Give Your Muscles A Rest

Taking time off between workout doesn't make you lazy- it makes you smart. The muscle damage caused by pumping iron saps your strength for up to two days. In fact, lifters who didn't wait at least 48 hours between bench-press workouts saw a significant drop in the number of reps they could perform. Resting a muscle group properly allows it to heal completely, which is part of the growth process. And strength is a great gauge: If you're weaker from one workout to the next, you need more recovery time. Of course, you can still train on back-to-back days, as long as you're working different muscles-upper body one day and lower body the next, for example.