Leg Extension
The leg extension is a machine exercise where you straighten your legs against a padded lever, so the work goes almost entirely into your quadriceps (the muscles on the front of your thighs). It is easy to learn, simple to load and well suited to beginners and experienced lifters alike. Use it to build thigh size and strength after your main leg exercises, or as part of a general fitness plan.
Muscles worked
The Leg Extension mainly works your quadriceps.
Setting up
- Adjust the backrest so your knees line up with the machine's pivot point (the hinge or axis on the side), and the back of your knees sit near the front edge of the seat. You should be able to bend your knees comfortably to about 90 degrees.
- Set the shin pad so it rests on the lower part of your shins, just above your ankles. If it sits on your feet, it is too low. If it sits mid-shin, it is too high.
- Choose a light weight to start with. Sit back with your hips and back against the pad, and hold the side handles to keep your body still.
- Point your toes up or slightly back towards you, and keep your feet relaxed rather than pushing them hard into the pad.
How to do the Leg Extension
- Sit with your back flat against the backrest and your hips pushed into the seat. Grip the handles and brace your core gently.
- Start with your knees bent and the pad resting on your shins, with the weight stack hovering just off the rest.
- Breathe out and straighten your legs by pushing the pad up and forwards in a smooth, controlled movement.
- Stop when your legs are straight or just short of straight, and squeeze the muscles on the front of your thighs for a second.
- Breathe in and lower the weight slowly, taking about two to three seconds, until your knees are bent again.
- Stop just before the weight stack touches down, then go straight into the next rep so the muscles stay working throughout the set.
Form tips
- Think about pushing your shins up and away, and feel the tension build across the front of your thighs as you go.
- Keep your hips pressed into the seat the whole time. If your bum lifts, the weight is too heavy or you are rushing.
- Take longer to lower the weight than to lift it. The slow lowering phase is where this exercise gets much of its value.
- Pause briefly at the top and tighten your quads, rather than letting the weight swing or bounce.
- Keep your toes in a relaxed, neutral position and your gaze forward, with shoulders down and away from your ears.
Common mistakes
Swinging the weight up
Using momentum takes the work away from your quads. Reduce the weight and lift smoothly, taking a full second or more to reach the top.
Hips lifting off the seat
This usually means the weight is too heavy. Lower the load, hold the handles and keep your hips pressed down for the whole rep.
Dropping the weight on the way down
Letting the stack crash down wastes half the exercise and is hard on your joints. Lower over two to three seconds and keep control right to the bottom.
Machine set up wrongly
If your knees do not line up with the pivot point or the pad sits on your feet, the movement will feel awkward. Take a minute to adjust the seat and pad before your first set.
Sets and reps
| Build strength | 3-4 sets of 6-10 reps with a challenging but controlled weight, resting 90-120 seconds between sets. |
|---|---|
| Build muscle | 3-4 sets of 10-15 reps, lowering slowly and squeezing at the top, resting 60-90 seconds between sets. |
| Fat loss and general fitness | 2-3 sets of 12-15 reps with a moderate weight, resting 45-60 seconds, as part of a full-body plan alongside cardio and other exercises. |
Pick a weight where the last rep or two of each set is hard but your form stays clean. When every set feels easy, it's time to go up.
Leg Extension alternatives
Machine taken, or want some variety? These work the same main muscles.
Leg Extension FAQs
Are leg extensions bad for your knees?
Many people use them without any trouble when they choose a sensible weight, set the machine up properly and move under control. Avoid jerking the weight or slamming it at the top. If you feel pain in or around your knee, stop and get it checked.
How much weight should I use on the leg extension?
Pick a weight you can lift for your target reps with smooth, controlled form, while feeling that the last couple of reps are hard work. Beginners should start light, often around 10-20 kg, and add small amounts once the movement feels steady.
Where should I feel leg extensions?
You should feel the work in the front of your thighs, strongest as your legs straighten and you squeeze at the top. If you feel it mainly in your back or you are lifting your hips, check your seat position and lower the weight.
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