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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

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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