BACKGROUND: This study aimed to analyze cardiorespiratory responses and energy expenditure during a high-intensity interval training (HIIT) session of deep-water running. METHODS: Three physically active young adults (2 women; 26.33 ± 11.02 years) participated in a session consisting of 5 minutes of warm-up followed by 15 minutes of interval exercise, alternating 30-second bouts at Borg scale 19 with passive recovery periods. Heart rate (HR) and oxygen uptake (VO*)-derived variables were continuously monitored using an optical heart rate monitor and a portable metabolic analyzer. Predicted maximal theoretical heart rate (HRmax = 208 * 0.7 × age) was also analyzed according to percentage (%). Metabolic equivalent (MET) values and energy expenditure (EE) were summarized for the session. RESULTS: Data were analyzed descriptively and presented as mean ± standard deviation. RESULTS: Average HR was 136.53 ± 13.27 bpm (71.16 ± 8.98% of predicted HRmax), with a peak of 168 ± 3 bpm. Mean metabolic demand was 6.43 ± 0.97 METs, indicating predominantly moderate-to-vigorous intensity. Average EE was 8.08 ± 2.70 kcal/min, totaling 206.78 ± 46.06 kcal per session. CONCLUSIONS: In this pilot study, the three participants showed individual cardiorespiratory and metabolic responses consistent with moderate-to-vigorous intensity, suggesting that deep-water running HIlT may represent a feasible exercise strategy. These findings are preliminary and should be interpreted with caution given the small sample size and descriptive design.
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