Ricard, M. D., Ugrinowisch, C., Hilton, S., parcel, A. C., Hunter, I, Knight, K., & Tricoli, V. (2006). Effects of the rate of force development on fatigue onset and location. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 2405.

In an established type of movement, increases in the rate of force development seem to change the pattern of motor unit activation. This study determined if the rate of force development affects fatigue onset and location. Untrained males (N = 10) had their knee extensors fatigued through maximal isometric contractions with distinct rates of force development: 30%, 60%, 90%, and 100% maxRFD/sec. Central activation ratio (twitch interpolation) was measured before and after the fatigue protocol. Amplitude (RMS) and median frequency (MF) of the surface electromyographic signal were estimated during the fatigue protocol on each contraction at four relative torque intervals (20%-30%, 45%-55%, 70%-80%, and 100%), for the vastus lateralis and vastus medialis muscles.

The slow rate of force development condition (30%maxRFD/sec) produced a faster drop in the impulse response through the fatigue protocol. However, central activation ratio and the EMG amplitude did not mimic the faster drop in the impulse response.

Implication. The slowest rate of force development condition produced a faster fatigue onset that seemed to be produced by peripheral factors. However, developing fatigue is only valuable when it is part of a specific overload. Activities such as weight room workouts designed to tire athletes through slow contractions against heavy resistances would be useless for improving specific performances involving rapid movements. As well, the amount of fatigue developed would not be the greatest possible. For general conditioning in the vast majority of functional sports, exercises that use fast rates of force development (i.e., explosive exercises) would be of greater benefit.

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