AGE

, 38:48

Age-related changes in motor unit firing pattern of vastus lateralis muscle during low-moderate contraction

  • Kohei Watanabe
  • Aleš Holobar
  • Motoki Kouzaki
  • Madoka Ogawa
  • Hiroshi Akima
  • Toshio Moritani
Article

Abstract

Age-related changes in motor unit activation properties remain unclear for locomotor muscles such as quadriceps muscles, although these muscles are preferentially atrophied with aging and play important roles in daily living movements. The present study investigated and compared detailed motor unit firing characteristics for the vastus lateralis muscle during isometric contraction at low to moderate force levels in the elderly and young. Fourteen healthy elderly men and 15 healthy young men performed isometric ramp-up contraction to 70 % of the maximal voluntary contractions (MVC) during knee extension. Multichannel surface electromyograms were recorded from the vastus lateralis muscle using a two-dimensional grid of 64 electrodes and decomposed with the convolution kernel compensation technique to extract individual motor units. Motor unit firing rates in the young were significantly higher (~+29.7 %) than in the elderly (p < 0.05). There were significant differences in firing rates among motor units with different recruitment thresholds at each force level in the young (p < 0.05) but not in the elderly (p > 0.05). Firing rates at 60 % of the MVC force level for the motor units recruited at <20 % of MVC were significantly correlated with MVC force in the elderly (r = 0.885, p < 0.0001) but not in the young (r = 0.127, p > 0.05). These results suggest that the motor unit firing rate in the vastus lateralis muscle is affected by aging and muscle strength in the elderly and/or age-related strength loss is related to motor unit firing/recruitment properties.

Keywords

Aging Multichannel surface electromyography Quadriceps femoris muscles 

Abbreviations

EMG

Electromyography

MVC

Maximal voluntary contraction

PNR

Pulse-to-noise ratio

SEMG

Surface electromyography

VL

Vastus lateralis

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Copyright information

© American Aging Association 2016

Authors and Affiliations

  • Kohei Watanabe
    • 1
  • Aleš Holobar
    • 2
  • Motoki Kouzaki
    • 3
  • Madoka Ogawa
    • 4
  • Hiroshi Akima
    • 4
    • 5
  • Toshio Moritani
    • 6
  1. 1.Laboratory of Neuromuscular Biomechanics, School of International Liberal StudiesChukyo UniversityNagoyaJapan
  2. 2.Faculty of Electrical Engineering and Computer ScienceUniversity of MariborMariborSlovenia
  3. 3.Laboratory of Neurophysiology, Graduate School of Human and Environmental StudiesKyoto UniversityKyotoJapan
  4. 4.Research Center of Health, Physical Fitness and SportsNagoya UniversityNagoyaJapan
  5. 5.Graduate School of Education and Human DevelopmentNagoya UniversityNagoyaJapan
  6. 6.Laboratory of Applied Physiology, Graduate School of Human and Environmental StudiesKyoto UniversityKyotoJapan

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