Regulatory, Integrative and Comparative Physiology

Neural factors account for strength decrements observed after short-term muscle unloading

Michael R. Deschenes, Jennifer A. Giles, Raymond W. McCoy, Jeff S. Volek, Ana L. Gomez, William J. Kraemer


Strength decrements observed after extended (4–6 wk) periods of muscle unloading are associated with significant atrophy. Because early (up to 2 wk) strength gains from resistance exercise are related to improved neural recruitment, we hypothesized that the loss of strength resulting from 2 wk of muscle unloading [unilateral lower limb suspension (ULLS)] was due to impaired neural activation of the affected muscle. Blood samples, muscle biopsy specimens, muscle function data, and electromyography (EMG) recordings were analyzed before and after 14 days of muscle unloading. Pre- to postunloading data showed significant (P ≤ 0.05) decrements in peak torque and total work performed by knee extensors and flexors. This was coupled with decreased EMG activity, but no change in neuromuscular efficiency (total torque/EMG). Resistance to muscle fatigue was enhanced after ULLS. The 14-day intervention failed to alter the size or fiber type distribution of muscle samples. However, resting plasma cortisol levels were significantly increased after muscle unloading, suggesting an endocrine environment favorable to muscle atrophy. Our data confirm that the diminution in muscle function displayed after 2 wk of unloading is mainly due to neural, rather than contractile, disturbances.

  • unweighting
  • neuromuscular
  • cortisol
  • adrenocorticotropic hormone
  • electromyography


  • Address for reprint requests and other correspondence: M. R. Deschenes, Dept. of Kinesiology, The College of William & Mary, Williamsburg, Virginia 23187-8795 (E-mail: mrdesc{at}

  • The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

  • 10.1152/ajpregu.00386.2001

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