Abstract
Although water-based exercise is one of the most recommended forms of physical activity, little information is available regarding its influence on cardiac workload and myocardial oxygen supply-to-demand. To address this question, we compared subendocardial viability ratio (SEVR, the ratio of myocardial oxygen supply-to-demand), cardiac inotropy (via the maximum rate of aortic pressure rise [dP/dTmax]), and stroke volume (SV, via a Modelflow method) responses between water- and land-based exercise. Eleven healthy men aged 24 ± 1 years underwent mild- to moderate-intensity cycling exercise in water (WC) and on land (LC) consecutively on separate days. In WC, cardiorespiratory variables were monitored during leg cycling exercise (30, 45, and 60 rpm of cadence for 5 min each) using an immersible stationary bicycle. In LC, each participant performed a cycling exercise at the oxygen consumption (VO2) matched to the WC. SEVR and dP/dTmax were obtained by using the pulse wave analysis from peripheral arterial pressure waveforms. With increasing exercise intensity, SEVR exhibited similar progressive reductions in WC (from 211 ± 44 to 75 ± 11%) and LC (from 215 ± 34 to 78 ± 9%) (intensity effect: P < 0.001) without their conditional differences. WC showed higher SV at rest and a smaller increase in SV than LC (environment-intensity interaction: P = 0.009). The main effect of environment on SV was significant (P = 0.002), but that of dP/dTmax was not (P = 0.155). SV was correlated with dP/dTmax (r = 0.717, P < 0.001). When analysis of covariance (ANCOVA) was performed with dP/dTmax as a covariate, the environment effect on SV was still significant (P < 0.001), although environment-intensity interaction was abolished (P = 0.543). These results suggest that water-based exercise does not elicit unfavorable myocardial oxygen supply-to-demand balance at mild-to-moderate intensity compared with land-based exercise. Rather, water-based exercise may achieve higher SV and better myocardial energy efficiency than land-based exercise, even at the same inotropic force.
Highlights
Aerobic exercise, such as walking, jogging, and cycling is a beneficial health strategy for non-pharmacologically preventing and treating cardiovascular disease
Absolute and relative VO2 progressively increased in water-based cycling (WC) and land-based cycling (LC) with no significant intensity-environment interaction effect (Table 1), indicating that VO2 was matched in both conditions at each intensity
Compared with the land condition, Stroke volume (SV) was significantly higher during water-based exercise even after dP/dTmax was considered using analysis of covariance (ANCOVA)
Summary
Aerobic exercise, such as walking, jogging, and cycling is a beneficial health strategy for non-pharmacologically preventing and treating cardiovascular disease. Not all populations, those with decreased walking ability, musculoskeletal pain and disorders, and anxiety of falling, can engage in regular exercise training. The clinicians have long been concerned that increases in central blood volume and cardiac preload may not be tolerated by patients with chronic heart failure and potentially worsen their symptoms and exercise capacity [10]. With this prevailing concern as a background, Adsett et al conducted a meta-analysis to determine the efficacy of aquatic exercise training for patients with heart failure compared with the traditional land-based exercise programs. Little information is yet available regarding myocardial oxygen demand and supply balance during water-based exercise in healthy individuals
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