Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, PC16

Poster Communications

Descending control of human trapezius and serratus anterior muscles

Alexander, C M; Stynes, S; Harrison, P J;

1. Department of Physiology, UCL , London, United Kingdom. 2. Department of Physiotherapy, Hammersmith Hospitals NHS Trust, London, United Kingdom. 3. Department of Health and Social Care, Brunel University, London, United Kingdom.


Trapezius (Tr) and serratus anterior (SA) are shoulder muscles which help to stabilise the scapula on the chest wall. In a previous study, we described interesting differences in the reflex properties of these two muscles (Alexander et al. 2005). Here we examine the descending control of these muscles using magnetic stimulation of the cortex. With informed consent from 14 subjects, EMG recordings were made from SA, upper Tr and lower Tr muscles using surface electrodes placed bilaterally. First, the optimal sites for stimulation of the motor cortex were examined. Using a grid marked on a cloth attached to the head, magnetic stimuli were applied to the scalp overlying the motor cortex in different positions until the largest amplitude contralateral MEP (cMEP) was evoked for each of the three muscles studied. In these positions, the stimulator output was varied from 20 to 100% of the stimulator output. The latency at 1.2 x threshold for the cMEP was 10.4

Where applicable, experiments conform with Society ethical requirements