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Discussion
Results suggest an association between gymnastics performance and the
ACTN3 (R allele), PPARGC1A (482Ser allele), Β3-AR (Arg allele) and possibly
the ACE (D allele). It is important to be aware of how authors statistically
analyse gymnasts, as a specific genotypic association cannot be attributed to
gymnasts unless they are the only athletes in a cohort. Results may otherwise
be skewed by the demands of other sports, as phenotypic heterogeneity is
introduced. Also, nationality and ethnicity may play a role in genotype and
allele distribution amongst a population. This is particularly relevant for the
distribution of the ACE gene polymorphisms.(14)
Athletic Performance
ACE Gene
The majority of studies in the review investigated the ACE gene. Two casecontrol studies, Kim and colleagues 2011 and Taylor and colleagues 1999,(15,
16)
discovered
no
association
between
gymnasts
and
ACE
gene
polymorphisms. Small numbers of gymnasts were included (13 and 5
respectively) and both studies employed gymnasts into mixed athletic
cohorts. The lack of an association could be due to the broad athletic cohorts,
as it has been suggested that well defined athletic cohorts are needed to find
associations with the ACE gene.(3) Myerson and colleagues 1999 placed
gymnasts in a cohort with divers, totalling a small sample of 23 athletes. They
also discovered no difference in allele distribution compared to controls.(17)
Boraita and colleagues 2010 performed a case study and investigated 12
gymnasts.
Placing
athletes
in
mixed
cohorts
using
the
Mitchell
classification,(18) presented no association between ACE gene polymorphisms
and the different sporting categories. Athletes were also grouped as power
(gymnastics, jumping, sprinting) and endurance athletes (middle/long
distance running, triathlon) whereby a significant association was discovered
for the power group with the DD genotype. When gymnasts were compared
individually, the highest frequency of the DD genotype was observed out of
the 12 sports (DD 66.6%, DI and II 16.6 %).(19)
Oh and colleagues 2007 investigated a small sample of 12 gymnasts. The
authors present results on a bar graph for individual sports. Gymnasts had
the lowest frequency of the I allele and II genotype compared to controls and
other athletes. However, no numerical values or p-values are provided.
Massidda and colleagues 2011 investigated 33 elite gymnasts and although
this is the largest sample of gymnasts for the ACE gene, statistical power is
still insufficient. No significant differences were found between gymnasts and
controls. Gymnasts had a lower frequency of the I allele compared to
endurance athletes from previous studies; rowers (Gayagay et al 1998 (5)
P=0.007), swimmers (Tsianos et al 2004(20) P=0.02) and long-distance
runners (Myerson et al 1999(17) P=0.006), however the Bonferroni-adjusted pvalue was not significant.
The association of the D allele and gymnastics performance is not consistent
between studies. The ACE gene is involved in a number of physiological
functions.(21) The D allele is associated with higher ACE activity in serum and
tissue compared to the I allele.(22) The consequence of this and the
mechanism behind the ACE gene’s effect on athletic performance is not
entirely understood.(3) The II genotype is believed to correlate with a higher
frequency of type I slow twitch muscle fibres and the DD genotype with type
II fast-twitch fibres.(10) The majority of evidence regarding other athletes
suggests an association between the D allele and power performance.(20, 23-25)
The ability to generate power is a major component in gymnastics, therefore
it seems plausible that the D allele may be associated with gymnastics
performance. Massidda and colleagues 2011 were given a quality assessment
score of eight, compared to the other studies which scored 3-4. Therefore
more credence could be given to Massidda and colleagues 2011 results,
where a lack of association was observed with ACE gene polymorphisms.
Nevertheless, there is insufficient evidence to definitively conclude whether
there is an association between ACE gene polymorphisms and gymnastics
performance.
PPARGC1A gene
Two authors investigated the Gly482Ser polymorphism of the PPARGC1A
gene. Maciejewska and colleagues 2012, completed an initial and replication
study. The replication study investigated 56 gymnasts alongside 27 other
sporting disciplines. A lower frequency of the 482Ser allele was discovered in
athletes compared to controls (30.3% vs. 34.5%, P=0.002). In contrast,
when the authors compared sports individually, gymnasts had a higher
frequency of the 482Ser allele compared to controls (43.6% vs. 34.5%,
P=0.045); the highest frequency out of all the sports.(26)
Ahmetov et al 2009 focused on endurance athletic status and genetic
polymorphisms. They grouped athletes into mixed cohorts (55 gymnasts were
placed in the power group). The authors indentified 10 genetic polymorphism
associated with endurance status, which included the Gly482 allele of the
PPARGC1A gene, and grouped them together as ‘endurance alleles’. The
authors then measured the number of ‘endurance alleles’ the athletic cohorts
possessed. Unsurprisingly, the number of endurance alleles was not
significantly different in the power group from controls.(27) The study provides
little evidence for the PPARGC1A gene as no independent numerical values
are provided for the gene.
