Altered chemoreceptor response and improved cycling performance following respiratory muscle training

Abstract

Cross-sectional studies have shown that well trained endurance athletes frequently have a lower peripheral and central chemoreceptor response (pRc and cRc) and a lower minute ventilation (Ve) during exercise compared to untrained individuals. Some recent prospective studies support these observations. We speculated that the reductions in chemoreceptor response and Ve may be the specific result of the high rates of ventilation occurring during endurance training. To test this idea, subjects performed voluntary eucapnic hyperpnea to simulate exercise hyperpnea while avoiding the metabolic consequences of physical exercise. We therefore examined the effects of respiratory muscle training (RMT: 20x30min sessions of voluntary eucapnic hyperpnea) on the pRc, cR, cycling performance, and Ve. Twenty endurance trained cyclists were randomized into RMT or control-groups. To indicate cRc both the hypercapnic ventilatory response at rest (HCVRr) and during light exercise (HCVRex) were measured in a background of 50% O2. The pRc was assessed by measuring the ventilatory response to a modified Dejours O2 test (4-6 trials of 10-12 breaths of 100% O2) during light exercise. Endurance performance and Ve were measured during a fixed-rate cycling endurance test, performed at 85% of the maximal workload until exhaustion. The RMT-group's cycling endurance improved significantly compared to controls (+3.26±4.98min versus -1.46±3.67min. p=0.027) but Ve was unchanged at all times analyzed. The pRc was significantly reduced in the RMT-group but unchanged in controls (-5.8±6.0% versus +O.1±4.6%, p=O.032). The cRc, both at rest and during exercise, was not significantly altered following RMT in either group. However, the X-intercept of HCVRex exhibited a significant shift to the left (-5.83±10.68mmHg, +O.38±2.48mmHg, p=O.047, RMT-group and controls respectively). The importance of this leftward shift and the reduced pRc, though statistically significant, is unclear because there were no significant changes in Ve during any test nor were there correlations between Ve or performance or the altered chemoreceptor responses. We conclude that exercise hyperpnea, as simulated by RMT in this study, is accompanied by a reduction in pRc and a leftward shift in the HCVRex, and improves cycling endurance; however, the altered chemoreceptor responses had little impact on Ve suggesting that their role in the control of ventilation during exercise is minor.