On assessment of shoulder exercise and load-elicited pain in the cervical spine. Biomechanical analysis of load--EMG--methodological studies of pain provoked by extreme position.

Abstract

Biomechanical analyses of load on locomotor structures are essential parts of physical therapy. Load moments of force, compressive and shear joint forces are associated with the risk of eliciting pain or causing excessive load during work and leisure activities as well as during rehabilitative training exercises. Two common therapeutic exercise movements were analysed with special emphasis on the effects of patient positioning on the load relations. Resistance was provided by an ordinary pulley apparatus. A computerized static model was developed, where positioning angle, pulley cord force and pulley distance could be varied. The best adaptation between the curves for induced load moment about the shoulder joint and maximum isometric muscle moment through joint angles was obtained when the subject during internal rotation exercises sat with the pulley located 40 degrees anterior to, and during external rotation exercises 20 degrees posterior to, a frontal plane through the shoulders at a distance of 1.3 m from the joint. EMG was recorded from the pectoralis major, latissimus dorsi and anterior deltoid muscles during internal rotation exercises, and from infraspinatus, deltoid and trapezius during external rotation. Pectoralis major and infraspinatus were the most active muscles during internal and external rotation respectively. Two methodological studies were made concerning pain provoked by loading joints in maintained extreme positions (i.e. positions at the limit of the motion sector). Sensations of discomfort/pain from healthy elbow and knee joints maintained in an extreme position increased with duration of provocation and decreased slowly after removal of loading weight. Using such joint loadings, a comparison of the Visual Analogue Scale with Borg's category-ratio scale showed that both be can be used for reliable assessments of load-elicited pain intensity. In one study cervical spine extreme position was found to be associated with sitting work postures where the thoraco-lumbar spine was slightly inclined backwards or where the whole spine was flexed. Healthy subjects participated in an experimental study in which a position involving extreme flexion of the lower-cervical-upper-thoracic spine (similar to a common work posture) was maintained. Pain was experienced by all ten subjects within 15 minutes, disappeared 15 minutes after the end of provocation, but was again experienced by nine subjects the same evening or the next morning and lasted up to four days. Neck extensor muscle activity was low.(ABSTRACT TRUNCATED AT 400 WORDS)