Weighted Leg Extension Crunch

How to do the Weighted Leg Extension Crunch

1. 1Sit upright on a stability ball with your feet flat on the floor, hip-width apart, and hold a weight plate or dumbbell against your chest.
2. 2Walk your feet forward and lean back until your mid-to-lower back rests on the ball, with your knees bent at roughly 90 degrees.
3. 3Brace your core and tuck your chin slightly toward your chest — maintain this neutral head position throughout the set.
4. 4Curl your upper body upward into a crunch by contracting the rectus abdominis, lifting your shoulder blades off the ball.
5. 5As you begin the crunch, simultaneously extend both legs forward until they are nearly straight and parallel to the floor.
6. 6Hold the top position for one count, feeling the contraction in your abdominals and the tension through your hip flexors.
7. 7Slowly reverse the movement — bend your knees back to 90 degrees and lower your upper body back onto the ball under control.
8. 8Recheck your position on the ball as needed, then repeat for the desired number of repetitions.

Form tips

• Keep the weight pressed close to your chest rather than extending it overhead — this limits lower-back strain and keeps the load manageable as the ball adds its own instability.
• Initiate the leg extension and the torso crunch at the same moment so the rectus abdominis and hip-flexor synergists share the demand evenly.
• Control the eccentric phase — lowering with the same deliberate pace you used on the way up develops as much strength as the lift itself.
• Keep your legs squeezed together as they extend — actively pressing the knees toward each other is what brings the adductor longus, adductor brevis, and pectineous into the rep.
• Position the ball so it supports your lumbar region at the bottom of the rep — too high on the back limits range of motion; too low reduces stability and increases injury risk.

Common mistakes

• Letting the hips drop toward the floor during the leg extension — this shifts the load off the rectus abdominis and compresses the lumbar spine instead of training the core.
• Using momentum to swing the torso upward rather than a controlled muscular contraction, which reduces abdominal activation and increases the risk of straining the lower back.
• Extending the legs all the way down to the floor, which over-recruits the iliopsoas and reduces the crunch component, making the movement a hip-flexor exercise rather than a core exercise.
• Choosing a weight that is too heavy, causing the neck to strain forward instead of the spine to flex — the chin should stay softly tucked, not jammed into the chest.
• Skipping the pause at the top of the rep, which eliminates the peak contraction where the rectus abdominis is most engaged and where much of the strength benefit is gained.

Frequently asked questions