Knee raises are an effective exercise for developing the muscles of the core, representing a significant step up from floor-based abdominal work. The movement involves lifting the knees toward the chest while the upper body is anchored, creating a demanding challenge for the midsection. When performed with correct form, this suspension-based exercise requires the core to stabilize the entire body, offering a comprehensive workout.
What Muscles Do Knee Raises Work?
The primary muscle targeted during a knee raise is the rectus abdominis, the long muscle running down the front of the abdomen. The lower portion of this muscle is particularly engaged as it works to flex the spine and pull the pelvis upward toward the ribcage. The hanging variation of this exercise can produce very high levels of muscle activation in this area.
The obliques, the muscles along the sides of the abdomen, also play a significant supporting role. They stabilize the torso, preventing the body from swinging or twisting as the legs are lifted. They maintain a rigid posture by resisting unwanted rotation.
Lifting the knees toward the chest is primarily a function of hip flexion, engaging the hip flexors, including the iliopsoas. To maximize abdominal engagement, the rectus abdominis must initiate the movement by tilting the pelvis, rather than allowing the powerful hip flexors to dominate the work.
How to Perform Knee Raises Effectively
The Hanging Knee Raise is the most common and demanding variation. Grasp a pull-up bar with an overhand grip, allowing your body to hang with arms fully extended. Engage your shoulders by pulling them slightly down to establish a stable starting position.
Initiate the movement by bracing your core and slightly tucking your pelvis backward, which activates the abdominal muscles. Slowly drive your knees upward toward your chest, aiming for your thighs to be at least parallel to the floor. Focus on curling your spine as you lift the knees.
Captain’s Chair Knee Raise
An alternative is the Captain’s Chair Knee Raise, performed using a vertical frame with padded armrests. Place your forearms on the pads and grip the handles to support your body weight. Your back should be pressed against the back pad, maintaining a straight, stable spine.
Slowly raise your bent knees toward your chest until your quads are parallel to the ground. This variation reduces the demand on grip and upper body stability, allowing for a more intense focus on the abdominal contraction. In both variations, the descent of the legs should be controlled and slow, returning to the starting position without losing core tension.
Technique Adjustments for Stronger Core Engagement
The most common flaw is allowing the hip flexors to dominate the movement, minimizing abdominal work. To fix this, focus on achieving a posterior pelvic tilt at the beginning of each repetition. This means actively engaging your abs to tilt the top of your pelvis backward toward your ribs before the knees start to rise.
This pelvic tuck ensures that the rectus abdominis is the primary muscle responsible for curling the spine. If you do not initiate the movement with this tilt, the exercise becomes a less effective hip flexor movement. Think of the movement as bringing your sternum and pubic bone closer together, which is the function of the abdominal muscles.
Another adjustment for maximizing results is to eliminate any swinging or momentum. Swinging converts the core work into a less productive, rhythmic motion that reduces the time your muscles spend under tension. Start each repetition from a dead-stop and concentrate on a slow, deliberate lift and an even slower lowering phase.
The eccentric, or lowering, phase of the knee raise is where significant muscle growth and strength gains occur. Lower your legs back to the starting position over a period of two to three seconds, fighting gravity the entire time. Maintaining this controlled tempo keeps the core muscles engaged throughout the full range of motion.