Leg extension variations…

Leg extensions are a popular exercise. Like any seated exercise machine, they are relatively simple to do, offer a comfortable workout position and you can feel and see the target muscles working quite clearly.

I’m sure you have experienced that intense burning in your quadriceps muscles as you near the end of a set of leg extensions and you might well think that anything feeling that intense must be doing you good! Well… maybe not.


Firstly, why are leg extensions so painful? What is that profound burning sensation and why is it that this exercise causes your thighs to burn like no other?

The answer is something called ischemia. Ischemia basically means that blood supply (and therefore oxygen) is cut off to your muscles. This causes a rapid and greater than normal increase in lactic acid – which is thought to be the cause of that burning sensation we all love/hate.

Ischemia occurs when you perform leg extensions because the muscles are always tensed and unlike many exercises, there is no point in the range of movement where your muscles get to relax and allow a little more oxygenated blood in. You could get a rest between reps by lowering the weight stack all the way down and taking your feet out from behind the foot rests but, a) your trainer will probably shout at you for ‘clanging the weights’ and b) this is hardly practical.In the end, the discomfort of ischemia is just one of those things and pretty much unavoidable. The main safety concern with leg extensions is something called shearing force.

In simple terms, the shearing force in leg extensions means that your femur (thigh bone) and tibia (shin bone) are under a large amount of stress which tries to force them to slide past each other (a phenomenon called tibial translation) rather than just hinge naturally. This puts tremendous strain on the anterior cruciate ligament. Your knees, it seems, are much better at dealing with compressive forces than shearing forces.

Finally, consider the action of leg extensions: do you ever perform this movement in real life?

Obviously, you do extend your knees, for example when kicking a football, but I can’t think of a single time you extend your knee with your thigh being supported. Kicking off your slippers while sat on your sofa perhaps? Leg extensions cannot be described as a ‘functional’ exercise. In most natural movements, your quads work in conjunction with your hamstrings, abductors, hip flexors, glutes and adductors.

It’s very rare that your quads work in isolation, as they do in leg extensions. But, before you turn your back on the leg extension forever, it is worth considering the exercise’s advantages. For starters, leg extensions allow you to place an emphasis on your vastus medialis muscle which is located on the inside of your lower thigh.

This muscle is important for knee stability and correct tracking of your patella and is especially active in the last 10 to 15 degrees of knee extension. Other leg exercises like leg presses get easier as you your knees straighten whereas leg extensions get harder. Also, leg extensions can be performed with very light weights.

While squats and lunges also work your thighs, if you lack sufficient leg strength to perform these exercises safely, leg extensions, combined with leg curls, will help you develop the necessary strength to progress to these exercises. Leg extensions are also a great way to work your thighs intensely but in relative safety – safety from getting ‘stapled’ by a heavy barbell anyway.

You can perform leg extensions to failure whereas squatting to failure could be very problematic. If you care about long-term knee health (and of course you should!), leg extensions should only be performed under control, using moderate weights and not too frequently. Consider them a supplemental exercise rather than a cornerstone. A few sets at the end of a leg workout are fine; a leg workout consisting of nothing but leg extensions is not.

Leg extension alternatives

Here are some exercises that offer similar benefits to leg extensions but without the nefarious shearing force that can be so problematic:

1. One and a half squats

One and a half squats place an additional load on your vastus medialis – the same quadriceps muscle emphasised in leg extensions. With your feet shoulder-width apart, squat down as normal and then stand up. Next, squat down again but only half way. Stand back up. This constitutes one repetition. Continue performing this double movement for the duration of your set. You can also apply the same one and a half rep principle to leg presses and lunges.

leg extension_2

2. Single leg box squats

Stand on an exercise bench or stable box. Shuffle to the side so that one foot is clear of the step. Bend your weight-bearing knee and lower your other foot to within an inch/couple of cm’s of the floor. Push back up and repeat. Lean forwards form your hips to keep your weight over your base of support. If necessary, hold something sturdy for balance. As you get stronger, hold dumbbells in your hands or wear a weighted vest.

3. Barbell squats with bands/chains

A powerlifting favourite, squatting with bands or chains means that there is more resistance at the top of the movement than at the bottom. This is called accommodating resistance and is a strength building principle that can be applied to numerous exercises to make them more challenging. You’ll need two long chains or resistance bands to do this – the right tools for the job are available from specialist strength training stores or you can rig up your own by visiting your local DIY store.

If you use bands, loop them over the ends of your bar and fix the other end to the bottom of your squat rack or weigh them down with heavy dumbbells. If you use chains, drape the chains over the ends of your bar so that, when you squat down, the chain will pool on the floor. Make sure neither the bands nor chains will slip off the bar. For more information on proper squat technique, see my article in issue 22-3.

4. Barbell hack squats

Not to be confused with the machine of the same name, barbell hack squats are named after wrestling legend George Hackenschmidt who was famed for his thigh development. To perform this exercise, and raise a few eyebrows at your gym, place a barbell on the floor and stand with your back to it.

The bar should be touching the back of your ankles. Squat down and grasp the bar with an overhand grip. Keeping your arms straight, drive down though your heels and stand up. The bar should track up the back of your thighs. Squat back down and repeat.

5. ‘Natural’ leg extensions

If you still want to do leg extensions but don’t want to expose your knees to so much shearing force, this exercise provides a viable alternative. Kneel down on all fours with your shoulders over your hands and your hips over your knees. Cross one foot over the other so that you are resting on your hands and one knee only.

From this position, straighten your weight-bearing leg and push your hips up into the air. When viewed from the side, your body should resemble an inverted V shape. Bend your leg and lower your knee to within an inch/couple of cm’s of the floor before pushing up again. Change legs and repeat.


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