Study of muscle strength imbalance at the shoulder joint between the young and the old

This study examined muscle imbalance in the cases of isokinetic movement of the shoulder joint, targeting the young and the old. The experiment was divided into the dominant and non-dominant sides and consisted of flexion, extension, abduction, adduction, external rotation, and internal rotation. Regarding the angular velocity, the peak torque was measured for the equal condition of 30, 60, and 120 deg/s. The concentric and eccentric muscular strengths were measured based on each motion. This study showed that concentric movement tended to decrease the peak torque on the dominant and non-dominant sides alike by increasing the angular velocity, whereas an eccentric movement had a tendency to boost the peak torque by increasing the velocity except for the dominant external rotation. In the case of the young, most of the motion showed that the dominant side had a higher peak torque than the non-dominant side regardless of the angular velocity. The results from the elderly were different from the young, and the non-dominant side tended to have a higher peak torque than the dominant one regardless of the angular velocity. According to the Antagonistic Strength relationships(Concentric) in the young and the old, young people's flexion/ extension ratio was 3 ~ 13%, abduction/adduction 1 ~ 16%, and external rotation/internal rotation 5 ~ 10%. The data from the elderly showed that the ratio of abduction/adduction under concentric contraction ranged from 20 to 31%, which was higher than that reported previously. The elderly showed an imbalanced muscle tendency. This result is expected to provide a useful basic guideline for measuring the shoulder function of the young and old, and consisted rehabilitation equipment and its programs.