Five common exercises you should never do.
By Trevor Thieme

The test of time usually works. Futile fads like sweatboxes, vibrating belts, and most tips from the odd, ponytailed Tony Little have died out quickly enough. But a few bad exercises have persisted, and exercise physiologists don't see how these ineffective and sometimes dangerous maneuvers have survived. Take the sit-up, which can be quite damaging if done improperly. "Locking your hands behind your head can torque your cervical vertebrae, " says David Pearson, Ph.D., director of the Strength Research Laboratory at Ball State University. The result: neck pain. In fact, sit-ups are the kind of "unsafe behavior" scientists at Arkansas State University say account for 63 percent of all weight—lifting–related E.R. visits, so purge them and the rest of these body breakers from your routine.

1. Posterior (Behind-the-Neck) Pull Downs: This exercise rotates your shoulders into a position that strains your rotator cuffs, paving the way for inflammation. "I've also seen guys pull the bar down so fast that they crack their spinous processes [little nubs on top of the vertebrae]," says Pearson.

Safe Alternative: Anterior (Front) Pull Downs: Not only is pulling the bar to your chest easier on your shoulders, but "it flexes the lats through a greater range of motion, accelerating muscle growth," says Pearson.

2. Behind-the-Neck Shoulder Presses: Just as posterior pull downs strain your shoulders on the way down, this exercise hurts them on the way up. Pearson says it also puts too much stress on the acromioclavicular joints (those little knobs on the tops of your shoulders), which can lead to an overuse injury commonly referred to as weight lifter's shoulder.

Safe Alternative: Alternating Shoulder Presses: Sit on a Swiss ball and hold a pair of dumbbells overhead with your arms straight and palms facing each other. Next, bend your left elbow and lower your left arm, moving your elbow out to the side, until your upper arm is parallel with the floor. Press it back up and repeat with your right arm.

3. Straight Bar Curls: If you let your arms hang loosely by your sides, you'll notice that your palms face inward. The problem with straight bar curls is that they lock your arms into an unnatural palms-up position. "In so doing, you're stressing your elbow joints, and that can lead to tendinitis," says Pearson.

Safe Alternative: E-Z Bar Curls: The bar is angled to put your elbows in a more natural neutral position.

4. Leg Extensions: The four parts of your quadriceps are designed to work together as one, but a recent study in Medicine & Science in Sports & Exercise found that leg extensions activate the sections slightly independently of one another. Even a five-millisecond difference can cause uneven compression between the kneecap and thighbone, inflaming the tendon that connects the kneecap to the shinbone (a painful injury known as jumper's knee).

Safe Alternative: Squats: To squat safely, place the bar across your shoulders (not your neck) and keep your back straight, bending slightly at the hips through the squatting motion. Proper form is crucial with this exercise.

5. Sit-ups: Not only are sit-ups bad for your neck, but they're also one of the least-effective abdominal exercises you can do, according to a recent study at San Diego State University.

Safe Alternative: Bicycle Crunches: That same study found the bicycle maneuver works the abs and obliques 250 percent better than traditional crunches or sit-ups. Lie on your back with your feet up in the air, then bend your knees at a 90-degree angle. With your hands behind your ears, pump your legs back and forth while moving your armpits (not your elbows) toward the opposite knees.