• B Harwood, K M D Cornett, D L Edwards, R E Brown, and J M Jakobi.
• Health and Exercise Science, University of British Columbia Okanagan, Kelowna, BC, Canada; Department of Physiology, University of Arizona, Tucson, AZ, USA.
• Acta Physiol (Oxf). 2014 Aug 1; 211 (4): 597-608.

BackgroundCompartmentalized responses in motor unit (MU) activity of the short head (SH) and long head (LH) of the biceps brachii are observed following forearm position change. Differential muscle spindle afferent distribution has been proposed as a potential mechanism underlying this behaviour. Tendon vibration is an effective, non-invasive method of increasing muscle spindle afferent activity of a target muscle group offering a paradigm in which this hypothesis may be investigated further.AimTo determine the effect of tendon vibration on MU recruitment and discharge rates of the SH and LH, muscle activity of the elbow flexors and triceps brachii, intermuscular coherence among the SH, LH, brachioradialis and triceps brachii and force steadiness in young males and females during isometric elbow flexion.MethodsIntramuscular electromyography (EMG) of the SH and LH, and surface EMG of the elbow flexors were recorded pre- and post-vibration during low-force isometric contractions. Motor unit recruitment thresholds, MU discharge rates and MU discharge variability; surface EMG amplitude, intermuscular coherence and force steadiness were determined pre- and post-vibration.ResultsDifferential changes in all MU properties, EMG amplitude and intermuscular coherence were observed among elbow flexors. Although MU properties exhibited differential changes, they accounted for little variance in isometric force steadiness. However, intermuscular EMG coherence among all muscles investigated was reduced post-vibration.ConclusionUncoupling of common oscillatory input as a result of differential muscle spindle afferent inputs to elbow flexors may be responsible for the reduction in force steadiness following tendon vibration and a forearm position change.© 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

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