Ischemic preconditioning

Heart attacks are a situation where the blood flow into the heart muscle is decreased drastically or cut off completely. In people who have suffered minor ischemic incidents prior to the major one (ischemia, from the Greek, meaning to restrict blood flow locally due to a mechanical obstruction) the heat muscle presents with less damage than for those who only had the one incident.
This got researchers wondering if it would work for maximal effort exercise. Having now been tested with the legs of cyclists and the arms of swimmers, it looks like the answer is a qualified yes. You can read for yourself here (thanks Dan for the link) but the gist is that nationally competitive swimmers who tried this took a time off equivalent to 2 years of high level training and cyclists had a similar improvement.
The protocol is 3x5min with blood flow reduced, with 5min recovery in between each one just prior to competition time.

Wish I had the opportunity to test it out.