Genetics and Fitness: How Much Do Your Genes Matter?

Two people follow the same training plan, and one gets much fitter than the other. Genes are part of the reason, though not the whole story. This guide explains what research shows about genetics and exercise, what a gene such as ACTN3 can and cannot tell you, and how to train well whatever your DNA says.

What heritability does and does not mean

Heritability is the share of variation in a trait, across a group of people, that is linked to genetic differences. It does not tell you what share of your own result is fixed. A review for strength and conditioning coaches reports lean body mass heritability estimates of 60 to 80 percent. A summary of exercise genetics research cites VO2max estimates from twin studies of 69 to 87 percent, with a pooled analysis of eight twin studies at about 72 percent, while other work puts it nearer 50 percent. The spread shows how much the figure depends on the population studied.

Why the same workout gives different results

The HERITAGE Family Study ran a 20-week aerobic training program. Gains in VO2max ranged from no change in some people to increases of more than 1,000 ml of oxygen per minute in others. The summary of findings adds that response to training differed 2.5 times more between families than within families, which points to a genetic component of trainability.

That does not mean a poor early response is permanent. It means some people need a different dose or type of training to see progress.

ACTN3 and the so-called speed gene

ACTN3 makes a protein found in fast-twitch muscle fibers, and its variants are associated with speed and power. A mini-review by Pickering and Kiely found 19 studies on how ACTN3 relates to training adaptation, recovery and injury risk. Results differed between studies, which the authors attribute partly to differences in participants and in the training programs used.

One gene explains little by itself. The coach-focused review counts more than 200 DNA variants linked to performance traits, and each has a small effect.

Do consumer DNA fitness tests help?

A 2023 overview in Frontiers in Genetics describes personalized, precision exercise as a goal of the field. It also lists direct-to-consumer testing companies among the threats, alongside ethical issues and gene doping. After a consumer test, MedlinePlus advises talking to your doctor before making major changes to diet or fitness. The MTHFR gene mutation diet plan shows how gene-based advice looks in practice, and science-backed wellness hacks lists habits with stronger evidence.

How to train when you cannot change your genes

Test, change one thing, and test again.

• Pick two or three measures, such as a timed 3 km walk or run, a lift for 5 reps, or resting heart rate
• Repeat them every 8 to 12 weeks, since the HERITAGE program itself ran for 20 weeks
• If a measure does not move, change the volume, intensity or type of training before concluding you are a poor responder
• Support training with enough protein, as covered in the high-protein diets and weight loss guide
• Build an easy aerobic base with the science of Zone 2 cardio
• Track recovery using the tips in increase HRV overnight with breathwork
• Add strength and movement skills from functional fitness

Genetics and fitness FAQ

Can my genes limit how fit I get?

They can shape how fast you improve and where your ceiling sits, but almost everyone gains fitness with regular training. Most people are nowhere near their genetic ceiling.

Should I take a DNA test to choose a sport?

The evidence does not support picking a sport from a consumer test. Try a few activities and see which you enjoy and improve at.

How long before I know how I respond to training?

Studies of training response run for weeks to months. Give a new program at least 8 to 12 weeks before judging it.

Train for the body you have

Genes influence fitness, but they are one input among training, food, sleep and consistency. Measure your own progress, adjust the plan, and use the science of sustainable weight loss for body composition goals.

This post is for information and is not medical advice.

Sources

• Genetics of Performance and Injury: Considerations for the Strength and Conditioning Coach
• Summary of findings on Genetics and Exercise, 2018
• Pickering and Kiely, ACTN3: More than Just a Gene for Speed, Frontiers in Physiology, 2017
• Genetics and athletic performance: a systematic SWOT analysis, Frontiers in Genetics
• MedlinePlus, results of direct-to-consumer genetic testing