Jack knife Floor

Instructions

1
Sit on the ground with torso reclined back at approximately 45 degrees, supported by hands placed behind the body with fingers pointing forward. Keep legs extended in front with feet together.
2
Engage core and maintain stable torso position. Ensure lower back remains neutral and shoulders are relaxed. Hands provide support but not excessive pressure.
3
Slowly lower one leg down toward the ground by flexing at the hip while keeping the knee slightly bent. The leg moves in a controlled manner as hip flexors lengthen. Maintain stability through the supporting hand position.
4
Drive the leg back up to the starting position by contracting the quadriceps and hip flexors, bringing the thigh parallel to or slightly above hip height. Repeat in a controlled manner and alternate legs.
PRIMARY MUSCLESRectus Femoris
SECONDARY MUSCLESVastus Lateralis, Vastus Medialis, Iliopsoas, Sartorius
EQUIPMENTBody weight
DIFFICULTYBeginner

Overview

Athletic trainers and bodybuilding coaches frequently recommend the Jack knife Floor because it challenges the Rectus Femoris through a dynamic range of motion. By relying on Body weight, it reinforces proper movement patterns and builds robust strength in the Waist region.

Benefits

  • Allows for a natural movement path that closely mimics functional daily activities.
  • Reduces the likelihood of Waist injuries by reinforcing connective tissue strength.
  • Promotes balanced muscular development by effectively recruiting the Rectus Femoris and associated synergists.
  • Significantly enhances the structural integrity and power of the Rectus Femoris.

Common Mistakes

  • Failing to achieve a full range of motion, which drastically limits Rectus Femoris engagement.
  • Using excessive momentum to swing the Body weight rather than controlling the eccentric phase.
  • Losing core tension, leading to poor spinal alignment and reduced power output.

Pro Tips

Keep your breathing rhythmic: exhale sharply on the concentric push/pull, and inhale smoothly on the way down.

Muscle Anatomy

The primary driver is the Rectus Femoris. However, the movement also recruits Vastus Lateralis, Vastus Medialis, Iliopsoas, Sartorius to maintain control of the Body weight.

Exercise Variations

  • Dumbbell Jack knife Floor
  • Cable Jack knife Floor
  • Banded Jack knife Floor

Beginner Tips

If you are new to the Jack knife Floor, focus on mastering the movement pattern with zero weight before adding Body weight.

Frequently Asked Questions