The elite athlete represents a highly complex phenotype, which reflects training, the desire to win, and perhaps most importantly, the individual`s genetic makeup. Variables such as the force-generating capacity of muscle fibres at high velocity, VO2max, anaerobic threshold, and the capacity of the individual to adapt to exercise training are all strongly genetically influenced. However the specific genes responsible are not known. We are currently studying skeletal muscle genes that may influence variations in erformance in the general population. The a-actinins are a multigene family of actin-binding proteins. The two skeletal muscle isoforms of a-actinin are major structural components of the Z-line, and are essential for maintaining the spatial relationship between myofilaments and in regulating myofibre contraction. In mice and humans, there are two genes encoding the skeletal muscle a-actinins (ACTN2 and ACTN3). ACTN3 is expressed only in type 2 (fast twitch) fibres, which are the fibres responsible for generating forceful muscle contractions at high velocity. We have identified a mutation in ACTN3 which results in the a-actinin-3 protein not being produced*. Surprisingly, 18% of the normal Australian population are deficient in a-actinin-3, because they are homozygous for this mutation. Although absence of ACTN3 does not cause muscle disease, this gene is highly conserved over a long evolutionary period, suggesting that it has been maintained by natural selection. In addition, certain ethnic populations (in particular the African Zulu population) have a very low frequency of this mutation, and thus the majority of Zulus (96%) express a-actinin-3. Thus, we suggest that the presence of a-actinin-3 provides a selective advantage by improving the function of skeletal muscle in generating forceful contractions at high velocity.
© Copyright 1999 5th IOC World Congress on Sport Sciences with the Annual Conference of Science and Medicine in Sport 1999. All rights reserved.