Passive and Active Tension-Length Diagrams of Intact Skeletal Muscle in Normal Women of Different Ages

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Abstract
The present study showed that in normal women max. contractile strength of the adductor pollicis brevis muscle was not attained by the early twenties and a decrease from max. contractile strength occurred in the years 51-61. These changes in contractile strength were associated with an increase in the stiffness of the non-muscle tissues as evidenced by the increased slope ([DELTA]T/[DELTA]L) of the passive tension-length curves in the elder women. We believe that the decrease in strength of voluntary contraction reported by others is,at least in part, accounted for by a decrease in the muscle/non-muscle ratio, which results in a stiffer muscle complex. The contraction period was prolonged and the rate of contraction faster in the isometric single twitches of the elder women. These changes are consistent with an alteration in muscle composition such as an increase in myoglobin, with an alteration in the speed of the chemical reactions of muscle contraction, with an increase in the size of the muscle fibers, with more synchronous contraction of the individual muscle fibers, and with an increase in stiffness of the non-muscle tissue.

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