I play college baseball, and we lift almost year round. Right now we lift three days a week, MWF. I think there is a better approach. Here's what I do when I lift on my own, and I've personally seen drastic results in this approach. Lift one day Upper body and arms, next day lift lower body and back, next day rest, then repeat. On a three day cycle like this you can really lift hard on your large muscle groups. It's been shown that large muscle groups, legs, chest, even biscep and tricep need two full days of rest the fully recover. One day isn't good enough. However, for smaller groups like forearms you can lift them everyday without much trouble, if you really wanted to. A lot of people try to do as much weight as they can for 4 reps or something stupid like that. Maximum muscle growth will occur after breaking down the muscle for 8-12 reps for 3-4 sets. It's also important to eat a lot of lean foods, but make sure to get a well balanced diet. I take two protein shakes per day when I work out along with three square meals a day and healthy snacks in between.