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Postural muscle tone in the body axis of healthy humans.

Abstract

Across the entire human body, postural tone might play its most critical role in the body's axis because the axis joins the four limbs and head into a single functioning unit during complex motor tasks as well as in static postures. Although postural tone is commonly viewed as low-level, tonic motor activity, we hypothesized that postural tone is both tonically and dynamically regulated in the human axis even during quiet stance. Our results describe the vertical distribution of postural muscle tone in the neck, trunk, and hips of standing human adults. Each subject stood blindfolded on a platform that axially rotated the neck, trunk, or pelvis at 1 degrees /s and +/-10 degrees relative to the neutral position (i.e., facing forward). The measured resistance to axial rotation was highest in the trunk and lowest in the neck and was characterized by several nonlinear features including short-range stiffness and hysteresis. In half of the subjects, axial muscle activity was relatively constant during axial rotation, and in the other half, muscle activity was modulated by lengthening and shortening reactions, i.e., decreasing activity in lengthening muscles and increasing activity in shortening muscles, respectively. Axial resistance to rotation was reduced in subjects whose muscle activity was modulated. The results indicate that axial tone is modulated sensitively and dynamically, this control originates, at least in part, from tonic lengthening and shortening reactions, and a similar type of control appears to exist for postural tone in the proximal muscles of the arm.

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  • Authors+Show Affiliations

    ,

    Neurological Sciences Institute, Oregon Health and Sciences University, 505 NW 185th Ave., Beaverton, OR 97006, USA. cordop@ohsu.edu

    , , , ,

    Source

    Journal of neurophysiology 96:5 2006 Nov pg 2678-87

    MeSH

    Adult
    Aged
    Arm
    Data Interpretation, Statistical
    Electromyography
    Female
    Hip
    Humans
    Male
    Middle Aged
    Muscle Tonus
    Neck Muscles
    Nonlinear Dynamics
    Postural Balance
    Posture
    Sex Characteristics
    Shoulder

    Pub Type(s)

    Journal Article
    Research Support, N.I.H., Extramural

    Language

    eng

    PubMed ID

    16837660