Weighted Jack-knife Sit-up

Muscles

Target

* Rectus Abdominis

Synergists

* Iliopsoas
* Tensor Fasciae Latae
* Pectineus
* Sartorius
* Adductor Longus
* Adductor Brevis
* Obliques

Dynamic Stabilizers

* Rectus Femoris

Instructions

Preparation

Sit on floor or mat. Place weight between ankles or use no weight. Lie supine with hands to sides.

Execution

Simultaneously raise knees and torso until hips and knees are flexed. Return to starting position with waist, hips and knees extended. Repeat.

Comments

Begin each repetition with upper back on floor to allow abdominal muscles to work dynamically. The Rectus Abdominis and Obliques dynamically contract only when actual waist flexion occurs. With no waist flexion, Rectus Abdominis and External Oblique will only isometrically contract to stabilize the pelvis and waist during hip flexion. See Spot Reduction Myth and Lower Ab Myth. This exercise is typically performed without added resistance.

Source: exrx.net