Say NO! to 10 Exercise Machines

Seated Leg Extension Machine
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.

Seated Shoulder Press Machine
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.

Seated Behind-the-Neck Lat Pull-Down Machine
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.

Seated Chest Fly Machine
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.

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.

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.

Seated Leg Press Machine
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.

Smith Machine Squats
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.

Roman Chair Back Extension Machine
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.

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.


More at :  http://health.yahoo.net/articles/fitness/photos/10-exercise-machines-avoid#10