The problem with most sports training programmes - and it has bugged me since I was a kid - is that their observed effectiveness suffers from survivorship bias.

The problem with most sports training programmes - and it has bugged me since I was a kid - is that their observed effectiveness suffers from survivorship bias. People that aren't doing well on the programme - are not making progress or get injured - simply stop following it and drop out. It would be really nice to see the stats from an actual coach on every trainee of theirs, what their outcome was or why they stopped, with some before/after stats as well.