I think you'll find this same problem with all of the high paid (physical) jobs, unless you invent the next macarena or something.

Quite possibly true. Unless it builds on things I already know.

What are your areas of physical expertise or experience?

You mean there is no physical activity that directly builds on top of a software engineering education? Yeah, I guess it was a stretch.

But I actually think that there might be a middle ground that involves sports and engineering. Perhaps a product or service and a reason to jump on the startup train.

There are, see my above reply about elevator mechanics. You are on your feet all day, you carry equipment around, you use hand tools, however you extensively troubleshoot and get creative with solutions to electrical and mechanical problems. So, combines the physical activity of a construction type of job (very rewarding filling), with the ingenuity/troubleshooting of programming.

I just mean that you said you are very active, so you maybe able to build on one of those specific activities. For example there are people who design artificial waves for surfers. This involves a lot of optimization work, But of course you also need it as the waves.

Suprisingly little training involved. A FOAF started doing this stuff on a dare and was well on his way 9-ish months later.