Rest in Peace to bodybuilder, gym owner, author, Doug Brignole at age 63, friend to champion Pro, Bill Pearl
At 15 years old, he could not afford a membership, so Bill allowed him to clean showers etc. in exchange for a membership at Bill's Pasadena, CA gym.
Doug went on to attain a championship physique, open his own gym and become a successful author and authority on weight training with his book, The Physics of Resistance Exercise.
Here's a good video where he talks about injuries / rehab / cortisol / adrenaline etc.
https://www.youtube.com/watch?v=Uy7IWSrKAB8