Maximal fat oxidation in navy divers

ABSTRACT Sjöblom C, Ekman L, Plogmark O, Mandić M, Rodríguez-Zamora L, Melin AK, Ekström M, Frånberg O. Maximal fat oxidation in navy divers. Undersea Hyperb Med. 2026 First Quarter; 53(1):19-30. Introduction: Oxidating fat as an energy substrate requires more oxygen than utilizing carbohydrates and can be acutely increased by hyperoxia. Therefore, substrate utilization may affect endurance performance and gas consumption in divers, but previous research is limited. This study aimed to evaluate changes in maximal fat oxidation (MFO) in navy divers during training. Methods: Seven explosive ordnance disposal (EOD) divers (age 20.0±1.4, BMI 23.5±1.6), five combat divers (age 23.6±3.0, BMI 26.2±1.2), and seven amphibious rangers (controls) (age 23.0±2.9, BMI 26.2±1.7) were recruited. MFO was measured with indirect calorimetry using an incremental test before and after diver training of 15 weeks (EOD divers) or 16 weeks spaced over nine months (combat divers and controls). EOD divers performed a treadmill protocol in normoxia and hyperoxia, and combat divers and controls performed a bicycle ergometer protocol in normoxia. Results: Combat divers increased their MFO with 0.14 g/minute ([95 % CI] 0.04 to 0.23) while no difference was observed in EOD divers (-0.05 g/minute; -0.19 to 0.08) or controls (0.00 g/minute; -0.14 to 0.14). Discussion: Combat diver training can increase fat oxidation, potentially affecting oxygen consumption and carbon dioxide production. A combination of training stressors, including hyperoxia, training load, and negative energy balance, may cause these changes. Keywords: hyperoxia; maximal fat oxidation; military diving