DAILY VARIATION IN STEP LENGTH OF TRAINED MALE RUNNERS

The purpose of this study was to quantify daily intra-individual varia bility in mean step length, a basic descriptor of the running pattern. Following 60 minutes of treadmill accommodation, nine trained male su bjects (X age = 34.2 yrs +/- 7.2, X VO(2)max = 57.0 +/- 4.8 ml kg(-1) min(-1)) performed daily (Mon-Fri) 6-minute treadmill runs at three su bmaximal speeds (2.68, 3.13 and 3.58 m s(-1)) over a 4-week period. To minimize extraneous influences, subjects refrained from road racing a nd completed the 20 running sessions (5 d wk(-1) 4 weeks for each spee d) at the same time of day and in the same footwear. Treadmill velocit y was calibrated for each 6-minute running bout and step length was de termined during the last 2 minutes of each run. Results indicated that mean step length and coefficient of variation values were 0.984 m and 2.50% at 2.68 m s(-1) 1.124 m and 2.22% at 3.13 m s(-1), and 1.254 m and 2.26% at 3.58 m s(-1). Reliability analyses indicated that the per centage of variation accounted for in step length across all speeds wa s high and improved very little as test number increased (range = 96% for two days vs 99% for five days). Taken together, these findings sug gest that when testing conditions are controlled, within-subject varia bility in step length measures obtained at multiple submaximal running speeds is small in trained subjects and that criterion step length va lues can be obtained by averaging duplicate measurements.