LAUSR

BACKGROUND Smokers without airflow obstruction have reduced exercise capacity, but the underlying physiological mechanisms are not fully understood. AIM To compare quadriceps function assessed using non-volitional measures, and ventilatory requirements during exercise, between smokers without airway obstruction and never-smoker controls. STUDY DESIGN AND METHODS Adult smokers (n=20) and never-smoker controls (n=16) aged 25-50 years with normal spirometry, underwent incremental cycle cardiopulmonary exercise testing to exhaustion with measurement of symptoms and dynamic lung volumes. Quadriceps strength and endurance were assessed non-volitionally using single and repetitive magnetic stimulation. Quadriceps bulk was assessed using ultrasound, as rectus-femoris cross-sectional area (QRF-CSA). Physical activity level was quantified using the SenseWearTM armband worn for 5 days. RESULTS Smokers had lower peak exercise workload, peak oxygen consumption and anaerobic threshold (AT) compared to controls (170+46 vs. 256+57 W; 2.20 ±0.56 vs. 3.18 ±0.72 L/min; 1.38±0.33 vs. 2.09±0.7 L/min, respectively; p<0.01 for all). Quadriceps endurance was lower in smokers (D force-time integral 54.9±14.7% vs. 40.4±14.7%; p=0.007), but physical activity, quadriceps strength and bulk were similar between groups. Smokers displayed higher ventilation (120W: 52.6±11.8 vs. 40.7±6.0 L/min; p<0.001), decreased ventilatory efficiency (higher ⩒E/⩒CO2) and were more breathless with greater leg fatigue at iso-workloads and iso-ventilation levels compared to never-smoker controls. Smokers showed no mechanical constraints on tidal volume expansion during exercise or ventilatory limitation at peak exercise. CONCLUSION Adult smokers without airflow obstruction have reduced skeletal muscle endurance and ventilatory efficiency compared to never-smoker controls, despite similar daily physical activity levels, which contributed to reduced peak exercise capacity.