Activity levels during isometric test contractions of neck and shoulder muscles.

In order to analyse isometric muscle test contractions in the neck and shoulder region, an electromyographic (EMG) study of ten healthy females was undertaken. A series of 13 standardized isometric contractions with manual resistance was performed in the sitting position. Rectified time-averaged EMG was recorded, using surface electrodes. All tests activated all muscles studied to some extent and at various levels, but four different patterns of activation could be identified. Maximum level of activity was obtained: 1) in the cervical erector spinae muscles during neck extension, 2) in the splenius and levator scapulae muscles during lateral flexion of the cervical spine, 3) in the trapezius, pars descendens muscle during abduction of the arm in the plane of the scapula, 4) in the thoracic erector spinae/rhomboids muscles during shoulder elevation or scapular retraction/elevation.