While factors like nutrition, motivation, environment and advances in equipment (running shoes, swim suits, skis, bicycles) can all contribute to huge improvements in athletic performance, the number one limiting factor is genetics – how our individual cells are put together from microscopic strands of DNA. Genes regulate our cardiovascular endurance and muscle fiber type, as well as other factors such as lung capacity, flexibility and muscular strength.
So, how much do these factors vary from person to person? It’s estimated that aerobic fitness is about 40-50% heritable (i.e. the difference from one person to the next due to genes), strength and muscle mass is around 50-60% and height is around 80%.
On top of this, there is another key factor known as ‘trainability’ - the idea that genetics control how people respond to exercise. In 2010, a landmark study looked into the genetics of why some people respond to endurance exercise so robustly, while others do not. Some men and women, for example, will take up running and quickly become much more aerobically fit. Others, however, doing the same programme will develop very little aerobic fitness. This study found that there are about 30 variations in how genes are expressed that significantly affect how fit a person becomes and that genes affect this response to exercise by around 23 percent.
If you’re intrigued to know how much your responsiveness to exercise is determined by your genes, you can now purchase a simple test to tell you. Yet only those who have a score in the lowest 18th percentile are classified as ‘low responders’. The advice for this group will be to focus on setting achievable fitness targets within these limitations. For those who find they aren’t low responders yet aren’t seeing the training results they are hoping for, they should look at amending their current exercise programme.
Of note, these tests only assess aerobic fitness and it’s important not to forget the many other beneficial effects of exercise such as muscular strength, lowering of blood pressure, cholesterol and blood sugars, help with weight loss and reduced risk of many cancers as well as the positive mental health benefits. So whether you’re a low or a high responder, there is no doubt that staying active will boost your current and future health.