Importance of hemoglobin concentration to exercise: Acute manipulations

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Abstract

An acute reduction of blood hemoglobin concentration ([Hb]), even when the circulating blood volume is maintained, results in lower V˙O2max and endurance performance, due to the reduction of the oxygen carrying capacity of blood. Conversely, an increase of [Hb] is associated with enhanced V˙O2max and endurance capacity, that is also proportional to the increase in the oxygen carrying capacity of blood. The effects on endurance capacity appear more pronounced and prolonged than on V˙O2max. During submaximal exercise, there is a tight coupling between O2 demand and O2 delivery, such that if [Hb] is acutely decreased muscle blood flow is increased proportionally and vice versa. During maximal exercise with either a small or a large muscle mass, neither peak cardiac output nor peak leg blood flow are affected by reduced [Hb]. An acute increase of [Hb] has no effect on maximal exercise capacity or V˙O2peak during exercise in acute hypoxia. Likewise, reducing [Hb] in altitude-acclimatized humans to pre-acclimatization values has no effect on V˙O2peak during exercise in hypoxia.

Introduction

This review focuses on the effects that acute changes in blood hemoglobin may have on maximal aerobic power and endurance capacity. Despite the enormous literature on blood doping, few studies have provided the key data necessary to explain how the acute alteration of blood hemoglobin (Hb) concentration influences maximal aerobic power. Most of the studies have been performed using whole body exercise models, particularly exercise on the cycle ergometer and running. Less is known about the influence that changes in blood hemoglobin may have on peak aerobic power and endurance capacity during exercise with a small muscle mass. The latter, would allow a more clear separation between central and peripheral effects of blood Hb concentration on oxygen transport and utilization. The acute alteration in blood Hb concentration is also associated with compensatory changes in the cardiovascular and respiratory response to exercise that, in this review, are treated only briefly.

Section snippets

Acute reduction of hemoglobin concentration and exercise performance

The effect of a direct manipulation of the total amount of hemoglobin in healthy volunteers was first examined by Karpovich and Millman (1942), who showed that a reduction of total hemoglobin caused by bleeding decreased performance of athletes to a greater extent in long than in brief sport events. This finding was later confirmed by Balke et al. (1954), who observed a 9% decrease in maximal oxygen uptake (V˙O2max), 1 h after a blood donation of 500 ml. However, pre-donation V˙O2max values were

Acute increase of hemoglobin concentration and exercise

The influence of an increase in blood Hb concentration on the cardiorespiratory response to exercise was first studied by Pace et al. (1947) in five subjects under conditions of normal hematocrit (46%) and after the transfusion of 1000 ml of red cells resulting in an elevation of hematocrit to 58%. After the blood transfusion, heart rate during submaximal exercise declined in direct proportion to the increase in CaO2 (Pace et al., 1947), suggesting a lower relative effort to sustain the

Hemoglobin concentration and the regulation of blood flow during exercise

In a series of studies carried out by Saltin's group, the effects of PaO2 and CaO2 on ventilatory and cardiovascular responses to exercise in humans were determined over wide ranges of PaO2 and CaO2 combining several exercise models and intensities (Koskolou et al., 1997a, Koskolou et al., 1997b, Roach et al., 1999, Gonzalez-Alonso et al., 2001, Calbet et al., 2002, Calbet et al., 2003b, Calbet et al., 2004). These studies show that PaO2 alone has a minor role in the regulation of vascular tone

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