Aims

In patients with a rotator cuff tear, tear pattern and tendon involvement are known risk factors for the development of pseudoparalysis of the shoulder. It remains unclear, however, why similar tears often have very different functional consequences. The present study hypothesizes that individual shoulder anatomy, specifically the moment arms (MAs) of the rotator cuff (RC) and the deltoid muscle, as well as their relative recruitment during shoulder abduction, plays a central role in pseudoparalysis.

The elbow flexor muscles of four men were trained using maximal voluntary isometric contractions. Thirty contractions a day were performed for five weeks. The four men and four control subjects were tested once a week: measurements of the supramaximally stimulated isometric twitch force, the time taken for the twitch force to peak and the tetanic force were carried out; simultaneously, measurements of the force of maximal voluntary isometric contraction and resistance to fatigue were made. The testing sessions produced no training effect on control subjects. Training produced a 20 per cent increase in the force of maximal voluntary isometric contraction after five weeks, but the forces of electrically evoked twitch and tetanus showed no increase. It was concluded that the increase in the force of maximal voluntary isometric contraction must be related to factors other than the force-generating capacity of the muscle fibres themselves