The contributions of peripheral muscle strength, disease severity, and physical activities of daily living to arm and leg ergometry capacity in chronic pulmonary disease patients
Chronic Pulmonary Disease (CPD) often causes a reduction in physical activity and lower limb dysfunction. Exercise tolerance generally declines across the stages of CPD, which might be related to a reduction in physical activities of daily living, due to breathing discomfort or increased leg/arm fatigue. The contributions of specific aspects of disease severity and deconditioning to exercise tolerance remains unclear. In addition, it is uncertain whether patients with CPD have reduced upper limb function, or if upper body aerobic training capacity (arm ergometry) may be preserved. To provide insight into why patients adopt a more sedentary lifestyle, the aims of this study were to determine: (1) the combined and individual contributions of physical activities of daily living (type and volume) and FEV1 to arm and leg ergometry capacity of patients with CPD; and (2) the predictability and odds ratio of high arm and leg ergometry capacity in CPD individuals with high and low arm and leg strength, while controlling for stage of disease, body composition and gender. Forty-four CPD patients, 16 males and 28 females (mean age = 59.8 ± 11.9 years), with a FEV1 of 22-89% predicted (mean FEV1% predicted = 54.6 ± 18.3) participated. All participants completed spirometry, International Physical Activity Questionnaire and Activities of Daily Living-Dyspnoea questionnaire, Medical Research Council grade, anthropometric assessment, sub-maximal arm and leg ergometry testing, grip strength, and isokinetic quadriceps and hamstrings strength and endurance testing. To determine contributing and predictor variables of arm and leg ergometry capacity, a progressive statistical procedure was implemented leading to multiple linear and binary regression analyses. No statistically significant relationships (p>0.05) were found between total activity, upper body activity and lower body activity, and peripheral muscle strength and aerobic capacity (controlling for age, gender and percentage body fat). Multiple regression analysis demonstrated that quadriceps strength (Nm), FEV1% and grip strength (kg) predicted 64% of peak wattage during submaximal leg ergometry testing (adjusted R2 = 64%, F = 26.387, p=0.00). Quadriceps strength showed the highest predictability of peak leg ergometry wattage (p=0.00, beta 0.844 and t=6.238), followed by grip strength and FEV1% (p=0.038, β=-0.270, t=-2.143 and p=0.028, β=-0.230, t=2.279, respectively). A second regression analysis determined that quadriceps strength (Nm), FEV1% and grip strength (kg) predicted 53% of peak wattage during submaximal arm ergometry testing (adjusted R2=0.53, F=17.018, p=0.00). Quadriceps strength was the only independent variable that showed predictability of peak arm ergometry wattage (p=0.00, beta 0.793 and t=5.125). The odds ratio analysis indicated that CPD patients with high quadriceps strength have 13.76 times higher odds of having high peak arm ergometry wattage. This odds ratio equated to an 85% probability of having high arm ergometry peak wattage if quadriceps strength is high. In summary, the main factors predicting leg ergometry capacity were quadriceps strength FEV1 and grip strength. Quadriceps strength was the only statistically significant predictor of peak arm ergometry wattage, suggesting that a reduction in leg function is associated with a reduction in arm function. This study highlights the importance of assessing upper and lower limb strength in patients with CPD, and endorses the incorporation of specified lower limb strength training in pulmonary rehabilitation, especially for those with reduced strength and physical activity levels. Pulmonary rehabilitation programs should incorporate both aerobic exercise and lower limb strength training.