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.
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.)
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.
A better exercise: Incline Pull-ups
Keeping your torso stiff, pull your chest to the bar 10 to 15 times. To make it harder, lower the bar; to make it easier, raise the bar.
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.
A better exercise: Incline Push-Ups
Aim for 15 to 20 reps. If this is too easy, progress to regular push-ups, and aim for five to eight reps.