What makes an endurance athlete world-class? Not simply a physiological conundrum

Abstract

Inter-individual variation in endurance performance capacity is a characteristic, not only of the general population, but also in trained athletes. The ability of sport scientists to predict which athletes amongst an elite group will become world-class is limited. We do not fully understand the interactions between biological factors, training, recovery and competitive performance. Assessment methods and interpretation of results do not take into account the facts that most research is not done on elite athletes and performances of world-class endurance athletes cannot be attributed to aerobic capacity alone. Many lines of evidence suggest that there is a limit to adaptation in aerobic capacity. Recent advances in molecular biology and genetics should be harnessed by exercise biologists in conjunction with previously used physiological, histological and biochemical techniques to study elite athletes and their responses to different training and recovery regimens. Technological advances should be harnessed to study world-class athletes to determine optimal training and competition strategies. In summary, it is likely that multiple factors are essential contributors to world-class endurance performance and that it is only by using a multidisciplinary approach that we will come closer to solving the conundrum: ‘What makes an endurance athlete world class?’

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).