Abstract
[Purpose] An experiment was carried out to investigate possible age-associated changes in the cross-sectional area of the type II fibers of the extensor digitorum longus (EDL) of male rats during hindlimb unweighting. [Subjects] Nine 3-month-old and seven 8-month-old rats were divided into three groups each. [Methods] One group was reared under hindlimb suspension for one week, another group for two weeks and a control group under normal rearing conditions for three weeks. The cross-sectional area of 200 to 230 muscle fibers of the right EDL from each rat was measured, followed by random sampling of 15 type II fibers from each of the six groups that were used for a comparison of their mean values. In addition, 50 type II fibers were selected for a comparison of their frequency distribution patterns. [Results] Significant atrophic changes were demonstrated in EDL of the 3-month-old rats in hindlimb suspension for one week in comparison to the control group, but the 8-month-old rats showed no significant atrophic changes in any of the groups. [Conclusion] The atrophying process of the rat EDL may differ depending on its age, and this process in aged skeletal muscle fibers may be delayed for a short period of time during unweighting.
