The purpose of this study was to develop a prediction equation that could be used to estimate maximal oxygen uptake (VO₂max) from a submaximal water running protocol. Thirty-two volunteers (n =19 males, n = 13 females), ages 18 - 24 years, underwent the following testing procedures: (a) a 7-site skin fold assessment; (b) a land VO₂max running treadmill test; and (c) a 6 min water running test. For the water running submaximal protocol, the participants were fitted with an Aqua Jogger Classic Uni-Sex Belt and a Polar Heart Rate Monitor; the participants’ head, shoulders, hips and feet were vertically aligned, using a modified running/bicycle motion. A regression model was used to predict VO₂max. The criterion variable, VO₂max, was measured using open-circuit calorimetry utilizing the Bruce Treadmill Protocol. Predictor variables included in the model were percent body fat (% BF), height, weight, gender, and heart rate following a 6 min water running protocol. Percent body fat accounted for 76% (r = -0.87, SEE = 3.27) of the variance in VO₂max. No other variables significantly contributed to the explained variance in VO₂max. The equation for the estimation of VO₂max is as follows: VO₂max ml.kg^-1·min^-1 = 56.14 - 0.92 (% BF).

• Body Fat is an important predictor of VO2 max.

• Individuals with low skill level in water running may shorten their stride length to avoid the onset of fatigue at higher work-loads, therefore, the net oxygen cost of the exercise cannot be controlled in inexperienced individuals in water running at fatiguing workloads.

• Experiments using water running protocols to predict VO2max should use individuals trained in the mechanics of water running.

• A submaximal water running protocol is needed in the research literature for individuals trained in the mechanics of water running, given the popularity of water running rehabilitative exercise programs and training programs.