In an effort to lose weight, build muscles, or any other reason why you exercise, sometimes you may overdo it … intentionally or otherwise. Doing so can have some serious side effects. Exercising realistically can provide these benefits.
Give your muscles time to recover:
When we exercise, especially strength training, small tears called micro-tears occur in the muscle fiber. As these repair themselves, the muscle becomes stronger and bigger. However, if you don’t give the muscle rest, it won’t have time to recover. Most experts agree that one day of rest per week is needed to rest and repair muscles.
Prevent a stall in your weight-loss efforts:
By exercising, people think that is the best way to burn more calories than they eat and as a result lose weight. But in reality, one can over-exercise and actually hit the infamous plateau. When this happens, the general tendency is to train even more to try and break through it. What is needed is less training.
The body has a built-in mechanism where it will stall weight loss if it thinks losing more weight could be detrimental. Rest or at least back-off on your training as the remedy.

Prevent burnout:
Some people train so hard in an effort to reach their fitness goals that they actually do not look forward to training anymore. Everything in life is about moderation and if training is taking up much more than its fair share of your time, eventually you will start avoiding working out altogether. The remedy?
Include at least one day of rest per week as part of your workout schedule. As far as the length of a workout, do what is right for you so that you can still look forward to each workout.

Working out for the wrong reasons:
Why do you exercise or more pointedly why do you over exercise? You should work out because you want to get fit and healthy, not because you want to fit into size 2 jeans when you are a size 12 now.
Be realistic in your goals. No amount of working out will get you to an unrealistic goal. The end result of overdoing your exercising will be burnout – both physically and mentally. The body cannot sustain overtraining.
Instead, train realistically and eat healthy nourishing food in the right portions. By maintaining a 500-calorie per day deficit, you’ll lose about a pound per week. Once at goal, burn the same number of calories as taken in to maintain your goal weight. If you keep your training regimen the same this means adding in about 500 more calories per day to your diet.

Fitness should not be about a number on the scale, but about having toned muscles, being healthy and feeling good about oneself.