The genetic basis of human athletic performance. Why are psychological components so often overlooked?

Abstract

We have read with interest the recent article in The Journal of Physiology by Williams & Folland (2008), who concluded that human physical performance is essentially multifactorial and determined by a range of environmental (physical training, nutrition and technological aids) and genetic factors. Identifying the genes relevant to human athletic performance has been difficult in the past, because each causal gene makes only a small contribution to overall heritability. Accordingly, the adoption of a ‘single-gene-as-magic-bullet’ philosophy is questionable, especially considering that the 2005 human gene map for physical performance and health-related phenotypes already includes 165 autosomal gene entries and quantitative trait loci, plus five others on the X chromosome (Lippi, 2008). All these genes contribute, however, to generate a cluster of phenotypes. Williams & Folland highlighted that, in addition to the well-established maximal rate of oxygen uptake, at least three other endurance phenotypes (economy of movement, lactate/ventilatory threshold and, potentially, oxygen uptake kinetics) contribute to the endurance performance phenotype (time taken to travel a given distance) seen in elite competition (Williams & Folland, 2008). Evolutionary forces (mutation, environment) apply to elements of the human neural system in precisely the same manner that they do to the physical body. They affect both the intellect and our instincts. Accordingly, human physiological trait variance also has both an environmental and genetic basis, although the classic gene–environment dichotomy is clearly too simplistic to explain the full range of variation for most proximate determinants of athletic performance (Brutsaert & Parra, 2006). It is undeniable that success in competition has a strong physiological basis. ‘Mental’ factors contributing to success in sports include mental toughness, game knowledge, tactical astuteness, team coherence, status of maturity, anticipation and decision making, and, last but not least, motivation to endure pain during training and competition. Aspiration to victory is an additional hallmark of the champion. Earlier studies have shown that genetic factors account for up to 62% of the variance in daily exercise behaviour and up to 83% of the variance in sports participation (Beunen & Thomis, 1999; Bryan et al. 2007). Regardless of the clear heritability of exercise and competition behaviours, prior research on genetics and sports has mainly focused on athletic performance phenotypes (Williams & Folland, 2008), and largely overlooked the genetic basis of psychological phenotypes that would characterize elite and top-class athletes. However, emerging evidence attests that research on the genetic basis of ‘physiological phenotypes’ might provide additional, valuable elements to determine ‘advantageous’ polygenic profiles. As an example, it has been shown that polymorphisms in the gene encoding for the brain-derived neurotrophic factor (BDNF), a growth factor that has a broad influence on central and sensory neuronal function, may exert a direct influence on positive mood and strong effects on ratings of perceived exertion and heart rate in response to a bout of aerobic activity (Bryan et al. 2007). It was also demonstrated that genetic variations of the serotonin transporter gene (5HTT) are closely related to the human adaptive ability to control emotions and might strongly influence aggressiveness, positivism and therefore success in competitions (Maliuchenko et al. 2007). The introduction of high-throughput genotyping technologies and microarray-based epigenetic technology now allow us to explore genome-wide associations, gene expression and gene regulation activity (Lippi, 2008). However, limiting the analysis to ‘physical’ favourable phenotypes would not permit the development of comprehensive predictive models, since a variety of environmental and psychological factors still influence athletic skill and performance. An advantageous physical genotype is not enough to build a top-class athlete, a champion capable of breaking Olympic records, if endurance elite performances (maximal rate of oxygen uptake, economy of movement, lactate/ventilatory threshold and, potentially, oxygen uptake kinetics) (Williams & Folland, 2008) are not supported by a strong mental background.