Influence of anthropometric and psychological variables pain and disability on isometric endurance of shoulder abduction in patients with rotator tendinosis of the shoulder

Abstract

Predictors of isometric endurance of shoulder abduction were investigated in 18- to 75-year-old women (n = 59, mean age 48 years) and men (n = 53, mean age 46 years) with unilateral rotator tendinosis of the shoulder (median duration 1-2 years). They were asked to keep both shoulders abducted at 45 degrees, both wrists loaded with 2 kg, for as long as possible. The average force exerted to keep the required position was 17% higher in men compared to women. Mean times to exhaustion were: 103 seconds (SD 109) for the involved shoulder and 160 seconds (SD 81) for the uninvolved shoulder in women; compared to 159 seconds (SD 109) and 289 seconds (SD 109) in men. Increased pain, emotional distress and disability were associated with decreased endurance in the involved shoulder. Gender and emotional distress were the most powerful predictors of time to exhaustion in the uninvolved shoulder, and accounted for 41.7% of the total variance (R2). Age, body weight, self-efficacy for pain and active coping were poor predictors. This study indicates that isometric endurance is a psychophysiological measure in patients with shoulder pain. Reported pain, emotional distress and disability should be taken into account for interpretation of results.