Weak Leg Strength in Bronchiectasis Predicts Worse Breathing and Quality of Life Over One Year

Bronchiectasis is a chronic airway disease marked by irreversible bronchial dilation, persistent cough, and sputum production. Beyond the lungs, it produces significant extrapulmonary effects including muscle wasting, bone loss, and reduced physical capacity. Despite growing recognition of these systemic features, no prior study had examined core muscle endurance in this population or tracked whether baseline muscle strength predicts clinical outcomes over time. This Australian study addressed both gaps through a secondary analysis of a cross-sectional characterisation study with embedded one-year longitudinal follow-up conducted at Hunter Medical Research Institute in Newcastle.

The study enrolled 71 adults with HRCT-confirmed bronchiectasis and 92 healthy controls. Participants underwent comprehensive assessment including DXA body composition scanning, isokinetic leg strength testing, shoulder strength via dynamometry, and three validated core endurance tests: the Biering-Sørensen (posterior core), Side Bridge (lateral core), and Partial Sit-Up (anterior core). Forty-three bronchiectasis participants completed the one-year follow-up, during which exacerbations, dyspnoea (mMRC), health-related quality of life (SGRQ), anxiety and depression (HADS), and exercise capacity (6MWT) were reassessed. Participants were classified as having retained or impaired leg strength based on the 10th percentile cutoff from control values, sex-stratified.

DXA results revealed that women with bronchiectasis had significantly lower appendicular skeletal muscle mass index (ASMMI) compared to female controls (p = 0.018), though this difference was not statistically significant in men. Both sexes with bronchiectasis had markedly lower femoral bone mineral density (BMD) than their control counterparts (p < 0.001). Osteopenia was three times more prevalent in women with bronchiectasis than female controls (54% vs. 18%), a clinically striking disparity with implications for fracture risk. Leg strength was reduced in bronchiectasis versus controls for both men (mean difference −25 kg, 95% CI −50 to −1) and women (mean difference −18 kg, 95% CI −29 to −7). Women with bronchiectasis also demonstrated significantly poorer lateral core endurance on the Side Bridge test compared to women without bronchiectasis (p ≤ 0.003).

The longitudinal analysis was the study's most novel contribution. Participants with impaired leg strength at baseline had significantly worse dyspnoea scores, lower SGRQ quality of life, and reduced 6-minute walk test performance at one year. Reduced leg strength explained up to 33% of the variance in these outcomes (p ≤ 0.001), making it one of the strongest modifiable predictors identified in this population to date. Importantly, leg strength did not significantly predict exacerbation frequency or HADS anxiety/depression scores, suggesting its prognostic value is more specific to functional and symptomatic domains.

The authors acknowledge several limitations. The study is a secondary analysis, the sample size at follow-up was modest (n = 43), and the control group was not followed longitudinally, limiting causal inference. The predominantly Australian cohort and exclusion of participants with active exacerbations may also affect generalisability. Nonetheless, the consistent finding across multiple functional domains — dyspnoea, quality of life, and walk distance — strengthens the argument that leg strength testing should become a standard component of bronchiectasis clinical assessment and that pulmonary rehabilitation targeting lower limb strength deserves prioritisation in disease management guidelines.