Physiological effects of dynamic hand work in subjects of different age and sex.

Thirty untrained subjects (group 1: 10 female, 20-30 years; group 2: 10 female, 36-46 years; group 3: 10 males, 20-30 years) performed dynamic hand work on a hand-grip dynamometer at loads varying from 20 to 100% MVC and three different working frequencies (20, 40, and 60 cpm). The mechanical muscle activity, the iEMG and the R-R interval were measured throughout the exercise. Before and after each exercise, the maximal hand-grip force (MVC) was determined together with the iEMG and the R-R interval. With the loads increasing gradually, the mean values of the duration of the contraction phase and of the iEMG of the four muscles increased in all test groups, but the duration of the rest phase and R-R interval decreased. Through an Analysis of Variance, evidence of systematic differences between the test groups was significant for the R-R interval only, while the effects of the loads (with exception of the rest phase) and of the working frequency proved significant for all parameters. The MVC, the iEMG and the R-R interval measured before and after the exercise did not show significant differences. This indicates that the exercise was not fatiguing.