Spleen contraction elevates hemoglobin concentration at high altitude during rest and exercise.

Purpose: Hypoxia and exercise are known to separately trigger spleen contraction, leading to release of stored erythrocytes. We studied spleen volume and hemoglobin concentration (Hb) during rest and exercise at three altitudes.

Methods: Eleven healthy lowlanders did a 5-min modified Harvard step test at 1370, 3700 and 4200 m altitude.