Personalized Fitness and Genetics: What Is Possible, What Is Not?

There is no single training method that works for everyone: people respond differently to the same program. Some of these differences are linked to genetics, but training history, sleep, nutrition, technique and motivation are often more decisive. In this article we explain what genetic tests can add to personalized fitness and where they fall short.

How much does genetics affect the response to training?

Muscle fiber composition, response to training and injury tendency are partly heritable; training, nutrition and load management also strongly influence these traits. Each of these traits is shaped by small contributions from many genes. That is why a single genetic finding cannot determine your entire training plan; it is only one of the pieces of information you can take into account.

ACTN3 and muscle fiber: what is known and the limits

The R577X variant of the ACTN3 gene is one of the most studied variants in sports genetics. It has been associated with power and sprint performance in elite athletes, and biopsy studies have also linked it to muscle fiber composition. However, genetic tests do not determine your muscle fiber type; muscle fiber proportions can only be measured by muscle biopsy. The effect of ACTN3 on performance is small; this variant has been associated not only with speed but also with other traits such as muscle damage and recovery.

Can a genetic test determine a sport or talent?

No. Genetic differences partly affect the response to training, but international consensus and position statements do not recommend using genetic tests to predict sporting performance, select talent or choose a sport. This principle is especially important for children. Results can help with the question "how can I plan my current training?", not "which sport should I do?".

Injury tendency and prevention

Some variants in connective tissue genes such as COL5A1 have been associated with tendon and ligament injuries; however, the results of meta-analyses contradict each other. Findings of this kind should therefore be interpreted with caution. The methods with the strongest evidence for preventing injuries are still regular warm-ups, gradual load progression, adequate recovery and strength–flexibility work; a genetic finding can be an extra reminder to pay attention to these measures.

Nutrition and homocysteine

Fitness is not only about exercise; nutrition also plays an important role. A common variant in the MTHFR gene has been associated with the folate cycle and with higher homocysteine levels; however, this variant on its own is not an indicator of heart disease. Homocysteine levels are measured with a blood test, and their assessment is a matter for your doctor. We cover genetics and nutrition in detail in our article on genetics and nutrition.

How can you use genetic information in your training?

• Share the findings with your coach and evaluate them together with your current performance measurements.
• Use a tendency toward power or endurance to review the variety and recovery times in your program; do not use it to drop one type of training entirely.
• Check the evidence level of each finding; do not make major changes based on findings with limited evidence.
• Observe the effect of any changes over several weeks.

You can see how power–endurance tendency, recovery and injury predisposition are presented in the sports genetics report on the Sports & Fitness Genetics page, and sample finding cards on our sample report page.

References

• Webborn N, Williams A, McNamee M et al. Direct-to-consumer genetic testing for predicting sports performance and talent identification: Consensus statement. Br J Sports Med 2015. PMID: 26582191. doi:10.1136/bjsports-2015-095343
• Vlahovich N, Fricker PA, Brown MA, Hughes D. Ethics of genetic testing and research in sport: a position statement from the Australian Institute of Sport. Br J Sports Med 2017. PMID: 27899345. doi:10.1136/bjsports-2016-096661
• Yang N, MacArthur DG, Gulbin JP et al. ACTN3 genotype is associated with human elite athletic performance. Am J Hum Genet 2003. PMID: 12879365. doi:10.1086/377590
• Vincent B, De Bock K, Ramaekers M et al. ACTN3 (R577X) genotype is associated with fiber type distribution. Physiol Genomics 2007. PMID: 17848603. doi:10.1152/physiolgenomics.00173.2007
• Pickering C, Kiely J. ACTN3: More than Just a Gene for Speed. Front Physiol 2017. PMID: 29326606. doi:10.3389/fphys.2017.01080
• Guo R, Ji Z, Gao S, Aizezi A et al. Association of COL5A1 gene polymorphisms and musculoskeletal soft tissue injuries: a meta-analysis based on 21 observational studies. J Orthop Surg Res 2022. PMID: 35241120. doi:10.1186/s13018-022-03020-9
• Fukuyama Y, Murakami H, Iemitsu M. Single Nucleotide Polymorphisms and Tendon/Ligament Injuries in Athletes: A Systematic Review and Meta-analysis. Int J Sports Med 2024. PMID: 39437988. doi:10.1055/a-2419-4359
• Frosst P, Blom HJ, Milos R et al. A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase. Nat Genet 1995. PMID: 7647779. doi:10.1038/ng0595-111