Leg extension machines are extremely popular in gyms. People strain away on them for reasons of either health or vanity. Here are three reasons why the leg extension machine should be avoided.
- No stabilisation necessary, meaning the quads are not trained as we normally use them in real life. The quads, the muscles on the front of the thigh, are designed to work as we walk, run, squat, lunge and so on. They contract when our foot is in contact with the floor; this is called closed chain: our body moves over the earth. Indeed, our quads do contract when we kick the cat or a football, neither of which are normally heavy objects; this is an example of open chain movement. And, indeed, if we choose to kick an enormously fat cat, we would almost certainly damage our knee. Plus make the cat laugh at us. So since our quads usually work as we propel ourselves about the planet, they need to work synergistically with various stabilising muscles and the other muscles of the legs. Sitting on a leg press machine does not require those stabilising muscles to work, with the result that our quad strength can quickly outstrip the strength of, say, our gluteus medius. Injury wise, this is not a happy scenario. And also, because of this, our brain stops our quads from getting any stronger, so an insuperable plateau will be hit. So if we are a runner trying to strengthen our quads on a leg extension machine, we may temporarily be able to run a little quicker, but our gluteus medius will not be up to the job of stabilising our hips as we run and so we will hit knee or ankle pain sooner rather than later. This also means, girls of either sex, that the bottom will be wiggling and bouncing about like a jelly on springs. Not goooood.
- Force curve of the quads. The leg extension machines found in gyms have a force curve that does not match the force curve of our quads. So our quads hit maximal tension about half way through, whereas the machines are designed for maximal tension when the leg is straight. Interestingly, there is a leg extension machine that does effectively match our quad’s force curve – and Charles Poliquin owns one. Apparently people don’t like using it because when the leg is straight, it doesn’t feel like particularly hard work, so they don’t get the burn. And so the chances of one appearing in a gym near you are absolutely nil. ((Charles P is an absolute geek when it comes to gym toys. He is extremely proud of his leg extension machine and went to considerable efforts to get his hands on it since they aren’t manufactured any more. His gym is full of wondrous bits of kit – weird shaped bars for doing reverse bicep curls with, making it exceedingly difficult to curl the bar alone and peculiar devices for grip strength. A gym boy’s paradise.))
- Knee stability and safety. If you still insist upon using the leg extension machine, then it is wise to get as much of the back of the thigh on the seat as possible: as we straighten the legs, the weight is over our ankles and the back of our knees are dangling mid air. If we don’t lock out the knee, the inner knee muscle, short hand name: VMO, does not contract fully, leaving us with it underdeveloped and wide open for knee pain. But if we do lock out the knee, essentially the knee joint is under pressure to bend backwards. Eek.
If we are terribly weak – post operation/trauma/recently bed ridden – then there is a case for using the leg extension machine for a very short period of time. We will be so weak, we can only use it 2 legged on the top plate – WEAK! After that, we really do have to progress to either the leg press machine, or, even better, light body weight work.
The best way to strengthen the quads is by full split squat variations ((Split squats are the static version of lunges. Lunges are dynamic movements, stepping forwards and back – or doing a walking lunge – whereas a split squat you put one foot in front and just go up and down until exhausted.)) or one of the many types of full squat. One leg rehab work is good to do – like the Petersen step up series. These start quite easy, and as soon as we are on one leg, our hip stabilisers have to get out of bed or we wobble about in a most humorous manner. As you strengthen your quads a) don’t neglect your hamstrings and b) look out for wobbly knees, hips sticking out or the body side bending. All these faults give strong clues as to what else isn’t pulling its weight in stabilising us and needs strengthening. The only weak stabiliser apparent on the leg extension machine is the inner unit as we arch our back in an effort to lift an increasingly heavy weight.