# Leg Extension (Machine): how to do it

- Main muscles: quads
- Equipment: machine
- Level: beginner
- 3D demo (side view): https://media.trainaq.com/exercises/leg_extension/6d32ee0458/side-m-720.mp4

## Steps

1. Sit back and line your knees up with the machine's pivot.
2. Set the pad on your lower shins, just above your ankles.
3. Hold the handles and straighten your legs until they are nearly straight.
4. Pause and squeeze your thighs.
5. 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.

## 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

| 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] |

## Sources

1. [ExRx, Lever Leg Extension](https://exrx.net/WeightExercises/Quadriceps/LVLegExtension)
2. [Escamilla et al. 1998, Med Sci Sports Exerc, "Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises"](https://pubmed.ncbi.nlm.nih.gov/9565938/)
3. [Larsen et al. 2024, SportRxiv preprint, "The effects of hip flexion angle on quadriceps femoris muscle hypertrophy in the leg extension exercise"](https://doi.org/10.51224/SRXIV.407)

Source: https://trainaq.com/exercises/leg-extension