The objective of this study is to compare the caloric expenditure and oxidative sources of underwater treadmill running and land-based treadmill running at maximal and submaximal levels. Underwater running has emerged as a low load bearing form of supplementary training for cardiovascular fitness, as a way to promote recovery from strenuous exercise while maintaining aerobic fitness, and as a way to prevent injury. Prior studies have reported conflicting results as to whether underwater treadmill running elicits similar cardiorespiratory responses to land-based running. It is important to further investigate the similarities and differences between the two to determine if underwater running is as efficient as land-based running for maintenance of fitness and for rehabilitative purposes. Purpose: To compare the caloric expenditure and oxidative sources of underwater treadmill running and land treadmill running during both maximal treadmill trials to exhaustion and during 30 minute submaximal treadmill trials. Methods: 11 volunteer experienced male triathletes, ages 18-45 were recruited as participants. Each completed 6 trials total which included a maximal and submaximal oxygen consumption trial for each of three conditions: running on a water treadmill with AQx® water running shoes, running on a water treadmill without shoes, and running on a land-based treadmill. Data analysis: Data was analyzed using repeated measures ANOVAs, paired t-tests, pairwise comparisons with bonferroni adjustments, and descriptive statistics were reported. Results: For maximal oxygen consumption trials VO2, RPE, RER, and BP were not significantly different between modalities. Maximal HR was found to be significantly different between modalities, and was shown to be greater on land than in the water. For submaximal VO2, trials HR, RPE, RER, and post BP were not found to be significantly different between modalities. Average VO2, total calories expended, and pre systolic BP were found to be significantly different, and were shown to be greater on land than in water. Conclusions: While maximal exertion running on underwater treadmills seems to elicit similar cardiorespiratory responses to running on land-based treadmills, differences were seen at submaximal exertion levels. It remains unclear whether underwater treadmill running can elicit similar training stimuli as land running at submaximal levels.

Running injuries are common, usually causing athletes to cease or significantly reduce participation in a particular sport. The recent development of aquatic treadmills (ATM), an alternative to land treadmill (LTM) running, provides another option. This study sought to examine the metabolic (VO2) relationship between varying jet resistances and running speed on an ATM versus LTM. This was accomplished by developing two linear regression equations and a prediction equation. One linear regression represented the predicted VO2 from a given speed and jet resistance setting in the water, the other linear regression predicted VO2 on land from a given speed and the prediction equation was designed to match land speed to a VO2 score derived from ATM running conditions. This study examined experienced runners (N = 18). Each subject completed an initial VO2 peak test, three LTM trials, and 18 ATM trials. Each ATM trial consisted of running for three minutes at either a relatively slow, moderate, or somewhat fast speed while one of six ATM jet settings ranging from 0 to 100% jet capacity in 20% increments were assigned to the trial. Oxygen consumption (VO2) and heart rate (HR) were measured during each trial while ratings of perceived exertion (RPE) were solicited immediately following each trial. Resulting analysis produced an ATM linear regression for each jet resistance setting and a LTM linear regression equation of VO2 = 4.16 * speed + 7.39. A prediction equation for each jet resistance setting was then determined from the linear regression equations for both the ATM and LTM conditions. Results showed that at and between 0-40% jet resistances that there is not a marked difference in metabolic cost but from 40-100% jet resistances the VO2 is influenced more strongly. These results demonstrate that ATM metabolic costs are not only influenced by jet resistance settings but at jet resistances of 40% or greater provide an intensity of exercise that mimics running faster on LTM. This provides an added benefit for those individuals who may be limited due to acute overuse-type injuries or returning to full LTM activity following lower extremity surgery.