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Bikram yoga is a 90 min series of postures performed in a heated (40.6 deg C) and humidified (40%RH) studio. Thirteen standing postures (50 min) are followed by 13 floor postures (40 min). Each class is instructed similarly according to highly standardized instructions. Typical room temperature yoga produces a relatively mild cardiorespiratory and metabolic stimulus. Although Bikram yoga is anecdotally described as physiologically demanding due to the difficult postures and heat stress, the acute physiological responses have never been quantified.PURPOSE: To characterize the metabolic (VO2), heart rate (HR), and thermal (TEMP) changes during a session of Bikram yoga.METHODS: Experienced Bikram yoga practitioners (N=19, 30±7yrs,19-40 yrs, 11 women, 9 men) performed a session of Bikram yoga to recorded audio instructions in an environmental chamber (40.6 deg C, 40% RH) while being monitored for VO2, HR, and TEMP. Subjects had performed Bikram yoga regularly (> 2x/wk) for at least 1 year (5.5±5 yrs). VO2 was measured using portable indirect calorimetry (Oxycon), HR with a Polar monitor, and TEMP with ingestible thermometer capsules (CorTemp). Water was available ad libitum. Data were telemetered, recorded online in 15s intervals, and then smoothed in 60s rolling windows for analysis.RESULTS: Metabolic rate tended to rise within several minutes and remain elevated during the standing postures. The average VO2 was 14.2±1.6 ml/kg/min during the standing postures and 11.4±1.0 kg/ml/min during the floor postures. The total caloric expenditure (5kcal/l O2 conversion) for the whole session averaged 378±78 kcal (range: 278-541 kcal, men: 459±55, women: 333±46kcal). HR averaged 144±13 bpm for standing postures and 123±5 bpm for floor postures. The average minimum TEMP at baseline was 37.2 deg C (99.0±0.7 deg F), while the average maximum TEMP during yoga was 38.2 deg C (100.8±0.5 deg F). For most subjects TEMP increased during the first 50 minutes and peaked near the end of the standing postures. The average TEMP across the ∼40 minute period after the peak was 38 deg C (100.3±0.5 deg F).CONCLUSION: For young, healthy, experienced Bikram practitioners, a single session of Bikram yoga produces moderate metabolic responses (∼3.5mph walking), robust heart rate responses, and a substantially elevated core temperature.