Dépense estimée selon votre poids
Mouvement d'isolation · 3 s par répétition
| Répétitions | Dépense estimée |
|---|---|
| 1 | 0,23 kcal |
| 10 | 2,3 kcal |
| 20 | 4,6 kcal |
| 50 | 11,5 kcal |
| 100 | 23,0 kcal |
Estimation à partir des équivalents métaboliques (MET) du Compendium of Physical Activities. La charge, le tempo et la durée des repos font varier le résultat du simple au double : à lire comme un ordre de grandeur, pas comme une mesure.
What is the leg extension machine actually for?
The leg extension machine does one thing: extending the legs from a seated position, from bent knees to straight knees. It's the simplest machine in the gym, and the one people set up worst.
Its value is isolation. On a squat, the load spreads across glutes, back and thighs. Here the work lands on the quadriceps, without your lower back cutting the set short. Useful when you want to build a specific area or finish off a leg session.
It's a building block, not a foundation. It rounds out compound lifts, it doesn't replace them.
Leg extension machine muscles worked: what really fires
The quadriceps is made up of four heads. All four are involved in the machine extension, to varying degrees depending on foot position.
Vastus lateralis and vastus medialis
The vastus lateralis sits on the outer side of the thigh. The vastus medialis is the teardrop just above the knee. Pointing your toes inward slightly shifts the emphasis to the outer head; toes out moves it toward the inner head. The effect is real but small: don't build a program around it.
Rectus femoris and vastus intermedius
The rectus femoris crosses the hip. It works better with an upright torso and your back flat against the pad. The vastus intermedius sits underneath and follows the movement; there's no way to isolate it.
In the gym, nine lifters out of ten load up too heavy and only use the last 30 degrees of range. The muscle gets less work than it would with half the weight taken through the full range.
What about the hamstrings?
The hamstrings don't push on this exercise. They brake, eccentrically, during the controlled lowering. To train them, you need the leg curl.
Adjusting the leg extension machine: the three settings that matter
A sloppy setup turns a safe exercise into shear on the knee joint. Three points are enough, and it takes thirty seconds.
- Backrest: the machine's pivot point should line up exactly with the side of your knee.
- Ankle pad: just above the top of the foot, never on the shin.
- Seat: the back of your knee at the edge of the seat, thighs fully supported.
After that, the only thing that changes is the load. Keep your hands on the side handles for stability, lift in 1 second, hold the contraction, lower over 2 to 3 seconds. Your lower back will tell you whether the seat is set right.
Leg curl and leg extension machine: two machines, one pair
The leg extension and the leg curl often sit side by side in gyms, and that's no accident. One does extension, the other flexion. Running both balances the front and back of the thigh.
| Criteria | Leg extension | Leg curl |
|---|---|---|
| Muscles | Quadriceps | Hamstrings |
| Movement | Extension | Flexion |
| Typical load | Moderate | Light |
| Reps | 10 to 15 | 10 to 15 |
| Position | Seated | Seated or lying |
A big imbalance between the two puts more strain on the knee. Two sets of each at the end of a session is enough to keep the ratio in check. Our strength training programs by goal put both machines in the same leg session for exactly that reason.
Basic-Fit, Technogym, Fitness Park: what changes
The movement is the same everywhere. What changes is the comfort and what the weight stack actually tells you.
- Technogym: fine backrest adjustment, adjustable starting range.
- Basic-Fit: plates in 5 kg steps, backrest often fixed.
- Fitness Park and Matrix: wide ankle pad, welcome on heavy sets.
The practical consequence: your reference load doesn't carry over from one gym chain to another. A longer lever arm makes the same setting feel 10 kg heavier. Write down the machine along with the load.
That's exactly what session tracking in MUSCU does: the load, the reps and the machine stay attached to each exercise, session after session, with a video of the movement on screen. You pick up where you left off without hunting for it.
Common mistakes to avoid
They're always the same, and your knees pay for them.
- Going too heavy: your hips lift off the seat and the range collapses.
- Swinging through the end of the set, legs bouncing.
- Dropping the weight on the way down: half the muscular work goes in the bin.
- Snapping into lockout at the top, knees jammed straight for a split second.
Two to three sets of 12 to 15 reps with a load you control through the full range beats one heroic set. On this machine, the load isn't the progress marker: movement quality is.
A leg extension machine for a home gym: worth buying?
For home use, a dedicated machine runs from 300 to 1,500 euros and takes up a square metre of floor. Second-hand, expect to pay about half that. The question really only comes up if you've stopped going to the gym altogether.
A credible alternative: weight benches with built-in extension and curl attachments. Less comfortable, half the price. Before you spend anything, check that your training already includes squats and lunges — without them, leg extensions alone won't build your thighs. The session generator based on the equipment you have will tell you what's possible with what you've already got.