Knee Ups, also known as Knee Raises, are a foundational exercise for strengthening the muscles of the torso. This movement involves lifting the knees toward the chest while maintaining stability in the trunk. The exercise is highly adaptable, making it accessible to nearly everyone, as it can be performed lying on the floor, seated on a bench, or while suspended from a bar.
Proper Execution and Posture
The lying Knee Up begins with the person supine on the floor, hands placed at the sides or lightly supporting the head. The knees are typically bent, and the feet are flat on the floor. The movement phase starts with a controlled exhalation as the abdominal muscles contract to lift the knees toward the chest.
The goal is to curl the hips and lower back off the floor slightly, focusing on controlled spinal flexion rather than just pulling the legs upward. The return phase involves a slow, deliberate lowering of the knees back to the starting position while inhaling. Maintaining muscle tension throughout the range of motion prevents the lower back from arching away from the floor upon extension.
Common errors include allowing the lower back to excessively round or arch, which shifts tension away from the targeted muscles. Also avoid using momentum to swing the legs up, which reduces the muscular work. To ensure proper form, the movement must be initiated by the abdominal muscles, keeping the upper body and head relaxed.
Primary Muscle Engagement
The Knee Up primarily targets muscles responsible for flexing the hip and stabilizing the trunk. The initial phase of lifting the legs is driven largely by the hip flexors, specifically the iliopsoas. The iliopsoas, composed of the psoas and iliacus muscles, runs from the lumbar spine and pelvis to the femur, making it a powerful flexor of the hip joint.
As the knees continue to rise, the abdominal muscles become increasingly engaged to curl the pelvis and rotate the spine. The rectus abdominis is the main muscle responsible for this spinal flexion. The oblique muscles, situated on the sides of the abdomen, also work synergistically to assist with torso stability and prevent unwanted side-to-side movement.
The involvement of the abdominal muscles increases significantly the higher the knees are raised, necessitating a greater degree of pelvic rotation. Maintaining a braced core throughout the movement also helps stabilize the lower spine against the forces generated by the moving legs.
Variations for Progression
Once the standard lying Knee Up is mastered, several variations exist to modify the intensity and challenge different aspects of the core. The Seated Knee Up is a moderate progression that requires more balance and core stability, as the base of support is reduced. This version is performed while sitting on the edge of a bench or chair, leaning the torso back slightly, and drawing the knees toward the chest.
The Hanging Knee Up is generally considered the most advanced variation, as it introduces the challenge of supporting the entire body weight while performing the movement. This requires substantial grip and upper-body strength, in addition to significant core activation. For the Hanging Knee Up, the knees are lifted toward the chest while suspended from a pull-up bar, demanding greater control to prevent the body from swinging.
Weighted Knee Ups can be performed by securing a light dumbbell between the feet or ankles, which increases the load on the hip flexors and abdominal muscles. Alternatively, twisting the knees to one side during the upward phase of the lift, known as a Twisting Knee Up, places a greater emphasis on the oblique muscles. For modification, reducing the range of motion or performing the movement with one knee at a time can lower the difficulty.