Improvement in Quadriceps Muscle Strength and Fucntional Capacities after a 3-month home-based Endurance Training in Lung Transplant Recipients

Background: Peripheral muscle dysfunction and reduced exercise capacity are well recognized in lung transplant recipients (LTR) in spite of improved lung function. However, the effect of exercise training in this specific population is still poor studied. We investigated the benefits of training on muscle function and cardio-ventilatory response during exercise in LTR. Methods: Twelve patients after lung transplantation (FEV1: 74 ± 24 % of predicted value) and 12 healthy subjects (C) were studied before and after a 3-month home-based endurance training. Quadriceps strength and fatigability were assessed by maximal twitch tension (TwQ) using magnetic stimulation of the femoral nerve and fiber diameters were obtained after biopsy of the vastus lateralis. Cardio-ventilatory responses were measured during both maximal and constant workload (W) cycle exercise and quality of life was assessed by the Chronic Respiratory Questionnaire. Results: At baseline, LTR had lower percentage of type I fibers, TwQ, Wmax, VO2max, VEmax and endurance time than C (< 50% of C each). After training, significant improvement in TwQ (+44 ± 26 N), Wmax (+13 ± 19 W), endurance time (+11.5 ± 11.1 min) and dyspnea score (CRQdyspnea: +3.1 ± 4.4 points) were observed in LTR (p < 0.05). Furthermore, VE was reduced at submaximal (VE at ventilatory threshold: -4.5 ± 6.8 L/min) and constant (65% Wmax) exercise (-6.4 ± 5.2 L/min) (P < 0.05). Decrease in exercise-induced fatigability correlated with decrease in VE at initial maximal workload in LTR (r = 0.72, P = 0.06) and in LTR + C (r = 0.56, P = 0.02) and increase in TwQ correlated to increase in CRQdyspnea in LTR (r = 0.74, P = 0.04). Conclusion: Gains in exercise capacity and in quadriceps strength were observed after endurance training in LTR. The latter may have been involved in improving exercise ventilatory response and dyspnea, supporting the benefit of peripheral muscle strength improvement in exercise tolerance in LTR and even the larger field of chronic respiratory diseases.