Muscular Strength and Endurance as a Function of Age and Activity Level

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Abstract
Muscular strength, endurance, and rate of fatigue were studied in populations of various ages actively engaged in strength and endurance training as compared with those not engaged in such activities. The strength and fatigability of the elbow flexor muscles were studied for 62 subjects at the ages of 20 (n = 11 active, 10 inactive), 35 (n = 11 active, 10 inactive), and 50 (n = 10 active, 10 inactive) years, tested within 2 years of the appropriate age. They performed a 6-min bout of maximal rhythmic contractions of the dominant arm at a rate of 30 contractions per min. Force applied to the transducer was converted into electrical activity and transmitted to a recorder, where differences in mean values for initial strength, final strength, absolute endurance, and relative endurance were examined for significance. Rates of fatigue and the fatigue curves were also obtained for each group. Results revealed significantly less muscular strength, absolute endurance, and relative endurance as the age of the subjects increased, but no significant difference for age was found in final strength at the conclusion of the exercise bout. Significant differences were found between active and inactive subjects in initial strength, final strength, and absolute endurance in favor of the active subjects. No significant interaction between activity level and age was found for any of the dependent variables. The rates of fatigue were similar for all ages except for the inactive 20-year-old subjects, whose rate of fatigue was markedly slower than that found for all other groups of subjects. It is concluded that active subjects engaged in strength training maintain higher levels of muscular strength and endurance than those who are inactive, but both functions deteriorate by 50 years of age. Rates of fatigue are generally unchanged by activity levels and age.