Isometric strength in flexors, abductors, and external rotators of the shoulder.

The aim of this study was to map the isometric shoulder muscle strength of 96 men and 90 women randomized from the population register of Stockholm citizens (reference groups), and of 83 male furniture removers and 89 female secretaries (aged 19-65 years, all four groups). Maximum isometric strength of the right-side shoulder flexors (90° joint angle), abductors, and external rotators (0°) was recorded with the subject sitting in a standardized position in an adjustable chair. Women had 43, 55, and 56% of the men's strength in the abductors, flexors, and external rotators respectively. Neither of the female test groups showed any change in maximum isometric strength with increasing age. Men from the reference group showed an age-related difference only in shoulder flexor strength, where the older men (45-65 years) had 89% of the younger men's (19-44 years) strength. The strength values of older furniture removers were 77-83% of the younger colleagues' values in all muscle groups tested. The muscular strength utilization ratio (MUR%) when holding the arm without external load at 90° shoulder flexion was 22-25 MUR% for the male groups and 34 MUR% for the female groups, which shows that the muscular load on the shoulder caused by the weight of the arm is of great importance.