Effect of fatigue level on rate of force development by the grip-flexor muscles

Fifteen college-age males were tested for maximum voluntary contraction (MVC) of the grip flexors and were then subjected to five trials in which their strength levels were degraded to either 80%, 60%, or 40% MVC. Immediately following the fatigue bout, the subject released his grip and upon command attempted to squeeze as rapidly and forcefully as possible. Testing was also administered under a non-fatigued state (1.00 MVC); every subject was tested under each condition with the order of administration assigned at random. The data were analyzed based upon the amount of force generated at 4, 8, 16, 32, 64, 128, 256, and 512 ms following the initial deflection from the baseline. All values were normalized by dividing the force expressed by the maximum force developed under that condition at 512 ms. The data analysis revealed that for each fatigue level the pattern of force uptake was sigmoidal; however, differences in normalized force were observed among fatigue levels at 64 and 128 ms. In general, at those time intervals there was an inverse relationship between fatigue level and expressed force. Analysis of the force velocities revealed that during the period from 8 to 64 ms, the rate of tension uptake was adversely affected as the level of fatigue was increased.