Effects of water immersion on systemic cardiovascular responses during recovery period following steady state land exercise

The aim of this study was to clarify the effects of water immersion on the cardiovascular recovery process following submaximal steady state exercise on land. Seven male subjects (23 yrs old) underwent experiments under four separate conditions on separate days (15 minutes of cycling exercise at 50% and 80% maximal oxygen consumption followed by 16 minutes of recovery in a sitting position in water and out of water). Concerning conditions in water, mean water temperature was 29.4 degrees, and the immersion level was set at xiphoid. Mean room temperature in out of water conditions, and during all conditions of exercise was 24.4 degrees. Oxygen consumption (V̇O₂), heart rate (HR) and blood pressure (systolic: SBP, diastolic: DBP) were measured under each condition. Mean blood pressure was calculated from SBP and DBP (MBP=1/3 X (SBP-DBP) + DBP). Stroke volume (SV) was measured by Doppler echocardiography, and then cardiac output (CO=SV X HR), total peripheral resistance (TPR=MBP/CO) and arterial-mixed venous oxygen difference (a-v̄ O₂diff=V̇O₂/CO) were calculated. In comparison with the same exercise intensity condition, there were no Significant differences between recovery processes of V̇O₂, HR, SBP, DBP and MBP in and out of water. SV and CO were significantly higher (p<0.05) during the recovery process in water than out of water (SV: at 50 and 80% maximal oxygen consumption conditions, CO: at 80% condition). The TPR and a-v̄ O₂diff were significantly lower (p<0.05) during the recovery process in water than out of water at 80% oxygen consumption condition. These results indicate that water immersion facilitates circulating blood volume during the recovery process without increasing blood pressure, especially during recovery after high intensity exercise. Therefore, we suggest that increased left ventricular preload with immersion would be an important factor in cardiovascular regulation not only at rest but also during recovery after exercise.