Hyperoxia may reduce energetic efficiency in the trained rat

Background: Several studies have been conducted in recent years in the attempt to improve running performance by the use of hyperbaric oxygen, but there is disagreement as to whether this has any beneficial effect. The purpose of this study was to measure the effect of 24 h breathing 100% O₂ in normobaric conditions on energetic efficiency in the trained rat. Methods: Experiments were carried out on trained rats whose oxygen consumption was evaluated during the training period and on its completion. At the end of the training period, the rats were divided into two groups: 1) rats exposed to air (21% O₂) in normobaric conditions; and 2) rats exposed to 100% O ₂ in normobaric conditions. In addition, two groups of sedentary rats were used: 3) sedentary rats exposed to air (21% O₂) in normobaric conditions; and 4) sedentary rats exposed to 100% O₂ in normobaric conditions. Energetic efficiency was estimated by measuring O ₂ consumption at submaximal exercise (45 m · min ^-1, 10° incline). Results: Training alone reduced O₂ consumption by 18% during submaximal exercise. Exposure to 100% oxygen for 24 h in normobaric conditions reversed the effect of complete training by elevating the O₂ consumption by 17%, which was close to the oxygen consumption of the rats during the incomplete training period. Conclusions: Our results suggest that prolonged exposure to hyperoxia induces a reduction in the energetic efficiency of the trained rat. The relevance of these findings to sports and diving is discussed.