The importance of haemoglobin mass for cycling performance

Author: Laura Garvican

Garvican, Laura, 2011 The importance of haemoglobin mass for cycling performance, Flinders University, School of Education

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Abstract

Delivery of oxygen during exercise is critically important for endurance athletes. Elite endurance athletes possess superior amounts of haemoglobin versus untrained counterparts, which enables a high rate of oxygen delivery during exercise. Haemoglobin mass (Hbmass) can be measured via carbon monoxide (CO) rebreathing. The research in this thesis utilizes the recently 'optimised' method for the measurement of Hbmass in elite endurance athletes, predominantly cyclists, with the aim of determining the importance of Hbmass for endurance performance by: 1. examining factors which influence changes in Hbmass in athletes, 2. the time course and magnitude of such changes and 3. the importance of changes in Hbmass for cycling performance as reflected by maximal mean power (MMP). The ability to accurately measure small changes in Hbmass is essential; thus the first part of this thesis is concerned with the methodology underpinning Hbmass measurement. Specifically, the uptake kinetics of CO during CO-rebreathing were investigated to identify potential sources of error associated with measurement in athletes. Compared with the conventional CO-rebreathing method, inhalation of a CO bolus during the optimised method resulted in faster carboxy-haemoglobin uptake, but did not shorten the time required for CO to mix completely throughout the circulation. Individual differences in circulatory mixing time and alterations of CO loss to extra-vascular compartments can confound the estimated Hbmass. The influence of stage-racing, iron supplementation, training load and altitude on Hbmass was examined. Hbmass remained stable throughout a 6-day pro-cycling stage race, despite plasma volume induced reductions in haemoglobin concentration and haematocrit. Iron supplementation of an anaemic female athlete had rapid and marked effects on Hbmass - increasing 49% within 2-weeks of supplementation and continuing to increase for 15-weeks. Hbmass varied by ~3% throughout a competitive season in female cyclists, and was related to chronic training load. Additionally, changes in Hbmass were associated with changes in MMP during training and racing. The time course of the Hbmass response during 3-weeks of natural altitude exposure (2760m) was determined, with a substantial increase (3%) in Hbmass observed within 10-days. The time course was consistent with the hourly rate of increase previously documented for simulated altitude. Hbmass and erythropoietin decreased on descent to sea level whilst ferritin increased (possibly indicative of neocytolysis), raising doubts as to the role of an enhanced Hbmass for subsequent performance benefits at sea level. Therefore, in the final part of the thesis, the importance of hypoxia-induced increases in Hbmass on cycling performance was examined. Using a unique study design, increases in Hbmass induced by altitude exposure were removed, effectively 'clamping' the Hbmass response. MMP4min increased by ~4%, despite blocking a ~5% increase in Hbmass suggesting that accelerated erythropoiesis is not the sole mechanism by which hypoxia improves performance. However, increases in Hbmass appeared to influence the aerobic contribution to high-intensity exercise which may be important for subsequent high-intensity efforts. Overall this thesis confirms some existing observations regarding the influence of various external factors on Hbmass, but challenges other notions regarding the importance of Hbmass for traditional measures of endurance performance.

Keywords: Endurance performance,altitude training,erythropoiesis
Subject: Health & Physical Education thesis, Human Physiology thesis

Thesis type: Doctor of Philosophy
Completed: 2011
School: School of Education
Supervisor: Professor Christopher Gore