THE HUMAN ENDURANCE ATHLETE - HETEROGENEITY AND ADAPTABILITY OF SELECTED EXERCISE AND SKELETAL-MUSCLE CHARACTERISTICS

In human subjects, large variations between individuals (up to 3-fold) exist in the capacity for endurance exercise performance. In a hetero geneous population, endurance performance is strongly related to whole body maximal oxygen uptake (VO(2)max). This is in part genotype depen dent (similar to 25%) but is adaptable with training. However, this re lationship does not hold within a homogeneous group of well-trained ru nners. Other physiological characteristics must contribute to enduranc e performance and these may include specific advantageous skeletal mus cle phenotypes. Muscle fibre type distribution is also heterogeneous, although less adaptable. In contrast, muscle oxidative enzyme capacity is highly adaptable with training. The genetic influences on these mu scle characteristics have been indirectly investigated by comparing Af rican endurance athletes, who dominate world-class events, to Caucasia n endurance athletes. We have established that African runners have gr eater resistance to fatigue than Caucasians (p < 0.01) and 50% greater oxidative enzyme activity in vastus lateralis samples (p < 0.05), des pite somewhat lower Type I fibre proportion. These differences were no t inherently present in a group of sedentary Africans, suggesting that the genotypic influence on athletic performance may be a superior ada ptation to training, rather than a baseline genetic effect. Combined p hysiological and genetic studies are likely to elucidate a polygenetic basis for superior endurance performance.