DAILY VARIATION IN STEP LENGTH OF TRAINED MALE RUNNERS

The purpose of this study was to quantify daily intra-individual variability in mean step length, a basic descriptor of the running pattern. Following 60 minutes of treadmill accommodation, nine trained male subjects (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 submaximal 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 and completed the 20 running sessions (5 d wk(-1) 4 weeks for each speed) at the same time of day and in the same footwear. Treadmill velocity was calibrated for each 6-minute running bout and step length was determined 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 percentage of variation accounted for in step length across all speeds was high and improved very little as test number increased (range = 96% for two days vs 99% for five days). Taken together, these findings suggest that when testing conditions are controlled, within-subject variability in step length measures obtained at multiple submaximal running speeds is small in trained subjects and that criterion step length values can be obtained by averaging duplicate measurements.