Abstract
BACKGROUND AND PURPOSE: Hypermobility Spectrum Disorder (HSD) is a common musculoskeletal condition that impairs function and quality of life. While exercise therapy has shown to improve outcomes, treatment standardisation is lacking and the relationship between strength and symptoms remains unclear. Therefore, our aim was to investigate the association between changes in shoulder strength and self-reported shoulder function, pain, and perceived effect in patients with HSD and shoulder symptoms. METHODS: This is a secondary analysis of a randomised controlled trial. Data from 76 participants (58 women; median age 35.5) were included. Primary outcomes were percentage change in relative strength (Nm/kg) measured in external rotation, internal rotation, and scaption, the Western Ontario Shoulder Instability Index (WOSI), the Numerical Pain Rating Scale (NPRS) and the Global Perceived Effect: Physical domain (GPEP). Secondary outcomes were achieving the Minimal Clinically Important Difference (MCID) in shoulder function and pain. Covariates were age, sex, Body Mass Index, hand dominance, previous shoulder dislocation, mechanical shoulder symptoms, and assigned intervention group. RESULTS: Increasing strength in external rotation and scaption were linearly associated with an improvement in shoulder function (WOSI adjusted -3.5 (95% CI -5.9; -1.1), and WOSI adjusted -2.6 (95% CI -4.6; -0.6) respectively), while scaption strength was associated with a reduction in shoulder pain (NPRS -0.01 (95% CI -0.02; 0.00)). Improvement in external rotation and scaption were associated with higher odds of reporting an important improvement measured for every 10% increase in strength (adjusted OR 1.18 (95% CI 1.00; 1.38) and 1.30 (95% CI 1.07; 1.59), respectively). DISCUSSION: Increased shoulder strength may be associated with improved outcomes in patients with HSD and persistent shoulder symptoms although our findings suggest limited clinical relevance. Further research is needed to understand the relationship between strength and symptom relief. TRIAL REGISTRATION: The study was registered in Clinicaltrials.gov (11 March 2019, NCT03869307).