# Stability Ball Leg Curl: how to do it

- Main muscles: hamstrings
- Also works: glutes, abs
- Equipment: stability ball
- Level: intermediate
- 3D demo (side view): https://media.trainaq.com/exercises/stability_ball_leg_curl/8e56801c25/side-m-720.mp4

## Steps

1. Lie on your back with your heels and lower calves on the ball.
2. Put your arms out to the sides and lift your hips into a straight line.
3. Pull your heels towards you, rolling the ball in.
4. Keep your hips high, then roll the ball back out slowly.

## Cues

- Squeeze your glutes to keep your hips up.
- Shoulders, hips and knees in one line.
- Roll out slowly; do not let the hips drop.

## Common mistakes

- Letting your hips sag as you roll the ball.
- Arching your lower back to lift higher.
- Letting the ball wobble off to one side.

## Starting position

A 65 cm stability ball (the size for a 1.73–1.90 m adult) on a mat. Lie on the back with the backs of the lower calves and heels on top of the ball, feet hip-width apart, ankles slightly flexed (toes towards the shins). Arms out to the sides at about 45°, palms down, head resting on the mat. Brace the stomach, then squeeze the glutes and lift the hips until the body forms a straight line from the shoulders to the heels.

## The movement

Keep the hips up and pull the heels towards the backside by bending the knees. The ball rolls in towards the hips and the soles of the feet roll onto it. As the heels come in, the hips rise a little further, so at the end the shoulders, hips and knees form one straight line with the thighs angled up. Pause, then straighten the knees slowly and roll the ball back out, keeping the hips high and level the whole time. Only the shoulders, upper back and arms touch the floor.

## End position

Start: knees almost straight, body straight from shoulders to heels. Rolling the ball in until the soles sit on its near side and the knees stay in line with the shoulders and hips needs about 90–110° of knee bend for a 1.75 m avatar; the hips end higher than at the start.

## Tempo

1.5 s curl, 0.5 s pause, 2 s roll out, 0.5 s with the legs long (hips still up).

## Form in numbers

| Measure | Target | Good range | Sources |
| --- | --- | --- | --- |
| Ball diameter (1.75 m avatar) | 65 cm | 55–65 cm | [3] |
| Feet spacing on the ball | hip width, about 20 cm | 10–25 cm | [1] |
| Arms on the floor, from the body | 45° | 30–90° | [1] |
| Knee flexion at the start | 5° | 0–15° | [1] [2] |
| Hip extension at the start (shoulder-hip-heel line) | 0° | −10° to +5° | [1] |
| Hip extension at the end (shoulder-hip-knee line) | 0° | −10° to +5° | [1] |
| Pelvis tilt side to side | 0° | ≤ 5° |  |

## Sources

1. [ACE, Stability Ball Hamstring Curl](https://www.acefitness.org/resources/everyone/exercise-library/59/stability-ball-hamstring-curl/)
2. [ExRx, Leg Curl (on ball) and Straight Hip Leg Curl (on stability ball)](https://exrx.net/WeightExercises/Hamstrings/BWBallLegCurl)
3. [ACE, ProSource, Play Ball!](https://www.acefitness.org/continuing-education/prosource/equipment-special-issue/4995/play-ball/)

Source: https://trainaq.com/exercises/stability-ball-leg-curl