Jack Knife Floor
Jack Knife Floor Exercise Description
The Jackknife (floor) is an advanced bodyweight core exercise that combines trunk flexion and hip flexion to create a controlled “V” position. It primarily targets the rectus abdominis and the hip flexors (iliopsoas and rectus femoris), with the obliques and deep abdominal wall assisting in lumbopelvic stability. Because the legs and arms act as long levers, the movement places high torque demands on the trunk, rewarding precise control over momentum. The goal is to lift the torso and legs simultaneously while maintaining a braced abdominal wall and neutral cervical spine. Performed smoothly with a deliberate lift and a slow, synchronized descent, the jackknife trains core stiffness against lumbar extension as the body moves through a large range of motion. Choose a range that lets you keep the ribs down and the pelvis stable throughout.
- Muscle Groups: Abs, Core, Hips, Quads, Waist
- Target Muscles: Iliacus, Psoas Major, Rectus Abdominis, Rectus Femoris
- Assisting Muscles: Sartorius, Tensor Fasciae Latae
- Stabilizing Muscles: External Obliques, Internal Obliques, Multifidus, Transversus Abdominis
- Body Area: Lower Body, Upper Body
- Body Parts: Core, Hips, Legs, Torso, Upper Legs
- Body Surface: Front
- Body Symmetry: Bilateral
- Equipment: Bodyweight
- Exercise Patterns: Other
- Exercise Type: Strength
- Functional Grouping: Hip Flexors, Knee Extensors, Trunk Flexors
- Joint Involvement: Multi-joint
- Muscle Location: Front Quad, Hip Flexor, Stomach
- Movement Direction: Other
- Muscle Position: Anterior
- Gender: Female
How To Do The Jack Knife Floor Exercise
‘- Lie supine with legs straight and together, arms extended overhead in line with your ears.
– Brace the abdominal wall; draw ribs down and gently posteriorly tilt the pelvis so the low back lightly contacts the floor.
– Set a neutral neck (gaze up), shoulders relaxed away from ears.
– Exhale as you simultaneously flex the hips and trunk, lifting straight legs and upper back off the floor.
– Reach hands toward shins or ankles; keep knees extended without locking and avoid shrugging.
– Balance on the sacrum at the top, forming a controlled “V” without collapsing through the lumbar spine.
– Pause briefly while maintaining abdominal tension and steady breathing.
– Lower the torso and legs together with control, keeping rib-to-pelvis connection and avoiding lumbar hyperextension at the bottom.
– Move smoothly—no bouncing or swinging—and avoid pulling on the neck with the arms.
– If you lose lumbopelvic control or feel low-back pressure, reduce the range or bend the knees slightly to maintain quality.
Jack Knife Floor Tips
‘- Begin lying supine with legs straight and together, arms extended overhead in line with your ears.
– Before lifting, brace the abdominal wall, draw the ribs down, and gently posteriorly tilt the pelvis so the low back lightly contacts the floor.
– Keep the neck neutral with your gaze up and shoulders relaxed away from the ears.
– Exhale as you simultaneously flex the hips and trunk, lifting straight legs and upper back off the floor together.
– Reach your hands toward your shins or ankles while keeping the knees extended without locking and avoiding shoulder shrugging.
– Balance on the sacrum at the top, forming a controlled “V” without collapsing through the lumbar spine.
– Pause briefly at the top, maintaining abdominal tension and steady breathing.
– Lower the torso and legs together with control, keeping the ribs connected toward the pelvis and avoiding lumbar hyperextension at the bottom.
– Move smoothly without bouncing or swinging, and avoid pulling on the neck with the arms.
– If you lose lumbopelvic control or feel low-back pressure, reduce the range of motion or bend the knees slightly to maintain quality.
Jack Knife Floor Beginner Introduction
The Jackknife (floor) is a challenging floor-based core movement that uses only bodyweight to train strong, coordinated flexion through the midsection and hips. From a fully lengthened position on the back, the body folds into a V-like shape as the upper body and legs rise together, with the arms and legs stretched long to increase the demand on the abs and hip flexors. The side abs and deep core muscles assist by helping the pelvis and lower back stay steady while everything moves as one unit.
Because the limbs stay relatively straight, each repetition creates significant leverage on the trunk, emphasizing control over momentum. The neck and head remain in line with the spine as the torso and legs come up and return down in unison, encouraging smooth, deliberate motion through a large range. This exercise highlights core tension, rhythm, and precise positioning rather than speed, rewarding practiced coordination and stability across the front of the body.