Quantitative EEG was recorded during 3 sessions, once a week, in 10 high-level amateur triathletes, who regularly competed in triathlon. At each session, the EEG was recorded 15 min after a submaximal exercise test. During the second session, the exercise test came immediately after 30 min of hyperbaric oxygenation (100% oxygen at 2 atmosphere absolute pressure). The others conditions of the EEG recording were the same for the 3 sessions. The purpose of the work was to study the variations of the EEG power spectrum (from 1 to 20 Hz) which occurred between the 3 sessions. Descriptive analysis of the results show, after hyperbaric oxygenation, a diffuse increase of absolute power for several frequencies in the theta, alpha and beta bands.