Attenuated activation of knee extensor muscles during fast contractions in older men and women

Eur J Appl Physiol. 2020 Oct;120(10):2289-2299. doi: 10.1007/s00421-020-04451-0. Epub 2020 Aug 13.

Abstract

Aim: 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.

Purpose: 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.

Methods: 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).

Results: 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.

Conclusion: 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.

Keywords: Aging; EMG; Neural activation; Rate of torque development; Sex differences.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Aging / physiology*
  • Electric Stimulation
  • Female
  • Humans
  • Isometric Contraction*
  • Knee / growth & development
  • Knee / physiology*
  • Male
  • Muscle, Skeletal / growth & development
  • Muscle, Skeletal / innervation
  • Muscle, Skeletal / physiology*
  • Reaction Time
  • Torque