P.W. Hodges, PhD 1 2 *, L.H.M. Pengel, MSc 3, R.D. Herbert, PhD 3, S.C. Gandevia, DSc 1

1Prince of Wales Medical Research Institute and the University of New South Wales, Sydney, New South Wales 2031, Australia
2Department of Physiotherapy, University of Queensland, Brisbane, Queensland 4072, Australia
3School of Physiotherapy, University of Sydney, Sydney, New South Wales 1825, Australia

Keywords: fascicle length • isometric contraction • muscle thickness • pennation angle • ultrasonography

Abstract
To investigate the ability of ultrasonography to estimate muscle activity, we measured architectural parameters (pennation angles, fascicle lengths, and muscle thickness) of several human muscles (tibialis anterior, biceps brachii, brachialis, transversus abdominis, obliquus internus abdominis, and obliquus externus abdominis) during isometric contractions of from 0 to 100% maximal voluntary contraction (MVC). Concurrently, electromyographic (EMG) activity was measured with surface (tibialis anterior only) or fine-wire electrodes. Most architectural parameters changed markedly with contractions up to 30% MVC but changed little at higher levels of contraction. Thus, ultrasound imaging can be used to detect low levels of muscle activity but cannot discriminate between moderate and strong contractions. Ultrasound measures could reliably detect changes in EMG of as little as 4% MVC (biceps muscle thickness), 5% MVC (brachialis muscle thickness), or 9% MVC (tibialis anterior pennation angle). They were generally less sensitive to changes in abdominal muscle activity, but it was possible to reliably detect contractions of 12% MVC in transversus abdominis (muscle length) and 22% MVC in obliquus internus (muscle thickness). Obliquus externus abdominis thickness did not change consistently with muscle contraction, so ultrasound measures of thickness cannot be used to detect activity of this muscle. Ultrasound imaging can thus provide a noninvasive method of detecting isometric muscle contractions of certain individual muscles. Muscle Nerve 27: 682-692, 2003



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