The leg extension machine is a piece of equipment that is best classified as a resistance training type of exercise. Leg extension machines come in all shapes and sizes as they are manufactured by quite a few different makers. Leg exercise equipment has a history that is relatively young: It can be traced back to only the 1950s with Jack LaLanne and Harold Zinkin. If you go into a gym or a weight room today, you should see this quite common piece of exercise equipment there. It is important to remember that while the leg extension machine does target the legs, it should not be considered a total leg workout, something that only the deadlift or the squat are considered to be.

The part of your body that gets the intended workout during leg extension exercises is your quadriceps muscles in your legs. Because it targets primarily this muscle group, the leg extension machine provides isolated exercises. The quadriceps are a large group of muscles that include the four main muscles on the front of your thighs. The quadriceps, as a note of significance, is the leanest and strongest muscle in the entire human body.

As an open chain exercise, the leg extension machine puts your foot in a free movement as you do the exercise. Some of these open chain exercises may put something called shearing forces on your knee, thus making the joints in your knee unstable. Due to the imbalance the leg extension machine creates on your quadriceps versus your hamstring muscles, your knee may be at risk for injury. To guard against this potential injury, ensure that you position yourself properly on the leg extension machine. As you sit on the machine's chair, place your feet on its foot pads in such a way that your shins touch it just above the ankles. After that, be careful to adjust its seat so that the back of your legs is adjacent to the machine's chair, and so that your back enjoys full support by the back of the seat.

There is not much more than one type of exercise to do on the leg extension machine, seeing as how straightforward it is to use. Basically, after you choose the weight you want, all you do is sit on the machine with your legs underneath the pad and your hands grasping the side bars. While exhaling, extend your legs out to the fullest, but make sure the rest of your body remains still and in place. At this contracted position, pause for a moment or two. While inhaling, lower the weight back down to its original position, but take care not to exceed the 90-degree angle limit. Repeat this procedure as many times as is comfortable.