When most of us think about getting in shape, we imagine ourselves exercising vigorously day after day. This is actually not the way to do it. Strenuous exercise is only one component of a good training regimen. It is highly important to include rest in your work-out schedule. I make a point of monitoring my energy level and relaxing after 3-4 days a week. By resting, I mean taking a break from my tough work-out and do something lighter such as walking. The reason this is vital is your muscle needs time to repair.
Doing exercise correctly is more important than doing it excessively. If you use muscles one day such as upper body strength training, you should avoid upper body training the next day. Keeping a balance between training and resting is also a good way to avoid low grade stress injuries. Have the best work-out ever!