The single leg extension is a great exercise for isolating the quads. Sit on the leg extension machine and adjust it so that the leg pad sits on your ankles.

Then adjust the back rest so that your knees are just off the end of the seat. Select the weight you want to use on the stack.

Take the weight off the stack by extending your legs slightly. This is the starting position for the exercise.

Holding onto the handles for stability, and bending at the knees only, extend your left legout as far as possible.

Hold for a count of 1 while squeezing your quads, and then slowly lower the weight back to the starting position. The weight should not touch the stack.

Repeat for desired reps and then repeat using your right leg.

Exercise Tips:

Use a slow and controlled movement - do not "kick" the weights up.

Pause at the top of the movement and squeeze your quads. This adds intensity to the leg extension.

Leg extensions can be used as a pre-exhaust exercise for squats or other big compound movements. It is also used for the second exercise in compound/isolation supersets.

Do not drop your toes down and back beyond your knees. At no point should your knees track out over your toes as it causes undue stress on the knee joints.