Combined Active and Passive Isothermic Heating Leads to Similar Core Temperature Compared With Exercise Alone

Context: The training stress of heat acclimatization optimizing exercise performance in a hot environment can be demanding. Objective: This study evaluated the efficiency of different single heating protocols to elevate core temperature. Design: Nonrandomized controlled trial. Setting: Laboratory. Patients or Other Participants: Ten male participants (age ＝25 ± 3 years) performed 4 different 60-minute heating strategies at least 1 week apart. Interventions: Sixty minutes passive heating (PAS), 30 minutes active heating using a high-intensity bike protocol (HIBP) in a hot environment with 30 minutes passive heating (EH-PAS), 60 minutes HIBP in a hot environment (EH), or 60 minutes HIBP at room temperature (EM). Main Outcome Measure(s): Body core temperature and heart rate. Results: The highest peak gastrointestinal temperature occurred in EH-PAS (39.1 ± 0.4°C), followed by EH (38.9 6 0.3°C), EM (38.4 ± 0.3°C), and PAS (38.1 ± 0.5°C). The average heart rate, measured as a control for intensity, was not different between exercise strategies (EH-PAS ＝142 ± 12.3 beats per minute [bpm], EH ＝ 146 ± 9.7 bpm, and EM ＝ 142 ± 13.3 bpm; P ˃ .05), but was different for PAS (98 ± 15.2 bpm; P ˂ .05). Conclusions: Adding passive heating to a shorter exercise protocol can be just as effective in keeping core temperature elevated as exercise in the heat alone during a 60-minute session. Therefore, a single-bout combination of exercise and passive heating may result in a similar body temperature induction compared with exercise heat stress alone.