THE | DIET DETECTIVE^®

One-Arm Row
Don't move your back. This popular non-machine move (which tones the upper back) seems simple enough. Lean over a bench, support your weight with one hand on the bench and extend the opposite arm toward the floor, weight in hand. By drawing the weight up to the side of the chest, you develop and shape the upper back muscles, but only if you do the move correctly. "The back needs to be parallel to the floor," cautions Jeffrey Horowitz, head pro trainer at Washington Sports Clubs in downtown Washington, D.C. "not bending over far enough lets your shoulders assist in pulling the weight upward."

It's these smaller muscles that tend to tucker out first, preventing you from getting the workout you're after. Keeping your back straight is one thing, keeping it still is another. "Twisting your torso as you raise the dumbbell is what most people believe is working the back muscles through a greater range of motion," says Horowitz. "What you're actually doing is allowing the obliques, lower back and shoulders to drag the weight up for you."

Do lock your back parallel to the floor. Your chest should be facing straight down toward the bench below you. As you perform the movement, close your eyes and concentrate on which muscles are in motion. "The only part of your body that should be moving throughout the exercise is the arm that's raising the weight," says Horowitz.

Lunge
Don't lean too far forward. Most people believe that the farther you extend your body forward as you lunge, the more you'll emphasize and develop your thigh muscles. Not true. "Your weight needs to stay on your heels," says Ann Marie Miller, codeveloper of the New York City Ballet Workout. "Shifting too far forward transfers your weight onto your toes, putting excessive torque on your knee joint."Lunge

Do keep your knee directly over your toes. Instead of lunging forward at a mirror, try standing sideways to it so you can watch how far you come down. If your knee moves past your toes, you're flexing your knee beyond 90 degrees and risking injury.

Dumbbell Curl
Don't let your wrists bend backward. Letting the weights pull your wrists back as you curl them upward is easy. However, bending the wrists back or forward takes the work away from the biceps muscles and places stress on the tendons in the wrist joint instead. "What this does is create a shelf to rest the weight on," says Miller. "This may feel comfortable early on, but doing it repeatedly can lead to carpal tunnel syndrome." Bending the wrists also leaves the muscles within the wrists and forearms constantly stretched, which can weaken them over time.

Do keep your wrists in line with your forearms. Keeping your wrists aligned with your forearms strengthens the tendons while keeping the emphasis of the exercise on the biceps. Miller suggests curling the weight up as slowly as possible, since raising the weight too quickly can make it harder to keep the wrists aligned. If you find yourself struggling with the "puppy paws" problem, try switching to a lighter weight and building up from there.

Chest Press
Don't lower the weights too far. Many trainers will have you lie on a bench with a set of dumbbells raised over your chest and have you lower the weights all the way down to your sides. Once your arms bend at an angle of 90 degrees or less, the chest muscles lose their ability to contract properly, causing the effort of supporting the weight to shift to smaller, weaker muscles within the shoulder joint. By dropping your elbows down, you leave your arms no choice but to bend at an angle less than 90 degrees, turning your chest-building exercise into a potentially dangerous shoulder move.

Do keep your biceps even with your chest. Never let your upper arms go any farther than parallel to the floor. The easiest way to remember this is to make sure your elbows are never lower than your shoulders. Tip: Since it's not wise to twist your neck during this exercise to see if your arms are in the correct position, have a partner tell you when to stop. Soon you'll be able to feel when you've got it right.

Shoulder Press
Don't pin your arms back. Raising a set of light dumbbells over your head, lowering them to your sides and then pressing them back up can tone and sculpt the shoulders. The problem? "Most people feel the need to draw their shoulders back to angle their arms right alongside their ears," says Horowitz.

This may look like proper form, but the position actually redirects some of the effort onto the rotator cuff, a series of tiny stabilizing tendons and muscles that aid in rotation within the shoulder joint. "It's these tendons that end up tiring out before the exercise has had a chance to thoroughly work your shoulder muscles," says Horowitz. This position can also lead to shoulder impingement, a persistent inflammation of these tendons that can hinder your exercise routine and even affect your normal daily activities.

Do shift your arms inward. Performing the exercise in front of a mirror is the easiest way to fix the problem. Try lowering your arms until they're bent at 90-degree angles and then look at your elbows. "If they're lined up with your sides, you have them pulled back too far," says Horowitz. "Instead, rotate your arms forward until your elbows are in line with your chest, positioning your arms at a slight angle in front of your body."

This position may feel unnatural, but it utilizes larger muscle groups within the shoulders and upper chest, making it safer and easier to raise the weight. One last tip: Turn your hands so that your palms face each other instead of the mirror. "This works the shoulder through more of a natural range of movement, leaving the rotator cuff out of the equation," says Horowitz.

Squat
Don't lock your knees. We tend to straighten our legs after each squat for a reason: Our muscles are tired. While locking the knees takes the weight off the hamstrings and quadriceps momentarily, unfortunately it redirects that pressure onto the knee joints. "Each time you lock your legs under pressure, you end up shearing the patella tendon just below the kneecap," says Rich Guzman, founder of L.A. Rox training consulting firm and celebrity personal trainer for more than 30 stars, including Minnie Driver, Jennifer Beals and Sheryl Crow. "Once you wear this tendon down, your knees can develop a chronic pain that persists even when you're not exercising."

Another reason to stay unlocked is stability. "Whenever you move during a standing exercise, you change your center of gravity, forcing your body to call upon certain muscles to keep itself stable," says Guzman. The leg muscles (quadriceps, hamstrings and hip flexors) are usually the ones used to help out, but locking your knees prevents these muscles from doing their job effectively. "All the effort gets redirected to the lower back and abdominals, which are already working to keep the body straight," says Guzman.

Do leave those legs straight and loose. Not straightening your legs at the top of the movement may feel like you're cheating yourself out of work, but you're actually forcing your legs to work even harder by keeping the muscles contracted. You'll also allow the quadriceps to keep you from toppling over.

One-Arm Triceps Extension
Don't let your arm wing out to the side. Raising a dumbbell above your head, lowering it down to shoulder level by bending your elbow and then raising it back up is a guaranteed way to firm up the back of your arms. However, the move isn't always easy to do without some assistance. "It's difficult for many people to perform the move without their elbow veering out to the side," says Horowitz. This prevents the exercise from working all three heads that make up the triceps, because the shoulder muscles end up coming to the rescue. This extra help can also trick you into believing you're capable of using more weight than you may be ready to handle.

Do lock your arm into place. Using your opposite hand to gently draw your upper arm close to the side of your head will keep it perpendicular to the floor. This position keeps all the attention of the exercise focused on the three heads of the triceps while letting you feel them working, which can be an extra incentive. From this position, you can choose to either drop the weight straight back behind your arm or along the back of your head - whichever motion feels the most natural to you.