Daily variation in running economy of moderately trained male runners.

The purpose of this study was to quantify total within-subject variation in running economy (RE) in moderately trained male runners (N = 10). Subjects (ages 20-34 yr) were monitored during treadmill running, five times a week (Mon-Fri) for 4 wk, at 2.68, 3.13, and 3.58 m.s-1. Oxygen consumption (VO2) was determined via the open-circuit method during each of the three running paces. Coefficients of variation among the three paces were not significantly (P greater than 0.05) different. An analysis of variance with repeated measures and a three-factor (3 x 4 x 5) design indicated that speed was the only significant (P less than 0.05) effect. Reliability tests performed on the data indicated that although there is an improvement in the percentage of variation accounted for as the number of tests conducted is increased, the benefit obtained by testing 5 d is very small when compared with testing 2 d. When effect sizes are used in the determination of subject numbers needed to detect significant effects, it is apparent that smaller anticipated effect sizes necessitate large sample sizes. In conclusion, RE appears to be a stable physiological measure in moderately trained male runners, and a criterion value based on the average of two measures per subject is recommended to obtain an acceptably stable RE value.