Isolation Exercises

If you have an inherent weakness in your quadriceps or hamstring muscle groups, or if you like to do some machine exercises, you'll want to jump on the leg extension machine for quadriceps work and on the leg curl machine for hamstring work. Although the multijoint exercises produce strong and stable legs and are far superior for overall strengthening, sometimes you need a little extra help. These machines isolate the muscles they are designed to work on and allow them to get an overload without other muscles helping out. I usually don't recommend using machines, but with weakness or injury machines are often a helpful adjunct.

The leg extension machine effectively isolates the quadriceps muscle group. If you have a quadriceps deficiency, then consider adding this exercise to your routine. The leg extension machine is useful for performing slow eccentric contractions (in which the weight is lowering) and for selecting a particular range of motion to train in.

A word of caution, though, for those women who try the leg extension machine and feel pain. There may be a reason why this machine bothers the knees and thus a reason why you shouldn't do them. Seek out professional help to evaluate and remedy the problem. Remember to use isolation exercises as an adjunct to your routine and not as a staple.

To understand why the leg extension machine may be the culprit in knee pain, it helps to understand how the joint works and what kinds of forces it may be susceptible to during daily activities and exercises. The patellofemoral joint reaction (PFJR) force is the result of the amount of knee flexion and the force of the quadriceps muscles creating pressure on the patella against the femur. As the knee flexes, the patella is mostly in contact with the femoral groove. This large contact area can help dissipate compressive forces. However, as the knee extends the patella has minimal contact with the groove. This small contact area cannot disperse compressive forces as effectively. Applying this concept to exercise, we find immense compressive forces when we perform a seated knee extension, because the quadriceps has to generate great force to overcome gravity and lift weight. The compressive forces remain great as the knee extends, and the patella cannot dissipate these forces. As the knee flexes while squatting, on the other hand, the PFJR force does increase but the load is more evenly distributed across the patella as it comes into contact with the femur.

Another reason more women have knee pain in the leg extension machine has to do with the design of the equipment itself. Most machines are designed with the standard male body in mind: 5 feet-10 inches, 180 pounds. Of course the manufacturers try to accommodate all different shapes of people by providing movable backrests and ankle bars. But let's face it-hey did not design one especially for you. Your unique body shape may fit with one leg extension machine and not another. You may be trying to force a round peg into a square hole, and that doesn't feel too good on your joints.

LEG EXTENSION

LEG CURL

CALF RAISE

TREADMILL CALVES