Leg raises are often featured in core workout routines, carrying a reputation as one of the most demanding exercises for the abdominal muscles. The movement involves lying on the back and raising the legs, which suggests a direct and powerful way to strengthen the entire front of the torso. However, the true effectiveness of the exercise for the abdominal muscles depends heavily on how the body is stabilized during the lift. The interaction between the muscles that move the legs and those that stabilize the spine determines whether the leg raise primarily targets the abs or another muscle group entirely.
Primary Muscles Activated During Leg Raises
The leg raise is anatomically a hip flexion movement, meaning the action of lifting the legs is primarily executed by the hip flexors, not the abdominal muscles. The most powerful hip flexor is the iliopsoas, a deep muscle group connecting the lumbar spine and pelvis to the femur. This muscle is highly activated throughout the leg-lifting motion.
The abdominal muscles, including the rectus abdominis and the obliques, are engaged isometrically to prevent the lower back from arching away from the floor. Lifting the legs creates a long lever that significantly increases the force attempting to pull the pelvis into an anterior tilt, which can strain the lower back. The role of the abdominals is to counteract this force by creating a posterior pelvic tilt, stabilizing the core.
Electromyography (EMG) studies confirm that while the leg raise is effective at strengthening the rectus abdominis, it also elicits significant activation of the hip flexor muscles. Abdominal engagement is therefore a stabilizing function, rather than the primary driver of the movement. The supine leg raise relies on the abs for stability.
Mastering Proper Form for Abdominal Engagement
Maximizing the recruitment of the rectus abdominis during a supine leg raise depends entirely on controlling the pelvis and spine. Before initiating the lift, the back must be secured against the floor by performing a slight posterior pelvic tilt. This means gently tucking the tailbone upward and drawing the navel toward the spine to flatten the lumbar curve.
A common mistake is allowing the lower back to arch as the legs are lowered, which immediately shifts the load away from the abdominals and onto the hip flexors and lumbar spine. If the back arches, the exercise becomes a high-risk hip flexor workout with minimal abdominal benefit. To prevent this, placing hands beneath the lower back or hips can help maintain that crucial contact with the floor.
The most effective part of the movement for abdominal engagement is the controlled lowering of the legs, known as the eccentric phase. The legs should only be lowered as far as the individual can maintain the contact between their lower back and the floor. This often means stopping well before the heels reach the ground. Concentrating on an abdominal brace and exhaling during the upward lift helps maintain the necessary intra-abdominal pressure for stability.
Modifying the Exercise and Alternative Core Movements
For individuals who struggle to keep their lower back flat during the straight-leg version, the exercise can be modified to reduce the leverage and hip flexor involvement. Bending the knees significantly shortens the lever arm, making the bent-knee leg raise, or reverse crunch, an excellent regression. Another modification involves performing a single-leg lower, where one leg remains bent with the foot on the floor for stability while the other leg is slowly lowered and raised.
A progression of the movement is the hanging leg raise, which allows the pelvis greater freedom to rotate, turning the exercise into a dynamic spinal flexion movement. Initiating the hanging version by rolling the hips up toward the torso helps engage the abdominal muscles to create spinal flexion, increasing their activation.
If leg raises prove unsuitable due to persistent lower back strain, several alternatives provide high abdominal activation with less reliance on hip flexors.
Alternative Core Movements
The reverse crunch, performed by curling the hips off the floor toward the chest while keeping the knees bent, is a highly effective way to target the rectus abdominis. Static holds, such as the plank, demonstrate superior engagement of the transverse abdominis and obliques, which are crucial for overall spinal stability. For a dynamic, rotational challenge, the bicycle crunch trains the rectus abdominis through spinal flexion and recruits the obliques through rotation.