Side Jackknife
A side-lying crunch that lifts the top leg and the upper body toward each other at the same time. It trains the obliques through side bending from both ends.
Primary muscles
- Obliques
Secondary muscles
- Abs (Rectus Abdominis)
- Gluteus Medius
- Sets
- 2–3
- Reps
- 10–15 per side
- Rest
- 30–60s
How to perform
Main muscles working (thicker lines)
Starting position
Lie on one side with legs straight and stacked, your bottom arm on the floor in front of you and your top hand behind your head.
Brace your abs and keep your body in one straight line.
Lift your top leg while crunching your upper body sideways toward it.
Bring your top elbow and knee as close together as you can and pause.
Lower both slowly back to the start, finish the set, then switch sides.
Breathing: Exhale as you lift, inhale as you lower.
Coaching tips
Squeeze the side of your waist
Leg and torso rise together
Don't roll forward or back
Common mistakes
Rolling onto your back
Swinging the leg up
Pulling the head with the hand
Safety notes
Keep your neck relaxed and in line with your spine.
This information is general fitness guidance, not medical advice. Stop if you feel pain and consult a qualified professional.