Defenders of stationary equipment argue that machines are designed to limit what you can do wrong. But seated machines often put heavier loads on the back and joints than is necessary, and almost always miss the mark when it comes to replicating the movements found in everyday life, according to Ultimate Back Performance and Fitness, by Stuart McGill, PhD, a professor of spine -biomechanics at the University of Waterloo, in Ontario. For this list of exercises, we consulted McGill; Nicholas DiNubile, MD, author of

FrameWork: Your 7-Step Program for Healthy Muscles, Bones, and Joints; and trainer Vern Gambetta, author of Athletic Development: The Art & Science of Functional Sports Conditioning.

1. Seated Leg Extension

What it's supposed to do: Train the quadriceps

What it actually does: It strengthens a motion your legs aren't actually designed to do, and can put undue strain on the ligaments and tendons surrounding the kneecaps.

A better exercise: One-legged body-weight squats. Lift one leg up and bend the opposite knee, dipping as far as you can, with control, while flexing at the hip, knee, and ankle. Use a rail for support until you develop requisite leg strength and balance. Aim for five to 10 reps on each leg. (If you are susceptible to knee pain, do the Bulgarian split squat instead, resting the top of one foot on a bench positioned two to three feet behind you. Descend until your thigh is parallel to the ground and then stand back up. Do five to 10 reps per leg.)

2. Seated Military Press

What it's supposed to do: Train shoulders and triceps

What it actually does: Overhead pressing can put shoulder joints in vulnerable biomechanical positions. It puts undue stress on the shoulders, and the movement doesn't let you use your hips to assist your shoulders, which is the natural way to push something overhead.

A better exercise: Medicine-ball throws. Stand three feet from a concrete wall; bounce a rubber medicine ball off a spot on the wall four feet above your head, squatting to catch the ball and rising to throw it upward in one continuous motion. Aim for 15 to 20 reps. Alternative: Standing alternate dumbbell presses. As you push the right dumbbell overhead, shift the right hip forward. Switch to the left side.

3. Seated Lat Pull-Down (Behind the Neck)

What it's supposed to do: Train lats, upper back, and biceps

What it actually does: Unless you have very flexible shoulders, it's difficult to do correctly, so it can cause pinching in the shoulder joint and damage the rotator cuff.

A better exercise: Incline pull-ups. Place a bar in the squat rack at waist height, grab the bar with both hands, and hang from the bar with your feet stretched out in front of you. Keep your torso stiff, and pull your chest to the bar 10 to 15 times. To make it harder, lower the bar; to make it easier, raise the bar.

4. Seated Pec Deck

What it's supposed to do: Train chest and shoulders

What it actually does: It can put the shoulder in an unstable position and place excessive stress on the shoulder joint and its connective tissue.

A better exercise: Incline push-ups. Aim for 15 to 20 reps. If this is too easy, progress to regular push-ups and plyometric push-ups (where you push up with enough force that your hands come off the ground), and aim for five to eight reps.

5. Seated Hip Abductor Machine

What it's supposed to do: Train outer thighs

What it actually does: Because you are seated, it trains a movement that has no functional use. If done with excessive weight and jerky technique, it can put undue pressure on the spine.

A better exercise: Place a heavy, short, looped resistance band around your legs (at your ankles); sidestep out 20 paces and back with control. This is much harder than it sounds.

6. Seated Rotation Machine

What it's supposed to do: Train abdominals and obliques

What it actually does: Because the pelvis doesn't move with the chest, this exercise can put excessive twisting forces on the spine.

A better exercise: Do the cable wood chop, letting your heels turn freely with your torso. Aim for 10 to 12 reps.

7. Seated Leg Press

What it's supposed to do: Train quadriceps, glutes, and hamstrings

What it actually does: It often forces the spine to flex without engaging any of the necessary stabilization muscles of the hips, glutes, shoulders, and lower back.

A better exercise: Body-weight squats. Focus on descending with control as far as you can without rounding your lower back. Aim for 15 to 20 for a set and increase sets as you develop strength.

8. Squats Using Smith Machine

What it's supposed to do: Train chest, biceps, and legs

What it actually does: The alignment of the machine the bar is attached to a vertical sliding track makes for linear, not natural, arched movements. This puts stress on the knees, shoulders, and lower back.

A better exercise: Body-weight squats. See "Seated Leg Press."

9. Roman Chair Back Extension

What it's supposed to do: Train spinal erectors

What it actually does: Repeatedly flexing the back while it's supporting weight places pressure on the spine and increases the risk of damaging your disks.

A better exercise: The bird-dog. Crouch on all fours, extend your right arm forward, and extend left leg backward. Do 10 seven-second reps, and then switch to the opposite side.

10. Roman Chair Sit-Up

What it's supposed to do: Train abdominals and hip flexors

What it actually does: The crunching motion can put undue stress on the lower back when it is in a vulnerable rounded position.

A better exercise: The plank. Lie facedown on the floor. Prop up on your forearms, palms down. Rise up on your toes. Keep your back flat and contract your glutes, abdominals, and lats to keep your butt from sticking up. Hold this pose for 20 to 60 seconds.

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