What do we know about genetics and physical traits in the area of athleticism?

This is not a question about why some people are more athletic than others. The question is what factors (genetic, environmental etc) contribute to a group of people being more athletic than another group. And if it is mainly genetics, what factors could contribute to this?

Can someone be trained to do certain tasks from an environmental influence at a young age, and can this environmental influence be passed on to offspring?

I hope I explained myself well enough that you know what I am getting at. Thank you.