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Isometric and dynamic explosive force production of leg extensor muscles in men at different ages

Abstract:

A group of 15 healthy men divided into three different age groups of young (Y) (range 22-24 years; n =5), middle-aged (M) (range 41-43; n = 5) and old (O) (range 71-77;n=5) voluntereed as subjects for examination of their explosive force production of the leg extensor muscles in both isometric (force-time curve) and dynamic actions (height, distance and power in the squat jump (SJ) and standing long-jump (SLJ)). Maximal strength of 1629 (± 332) N in O was 30% lower (p<0.001) than that of 2323 (±415) N recorded in M. Height in SJ and distance in SLJ in O were 50% and 38% lower than in M (p>0.001) and 60% and 46% lower than in Y (p<0.001). The rate efforce development in the isometric force-time curve was 47% lower in O (p<0.01) than in M. In O and in a combined group of M and O, dynamic explosive force correlated significantly with explosive isometric force (r = 0.81 ; p<0.05 in O and r = 0.76; p<0.001 in M+O) and in M+O also with maximal strength (r = 0.60; p<0.05). The present results suggest that explosive force decreases drastically and more than maximal strength with increasing age, especially in old age. This indicates that atrophying effects of aging may be especially great on fast twitch fibers and/or there is a selective loss of these fibers and/or a decline in the ability for rapid recruitment of motor units. In younger subjects no significant correlation existed between the dynamic and explosive isometric actions, while in older subjects with greater interindividual variation it was significant. Also a low level of maximal strength in older subjects seemed to be associated with a lower ability of the neuromuscular system to develop force rapidly. The results also suggest that in order to minimize age-related decreases in neuromuscular performance proper strength training among elderly subjects could include exercises for maximal strength as well as those of an explosive nature. ©1996 Teviot Scientific Publications.