Changes in recruitment order of motor units in the human biceps muscle

B.M. Haar Romenij, ter, J.J. Denier van der Gon, C.C.A.M. Gielen

    Research output: Contribution to journalArticleAcademicpeer-review

    138 Citations (Scopus)


    Changes in recruitment threshold of individual motor units of the human biceps (caput longum), a multifunctional muscle, were investigated during different tasks, i.e., isometric flexion of the elbow, isometric supination of the forearm, and isometric exorotation of the humerus of the 110° flexed semiprone horizontal arm. The activity of 17 motor units was recorded by means of fine wire electrodes. Some units were found that could be recruited only by one force, e.g., flexion. In such cases recruitment did not depend on other forces. Most units, however, were recruited when a linear combination of exerted forces exceeded a certain threshold. The contribution of a force to this combination could be different for different motor units. Units with a high threshold for flexion tended to show a lower threshold while simultaneously exerting force in another direction. Units with a low threshold for flexion were more difficult to recruit under this condition. The findings support the view that movements are programmed "directionally".
    Original languageEnglish
    Pages (from-to)360-368
    Number of pages9
    JournalExperimental Neurology
    Issue number2
    Publication statusPublished - 1982


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