Attenuated Activation of Knee Extensor Muscles During Fast Contractions in Older Men and Women
European Journal of Applied Physiology
Reduced physical function and increased risk of falls in older adults are accompanied by age-related reductions in torque development of leg muscles, although the mechanisms and potential sex differences are not understood.
To determine the mechanistic origins (neural vs. muscular) for the age-related reduction in torque development, we compared the peak rates of torque development (RTD) during electrically-evoked and fast voluntary contractions of the knee extensors between young and older men and women.
Sets of single- and double-pulse electrical stimulations evoked contractions of the knee extensor muscles in 20 young (23.0 ± 0.8 years; 10 women) and 20 older adults (78.2 ± 1.5 years; 10 women), followed by voluntary isometric knee extension contractions with torque development as fast as possible that matched the torque during electrically-evoked contraction (10–40% maximal torque).
Peak RTD during fast-voluntary contractions was 41% less than electrically-evoked contractions (p < 0.001), but more so for older adults (44%) than young (38%, p = 0.04), with no sex differences. Peak RTD during fast-voluntary contractions was more variable between contractions for the older than young adults (77%MVC s−1 vs. 47%MVC s−1, p < 0.001). Additionally, older women exhibited greater variability than older men (81%MVC s−1 vs. 72%MVC s−1, p = 0.04) with no sex-related differences within the young adults.
Older adults had slower and more variable RTD during voluntary contractions than young adults, particularly older women. The limited age-related differences in electrically-evoked RTD suggest the primary mechanism for the slower torque development of the knee extensor muscles in older men and women involve reduced neural activation.
Kwon, Min-Hyuk; Senefeld, Jonathon; and Hunter, Sandra K., "Attenuated Activation of Knee Extensor Muscles During Fast Contractions in Older Men and Women" (2020). Exercise Science Faculty Research and Publications. 203.