While physical activity is an essential part of getting fit, it鈥檚 not the whole story. An individual鈥檚 fitness level also depends on how they respond to that activity, which is largely determined by their genes.
The landmark research in this field is the Heritage family study, begun in the 1990s. US and Canadian researchers recruited 481 sedentary people from 98 families, and subjected them to a rigorous 20-week training programme. They then put them through a battery of tests.
While many people鈥檚 aerobic fitness improved dramatically, others showed a less marked response. The disheartening news is that about 1 in 10 showed no change whatsoever in their aerobic fitness, despite doing 45 minutes of vigorous exercise three times a week for the final six weeks of the programme (Journal of Applied Physiology, vol 87, p 1003).
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The degree of response turned out to be largely down to the participants鈥� genes. If your parents find it hard to get fit, there鈥檚 a good chance you will too. 鈥淲e had families where all of them were low responders and other families where they were all high responders,鈥� says Claude Bouchard, now director of the Pennington Biomedical Research Center at Baton Rouge, Louisiana, who led the study.
Happily, even those whose aerobic fitness did not change had lower blood pressure and cholesterol, more normal insulin levels, and less abdominal fat. 鈥淵ou鈥檙e never a complete non-responder,鈥� says Bouchard.