Quads exercise
Leg Extension (Machine)How to do it, with form in numbers
How to do it
How do you do the Leg Extension?
- Sit back and line your knees up with the machine's pivot.
- Set the pad on your lower shins, just above your ankles.
- Hold the handles and straighten your legs until they are nearly straight.
- Pause and squeeze your thighs.
- Lower slowly until your knees are bent to a right angle.
Cues
- Lift smoothly; no kicking.
- Keep your hips down on the seat.
- Lower slower than you lift.
Common mistakes
- Swinging the weight up with momentum.
- Lifting your hips off the seat.
- Letting the weight drop back down fast.
Form in detail
What does good form look like?
Starting position
Selectorised leg extension machine. Seat top 52 cm above the floor; the back pad is reclined 12° from vertical. Adjust the back pad so the knee joint lines up with the machine's pivot, with the back of the knees close to the front edge of the seat. The roller pad sits on the front of the lower shins, just above the ankles (about 7–8 cm above the ankle joint). Sit tall with the back and hips against the pad, thighs flat on the seat, and hold the handles beside the seat. Start with the knees bent to about 90° and the weight stack lifted just off its rest.
The movement
Only the knees move. Straighten both knees together, lifting the roller in an arc around the pivot, until the legs are nearly straight. Pause and squeeze the front of the thighs, then lower slowly back to the start. The thighs stay on the seat, the hips stay against the back pad and the trunk does not rock. The feet stay relaxed, toes up and pointed a little.
End position
Bottom: knees at about 90°.
Tempo
1.5 s up, 0.8 s pause at the top, 2.2 s down, about 0.5 s at the bottom.
Form in numbers
What are the angles and distances?
| Measure | Target | Good range | Sources |
|---|---|---|---|
| Seat top above the floor | 52 cm | 45–55 cm (machine) | |
| Back pad recline from vertical | 12° | 5–20° (machine) | |
| Roller above the ankle joint | 7.5 cm | 5–10 cm | [1] |
| Knee flexion at the start | 90° | 80–100° | [1][2] |
| Knee flexion at the top | 5° | 0–10° | [1][2] |
| Thigh lift off the seat | 0 cm | ≤ 1 cm | [1] |
| Trunk rock over the rep | 0° | ≤ 3° | [1] |
The targets our 3D demo was built to, from the references below. Bodies differ, so treat the ranges as a guide for your own build.
For coaches
Use this demo in your clients’ programs
The Leg Extension is in Trainaq’s exercise library. Add it to a workout, and your client sees this demo in the free Trainaq app above the sets they log.
Sources
Sources
- ExRx, Lever Leg Extension
- Escamilla et al. 1998, Med Sci Sports Exerc, "Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises"
- Larsen et al. 2024, SportRxiv preprint, "The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise"
