revista motricidade

68 | A. Pereira, A.J. Silva, A.M. Costa, E.B. Almeida, M.C. Marques
Over several decades many researchers have
recognized numerous physiological characteristics
associated with sports performance,
describing the athlete’s typical response to
training. Indeed, regular exercise induces
significant effects on different biological
structures and functions, which leads to
specific adaptations in strength and muscular
endurance (Maughan, 2005; Timmons, 2011).
However, while some individuals have a minor
response to exercise others show remarkable
adaptations far beyond the expected typify
response. From this perspective, the expected
average adaptation value (e.g., anaerobic
power) masks the true extent of individual
variability in a particular phenotype (Roth,
2008). Whether they are recreational or elite
athletes, knowing how each subject is going to
adapt would enable the application of
exercise/training programs highly individualized.
Moreover, “... greater knowledge of the
mechanisms and interaction of exercise-induced
adaptive pathways in skeletal muscle is important for
our understanding of the etiology of disease,
maintenance of metabolic and functional capacity
with aging, and training for athletic performance”
(Coffey & Hawley, 2007, p. 9).
Because genetic factors are thought to
determine 20–80% of the variation in a
number of traits important to athletic
performance (MacArthur & North, 2007;
McCauley, Mastana, & Folland, 2010), the
contribution of molecular biology technologies
have been crucial over the past years to the
progress of knowledge in this area. With effect,
the Human Gene Map for Performance and
Health-related Fitness Phenotypes reports
several genes and quantitative trait loci shown
to be related to physical performance of healthrelated
phenotypes (Bray et al., 2009). One of
the polymorphisms within specific gene loci
that clearly emerges as a potentially candidate
that could explain part of the performance
variation particularly in sports requiring high
levels of power and speed is the alpha-actinin-3
(ACTN3) R577X polymorphism (Berman &
North, 2010). Despite the apparent low feature
of ACTN3 in humans, several genotype screens
in high-level athletes from various sporting
disciplines noted that Caucasian sprint/power
athletes showed a very low frequency of
homozygosity for the ACTN3 premature stop
codon 577X mutation. Also, the frequency of
the 577XX genotype appears to be relatively
higher in Caucasian elite endurance athletes.
In other populations, ACTN3 seem to
influence strength and functional capabilities
at baseline (Moran et al., 2007; Walsh, Liu,
Metter, Ferrucci, & Roth, 2008) and in
response to strength training (Clarkson et al.,
2005).
In brief, this article reviews the current
state of knowledge regarding the genetic
effects of the ACTN3 R577X polymorphism on
sports performance traits, such as aerobic
endurance, muscular strength and power.
Alpha-actinin-3 (R577 Allele) as a possible
candidate gene for sports performance
The α-actinins are a family of actin-binding
proteins that play a key role in the
maintenance and regulation of the
cytoskeleton (Blanchard, Ohanian, & Critchley,
1989). In skeletal muscle, both family
members alpha-actinin 2 and alpha-actinin 3
are major components of sarcomeric Z-lines.
They are responsible from stabilizing the
contractile structure (McArthur & North,
2004), where they function to anchor actioncontaining
thin filaments in a constitutive
manner (Mills et al., 2001). Several binding
studies suggest that alpha-actinins also play a
role in the interaction between the sarcomere
cytoskeleton and the muscle membrane
(Hance, Fu, Watkins, Beggs, & Michalak,
1999; Otey, Vasquez, Burridge, & Erickson,
1993) and in the regulation of myofiber differentiation
and/or contraction (North, 2008).
The expression pattern of these two
humans alpha-actinins has diverged during
evolution (Macarthur & North, 2004): alphaactinin
2 (ACTN2) is expressed in all heart and
oxidative skeletal muscle fibers while
expression of alpha-actinin 3 (ACTN3) is