Increase of hemoglobin concentration after maximal apneas in divers, skiers, and untrained humans.

Human splenic contraction occurs both during apnea and maximal exercise, increasing the circulating erythrocyte volume. We investigated the hematological responses to 3 maximal apneas performed by elite apneic divers, elite cross-country skiers, and untrained subjects. Post-apnea hemoglobin concentration had increased in all groups, but especially in divers. The increases disappeared within 10 min of recovery. Apneic duration across apneas also increased the most in divers. Responses in divers could be more pronounced as a result of apnea training.