Roughly half of all Americans say they exercise regularly. Want to join them? Maybe you don't want to join a gym because you lack the time or money -- or you are too embarrassed to exercise in front of other people. No problem. You can train at home and see great results.

You can work out in the convenience of your own home with no equipment, using exercises like calisthenics. Traditional push-ups are great for your arms and shoulders and can be made easier or more difficult, depending on the technique.

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For instance, you can put your feet up on a chair, or do one-handed pushups to make them more difficult. To make them easier, you can put your knees on the floor. A variation of the regular push-up is the wall-leaning vertical push-up. Start with your arms outstretched six inches from the wall; lean into the wall, and place your hands shoulder-width apart.

Continue the exercise by doing a regular push-up on the wall with your body straight. A chair dip, done by standing in front of a chair, placing your hands on the seat, dipping your hips until your elbows reach a 90-degree angle, and pushing back up again is a great exercise for your shoulders and triceps.