Inspiratory flow resistive loading improves respiratory muscle function and endurance capacity in recreational runners

The purpose of this study was to assess the efficacy of inspiratory flow resistive loading (IFRL) on respiratory muscle function, exercise performance and cardiopulmonary and metabolic responses to exercise. Twenty-four recreational road runners (12 male) were randomly assigned from each gender into an IFRL group (n=8) and sham-IFRL group (n=8), which performed IFRL for 6 weeks, or a control group (n=8). Strength (+43.9%delta), endurance (+26.6%delta), maximum power output (+41.9%delta) and work capacity (+38.5%delta) of the inspiratory muscles were significantly increased (P < 0.05) at rest following the study period in IFRL group only. In addition, ventilation (-25.7%delta), oxygen consumption (-13.3%delta), breathing frequency (-11.9%delta), tidal volume (-16.0%delta), heart rate (HR) (-13.1%delta), blood lactate concentration (-38.9%delta) and the perceptual response (-33.5%delta) to constant workload exercise were significantly attenuated (P < 0.05), concomitant with a significant improvement (P < 0.05) in endurance exercise capacity (+16.4%delta) during a treadmill run set at 80% VO(2max) in IFRL group only. These data suggest that IFRL can alter breathing mechanics, attenuate the oxygen cost, ventilation, HR, blood lactate and the perceptual response during constant workload exercise and improve endurance exercise performance in recreational runners.