Age-related differences in twitch contractile properties of plantarflexor muscles in women

This study compared maximal voluntary isometric strength and electrically e voked twitch characteristics of the plantarflexor muscles among the groups of women of the 3rd (n = 14), 4th (n = 13), 5th (n = 11), 6th (n = 12) and 8th (n = 13) decade. A significant decrease (P < 0.05-0.001) has been found in isometric maximal Voluntary contraction (MVC) force from the 5th decade and in twitch maximal force from the 6th decade. The 3rd decade group prod uced 72% greater MVC force and 43% greater twitch maximal force than the 8t h decade group (P < 0.001). A prolongation (P < 0.01) in twitch contraction time was observed from the 5th decade. Twitch contraction time in the 3rd decade group was 16% shorter (P < 0.001) compared with the 8th decade group (P < 0.01). Twitch half-relaxation time did not differ significantly (P >0 .05) among the groups. A decrease (P < 0.05-0.001) has been found in twitch maximal rate of force development from the 5th decade and in twitch maxima l rate of relaxation from the 6th decade. The 3rd decade group produced 63% greater (P < 0.001) twitch maximal rate of force development than the 8th decade group. it was concluded that in women a marked age-related reduction in maximal voluntary force-generating capacity of the plantarflexor muscle s and speed of contraction of the electrically evoked twitch takes place af ter 40 years of age, while reduction in maximal force-generating capacity a nd speed of relaxation of the twitch occurs after 50 years of age.