REPEATED EXERCISES TO FATIGUE REDUCES THE ABILITY TO PRODUCE FORCE
Stewart, R. D., Duhamel, T. A., Rich, S., Tupling, A. R., & Green, H. J. (2008). Effects of consecutive days of exercise and recovery on muscle mechanical function. Medicine and Science in Sports and Exercise, 40, 316-325.
This study investigated the effects of three consecutive days of prolonged exercise on muscle mechanical function. Ss (N = 12) cycled at approximately 60% VO2peak until fatigue. Quadriceps muscle function was assessed before and after exercise on days E1 and E3 and during three consecutive days of recovery (R1, R2, R3), using both voluntary and electrically induced contractions at various stimulation frequencies.
Exercise on E1 and E3 resulted in a 40% and 35% deficit in force at 10 Hz, respectively, which remained depressed by 32-34% during R1 through R3. At 100 Hz force, although not altered by exercise at E1 or E3, it was decreased by 12-16% during recovery. The maximal rate of relaxation at 10 Hz was reduced by 38% on E1, by 32% on E3, and remained depressed by 38% through R3. At 100 Hz, the rate of relaxation was only depressed during recovery. Maximal rate of force development at 10 Hz was reduced by exercise, but not in recovery. Maximal voluntary contraction force was depressed by exercise at both E1 and E3 and remained depressed throughout recovery. The reduction in motor unit activation observed during recovery (assessed with the interpolated twitch technique), suggests that part of the incomplete recovery (weakness) is central in origin.
Implication. These results demonstrate that three consecutive days of prolonged exercise result in a weakness (loss of ability to produce force) that persists for at least three days of recovery.
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