Endurance exercise performance: the physiology of champions

Abstract

Efforts to understand human physiology through the study of champion athletes and record performances have been ongoing for about a century. For endurance sports three main factors--maximal oxygen consumption (.VO(2,max)), the so-called 'lactate threshold' and efficiency (i.e. the oxygen cost to generate a given running speed or cycling power output)--appear to play key roles in endurance performance. and lactate threshold interact to determine the 'performance .VO(2)' which is the oxygen consumption that can be sustained for a given period of time. Efficiency interacts with the performance .VO(2) to establish the speed or power that can be generated at this oxygen consumption. This review focuses on what is currently known about how these factors interact, their utility as predictors of elite performance, and areas where there is relatively less information to guide current thinking. In this context, definitive ideas about the physiological determinants of running and cycling efficiency is relatively lacking in comparison with .VO(2,max) and the lactate threshold, and there is surprisingly limited and clear information about the genetic factors that might pre-dispose for elite performance. It should also be cautioned that complex motivational and sociological factors also play important roles in who does or does not become a champion and these factors go far beyond simple physiological explanations. Therefore, the performance of elite athletes is likely to defy the types of easy explanations sought by scientific reductionism and remain an important puzzle for those interested in physiological integration well into the future.

Figure 1. A. V. Hill's (Hill, 1925) original plot of world record performance time on the X-axis versus performance speed on the Y-axis

The top tracing is for speed-skating, the middle tracing is for running by males, and the bottom tracing is for running by women. The shape of the curve led to Hill's original ideas about differing causes of muscle fatigue for exercise bouts of different durations.

Figure 2. Overall schematic of the multiple physiological factors that interact as determinants of performance velocity or power output

This figure serves as the conceptual framework for the ideas discussed in this review.

Figure 3. Plot or blood lactic acid concentration versus race distance (Costill, 1970)

This figure is an example of the diminishing contribution of so-called ‘anaerobic’ energy sources as race distance increases. This paper also set the stage for a number of later investigations related to the fraction of (e.g. performance ) that could be sustained in competition.

Figure 4. Individual record of treadmill velocity and versus blood lactate concentration in subject capable of breaking 2:30 h for the marathon (Farrell et al. 1979)

In untrained subjects the upturn in lactic acid concentrations is seen at about 60% of . Trained subjects can usually exercise at 75–85% of before there is a marked increase in blood lactate concentration. This figure also illustrates the concept of performance and performance velocity.

Figure 5. Time to fatigue during exercise at 88% of plotted against lactate threshold (LT) in 14 highly trained cyclists and triathletes (data plotted from Coyle et al. 1988; Coyle, 1995)

These athletes all had similar values and uniformly high muscle oxidative enzymes. A subgroup of 4 athletes (subjects 1, 2, 7 and 8) with exceptionally high capillary density seemed to ‘overachieve’ in comparison with their lactate threshold values compared with other members of the group.

Figure 6. Regression lines for high, average and low running economy (efficiency) in elite endurance athletes based on values gleaned from a number of sources (Joyner, 1991)

Since there has been little systematic data collected above ∼18 km h⁻¹ the filled triangles in the figure are individual data from a limited number of champions with exceptional running economy. This figure emphasizes the importance of efficiency among groups of elite performers with relatively uniform and lactate threshold values. It is also of note that the physiological determinants of efficiency (especially for running) are poorly understood.