Exercise guide
Lying Alternate Knee Tuck
- Beginner
- Compound
- Rep-based
- Waist
The Lying Alternate Knee Tuck is a beginner-friendly core exercise that strengthens the lower abdominals and hip flexors while improving hip mobility. By alternating legs, you challenge core stability and engage the quadriceps and glutes through controlled leg extension.
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 feet together.
- Place your arms by your sides with palms down, or tuck your hands slightly under your glutes for extra lower back support.
- Engage your core by pressing your lower back firmly into the floor to eliminate any arching.
How to do it
- Exhale as you pull your right knee toward your chest, squeezing your abs at the top of the movement.
- Inhale as you slowly extend the right leg back to the starting position, engaging your quadriceps as the leg straightens.
- Repeat the movement with your left leg, alternating sides for the duration of the set.
- Maintain a controlled 2-1-2 tempo: two seconds to tuck, a one-second squeeze, and two seconds to extend.
Form checklist
- Keep your lower back in constant contact with the floor throughout the movement.
- Avoid using momentum; move the legs with slow, deliberate control.
- Ensure the non-moving leg remains active and straight.
- Keep your neck neutral and shoulders relaxed against the mat.
Pro tips
- To maximize glute and quad engagement, flex your toes toward your shins and drive through the heel as you extend the leg.
- Focus on the 'hollow body' position by pulling your belly button toward your spine to ensure deep transverse abdominis activation.
Make it harder
- Keep both feet hovering 2-3 inches off the ground throughout the entire set to maintain constant tension on the core.
- Slow down the eccentric (lowering) phase to 4 seconds to increase time under tension.
Frequently asked
- What muscles does the lying alternate knee tuck work?
- The lying alternate knee tuck primarily targets the abs, and also works the obliques as secondary muscles.
- What equipment do you need for the lying alternate knee tuck?
- The lying alternate knee tuck requires no equipment — just your body weight.
- Is the lying alternate knee tuck good for beginners?
- Yes. The lying alternate knee tuck is a beginner-friendly movement and a strong foundation to build on.