Lower-Limb Resistance Training Reduces Exertional Dyspnea and Intrinsic Neuromuscular Fatigability in Individuals with COPD

Skeletal muscle atrophy, dysfunction and fatigue are important complications of COPD. Greater reliance on glycolytic metabolism and increased type III/IV muscle afferent activity increase ventilatory drive, promote ventilatory constraint, amplify exertional dyspnea, and limit exercise tolerance. To investigate whether muscular adaptation with resistance training (RT) could improve exertional dyspnea, exercise tolerance, and intrinsic neuromuscular fatigability in individuals with COPD (n=14, FEV1=62±21% predicted), we performed a proof-of-concept single-arm efficacy study utilizing four-weeks of individualized lower limb RT (3×/week). At baseline, dyspnea (Borg scale), ventilatory parameters, lung volumes (inspiratory capacity maneuvers) and exercise time were measured during a constant-load test (CLT) at 75% maximal workload to symptom limitation. On a separate day, fatigability was assessed using 3 minutes of intermittent stimulation of the quadriceps (initial output of ~25% maximal voluntary force). Following RT, the CLT and fatigue protocols were repeated. Compared to baseline, iso-time dyspnea was reduced (6.0±2.4 vs 4.5±2.4 Borg Units, p=0.02) and exercise time increased (437±405s vs 604±447, p<0.01) following RT. Isotime tidal volume increased (p=0.01) while end-expiratory lung volumes (p=0.02) and heart rate (p=0.03) decreased. Quadriceps force, relative to initial force, was higher at the end of the stimulation protocol post-training (53.2±9.1 vs 46.8±11.9%, p=0.04). This study provides evidence that four-weeks of RT attenuates exertional dyspnea and improves exercise tolerance in individuals with COPD, which in part, is likely due to delayed ventilatory constraint and reduced intrinsic fatigability. A pulmonary rehabilitation program beginning with individualized lower-limb RT may help mitigate dyspnea prior to performing aerobic-training in individuals with COPD.