Is Fitness All in the Genes?

Why do some people respond to an aerobic workout routine by becoming incredibly fit, whereas others who exercise just as hard for months end up no fitter than when they began?

That question has bedeviled countless people who’ve started exercise programs. It has also motivated a major new study of the genetics of fitness. 

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The researchers looked at 324,611 individual snippets over all. Each of the volunteers had already completed a carefully supervised five-month exercise program, during which participants pedaled stationary bicycles three times a week, at controlled and identical intensities. Some wound up much fitter, as determined by the increase in the amount of oxygen their bodies consumed during intense exercise, a measure called maximal oxygen capacity, or VO₂max. In others, VO₂ max had barely budged. No obvious, consistent differences in age, gender, body mass or commitment marked those who responded well and those who continued to huff and struggle during their workouts, even after five months.

But there was a divergence in their genomes. The researchers identified 21 specific SNPs, out of the more than 300,000 examined, that differed consistently between the two groups. SNPs come in pairs, since each of us receives one paternal copy and one maternal copy. So there were 42 different individual versions of the 21 SNPs. Those exercisers who had 19 or more of these SNPs improved their cardiorespiratory fitness three times as much as those who had nine or fewer.