Age-Associated Changes in Motor Unit Physiology: Observations From the Baltimore Longitudinal Study of Aging

Shari M. Ling, Robin A. Conwit, Luigi Ferrucci, E. Jeffrey Metter

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Ling SM, Conwit RA, Ferrucci L, Metter EJ. Age-associated changes in motor unit physiology: observations from the Baltimore Longitudinal Study of Aging. Objective: To examine motor unit characteristics (size and firing rate) associated with aging. Design: Cross-sectional, observational. Setting: Community. Participants: Baltimore Longitudinal Study of Aging participants (N=102), aged 22.2 to 94.1 years, were studied. Interventions: Not applicable. Main Outcome Measures: Surface-represented motor unit size and firing rate were collected from the vastus medialis during knee extension at 10%, 20%, 30%, and 50% of each subject's maximum isometric voluntary contraction (MVC). Results: MVC declined with older age (P<.0001). Adjusting for differences in MVC, both firing rate and motor unit size per newton force generated began to increase in the 6th decade of life. Motor unit size increased per newton force to a greater extent than firing rate. Those over the age of 75 years also activated significantly larger motor units per unit force (P=.04). Relative to force generated, the average firing rate began increasing at 57.8±3.4 years and between 50.2 and 56.4 years (±4y) for motor unit size. Conclusions: The size of motor units and firing rates used to achieve a given force changes with age, particularly after middle age. Whether these changes precede, follow, or occur concurrent to age-related modifications in muscle structure and contractile properties or sarcopenia is not known.

Original languageEnglish (US)
Pages (from-to)1237-1240
Number of pages4
JournalArchives of physical medicine and rehabilitation
Issue number7
StatePublished - Jul 2009
Externally publishedYes


  • Aging
  • Muscles
  • Rehabilitation

ASJC Scopus subject areas

  • Physical Therapy, Sports Therapy and Rehabilitation
  • Rehabilitation


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