Importance of hemoglobin concentration to exercise: Acute manipulations

Abstract

An acute reduction of blood hemoglobin concentration ([Hb]), even when the circulating blood volume is maintained, resultsin lower ̇VO2maxand endurance performance, due to the reduction of the oxygen carrying capacity of blood. Conversely, anincrease of [Hb] is associated with enhanced ̇VO2maxand endurance capacity, that is also proportional to the increase in theoxygen carrying capacity of blood. The effects on endurance capacity appear more pronounced and prolonged than on ̇VO2max.During submaximal exercise, there is a tight coupling between O2demand and O2delivery, such that if [Hb] is acutely decreasedmuscle blood flow is increased proportionally and vice versa. During maximal exercise with either a small or a large musclemass, neither peak cardiac output nor peak leg blood flow are affected by reduced [Hb]. An acute increase of [Hb] has no effect onmaximal exercise capacity or ̇VO2peakduring exercise in acute hypoxia. Likewise, reducing [Hb] in altitude-acclimatized humansto pre-acclimatization values has no effect on ̇VO2peakduring exercise in hypoxia.