Quality assessment revealed Maciejewska and colleagues 2012 study to be
superior to that of Ahmetov et al 2009 (scores of 6 and 4 respectively),
endorsing an association between gymnastics performance and the 482Ser
allele. The PPARGC1A gene is a coactivator of the subset genes that control
oxidative phosphorylation and is abundantly expressed in skeletal muscle
modulating muscle oxidative capacity.(10) The Gly482 allele is believed to
benefit endurance athletic performance and positively influence VO2max.(28-32)
Therefore research should establish whether the 482Ser allele benefits
anaerobic or power performance. As the anaerobic system is responsible for
supplying the energetic demands of gymnastics performance, this could be
the reason why 482Ser allele is associated with gymnasts.
Β3-AR gene
Kim and colleagues 2010 investigated the Β3-AR gene in a small sample of 8
gymnasts (quality assessment score of five). Of all the sports, gymnasts were
found to have the highest frequency of the Trp/Arg genotype (5 gymnasts
62.5%) and Arg allele (31.3%) and lowest frequency of Trp allele (68.7%).
However a contradiction made by the authors, casts doubt on the reliability of
the entire article. Athletes with the Trp/Trp genotype are described as having
a significantly lower HDL-C (p=0.023) and higher plasma glucose (p=0.017),
however later in the discussion the authors state that both HDL-C levels and
plasma glucose levels were lower in athletes with the Arg allele.(33)
The Β3-AR gene is believed to play a role in energy metabolism (lipolysis,
thermogenesis) and cardiovascular function.(34,
35)
There seems to be an
association with the Arg allele and gymnastics performance. This is in contrast
to a study by Santiago and colleagues 2009 who discovered the Arg allele to
be associated with endurance performance,(34) as gymnastics is not an
endurance sport. It is possible that Kim and colleagues 2010 results were
unique for their subjects or the consequence of a small sample size.
Alternatively, the Arg allele may have another undiscovered advantage,
related
to
another
physiological
component
relevant
to
gymnastics
performance.
ACTN3
Massidda and colleagues 2009 investigated the ACTN3 gene in 35 elite
gymnasts. Compared to controls, gymnasts had a lower frequency of the X
allele (P=0.039) and XX genotype (P<0.03). It was discovered that this
significance was due to an association with male gymnastic performance.
Male gymnasts had a significantly higher frequency of the RR genotype and a
lower frequency of the XX genotype compared to controls and male
endurance athletes, but not sprint athletes. No significant differences were
discovered for female gymnasts compared to endurance or sprint athletes. It
is worth noting that only one female gymnast carried the XX genotype. Thus
it is possible the lack of significance may change with a larger sample size. As
their study received a high quality assessment score of eight, these results
strongly influence opinion on the ACTN3 gene and gymnastics performance.
The ACTN3 gene encodes for α-actinin-3, a structural protein in skeletal
muscle and is believed to influence muscle function.(10) The XX genotype
encodes a stop codon and results in deficiency of α-actinin-3.(11) Little is
known of the function of the ACTN3 gene on athletic performance.(3) It has
been suggested that the R allele is associated with type II muscle fibres. This
may be the reason for its association with power performance, and
subsequently gymnastics performance.(36) With regards to gender differences,
this was the only study in the review to find a significant difference in allele
distribution between male and female athletes. The authors hypothesise that
the α-actinin-3 protein may benefit male gymnastics performance more than
female gymnastics performance because of an increased demand for
muscular strength in male gymnastics.(11)
Other genes
The study by Ahmetov 2009 compared nine other genes (in addition to the
PPARGC1A gene) with gymnasts; the PPARA, PPARD, PPP3R1, UCP2, UCP,
VEGFA, NFATC4, PPARGC1B and TFAM genes. As they were analysed
collectively the study provides little evidence on the individual genes.
