In a model work place (hand-grip dynamometer), eleven subjects performed rhythmical hand-grip contractions to exhaustion (frequency 30/min). In each working cycle the contraction and rest phases were distinguished. The work to exhaustion was repeated four times (four working periods with 156-min rest intervals). The tests were performed at 40, 60, 80, 100% MVC. Analysis of Variance showed no difference in the group means (mean values of each working period and load level) for the duration of the contraction or rest phases, the integrated bioelectrical muscle activity (iEMG) of flexors, extensors, brachioradialis (iEMG referred to working cycle and contraction phase) or iEMG of the thenar muscles (referring to the working cycle), or in the duration of the R-R interval in the ECG during comparable periods of the experiments. The endurance times decreased from working period 1-4, and a similar decrease occurred in the force-time product. It may be concluded from these results that 15 min rest is insufficient for adequate recovery from hand-exhaustion exercise.
Four groups of subjects of different ages and sex (group I: 20-29 years, women; group II: 20-29 years, men; group III: 30-39 years, women; group IV: 30-39 years, men) undertook dynamic one-hand work (load range 40%-80% of maximum voluntary contraction, at 60 working cycles/min) to allow a study of cardiovascular responses as shown by the resultant changes in blood pressure and heart rate. During fatiguing dynamic one-hand work, there was a large increase in systolic and diastolic blood pressures in both sexes after a few minutes. For all load levels, the systolic blood pressure was found to be higher by about 4 kPa in men (groups II and IV) than in women (groups I and III). Other age-related differences became evident in the diastolic blood pressure changes. The values obtained for the older groups were higher than those in the two younger groups. These differences in blood pressure response are possibly due to sex-related differences in the release of catecholamines, or to age-related organic changes in the vessels.
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.
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