Respiratory muscle strength at rest, during and after maximal exercise in healthy subjects

Background: Respiratory muscle weakness can contribute to limit exercise. However, respiratory muscle recruitment and exercise-induced weakness is not fully described even in healthies. Objectives: To describe the recruitment of respiratory muscles and thoraco-abdominal synchrony at rest and during exercise in healthy subjects; to measure the non-volitive strenght after exercise. Methods: 42 healthies separated in two groups: 20-39 (A) and 40-59 y (B) underwent maximal cycle test. Esophageal (Pes), gastric (Pgas) and transdiaphragmatic pressures were measured. Sniff and magnetic stimulation (Tw) were performed. The accessory respiratory muscles were monitored by surface electromyography and thoraco-abdominal synchrony by respiratory inductance plethysmography. Tw was performed to diaphragm and abdominal muscles (T10) pre and post cycle. Results: Ventilatory strength at rest was similar between groups. There was no difference in maximal workload and minute ventilation, with similar ventilatory muscle recruitment. However, at intense exercise, the A had greater Pes than B (-19.7±11.2 vs -13.8±6,3, p:0.03), with a higher phase angle (11.4±11 vs 2.3±7.2o, p: 0.004) and predominance of ribcage expansion. Although there was no ventilatory limitation, after exercise, B group had significant decrease in TwPDI (6.7±7.7 vs 1.7±6.3 cmH 2 O, p:0.04), but not in TwT10 Pgas (6±8.7 vs 19.8±26 cmH 2 O, p: 0.07). Conclusion: During exercise, although the pattern of ventilatory muscles recruitment is similar between groups, the youngers generated a greater pleural pressure with more ribcage predominance. In the olders, after maximal exercise, there was a greater drop of diaphragm strength.