Firing rates of motor units during strong dynamic contractions

Alejandro Del Valle, Christine K. Thomas

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Muscle behavior is usually studied during isometric contractions but many tasks include contractions that involve changes in muscle length. Our aim was to record motor unit action potentials and surface electromyograms (EMGs) from triceps brachii muscles during rhythmic dynamic contractions (3-s concentric, 3-s eccentric; 40°/s; four subjects) performed at the highest voluntary forces subjects could exert (maximal concentric contraction) and at various submaximal intensities. Mean unit firing rates and surface EMG increased significantly with contraction intensity in both concentric and eccentric contractions, but at each intensity mean concentric values were significantly higher than eccentric values. In contrast, mean unit firing rates and surface EMGs were similar during maximal concentric and maximal isometric contractions. These data suggest muscles were activated maximally during the strongest concentric contractions but submaximally during the strongest eccentric efforts. After estimated eccentric contraction intensity was adjusted using surface EMG data, mean unit firing rates during eccentric contractions were still lower than the concentric values. Thus, protective mechanisms may limit motor unit firing rates during forceful lengthening contractions to minimize damage.

Original languageEnglish (US)
Pages (from-to)316-325
Number of pages10
JournalMuscle and Nerve
Issue number3
StatePublished - Sep 2005


  • Concentric contractions
  • Eccentric contractions, isometric voluntary contractions
  • Motor unit firing rates
  • Muscle length

ASJC Scopus subject areas

  • Clinical Neurology
  • Neuroscience(all)


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