Relation between location of a motor unit in the human biceps brachii and its critical firing levels for different tasks

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

    Research output: Contribution to journalArticleAcademicpeer-review

    164 Citations (Scopus)

    Abstract

    Critical firing levels (CFLs) of single motor units (MUs) in the long head of the human biceps brachii muscle were determined in combinations of two isometric tasks: flexion of the elbow, supination of the lower arm, and exorotation of the humerus, as well as the corresponding antagonistic tasks. The MU activity was recorded by 25-?m bipolar wire electrodes. Four main patterns of MU recruitment, related to the recording location in the muscle, were found: (i) MUs active only when flexing the elbow were located mostly laterally. (ii) MUs active only when supinating were all located medially. (iii) MUs whose CFL depended on a linear combination of flexion and supination forces were all located medially. Some of these MUs could not be recruited during pronation. (iv) Nonlinearly behaving MUs, located centrally. The relative weights of flexion and supination input were constant for all units, whose CFL depended on a linear sum of flexion and supination forces, as well as for the nonlinearly behaving units. Supination and exorotation showed equivalent CFL changes when they were combined with the flexion task. Extension did not change the CFL for supination- or exorotation tasks. No clear difference was found between the ratios of the peak twitch forces in flexion and supination direction for laterally and medially located small muscle areas or single MUs. A simple model of the motoneuron pool organization is proposed to explain our findings.
    Original languageEnglish
    Pages (from-to)631-650
    Number of pages20
    JournalExperimental Neurology
    Volume85
    Issue number3
    DOIs
    Publication statusPublished - 1984

    Fingerprint Dive into the research topics of 'Relation between location of a motor unit in the human biceps brachii and its critical firing levels for different tasks'. Together they form a unique fingerprint.

    Cite this