Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
ReviewWhat makes an endurance athlete world-class? Not simply a physiological conundrum☆
Introduction
In humans endurance performance capacity is characterized by a large degree of inter-individual variation in the general population (Bouchard et al., 1993) and even in well-trained, athletic individuals. This capacity was historically, typically assessed by exercise scientists using physiology, biochemistry and histology techniques (see Fig. 1). The most frequently used tests included determination of the whole body maximal and sub-maximal oxygen consumption and the lactate turnpoint (Costill, 1967), oxidative enzyme activities and the percentage of slow twitch fibers (Booth and Narahara, 1975, Bylund et al., 1977). All these parameters correlate well with endurance performance in events ranging from 3000 m to various ultramarathon distances in heterogeneous groups with elite endurance athletes clearly different from recreational runners (Larsen, 2003). But when the conundrum is posed: ‘What makes an endurance athlete world-class?’ one must ask whether the above-mentioned methods are sufficient for assessing and distinguishing between elite- and truly world-class athletes. The first point that this review will make is that the above measures are not effective as performance predictors amongst relatively homogenous groups of well-trained elite or even sub-elite athletes. Having ascertained this, new questions can be raised, e.g. ‘Are newer assessment methods more useful? Do other biological factors contribute to endurance performance?’
The second major objective is to review the literature that could help us to answer the above questions, focusing mainly on the past decade, and to update the schema presented in Fig. 1, appropriately. In particular, it will become clear that exercise scientists in the new millennium should at least understand, if not integrate into their research programs, contributions made in the fields of genetics and molecular biology. The third major objective is to provide a more integrated schema that reflects the multidisciplinary approach that I propose exercise scientists should take over the next few years. Fig. 1 also presents scientifically based training as a necessary component of elite endurance performance. However, are current training methods of elite athletes really scientifically based, or are scientific studies based on what elite athletes are already doing in training? The concepts in the central portion of the schema presented in Fig. 1 are certainly not new, but this review will argue, on the one hand, that many questions remain to be adequately answered and on the other hand, that new information needs to be added for us to understand what optimal training leading to truly world-class performance actually is. Therefore, as the review progresses, the framework will be updated to reflect the contributions of other branches of biology and new focuses of exercise science, and to reflect the dual necessities of studying elite athletes and using the most integrative, multidisciplinary approach possible in the future.
Although studies on endurance cyclists, tri-athletes and cross-country skiers have contributed substantially to our understanding of ‘the endurance athlete’, I will focus, where possible, particularly on studies on runners. The dominance of the Kenyan endurance runners in world competition has returned time and again to the stage of the popular media. Equally intriguing are the sheer numbers of African distance runners who at times have beaten, but more frequently follow closely in the Kenyans’ footsteps. This article will mention, where appropriate, those comparative studies that have, albeit in a fairly limited way, explored a physiological and/or biochemical basis for these phenomena. It is pertinent to address the fact that most studies in the scientific literature are on sub-elite, rather than elite or world-class athletes, and that this should be taken into account when interpreting the literature (cf. Larsen, 2003).
Section snippets
The in vivo physiology of endurance performance
Hill and Lupton (1923) suggested that Vo2max was higher in endurance-trained athletes when compared to less trained controls. Since this early study, many other studies over the years have concurred that, in general, Vo2max is a good predictor of endurance running performance (e.g. Costill, 1967, Foster et al., 1978, Sjödin and Svedenhag, 1985). But, this is not the case in groups of elite or sub-elite athletes with more homogeneous race performances (Conley and Krahenbuhl, 1980). It was also
Implications of the schematic framework
The central framework in Fig. 1, represents not only multiple important factors crucial for elite athletic performance, but also an analogy to illustrate their relative importance. The schema is analogous to a series of three-legged stools and this has two implications: firstly, if any one leg is absent, the stool will topple; secondly, if any one leg is unstable, the stool will collapse if placed under sufficient pressure. The three disciplines represented together as components of exercise
Factors related to endurance performance that are assessed in vitro
As mentioned above and indicated in Fig. 1, endurance performance is reliant on at least three components: physiology, biochemistry and histology. The ‘boundaries’ between physiology and biochemistry were bridged by exercise scientists many years ago (e.g. Foster et al., 1978), but for the purposes of this review I have discussed whole body assessments and plasma analyses of blood samples taken during exercise under physiology and will now discuss other assessments that are made on the basis of
The adapted framework
Fig. 1 illustrated at least three branches of scientific endeavor that were typically used to investigate scientific aspects of athletic performance. However, the mushrooming of research in genetics and other branches of biological science over the past decade includes many studies related to exercise and truly emphasizes its biological nature. To accommodate this change, Fig. 2 now represents histology as a branch of physiology and combines biochemistry and other branches of molecular biology
Molecular biology, genetics and endurance performance
In the previous section, I discussed adaptive responses to endurance training at the level of protein expression, organelle and muscle cell size focusing primarily on observations in the muscle of endurance trained athletes. Some of those data have been available for decades, so the purpose was to highlight new additions, new interpretations or neglected aspects. However, as stated in a recent review by Hoppeler and Flück (2002), we still know relatively little about the molecular signals
Factors outside of biology that influence world-class endurance performance
The biological factors discussed above are clearly permissive with respect to adaptations favorable for endurance performance. However, this review would not be complete without mentioning the possibility that factors outside of the biological may actually underpin world-class athletic performance.
The multidisciplinary and integrative framework for future research
Collins (2002) recently proposed that it is only by using a multidisciplinary and interdisciplinary approach that life scientists can cope with the current rapid changes in biology, and I propose that this is also true for exercise science. This review led to the development of the schema in Fig. 2 that presents the branches of biology as overlapping, inter-related disciplines. Exercise science is presented as a multidisciplinary research endeavor encompassing the various inter-related
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This paper is part of a collection of inter-disciplinary, peer-reviewed articles under the Theme: ‘Origin and Diversity of Human Physiological Adaptability’ invited by K.H. Myburgh and the late P.W. Hochachka.