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Why the Leg Extension Machine Is Still Around

Thursday, September 23, 2010 5:42 AM

The leg (or knee) extension machine has endured as one of the most popular exercise machines in health clubs, school weightrooms and physical therapy clinics. Here are five reasons for its popularity:

1. Most individuals will avoid squats because they are way more taxing than leg extensions. In other words, our culture teaches us to use the easiest route, not the most rewarding one. However, in life you get out what you put in. No amount of leg extensions will equal a full squat in terms of gains in strength, hypertrophy and power.

2. Most geeks will rationalize (i.e., “rational lies”) that isolation exercises are better than compound exercises – this way they can repress their feelings of guilt for avoiding demanding, gut-wrenching exercises. Many trainees believe leg extensions isolate the quadriceps better. Not so. Even though your quadriceps are actually isolated during leg extensions, this exercise has very little actual transfer capacity to daily activity.

3. The early ’70s philosophy of “machines are better than free weights,” which was launched by exercise equipment companies such as Universal and Nautilus, made gym owners jump on the bandwagon and purchase leg extension machines by the thousands. (As with Coke, this turned out to be a major marketing success story.)

4. You can be a motor moron and still be able to perform the leg extension.

5. Most personal trainers are hired on two premises: they have a pulse, and they’re old enough to make someone sign a contract. Not having to be concerned about coaching enables them to focus on making sales.

If you’re still on the fence about using leg extensions, here are a few facts to consider.

The leg extension exercise is a so-called “open chain” exercise, which means that the resistance encountered is overcome by the force applied by the working extremity. With this type of exercise, the recruitment patterns of the muscles and kinematics of the joints are completely out of phase with a closed-chain activity, such as squatting or skating.

When you walk or squat, your femur (the upper thigh bone) moves across your tibia (a lower thigh bone). As it does so, the body must balance its center of gravity over the base of support (or within a recoverable-stance phase), which requires force-coupled actions from a variety of muscle groups. In contrast, the fixed, stable position inherent in the leg extension doesn’t require the recruitment of the numerous synergistic muscles that are involved in walking. In other words, due to the unidimensional action of the leg extension, the brain can disproportionately recruit prime movers in relation to stabilizers and neutralizers. As such, these smaller muscles don’t get the proper workout they would get in a squat.

Of course, the squat is an exercise that needs to be taught properly, and it’s not always the best option for a beginner who has certain orthopedic issues. If you want to learn how to squat properly, I suggest that you enlist of a PICP coach certified at Level 2 and beyond.

To find a certified coach near you, go to: http://www.charlespoliquin.com/TrainerDirectory/FindaCoach.aspx
 

Copyright ©2010 Charles Poliquin

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