There are many different views on proper exercise frequency. In bodybuilding for example, some argue for very frequent training, while others work out only once a week. Some people try frequent training and do well with it, while others burn out. I've had a hunch about why this happens for a while, but I finally came across some supporting research.
My idea centers around prenatal testosterone. In the womb, babies can be exposed to different levels of testosterone. Once born, this exposure can be roughly measured by the ratio of the 2nd to 4th fingers/digits, also called the 2D:4D ratio. The 2D:4D ratio has been shown to be correlated with athletic performance in a number of studies.
This paper looks at the relationship between prenatal testosterone exposure and physical fitness. As predicted, the 2D:4D ratio predicted the "physical education grade" in both young girls and boys. But the authors also looked at exercise frequency. They found that in boys, the 2D:4D ratio was related to a higher exercise frequency, which of course can help lead to higher physical fitness.
My hypothesis is this: men who had higher prenatal testosterone exposure are better "built" for more frequent exercise. All else being equal, if a person can recover from exercise and exercise more frequently, they will be able to perform better than someone who doesn't recover as quickly.
If this idea is correct, it solves a lot of issues I've wondered about. In many sports, you see the respective champions training with a high training frequency. You see this in bodybuilding, where many drug-free bodybuilders do well with frequent training. You see this in running, where the top runners put in tons of miles.
Others try to duplicate this frequency and often end up injured and burn out. Their bodies are just not built the same way. I don't know how many times I've read about this in running, where a person tries to model a champion's routine by putting in 80 to 100 miles a week. They end up seriously injured and have to switch to more moderate miles.
I almost wonder if in the future people will be able to receive an "exercise prescription" based on their 2D:4D ratio. It would probably save a lot of time and frustration in helping a person determine their optimal exercise frequency.
