Before the 1970s and the advent of bodybuilding, almost all exercises relied on body weight for resistance. Oh, sure, a small percentage of people used medicine balls, barbells, and dumbbells for their workouts, but even dedicated exercisers relied on the most basic exercises, such as pushups, pull-ups, and sit-ups.

Once people began to understand more about how the human body became stronger, exercise machines were invented, and more exercises were designed for the use of those machines. But the fact is, body-resistance exercises (which use only the body and not weights) are, in many ways, the toughest moves around. In the first place, most of us can't lift more than our own bodies. So, for example, if you do a pull-up, which uses a number of muscles, including your biceps, and then if you do a biceps curl, chances are the resistance will be roughly the same, since the 8 or 10 pounds with the dumbbell will be equal to the percentage of your upper body weight that your bicep carries during the pull-up.

The following program comprises six exercises. If you try this program right now, chances are you will only be able to do one or two of each move — that's how hard they are. In fact, these exercises are such good indicators of true fitness that you might consider doing this program at least once or twice a week (it doesn't take long, especially if you aren't that strong and can only do one or two of each move) just to see how you progress. The individual exercises are listed first, with details of each exercise following:

• Squat thrusts

• Pull-ups (or pull-up variations)

• Pushups

• Walking lunges

• Crunches

• Supermans

Squat Thrusts

Stand with your feet hip distance apart, shoulders away from your ears, abs contracted, and hands on your hips. Bend your knees and come down into a full squat so that your butt is right on top of your heels, which are lifted off the floor. Bring your hands down to the floor as you get into this position, making sure they are secure, because in the very next second you're going to throw your legs out behind you and come into what looks like the top section of a pushup. Then come right back to the squat and stand up, bringing your hands to your hips. The squat thrust works your heart (because you're moving your limbs quickly), as well as your arms, chest, back, legs, and butt. Try to do this ten times, working your way up to fifty.

Pull-ups

With a pull-up bar in your doorway, put your hands on either side, palms facing toward you. Grasp the bar very securely. Pull yourself slowly up, bending your elbows and keeping your back and abs straight and contracted. Bring yourself up and over the bar. Then lower yourself down slowly. When you get to the bottom, don't lock your elbows. Try to work your way up to fifteen.

Pull-up Variations

Pull-ups are a great exercise, but you do need a bar to do them. If you don't have one, they're only about $20 at a sporting goods store. Once you get a bar, put it up in a doorway.

The other thing about pull-ups, though, is that they are tough! If you can't do them (and most women can't), here are a few other options:

• Put a bar or dowel across two chairs, and do the pull-up lying down on your back. You won't be lifting your full body weight, but you will still be exercising your upper body quite effectively.

• Try negative pull-ups. Put a chair under the bar so that when you stand on the chair the top of your head is level with the bar. Pull yourself up and bend your knees so that you're holding your weight at the top of the move (with your arms bent), then slowly straighten your arms and let your body go down slowly.

Pushups

Put your hands and knees on the floor, then straighten your legs so that you're balancing on your toes and hands. Your fingers should be facing forward, and the back of the neck should be long so that you're looking at the ground in front of your fingers. Be sure your body is long, too, from your heels to your head, and that your abs are contracted, your hands are directly under your shoulders, and your shoulders are pulled away from your ears. Bend your elbows and lower your body toward the floor without letting your abs sag down. Start with one and work your way up to twenty.

Walking Lunges

Stand with your feet a few inches apart, with your shoulders relaxed and your abs contracted. Step forward with your right foot and bend your left knee toward the ground as you also bend your right knee. As you come up, bring your left leg forward and do the lunge with the opposite leg. Go across the room and back, doing a total of twenty lunges on each leg.

Crunches

Lie down with your back pressed gently into the floor, your elbows bent, your hands behind your head, your shoulders away from your ears, your abs contracted, and your head and shoulders lifted off the floor. On an exhale, come up about six inches, eyes looking in a diagonal at the ceiling. Come back down when you inhale without letting your head and shoulders go down to the floor. Repeat up to twenty times.

Supermans

Lie with your stomach on the floor, arms out straight in front of you, legs straight behind you, and face the floor (if you're uncomfortable with this, put a folded towel under your forehead). On an inhale, raise your arms and legs just a few inches above the floor. On an exhale, come down. Repeat up to fifteen times.