Open vs Closed Chain: Why Squats Will Always Beat Leg Extensions

Walk into any gym and you'll see both of them happening simultaneously.

One person under a barbell, squatting. Hips below knees, whole body working, feet planted and driving through the floor.

Ten feet away, someone else is sitting on a padded machine, pushing a lever forward with their shin, watching their quad contract in the mirror.

Both of them are training legs. Both of them are sweating. Both of them think they're doing something useful.

But they are not doing the same thing. Not even close.

And understanding the difference will change how you think about training — not just in the gym, but for the rest of your life.

Let's Keep the Definition Simple

There are two categories of movement in exercise. You don't need complicated biomechanics to understand them.

Closed chain movements are movements where your feet — or hands — are fixed to a surface. The ground pushes back. Multiple joints have to coordinate simultaneously. Your body has to stabilise itself while generating force.

Squats are closed chain. So are lunges, step-ups, and deadlifts. So is walking, climbing stairs, and getting up off the floor.

Open chain movements are movements where the end of the limb — your foot or hand — is free and moving through space. The load is applied to that free end. One joint does most of the work. The rest of the body sits relatively still.

The leg extension machine is the clearest example. You sit in a padded seat. Your thigh is fixed. Only the knee moves. The quad contracts to push the lever. That's the entire movement.

That's the difference. Fixed versus free. System versus isolation. Multi-joint versus single joint.

What Your Body Was Actually Built to Do

Here's what most people in gyms have never stopped to consider.

The human body was not designed to sit on machines. It was designed to stand, walk, squat, carry, climb, change direction, and move through space under load. Every one of those movements is closed chain. Every one of them requires the ankles, knees, hips, and spine to work in coordination. Every one of them demands that your body stabilise itself while producing force.

This is not an opinion about training philosophy. It's anatomy. The muscles of your lower body — the glutes, hamstrings, quads, calves, hip stabilisers — evolved to work together as a system. They are wired to coordinate with each other. They are wired to respond to ground reaction force — the push of the earth coming back up through your foot.

When you train closed chain movements, you train the system the way it was designed to operate.

When you train open chain movements exclusively, you train individual parts in isolation. And isolated parts don't automatically combine into a functioning system.

What Actually Happens in Each Movement

In a squat, your feet are planted. The ground pushes back against them. Your ankles dorsiflex — the foot bends upward toward the shin — to allow the knee to track forward. Your hips hinge and load. Your spine has to remain neutral under load, which means your core has to work. Your glutes, hamstrings, and quads all fire simultaneously to control the descent and drive the ascent.

Your body is learning stability. It's learning to produce force while remaining balanced. It's learning how to coordinate a chain of joints under real load.

This is what transfers to real life. Standing up from a chair. Getting off the floor. Climbing stairs under a heavy backpack. Catching yourself before you fall.

In a leg extension, you sit down. You are supported. Your thigh is fixed by a pad. Your hip is not loaded. Your ankle is not involved. The only joint moving is the knee. The quad contracts to push a lever. The machine controls the path of movement for you.

Your body is learning how to extend the knee in a seated position against a guided resistance.

That's genuinely all it's learning.

The Gap Nobody Talks About

I've seen this pattern repeatedly with clients who have trained for years on machines.

Strong numbers in the gym. Decent quad development. Confident on the leg press and leg extension. But ask them to squat their own bodyweight with control and depth — they struggle. Ask them to do a single leg step-up with any load — they wobble. Ask them to sit down on the floor and stand back up without using their hands — it's an event.

The machine made one muscle stronger in one movement pattern. The body as a functional unit remained undertrained.

The machine made one muscle stronger. The body as a system remained undertrained.

This is the gap. And it's a gap that shows up in real life before it shows up in the gym.

You don't extend your knee in isolation while seated in real life. You stand, walk, turn, catch yourself, carry things, climb. All of those require the whole system. And if the whole system hasn't been trained, the strength you built on the machine doesn't transfer where you need it.

Are Leg Extensions Useless? Be Honest About This.

No. And I want to be clear about that.

Open chain exercises including leg extensions have genuine uses. In rehabilitation, isolating a specific muscle when the joint cannot tolerate closed chain load is often appropriate and necessary. For bodybuilders trying to add specific quad thickness, targeted isolation work has a role. For athletes who need to address a specific muscle imbalance, open chain work can complement their closed chain foundation.

The problem is not the leg extension itself. The problem is using the leg extension as a substitute for the squat rather than a complement to it. The problem is spending an hour on machines and zero time doing the closed chain movements that actually prepare your body for how it will need to function outside the gym.

If your training is built around machines and you add some squat work on the side — you have it backwards.

The squat is the foundation. The machines are optional additions on top of it.

Where to Start If Squatting Feels Difficult

Most adults who struggle with squats are not dealing with a squat problem. They're dealing with the accumulated consequence of years of machine-based training, chair-shaped posture, and closed chain movement deprivation.

The answer is not to avoid squats. The answer is to rebuild them properly.

Start with bodyweight chair squats — sitting back to a surface and standing up with control. Progress to goblet squats holding a light weight at your chest, which helps you stay upright and find your balance. Add assisted squat holds to spend time in the bottom position. Build ankle mobility and hip strength through the movements that have been neglected.

The squat is a skill. It requires practice, patience, and a willingness to start where you actually are rather than where your ego thinks you should be.

But it is absolutely worth building. Because every closed chain exercise you master — every squat, lunge, step-up, and hinge pattern you own — is direct preparation for the physical demands of the life you're trying to live well into your later decades.

One Simple Rule That Cuts Through Everything

If an exercise looks like something your body does in real life — it's probably worth being good at.

Squatting looks like sitting down, standing up, picking something up from the ground, and getting off the floor. These are movements you will need until very late in life, and the quality of your life will depend in part on how well you can do them.

Leg extensions look like nothing you do in real life.

That's not a reason to never do them. It's a reason to know exactly where they sit in your priorities — and to make sure the foundation is built before the additions are added.

Build the closed chain foundation. Own your squats. Train like a body, not a collection of parts.

— Shiva Malhotra, Barefoot Protocol

ACE Certified Personal Trainer | Sydney, Australia