Effectiveness of exercise training in patients with COPD: the role of muscle fatigue.

The improvement in exercise performance in response to exercise training varies greatly from one patient with chronic obstructive pulmonary disease to another. It is possible that in a portion of patients the muscle stimulus applied during exercise training is insufficient to elicit training effects. We investigated whether patients presenting quadriceps contractile fatigue after training have more favourable effects of a rehabilitation programme. 46 patients followed a 3-month high-intensity exercise training programme. Exercise capacity, quadriceps force and quality of life were measured before and after the programme. Exercise training-induced quadriceps contractile fatigue was assessed after 1 month of rehabilitation with magnetic stimulation. A fall in quadriceps force of ≥15%, 15 min after training was considered as significant fatigue. 29 (63%) out of 46 patients developed significant fatigue. Patients with fatigue had a higher increase in 6-min walk distance (median (interquartile range) 57 (47-103) m versus 17 (-7-46) m; p=0.0023) and Chronic Respiratory Disease Questionnaire score (mean±sd 22±12 points versus 14±12 points; p=0.028) after the training programme compared with patients without fatigue. Improvements in quadriceps force and maximal exercise capacity were similar in both subgroups. Patients who develop quadriceps contractile fatigue during exercise training show greater training effects in terms of functional exercise capacity and health-related quality of life.