Pulmonary Responses During Exercise On Dryland Vs. Immersible Ergocycle

Abstract

Water immersion can affect respiratory responses during exercise relative to exercise on dry land. Exercise training in an aquatic environment has added benefits relative to training on land, improving central hemodynamic responses as stroke volume (SV), cardiac output (Q) and heart rate recovery (HRR) as well as increasing cerebrovascular blood flow, relative to land-based exercise of a similar intensity, in healthy humans. PURPOSE: We sought to compare pulmonary responses during an incremental exercise done on immersible ergocycle (IE) vs dryland ergocycle (DE) at the same external power output (Pext). METHODS: Ten (10) young healthy subjects (Age: 31±9 years; BMI: 23.3±1.9 kg/m2) performed incremental exercise tests on IE at chest level immersion and DE at equal external power output (Pext). Pulmonary responses were measured and Pext on IE was calculated according to the general fluid equation Fd = ½ρ Av2Cd. Tangential speed of the pedaling mechanism was calculated by 2 πr (rpm), 2 π (r/2)(rpm) and ω2 π (r/2)/360°(rpm), for pedals, paddles-rods, and legs, respectively, as used in previous studies. RESULTS: VO2 (p=0.0087) and VCO2 (p=0.0138) were significantly lower during exercise on IE at every stage of the incremental test relative to DE. No differences were detected between IE and DE for respiratory exchange ratio (RER) ventilation (VE), breathing frequency (f), tidal volume (VT), fraction of expired O2 and CO2 (FetO2 and FeCO2, respectively), time of inspiration (Ti), time of expiration (Te), time of respiratory cycle (Ttot), duty cycle (Ti/Ttot), and partial pressure of end tidal O2 and CO2 (PetO2 and PetCO2, respectively). CONCLUSIONS: Exercise during water immersion results in a significantly lower mean VO2, relative to a land exercise of equivalent power output. No differences were detected in the respiratory parameters suggesting that the lower VO2 reached with IE is not attributed to changes in ventilation, but rather to central or peripheral convection (cardiac output) or diffusion (capillary O2 extraction) factors. We have previously shown that hemodynamic factors (convection) are modestly improved, but not sufficiently to explain the large gap in VO2 between IE and DE. We hypothesize that diffusion is improved by an unknown mechanism that remains to be explained.