Exercise guide
Leg Extension Crunch With Stability Ball
- Intermediate
- Compound
- Rep-based
- Lower legs
- Waist
This compound movement targets the rectus abdominis and quadriceps by combining spinal flexion with a weighted leg extension, improving core stability and lower body control.
Reviewed by the Crucible team · Updated June 2026
Muscles worked
Setup
- Lie flat on your back on a mat with your arms extended by your sides or behind your head for support.
- Place a stability ball between your lower legs, gripping it firmly with your ankles and shins.
- Lift your legs so your knees are bent at a 90-degree angle in a tabletop position.
How to do it
- Exhale as you simultaneously crunch your shoulder blades off the floor and extend your legs straight out at a 45-degree angle.
- Squeeze your quadriceps at the peak of the extension while maintaining firm pressure on the ball.
- Inhale as you slowly lower your upper body and return your knees to the 90-degree starting position.
- Maintain a controlled 2-1-2 tempo, avoiding the use of momentum between repetitions.
Form checklist
- Keep your lower back pressed firmly into the floor to protect the lumbar spine.
- Maintain constant inward pressure on the ball with your ankles to keep the adductors and quads engaged.
- Avoid pulling on your neck; lead the crunch with your chest and keep your chin slightly tucked.
- Ensure your legs do not drop so low that your back arches off the mat.
Pro tips
- To maximize quadriceps activation, focus on fully locking out your knees and flexing your toes toward your shins at the end of the extension.
- Visualize pulling your ribcage toward your pelvis to deepen the contraction of the rectus abdominis.
Make it harder
- Lower your legs closer to the floor during the extension phase to increase the lever arm and core demand.
- Perform a 'ball pass' by reaching up and taking the ball with your hands at the top of the crunch, then alternating between leg and arm extensions.
Frequently asked
- What muscles does the leg extension crunch with stability ball work?
- The leg extension crunch with stability ball primarily targets the abs, and also works the quadriceps and serratus anterior as secondary muscles.
- What equipment do you need for the leg extension crunch with stability ball?
- The leg extension crunch with stability ball uses stability ball.
- Is the leg extension crunch with stability ball good for beginners?
- The leg extension crunch with stability ball is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.