Influence of Fatigue on the Efficiency of Men During Exhausting Runs

¹ From the Department of Physiology, Indiana University Medical School, Bloomington, Indiana

In three experiments a man ran on the treadmill at 6.84 yd/sec. for the exact times of 1 minute, 2 minutes and 2.58 minutes, respectively. In previous trial runs this speed was found to exhaust the runner in 2.58 minutes. For each run his O₂ intake and O₂ debt were determined and samples of venous blood drawn before and 4 minutes after work were analyzed for lactic acid. The runner's O₂ requirement was found to decrease in the 2nd minute of the 2.58-minute run at constant speed and then to increase markedly in the last half minute as he approached exhaustion. The rate of accumulation of lactic acid was also greatly accelerated in the last half minute of the run. These results are confirmed by similar experiments on two other subjects. In other experiments it was found that a runner who was exhausted in 3.37 minutes of running at a constant speed of 6.84 yd/sec. could cover the same distance (1382 yd.) in the same total time with a lower O₂ requirement and less elevation of lactic acid if he ran the first 2.37 minutes at 6.63 yd/sec. and the last minute at 7.33 yd/sec.; whereas, if he ran the 1st minute at 7.33 yd/sec. and the last 2.37 minutes at 6.63 yd/sec. both his O₂ requirement and blood lactate were higher than when he ran at constant speed. It is clear from the data that in order to run a given middle distance race in minimum time the runner should follow a pace which will delay until near the end of the race the sudden change in physiological state in which the energy cost of running and the development of fatigue are so greatly accelerated, i.e. he should run the first part of his race a little slower than the average speed and make a faster finish in order to utilize the O₂ debt to the maximum.