The effect of altitude on cycling performance - A challenge to traditionalconcepts

Acute exposure to moderate altitude is likely to enhance cycling performanc e on flat terrain because the benefit of reduced aerodynamic drag outweighs the decrease in maximum aerobic power [maximal oxygen uptake ((V) over dot O-2max)]. In contrast, when the course is mountainous, cycling performance will be reduced at moderate altitude. Living and training at altitude, or living in an hypoxic environment (simil ar to 2500m) but training near sea level, are popular practices among elite cyclists seeking enhanced performance at sea level. In an attempt to confi rm or refute the efficacy of these practices, we reviewed studies conducted on highly-trained athletes and, where possible, on elite cyclists. To ensu re relevance of the information to the conditions likely to be encountered by cyclists, we concentrated our literature survey on studies that have use d 2- to 4-week exposures to moderate altitude (1500 to 3000m). With acclima tisation there is strong evidence of decreased production or increased clea rance of lactate in the muscle, moderate evidence of enhanced muscle buffer ing capacity (pm) and tenuous evidence of improved mechanical efficiency (M E) of cycling. Our analysis of the relevant literature indicates that, in contrast to the existing paradigm, adaptation to natural or simulated moderate altitude doe s not stimulate red cell production sufficiently to increase red cell volum e (RCV) and haemoglobin mass (Hb(mass)). Hypoxia does increase serum erthyr opoietin levels but the next step in the erythropoietic cascade is not clea rly established; there is only weak evidence of an increase in young red bl ood cells (reticulocytes). Moreover, the collective evidence from studies o f highly-trained athletes indicates that adaptation to hypoxia is unlikely to enhance sea level (V) over dot O-2max. Such enhancement would be expecte d if RCV and Hbmass were elevated. The accumulated results of 5 different research groups that have used contr olled study designs indicate that continuous living and training at moderat e altitude does not improve sea level performance of high level athletes. H owever, recent studies from 3 independent laboratories have consistently sh own small improvements after living in hypoxia and training near sea level. While other research groups have attributed the improved performance to in creased RCV and (V) over dot O-2max, we cite evidence that changes at the m uscle level (pm and ME) could be the fundamental mechanism. While living at altitude but training near sea level may be optimal for enhancing the perf ormance of competitive cyclists, much further research is required to confi rm its benefit. If this benefit does exist, it probably varies between indi viduals and averages little more than 1%.