THE BENEFIT OF GENETIC TESTING FOR SPORTS PERFORMANCE is not to determine whether or not an individual can become an elite athlete, but rather to determine in which sport an individual may compete successfully.
The alpha-actin 3 (ACTN3) gene, also known as 'the speed gene', is well-known for its association with sports performance. In humans, a-actinin 2 (ACTN2) is expressed in all skeletal muscle fibres, while a-actinin 3 (ACTN3) is only expressed in type 2 (fast twitch) fibres.
The ACTN3 gene stands out due to a frequent nonsense polymorphism R577X that may influence muscular performance. You may be homozygous for XX or RR or you may be heterozygous for XR.
Individuals homozygous for the X allele do not produce ACTN3 protein in their muscles. In this instance, the ACTN2 gene which is expressed in both type 1 and type 2 myofibers, compensates for the loss of of ACTN3 protein in type 2 myofibers.
From this research it seems that the presence of ACTN3 R alleles may be associated with greater success in activities requiring sprint or power performance.
On the flip side, ACTN3 deficiency ( XX genotypes) may result in an advantage for endurance athletes.
A comparison between elite level sprinters showed that the R allele is more frequently found in top-level and national level sprinters. This makes sense because type 2 fibres are responsible for producing 'explosive' powerful muscle contraction.
Interestingly, Shang et al. found that in the Han Chinese population, XX genotypes were significantly over-represented in female endurance athletes, compared to controls, while no such difference was observed in male endurance athletes.
The presence of the ACTN3 X genotype is also relevant to distance.
A study of Russian speed skaters revealed that XX genotypes have a higher proportion of type 1 fibres and prefer to skate long-distance races.
Personal best times for elite male sprinters showed that the RR and RX genotypes excelled in 200m distance.
Looking at an athletes combination of genes such as ACE ID and ACTN3 XR, and the ability to hold world records is very interesting.
Elite male sprinters and Olympic qualifiers with ACE DD and ACTN3 RR genotype combinations show personal best times for 200m and 400m events, while ACE II and ACTN3 XX genotype combinations are detrimental for 200m-400m sprint events.
A study on professional soccer players (Pimenta EM, et al) concluded that players homozygous for ACTN XX are more susceptible to eccentric damage and present with a higher catabolic state, in comparison to ACTN RR and RX genotypes.
Matching an individual's genotype to their appropriate training modality also leads to more effective resistance training.
Resistance training is used across all sporting disciplines to enhance strength, power, speed, muscle growth, coordination, flexibility and to reduce body fat.
There is a large amount of variation in muscle and strength gains in both men and women due to variations in genotypes. Some people achieve greater gains than others.
Jones N, et al. reported that athletes with endurance genotype profiles had greater benefits from low-intensity resistance training, while athletes with power genotype profiles responded better to high-intensity resistance training.
34 athletes performed matched training - high- intensity for power genotypes and low-intensity for endurance genotypes, while 33 athletes were placed into mismatched groups. The mismatched athletes showed non-significant improvement, while the matched groups showed significantly greater performance changes.
Training programs personalised to an individual's genetic profile may enhance performance and reduce injury risk.