K.T. Hennes, D.A. Chang, S.O. Henry

Pacific University, Forest Grove, OR

As the popularity of water based exercise grows, quantifying physiological reactions experienced in aquatic environments becomes increasingly important. Unlike swimming, relatively little is known about physiological responses and efficiency during other water exercise modalities, such as cycling. PURPOSE: To investigate differences in efficiency and physiological responses while performing cycle ergometry on land and in water. METHODS: Eighteen healthy volunteers (12:6, female:male; age, 20.1 ± 1.3 yrs; stature, 164.7 ± 10.3 cm; mass, 62.4 ± 9.8 kg) completed two cycling sessions of the same protocol under counterbalanced environmental conditions (water, land) on a custom-built cycle ergometer capable of directly measuring watts (W) underwater. Sessions consisted of two continuous trials, each trial comprised of a five-minute rest period (0 rpm at 0 W) followed by three two-minute stages in stepwise progression (0, 50, 100 W) with counterbalanced pedaling frequencies (40 and 80 rpm). Steady-state heart rate (HR), rate of perceived exertion (RPE), minute ventilation (VE), volume of oxygen consumed (VO2), and volume of carbon dioxide produced (VCO2) were measured. For analysis, the last 30 s of each stage were used to represent steady-state. Water immersion level and temperature (32 ± 2 oC) were held constant across all tests. Utilizing principles of indirect calorimetry, energy expenditure (EE, J·s-1) and net efficiency (%) were calculated for each stage. RESULTS: For net efficiency, repeated measures 2x2x2 ANOVA (50/100 W, 40/80 rpm, land/water), and appropriate post-hoc tests comparing land to water, showed cycling efficiency was lower at all levels of power and rpm (p < 0.05). The difference was magnified at higher rpm (80 rpm) and power (100 W), with efficiency 11.88% lower in water compared to land (7.4 ± 0.014 %, 19.2 ± 3.9 %, respectively; p < 0.01). In similar manner, but opposite direction, 3x2x2 ANOVA (0/50/100 W, 40/80 rpm, land/water) and post-hoc tests showed RPE and VE increased in water at all levels of power and rpm (p < 0.05). CONCLUSION: Consistent with previous studies, our results show cycling in water at greater intensities is more demanding than on land. More importantly, as our experiment is one of the first to successfully manipulate underwater power (W) as a variable, we quantified the increase of RPE and VE and the decrease in efficiency that occurs when cycling in water versus on land at a given workload.

Supported by Pacific University College of Arts and Sciences grant.

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