Jackknife

Jackknife Exercise Description

The Jackknife (often called a V-up) is a bodyweight core exercise that combines trunk flexion and hip flexion to form a controlled “V” position. It primarily targets the rectus abdominis and obliques, with assistance from the hip flexors (notably iliopsoas and rectus femoris) to lift the legs. Because both the upper and lower body move together, it challenges lumbopelvic control, coordination, and midline stability. Proper execution emphasizes a strong abdominal brace, ribs down, and a neutral cervical spine to limit excessive lumbar extension. Range of motion is determined by your ability to keep the low back stable and the legs reasonably straight; a slight knee bend is acceptable if hamstring tension or pelvic position would otherwise be compromised. Performed with smooth, controlled tempo and clear breathing, the jackknife is a focused core-strength movement rather than a stretch or conditioning drill.

Muscle Groups: Abs, Core, Waist
Target Muscles: Rectus Abdominis
Assisting Muscles: External Obliques, Iliacus, Psoas Major, Rectus Femoris
Stabilizing Muscles: Multifidus, Quadratus Lumborum, Transversus Abdominis
Body Area: Upper Body
Body Parts: Core, Torso
Body Surface: Front
Body Symmetry: Bilateral
Equipment: Bodyweight
Exercise Patterns: Other
Exercise Type: Stretching
Functional Grouping: Trunk Flexors
Joint Involvement: Multi-joint
Muscle Location: Stomach
Movement Direction: Other
Muscle Position: Anterior
Gender: Female

How To Do The Jackknife Exercise

‘- Lie supine with legs together and extended, arms overhead in line with your ears, palms facing up.
– Brace your abdomen to lightly posteriorly tilt the pelvis; keep ribs down and neck long.
– Inhale to prepare. Exhale as you simultaneously lift your shoulder blades and straight legs, flexing at the trunk and hips.
– Reach hands toward shins/feet, keeping shoulders away from ears and gaze toward knees/toes.
– Pause briefly when torso and thighs form a “V,” maintaining the abdominal brace.
– Inhale and lower with control, touching heels and shoulder blades down lightly at the same time without arching the low back.
– Keep movement smooth—avoid swinging, yanking the neck, or letting the ribs flare.
– If the low back lifts off the floor or hamstrings limit position, slightly bend the knees or reduce the range to keep spinal control.

Jackknife Tips

‘- Start lying with legs together and extended, arms overhead in line with your ears, palms facing up.
– Brace your abdomen to lightly posteriorly tilt the pelvis and keep your ribs down before you move.
– Keep your neck long and gaze toward your knees or toes to maintain a neutral cervical spine.
– Inhale to prepare, then exhale as you simultaneously lift your shoulder blades and straight legs.
– Reach your hands toward your shins or feet while keeping your shoulders away from your ears.
– Pause briefly when your torso and thighs form a “V,” maintaining your abdominal brace.
– Inhale and lower with control, touching your heels and shoulder blades down lightly at the same time.
– Avoid arching your low back, swinging your body, yanking on your neck, or letting your ribs flare.
– If your low back lifts off the floor or hamstrings limit your position, slightly bend your knees or reduce your range of motion.

Jackknife Beginner Introduction

The Jackknife, also known as a V-up, is a bodyweight core move performed on the floor that brings the upper and lower body toward each other into a compact “V” shape. It blends bending at the waist with lifting from the hips, so the abs, side abs, and hip flexors all share the workload. Because the shoulders and legs rise together, the exercise places strong emphasis on control through the lower back and hips, along with solid overall core stability.

This movement centers on a firm, steady midsection rather than speed or momentum. The neck and head stay in line with the body while the torso and thighs approach each other, with the hands reaching toward the legs at the top. The motion is smooth in both directions, with the heels and upper back lightly returning to the floor together. A small bend in the knees or a slightly smaller V position still fits the intent of the exercise, as long as the midsection stays stable and the action remains deliberate.