7 Most Effective Exercises

3. Squats continued...

"What makes an exercise functional is how you perform the exercise," he says. "If you have bad technique, it's no longer functional."

For perfect form, keep feet shoulder-width apart and back straight. Bend knees and lower your rear, says Cotton: "The knee should remain over the ankle as much as possible."

"Think of how you sit down in a chair, only the chair's not there," suggests Gotlin.

Physical therapist Adam Rufa, of Cicero, N.Y., says practicing with a real chair can help.

"Start by working on getting in and out of a real chair properly," he says. Once you've mastered that, try just tapping the chair with your bottom, then coming back up. Then do the same motion without the chair.

Gotlin sees lots of patients with knee pain, and says quadriceps weakness is the cause much of the time. If you feel pain going down stairs, he says, strengthening your quads with squats may very well help.

4. Lunges

Like squats, lunges work all the major muscles of the lower body: gluteals, quadriceps, and hamstrings.

A lunge is a great exercise because it mimics life, it mimics walking," only exaggerated, says Petersen.

Lunges are a bit more advanced than squats, says Cotton, helping to improve your balance as well.

Here's how to do them right: Take a big step forward, keeping your spine in a neutral position. Bend your front knee to approximately 90 degrees, focusing on keeping weight on the back toes and dropping the knee of your back leg toward the floor.

Petersen suggests that you imagine sitting on your back foot. "The trailing leg is the one you need to sit down on," he says.

To make a lunge even more functional, says Rufa, try stepping not just forward, but back and out to each side.

"Life is not linear, it's multiplanar," says Rufa. And the better they prepare you for the various positions you'll move in during the course of a day, the more useful exercises are.

5. Push-ups

If done correctly, the push-up can strengthen the chest, shoulders, triceps, and even the core trunk muscles, all at one time.

"I'm very much into planking exercises, almost yoga-type moves," says Petersen. "Anytime you have the pelvis and the core [abdominals and back] in a suspended position, you have to rely on your own adherent strength to stabilize you."

Push-ups can be done at any level of fitness, says Cotton: "For someone who is at a more beginning level, start by pushing from the kitchen-counter height. Then work your way to a desk, a chair, the floor with bent knees, and, finally, the floor on your toes."

Here's how to do a perfect push-up: From a face-down position, place your hands slightly wider than shoulder-width apart. Place your toes or knees on the floor, and try to create a perfect diagonal with your body, from the shoulders to the knees or feet. Keep the glutes [rear-end muscles] and abdominals engaged. Then lower and lift your body by bending and straightening your elbows, keeping your torso stable throughout.

There are always ways to make it harder, says Rufa. Once your form is perfect, try what he calls the "T-stabilization" push-up: Get into push-up position, then do your push-ups with one arm raised out to the side, balancing on the remaining three limbs without rotating your hips.