Athletes rarely respond to the same training in the same way. Sports science has documented this difference for a long time, and two areas of research now try to explain part of it: the genome of the athlete and the community of microbes in the gut.
Both fields are developing rapidly, although the evidence supporting practical applications remains limited.
What Genetics Has Shown So Far
When studies are pooled, recent meta-analyses find no statistically significant effect on athletic performance for the genetic variants studied [1,2].
That conclusion follows years of studies on two genes in particular, ACTN3 and ACE, often nicknamed the “speed” and “endurance” genes. In some of these studies, one version of each gene was more common among sprinters and power athletes, and the other version among endurance athletes [2]. A 2025 meta-analytical review reported associations with generally modest effect sizes; confirm the precise outcomes and effect estimates in reference [3].
Taken together, the results are consistent with performance depending on many small genetic effects that interact with training and recovery, and they help explain the move toward the genome as a whole.
From Single Variants to the Whole Genome
A polygenic score adds up thousands of small genetic effects into a single estimate of tendency. It needs data from across the genome, which the whole-genome sequencing provides by reading nearly all of a person’s three billion DNA letters. The result is a probability and cannot say with certainty what will happen to an individual athlete. Authors of the recent reviews ask for larger genome-wide studies that include athletes from different backgrounds [2,3].
Scores tend to be less accurate outside the populations in which they were developed, and most genetic studies so far have included mainly people with European ancestry [4]. Making the inclusion of Latin American and Middle Eastern athletes in future studies a priority.
The Athlete’s Gut
Physically active people tend to carry more bacteria that produce short-chain fatty acids, compounds that support gut health, and athletes seemed to have richer microbiomes, according to a 2024 systematic review.
However, the included studies differed substantially in design and methods, and the review did not identify a consistent association with overall microbiome diversity [5]. The gut microbiome is the community of bacteria that helps digest food and communicates with the immune system, and one of its best-known athletic findings comes from marathon runners. Their gut bacteria included Veillonella atypica, a species that converts lactate into a compound the body can use. Mice given this bacterium ran longer on a treadmill, and the effect remains to be tested in people [6].
Probiotics have been tested in athletes in many different ways. A systematic review of 41 studies reported benefits mainly for respiratory infections and gastrointestinal symptoms, yet about half of the studies showed no improvement and the methods varied widely [7].
A recent review suggested that certain probiotic interventions might reduce perceived fatigue under specific study conditions, but findings cannot be generalized to all probiotic strains or used as a universal dosing recommendation [8].
These results are best described as associations.
Looking Ahead
The next steps are clear. Genome-wide analyses in large and diverse groups of athletes [2,3], together with human microbiome studies that follow athletes through training, would address could help address the main challenges of the field. As that evidence accumulates, the interpretation of results will be refined, and today’s findings are best read as tendencies that may change with new data.
The potential is considerable. It lies in a better understanding of why people respond differently to the same training, and in how injury risk might one day be anticipated.
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References
1. Psatha A, Al-Mahayri ZN, Mitropoulou C, Patrinos GP. Meta-analysis of genomic variants in power and endurance sports to decode the impact of genomics on athletic performance and success. Hum Genomics. 2024;18(1):47. doi:10.1186/s40246-024-00621-9
2. Ferreira CP, Silvino VO, Trevisano RG, de Moura RC, Almeida SS, dos Santos MAP. Influence of genetic polymorphism on sports talent performance versus non-athletes: a systematic review and meta-analysis. BMC Sports Sci Med Rehabil. 2024;16:223. doi:10.1186/s13102-024-01001-5
3. Łosińska KW, Cięszczyk P, Ghiani G, Maszczyk A. Effect size and replicability in genetic studies of athletic performance: a meta-analytical review. Genes (Basel). 2025;16(9):1040. doi:10.3390/genes16091040
4. Martin AR, Kanai M, Kamatani Y, Okada Y, Neale BM, Daly MJ. Clinical use of current polygenic risk scores may exacerbate health disparities. Nat Genet. 2019;51(4):584-91. doi:10.1038/s41588-019-0379-x
5. Pérez-Prieto I, Plaza-Florido A, Ubago-Guisado E, Ortega FB, Altäe S. Physical activity, sedentary behavior and microbiome: a systematic review and meta-analysis. J Sci Med Sport. 2024;27(11):793-804. doi:10.1016/j.jsams.2024.07.003
6. Scheiman J, Luber JM, Chavkin TA, MacDonald T, Tung A, Pham LD, et al. Meta-omics analysis of elite athletes identifies a performance-enhancing microbe that functions via lactate metabolism. Nat Med. 2019;25(7):1104-9. doi:10.1038/s41591-019-0485-4
7. Heimer M, Teschler M, Schmitz B, Mooren FC. Health benefits of probiotics in sport and exercise: non-existent or a matter of heterogeneity? A systematic review. Front Nutr. 2022;9:804046. doi:10.3389/fnut.2022.804046
8. Kearns RP, Dooley JSG, Matthews M, McNeilly AM. Do probiotics mitigate GI-induced inflammation and perceived fatigue in athletes? A systematic review. J Int Soc Sports Nutr. 2024;21:2388085. doi:10.1080/15502783.2024.2388085
