The mechanical efficiency of treadmill running against a horizontal impeding force.

1. A method for determining the apparent mechanical efficiency of running against a horizontal impeding force is described. The results of studies on three well trained athletes have been summarized.2. A linear relation was found between metabolic rate and external work rate. The apparent mechanical efficiency was calculated as the inverse of the slope of the linear regression line of metabolic rate on external work rate x 10(2) (percentage).3. The over-all mean for apparent load-running efficiency (LRE) was 36.1%. The differences in LRE between subjects were not statistically significant. No measurable change in LRE occurred with habituation.4. Values are given for E(k), the net energy cost of unloaded horizontal treadmill running per kilogram of bodyweight and per kilometre of distance covered. The over-all mean for E(k) was 0.83 kcal. kg(-1). km(-1).5. The efficiency values obtained are discussed and compared with other values of running efficiency obtained by different methods, and with studies on isolated muscle.