Most people overlook the importance of the days of rest that are recommended during each week of a workout or training routine. These days are crucial not only allowing your body to rest and recharge, but also, to allow your muscles to build and repair themselves so that they can grow bigger and stronger.
One guy I knew wasn't happy with his biceps though he seemed satisfied with the rest of his physique. He would go to the gym and work on his biceps everyday. One day he'd do curls with dumbbells, followed by barbells on day #2 and some other type of curls the next day-without a day in between. He couldn't understand why he wasn't getting anywhere.
When you lift weights as part of a fitness program, and do your exercises correctly so that the last couple of repetitions in your sets are very challenging, small muscle micro fibers are tearing- not in a pathological or dangerous way, but as a response to lifting weight that the muscle would normally not be used to. If you work your biceps on Monday and are sore on Tuesday and Wednesday that is indicative of muscle micro fiber tears- that's ok- you want micro fiber tears. The key is, those tears then repair themselves, or at least try to repair themselves on your days of rest.
The problem with the guy I mentioned earlier is that he wasn't giving his biceps micro fibers a chance to repair themselves. When muscle fibers repair themselves, they usually build mass, hence leading to increased size and strength of the muscle. In fact, not only does working the same muscle groups on consecutive days actually prevent their growth, but overworking any muscle group can lead to serious injury of the muscle, hence sidelining you for much longer than a couple of days.
If you're a die hard who must workout daily, consider "split routines". That's where you can work certain muscle groups on one day and other muscle groups the next. For instance, if you work biceps and back on Monday, you can work chest, triceps and legs on Tuesday. Be careful though. Don't do too much "overlap". For example, doing the bench press not only works your pectoral muscles, it also works your triceps and shoulders- you'd want to do those exercises on the same day and then rest them. Don't do triceps on Monday and chest and shoulders on Tuesday- you'll be overworking the triceps and shoulders.
If you're not sure what exercises work what muscles, buy a cheap weightlifting book, check out a fitness magazine, or have a staff member at your gym show you. As always, be sure to inform your primary care provider when beginning any fitness program and ask him or her about any aches or discomfort you may experience when training.