Summary
Overall the results suggest that there are associations between gymnastics
performance and the ACTN3 (R allele), PPARGC1A (482Ser allele), Β3-AR (Arg
allele) and possibly the ACE (D allele). Current evidence is limited and
therefore these conclusions can only be deemed as preliminary. For
confirmation, future studies should employ large samples of well-defined
cohorts of gymnasts and control for competitive level, gender and ethnicity.
Future research
More genetic polymorphisms need to be examined in gymnasts, as only four
out of the hundreds that are associated with athletic performance have been
investigated. Furthermore, investigations should explore whether genetics
plays a role in why some gymnasts excel on one apparatus. The separate
apparatus require a different combination of skills and hence, it would be
interesting to explore the possibility of different genotypes benefiting certain
apparatus performance.
Genetics is an extremely complex area and research has only just begun to
understand its vast role in athletic performance. Many human phenotypes are
polygenic and it is unlikely gymnastics performance is any different. Research
is yet to unveil the effect different genetic interactions have on athletic
performance. It is possible particular combinations of genetic polymorphisms
may be associated with gymnastics performance.
Injury
After searching the databases, no relevant articles could be retrieved on
genetic polymorphisms associated with gymnastics injuries. It seems that
thus far no studies have investigated this topic, clearly highlighting a large
gap in the field. Studies should be conducted which correlate injury
occurrence data and genetic testing of gymnasts genotypes, to identify
specific alleles which predispose to injury.
Future implications
In the future genetic testing could be used as part of the selection process for
National Squads. Whether it is ethical to use information on a gymnast’s
genetic makeup to help decide whether to accept or reject them, is
debateable. Additionally, if certain genotypes were discovered to be
advantageous to apparatus performance, genetic testing could be used to
guide a gymnast into specialising on a particular apparatus, thus helping them
reach their potential.
An example of genetic polymorphisms associated with injury is the FokI and
BsmI polymorphisms of the VDR gene; suggested to increase the risk of
stress fractures.(37) Future research may identify gymnasts with these
polymorphisms as having a greater risk of developing stress fractures and
hence, genetic testing of young gymnasts could be instigated. If a gymnast
was found to have the FokI or BsmI polymorphism, coaches could
concentrate on reducing high impact loading though the increased use of
protective matting or soft landing surfaces.
Limitations
The primary limitation of the studies, are the small sample sizes of gymnasts.
This may conceal a true association of a genetic polymorphism with
gymnastics performance or give a false indication of an association.
One limitation of this systematic review is the possibility of publication bias, as
unpublished studies from conference proceedings are excluded. Another
limitation is the inclusion of articles in the English Language only. An article in
Korean by Lim et al 2006 which reports on the Β3-AR gene,(38) is known to
have investigated gymnasts.
Quality assessment was conducted using the Newcastle-Ottawa scale.(13)
Content validity and inter-rater reliability have been established and criterion
validity and intra-reliability are still under assessment.(13) As the NewcastleOttawa scale relates to cases with diseases, whereas in this instance cases
were gymnasts, the scale needed to be adapted slightly which may have
affected validity. The Pedro scale is a more reliable and valid tool of quality
assessment, however the studies in the review are not randomised control
trials and so this method could not be applied.(39)
Conclusion
Artistic gymnasts are required to implement a range of physical and technical
skills into their performance. Gymnastics performance and injury are
influenced by environmental and genetic factors. The discovery of genetic
influences may provide new ways of approaching how gymnasts train and
perform.
The results of this systematic review identified only four genetic attributes
associated with gymnastics performance: ACTN3 (R allele), PPARGC1A
(482Ser allele), Β3-AR (Arg allele) and possibly the ACE (D allele).
Physiological effects of the genes differ, but a pattern emerges of gymnastic
performance relating to those alleles associated with power performance and
alleles unrelated to endurance performance.
Results should be classed as preliminary as studies are limited by small
sample sizes and occasionally mixed cohorts of athletes. The role of ethnicity
and gender on allele distribution needs to be further investigated and
controlled in future studies. Moreover, it is evident from this review that there
is a large gap in the field and subsequent studies should explore genetic
variants that may predispose to injury in gymnasts. This could lead to the
implementation of preventative measures thus benefiting those gymnasts
susceptible to certain injuries.
It is evident that more studies are needed on gymnasts. This review has
revealed that for artistic gymnastics, the field of genetics is currently a long
way from influencing practice and benefiting those who participate in the
sport.