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Muscular endurance of upper and lower extremities may provide a more practical measure of muscle function related to normal daily activity than measures of strength, especially with the elderly. Maximal isometric intermittent endurance of the finger flexors, thumb abductors, dorsiflexors, and plantar flexors were characterized by peak force, impulse, percent total impulse, and percent force decrement in men aged 20-74 yr. Volunteers (N = 153) were placed into appropriate 5-yr age groups: 20-24, 25-29, ..., 70-74 yr. The intermittent endurance task consisted of 11 consecutive, 2-s maximal contractions, each separated by 3-s rest. Age group differences within each 2-s interval as well as differences in endurance were determined by ANOVA, and after adjusting for differences in body composition, by ANCOVA. The lower extremities had the greatest declines in absolute measures of force within each 2-s interval, and declines occurred earlier than previously reported. When values were expressed as percent change over the entire endurance task, there was generally no age group difference in force or impulse; however, there were significant muscle group differences. In conclusion, declines in absolute measures of force occurred at different ages depending on the muscle group; however, relative measures of muscular endurance were maintained for all age groups but varied by muscle group location.

The age-related force production characteristics of six muscle groups in 143 women aged 25-74 years were examined. Measures of maximal force (MFR) were obtained on the finger flexors (FF), thumb extensors (TE), forearm flexors (FAF), forearm extensors (FAE), dorsi flexors (DF), and plantar flexors (PF) utilizing a linear voltage differential transducer. The subjects were categorized by age into ten 5-year groups. The magnitude of decline across age in MFR ranged from 36.2% IFAE) to 45.1% (PF). There were differences among muscle groups in the age at which a significant decline in MFR was first detected. The earliest drop off in MFR was observed in FF and FAF (45-49 years), while the latest significant decline across age was noted in FAE (65-69 years). Since the magnitude of maximal force decreases with age, and because these charactemtics can not be entirely explained by age-related decrements in €at-free mass, it appears that the quality in addition to the quantity of senescent muscle tissue may be compromised. However, the magnitude of decline in maximal force is dependent upon the muscle group considered.