Today, we know that individual differences in fitness and exercise performance are both due to training and genetics. However, scientists still wonder, how much do our genes actually contribute to different fitness phenotypes?
The world’s leading exepert on the genetics of exercise performance, Professor Claude Bouchard, has spent several years getting closer to solving the puzzle. He has published more than 150 papers on related topics and is also giving a lecture at our Seminar on Exercise in Medicine in Trondheim on December 14-15th, 2011.
Twin studies to determine genetic impact
One of the best ways to predict the genetic influence on different fitness phenotypes is by doing twin-studies. In twin-studies researchers most often study both identical twins and non-identical twins. The identical twins are genetically similar, whereas the non-identical twins only share 50% of their genes. If genetic factors are important for the trait we are studying, the identical twins will turn out to be more similar then the non-identical twins.
For instance researchers can compare the twins’ resting heart rate, their blood pressure, their muscle strength, their endurance capacity etc. By complex mathematical models the researchers are able determine the amount of genetic influence on the trait in question (providing a percentage of the total influence on the trait, given that environment factors account for the remainder).
Years of research have led to these conclusions:
- An individual’s hemoglobin level has a large genetic component. Hemoglobin is the oxygen-carrying component in the blood, and is likely to influence an individual’s maximal oxygen uptake (VO2max). This is also likely to play a part in the ability to succeed in endurance sports like running, biking and skiing.
- Genes play a large part in determining heart structure, size and function. Since the size of the heart is an important determinant of stroke volume – a limiting factor in aerobic performance – it appears that genetics play a crucial role in determining the aerobic capacity potential.
- The capacity of skeletal muscle to utilize oxygen has strong genetic components. The maximal ability of skeletal muscle to utilize oxygen will depend on the proportion of slow twitch muscle fibres in the working muscle (slow twitch muscle fibres have a higher capacity to consume oxygen than fast twitch muscle fibres). Strength or endurance training is unable to change these proportions, but it can alter the capacities of these fibres. For example, endurance training will increase the ability of certain fast twitch muscle fibres to use oxygen, thereby increasing the endurance potential of the muscle.
- Researchers have estimated that 25-90% of an individual’s maximal oxygen uptake is determined by genes. Despite the growing number of studies on this issue, there is still a large uncertainty of the genetic contribution to VO2max. In the last years, it does however seem like researchers, including Dr. Bouchard, agree that the heritability is above 50 %, but not as much as 90 %. Interestingly, the researchers found that the genes inherited from the mother are very important in determining the offspring’s aerobic capacity. So choose your mother with care! 🙂
Written by Anja Bye, Postdoctor at CERG.