Exercise guide
Alternating Under Knee Clap
- Intermediate
- Compound
- Rep-based
- Upper legs
- Waist
This dynamic core exercise targets the lower abdominals and obliques while improving hip flexor mobility and coordination. By lifting the leg and crunching the torso to clap underneath, you maximize muscle fiber recruitment through a full range of motion.
Reviewed by the Crucible Fit team · Updated June 2026
Muscles worked
Setup
- Lie flat on your back on a mat with your legs fully extended and arms by your sides.
- Engage your core by pressing your lower back firmly into the floor to eliminate any arch.
- Lift your head, neck, and shoulders slightly off the ground to create initial tension in the upper abdominals.
How to do it
- Exhale as you simultaneously drive one knee toward your chest and crunch your upper body forward.
- Reach both hands under the raised thigh and clap them together at the peak of the contraction.
- Inhale as you lower your leg and torso back to the starting position with control, keeping your heels and shoulder blades hovering just off the floor.
- Repeat the movement on the opposite leg, alternating sides in a fluid, rhythmic motion.
Form checklist
- Keep the lower back glued to the mat throughout the entire movement.
- Ensure the 'clap' happens behind the thigh, not in front of the knee, to force a deeper crunch.
- Maintain a steady tempo and avoid using momentum to swing the legs.
- Keep the non-working leg hovering 2-3 inches off the ground to maintain constant tension.
Pro tips
- Focus on 'shortening' the distance between your ribcage and pelvis during the clap to maximize abdominal engagement.
- Pause for a split second at the moment of the clap to emphasize the peak contraction of the obliques.
Make it harder
- Perform the movement with straight legs (V-up style) and clap behind the calf or ankle.
- Hold a light medicine ball or weight in your hands, passing it under the leg instead of clapping.
Frequently asked
- What muscles does the alternating under knee clap work?
- The alternating under knee clap primarily targets the abs and obliques, and also works the glutes and hamstrings as secondary muscles.
- What equipment do you need for the alternating under knee clap?
- The alternating under knee clap requires no equipment — just your body weight.
- Is the alternating under knee clap good for beginners?
- The alternating under knee clap is rated intermediate. Build a base with simpler variations first, then progress to it with light load and strict form.