Fig. 7. Response of muscle blood flow and heart rate during a 5 min submersion of seal S following completion of the 3 min submersion training. Muscle blood flow is given as a percentage of resting muscle blood flow (%RMBF) prior to submersion. After the standard 3 min of submersion (*), heart rate and muscle blood flow return to the levels typically found during submersion of naive seals. Pulsations in muscle blood flow during the last 2 min correspond to individual heart beats. Arrows indicate the start and end of the 5 min submersion.