It might! Masturbation takes a lot out of the body and many people don't realize that. It wont affect you as much as sex might but still it does make a difference. But having said that, if you have good stamina, there is no reason to fret. All you have to do is to drink lots of fluids before you workout. Get some energy into you and then go in for a workout. Protein bars, shakes and fruit juices will help restore some of the lost energy. You could also try eating some chocolates, but don't overdo it. Good Luck!