21 % increase in stride length experienced by the FCSL
ation on oxygen uptake during distance running. Med Sci Sports Exercl4:30—35, 1982. Clausen J. P., Larsen, 0. A., Trap-Jensen J.: Physical training in the management of coronary artery disease. Circulation 40: 143—154,
6
group was not sufficient to elicit significant changes in heart rate. 8
Following the 5th week of training, there was a
non-significant increase in heart rate in both groups. If this change had occurred only in the FCSL group, the small increase could have been attributed to the decline in stride length
that was observed during the final three weeks of training. Since heart rate increased in both groups after week 5, the increases may be attributable to within subject variability or to the alteration of mechanical variables other than stride length.
Stride Length and Ratings of Perceived Exertion Local and general ratings of perceived exertion have been shown to increase when stride length is altered from that which is freely chosen (12). Thus, it was hypothesized that
a significant difference in stride length between the groups would produce similar differences in RPE. Since significant differences in percent changes in absolute stride length between the groups existed only during the 4th week of training at the 20th mm of exercise, it is here that differences in RPE would be most apparent. No significant differences, however,
1969. Dillman C. J.: Kinematic analyses of running. Exerc Sport Sci Rev 3:193—218,1975. Ekblom B., Astrand P. 0., Saltin B., Stenberg J., Wallstrom B.: Effect of training on circulatory response to exercise. J Appi Physiol 24:518—528,1968. Frederick F. C.: Synthesis, experimentation, and the biomechanics of economical movement. Med Sci Sport Exerc 17:44—47, 1985. Hogberg P.: How do stride length and stride frequency influence the energy-output during running? Arbeitsphysiologie 14:437—441, 1952.
Kirk R. E.: Experimental design. Procedures for the behavioral sciences. Belmont, CA: Brooks/Cole Publishing. pp 365—379, 1982.
Knuttgen H. G.: Oxygen uptake and pulse rate while running with undetermined and determined stride lengths at different speeds. 12 ActaPhysiolScands2: 366—371,1961. Messier S. P., Franke W. D., Rejeski W. J.: Effects of altered stride lengths on ratings of perceived exertion during running. Research 13 QuarterlyforExerciseana'Sport57 (4): 273—279, 1986. Schieb D. A.: Kinematic accommodation of novice treadmill runners. Research QuarterlyforExercise andSport 57: 1—7, 1986. Stephen P. Bailey Dept. of Exercise Science Blatt P. E. Center
University of South Carolina Columbia, SC 29208 (803)777—8421
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investigations have also indicated that the freely chosen stride length of experienced runners is physiologically near optimal (4, 9). The results of our investigation found relative submax V02 to be reduced significantly in both groups following the training period at the 12th minute of exercise and a trend for a reduction in relative submax V02 in both groups at the 20th minute of exercise (Fig. 2). It is entirely possible that the reductions in relative submax V02 across the training period are a resuit of the concurrent increases in body mass in both groups. This possibility is substantiated by the nonsignificant changes in absolute submax V02 observed in both groups, at both time intervals, across the training period (Fig. 3).
S. P. Bailey, S. P. Messier
