Leg Extensions: The Exercise I Finally Made Peace With

For years, I avoided leg extensions.

Not because I thought they were a terrible exercise, but because I had been told they could be bad for your knees. And when you've spent decades dealing with a knee that has a pretty extensive history of cartilage damage and arthritis, you tend to listen when someone tells you an exercise could make things worse.

But I've changed my mind.

In fact, about a year ago I started programming leg extensions into my own strength training, and I've also started using them with clients when they are appropriate for the individual. The interesting part is that my quadriceps have gotten significantly stronger without an increase in knee pain or a loss of range of motion. And that has made me rethink not just leg extensions, but the way we often talk about exercises in general.

This subject has become even more relevant for me recently. I finally scheduled my initial knee replacement consultation for October 23, 37 years after tearing the cartilage in my knee, roughly 30 years after developing arthritis, and about 17 years after being told that a replacement was probably the next step. So yes, I have spent a considerable amount of time thinking about what I should and shouldn't do with my knees.

One of the biggest lessons I've learned is that we need to stop treating exercises as either “good” or “bad.” An exercise is a tool, and whether that tool is appropriate depends on the person using it, the goal, the amount of resistance, the number of repetitions, the range of motion, the frequency and the individual's current capacity.

Can leg extensions irritate someone's knees? Absolutely. But so can squats, lunges, running, jumping, stairs and plenty of other activities. The fact that an exercise can produce discomfort in some circumstances doesn't automatically make the exercise dangerous. Sometimes the exercise needs to be modified. Sometimes the load needs to be reduced. Sometimes the volume needs to come down. And sometimes that particular exercise simply isn't the right choice for that person at that particular time. That's what good programming is supposed to address.

This is also where the conversation about “stress” and “damage” gets confusing. Leg extensions can create significant forces around the knee, including shear forces and increased loading at the patellofemoral joint. But force is not the same thing as damage. Your knee experiences different types of forces every time you walk, climb stairs, squat, ride a bike, run or get up from a chair. The human body is designed to tolerate mechanical stress, and our tissues adapt to appropriately applied stress over time.

That's actually one of the fundamental principles behind resistance training. We expose the body to a manageable challenge, allow it to recover and then gradually increase the challenge. Muscles get stronger. Tendons adapt. Bones respond to loading. Our capacity increases. The goal of training isn't to eliminate force from our lives. If it were, we'd all be spending our days sitting on the couch trying not to stress anything, and I'm pretty sure that isn't going to help us stay strong and independent.

The same principle applies to the concern that leg extensions are an “open-chain” exercise. Open-chain simply describes how the movement occurs. During a leg extension, your foot is free to move rather than being fixed against the floor. That's not a synonym for dangerous. Biceps curls, hamstring curls and many other common exercises are also open-chain movements. The terminology describes the mechanics of the exercise. It doesn't tell us whether the exercise is appropriate for a particular person.

In fact, open-chain knee extensions have been studied extensively in rehabilitation, including after ACL reconstruction. Research has found that appropriately programmed open-chain quadriceps exercises can help restore strength without automatically creating the problems that have historically made some clinicians hesitant to use them. Other research involving people with knee pain has also found that both open- and closed-chain strengthening approaches can improve pain and physical function.

And that matters because strong quadriceps aren't just about having bigger thighs. Your quadriceps help you stand up from a chair, climb stairs, control your body when walking and maintain your ability to perform everyday activities. For someone who is deconditioned, recovering from an injury or struggling with a particular movement, a leg extension can provide a relatively simple way to directly train the quadriceps without requiring them to perform a heavy squat or lunge.

That doesn't mean leg extensions are automatically better than squats, lunges or other lower-body exercises. It means they are another tool we can use when the situation calls for it.

This is really the bigger lesson I've taken from changing my mind about leg extensions. We shouldn't be trying to find exercises that place zero stress on our joints because such exercises don't exist. Instead, we should be asking whether our bodies have the capacity to tolerate the stress we're giving them and whether we're increasing that stress at an appropriate rate.

The same exercise can be too much for one person and exactly what another person needs. A 20-year-old athlete recovering from an injury, a sedentary 70-year-old trying to regain the strength to climb stairs and a 58-year-old guy with a knee that has been giving him trouble for 37 years may all need completely different approaches. That's why good training isn't simply a list of exercises. It's about matching the right exercise, the right dose and the right progression to the individual.

So yes, I've changed my mind about leg extensions. I'm not saying everyone should start doing them tomorrow, and I'm certainly not saying they are some magical knee-saving exercise. I'm saying I've stopped judging the exercise based on the movement itself and started paying more attention to how, when and why it is being used.

After decades of dealing with my own knee problems, I'm still training my quads. I'm still loading my knees. And I'm still trying to increase my body's ability to handle the demands of everyday life.

Because the goal of training isn't to avoid every force our bodies experience. The goal is to become strong enough to handle those forces.

And sometimes, one of the tools that helps us get there is the exercise we were once told to avoid.

If you've been avoiding certain exercises because you've been told they're “bad” for your knees, back or joints, it may be time to take another look.

The right exercise isn't necessarily the one that puts the least stress on your body. It's the one that helps you build the capacity to handle the demands of the life you want to live.

If you're ready to stop guessing and start training with a plan built around your body, your goals and your current capacity, let's talk.

Schedule your free 15-minute Fitness Strategy Call and let's figure out what makes sense for you.