Stay Hungry (movie, 1976)

A dishonest businessman asks rich layabout Craig Blake to help him buy a gym, which will be demolished for a development project in Alabama. But after spending time with weightlifter Joe Santo and gym worker Mary Tate Farnsworth, Craig wants out of the deal. The property negotiations turn ugly, causing a brawl at the gym and a spectacle at a big bodybuilding meet, as Craig learns that it's not easy to turn your back on fair-weather friends.