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Half Jackknife

Step by step instructions, muscle activation and variants for the Half Jackknife.

EasyAbs

About this exercise

The half jackknife is a beginner-friendly core exercise performed lying on your back where one leg is raised to meet the opposite hand, forming a partial V shape. It targets the rectus abdominis and obliques while being less demanding on hip flexors and spinal flexors than a full jackknife. It is a good entry point for building core strength and coordination.

How to Perform

  • Lie flat on your back with arms extended overhead and legs straight on the floor
  • Simultaneously lift one straight leg toward the ceiling and reach the opposite arm to meet it
  • Crunch your upper body slightly off the floor as you bring the hand and foot toward each other
  • Hold the peak contraction briefly, then lower both limbs back to the floor under control
  • Repeat on the same side for the desired reps, or alternate sides each rep

Muscle Activation

Primary
Abs
Secondary
CoreObliques

Common Mistakes

Common mistakes content is coming soon.

About the Half Jackknife

The Half Jackknife is a foundational movement that builds strength and muscle through controlled, progressive overload. Train it 1 to 2 times per week with 3 to 5 working sets per session, gradually adding weight or reps as form holds up.

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