Relationships between motor unit size and recruitment threshold in older adults: Implications for size principle

Brett Fling, Christopher A. Knight, Gary Kamen

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

As a part of the aging process, motor unit reorganization occurs in which small motoneurons reinnervate predominantly fast-twitch muscle fibers that have lost their innervation. We examined the relationship between motor unit size and the threshold force for recruitment in two muscles to determine whether older individuals might develop an alternative pattern of motor unit activation. Young and older adults performed isometric contractions ranging from 0 to 50% of maximal voluntary contraction in both the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles. Muscle fiber action potentials were recorded with an intramuscular needle electrode and motor unit size was computed using spike-triggered averaging of the global EMG signal (macro EMG), which was also obtained from the intramuscular needle electrode. As expected, older individuals exhibited larger motor units than young subjects in both the FDI and the TA. However, moderately strong correlations were obtained for the macro EMG amplitude versus recruitment threshold relationship in both the young and older adults within both muscles, suggesting that the size principle of motor unit recruitment seems to be preserved in older adults.

Original languageEnglish (US)
Pages (from-to)125-133
Number of pages9
JournalExperimental Brain Research
Volume197
Issue number2
DOIs
StatePublished - Aug 2009
Externally publishedYes

Fingerprint

Neurophysiological Recruitment
Muscles
Needles
Young Adult
Electrodes
Fast-Twitch Muscle Fibers
Isometric Contraction
Motor Neurons
Action Potentials

Keywords

  • Aging
  • Elderly
  • EMG
  • Motoneuron
  • Muscle
  • Strength

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this

Relationships between motor unit size and recruitment threshold in older adults : Implications for size principle. / Fling, Brett; Knight, Christopher A.; Kamen, Gary.

In: Experimental Brain Research, Vol. 197, No. 2, 08.2009, p. 125-133.

Research output: Contribution to journalArticle

Fling, Brett ; Knight, Christopher A. ; Kamen, Gary. / Relationships between motor unit size and recruitment threshold in older adults : Implications for size principle. In: Experimental Brain Research. 2009 ; Vol. 197, No. 2. pp. 125-133.
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