Exercise during water immersion is becoming increasingly popular given that is less traumatic than exercise on dry land and may be more suitable for obese subjects and those with musculoskeletal or articular injuries. Water immersion may result in different hemodynamic and cardiorespiratory responses during exercise relative to exercise on dry land. We sought to compare cardiopulmonary and hemodynamic responses during an incremental exercise done on dryland ergocycle (DE) vs immersible ergocycle (IE) with immersion to chest level, with both sessions employing the same external power output (Pext).
Healthy informed participants (n=22) performed incremental exercise tests on IE and DE of equal external power output. Exercise on IE began at 40 rpm and increased by 10 rpm every minute until exhaustion. Exercise on DE began with an initial load of 25 W and by 25 W each minute until exhaustion. External power output (Pext) on IE was calculated according to the general fluid equation Fd = ½ρ Av2Cd and tangential speed was calculated by 2πr (rpm), 2π(r/2)(rpm) and ω2π(r/2)/360°(rpm), for pedals, paddles, rods and legs respectively.
The VO2 (p< 0.001), and O2 pulse (p=0.0015) were significantly lower during IE, while the A-VO2 difference tended to be lower (p=0.06) and ventilation was similar during IE and DE exercise. Mean heart rate was lower by 4 % (p=0.03) during exercise on IE relative to DE. In contrast, RER was significantly higher during IE (p<0.005). Among 9 participants in whom central hemodynamic responses were tested, cardiac output and systolic ejection volume increased non-significantly during IE relative to DE.
Exercise during water immersion results in a significantly lower mean VO2, O2 pulse and heart rate relative to a land exercise of equivalent power output. These differences are believed to be in part due the hydrostatic forces of water on the body, leading to increased venous return and subsequent rise in cardiac output and compensatory reduction in heart rate, as well effects on ventilation from external pressure to the chest wall. Further studies with a larger sample size are needed to confirm or discount the present findings. If confirmed, these findings could suggest that exercise during water immersion may be more efficient from a cardiorespiratory standpoint.
© 2012 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.