How often should you work out?

How often should you work out? Once a week? Twice a week? Every day? There are several things to consider. You have to balance weight management and muscle gains with how much time you're willing to invest.

There are two different activities people do when they try to get in shape. Cardio and resistance training.

Cardio exercises -- are designed to increase the amount of oxygen your body is consuming and burn off fat. Your heart and lungs pump blood to the arteries to deliver oxygen to the working muscles. More oxygen gives your muscles a greater capacity to work. When you do these activities in your "aerobic zone" it means you're burning fat at an optimal level.

Resistance training programs -- are meant to increase your muscle mass. When you workout, the muscles are torn down. As you rest, they rebuild themselves and come back stronger.

The bottom line: Cardio activity is best at burning fat and resistance training is best at building muscle. They should be used together for best results. Now this begs the question, how often should you work out?

Let's face it, most people don't (or won't) spend an hour a day exercising. But you can see results putting in less time. If you're new to working out or have been exercising for less than six months,, here are some suggestions.

When fat loss is your primary goal, you should consider cardio exercise four to six times a week, for at least 30 minutes per session. Don't do this for more than an hour though, because after an hour your body will start eating into muscle to keep fueling your body. Resistance train three days a week for about 30 minutes per session so you don't lose muscle mass as the weight drops off. Your Total Time Commitment: Minimum Three Hours Weekly.

If you want to see even greater weight loss, increase your resistance training to as high as 60 minutes per session. The reason is simple. The more muscle you have, the higher your metabolism is. A higher metabolism burns more calories throughout the day...making the task of losing weight easier. Your Total Time Commitment: Minimum Four and a Half Hours Weekly.

When building muscle is your main goal, drop the cardio activity down to between three to five days a week for 20 to 30 minutes. Engage in a resistance training program for at least three -- at most five -- days a week. Your resistance programs should last between 30 and 60 minutes. If you're short on time, schedule cardio exercise on the same day as your resistance training, and put it at the end of your workout. Your Total Time Commitment: Minimum Three Hours Weekly.

Those recommendations remain fairly consistent for young adults to people all the way up into their 70s and 80s.