The leg raise is a strength training exercise which targets the iliopsoas (the interior hip flexors). This is an excellent exercise if you find it difficult to feel the work on your lower abdominals.
Because the abdominal muscles are used isometrically to stabalize the body during the motion, leg raises are also often used to strengthen the rectus abdominis muscle and the internal and external oblique muscles.
Lying Leg Raise
The lying leg raise is done by lying on the floor on the back. It is done without apparatus except possibly cushions or weights for added resistance.
Trainees generally caution to keep the lower back in contact with the floor and place hands to sides or under lower back for support.
Due to leverage, the hardest portion of a supine (lying) leg raise is generally the first part when the legs are on the floor, as this is when the femur is parallel with the earth and perpendicular to the pull of gravity.
For more advance level perform them on an incline bench. Because this exercise is difficult, beginners should adjust the board to lower angle.
Hanging Leg Raises or Tractioned
Leg raises can also be performed hanging onto an overhead bar. These are known as hanging leg raises and are more challenging than lying leg raises.
Extending the knee joint increases the demands of leverage on both hip and spine flexors. It also reduces the contribution of the rectus femoris muscle via over-active insufficiency, creating more work for the non-quadriceps hip flexors.
The generic term “leg raise” usually indicates a bended knee, though the term “knee raise” is used to distinguish it from the category which includes both variations.
They can also be performed on other apparati such as dip bars and captain’s chairs, which also involve the torso being suspended in the air, except that the stress through the arms is different.
This variation of leg raise allows the pelvis to freely rotate. It is generally the more difficult variation for the abdominal muscles due to having to support the pelvic weight as opposed to simply stabilizing its alignment.
Alongside this however, it is also potentially the easiest to use bad form on, because users may use a swinging motion to ‘cheat’ by building up momentum. If the abs are not properly engaged, the spine can easily hyperextend and go into anterior pelvic tilt. It should be going into posterior pelvic tilt if the movement is being done to target the rectus abdominis.
This movement can also be done with “ab slings” which hold the humeri in ~90 degrees of shoulder flexion. This allows one to do a more traditional crunch by bringing the knees up to touch the elbows. It is however possible to assist in this movement by using the lats and other muscles to perform shoulder extension.
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Watch this Graphical Hanging Leg Raise Video
Seated Leg Raise
A “knee raise” type of seated leg raise or also known as knee tuck, with flexed knee joint.
A seated leg raise is halfway between a lying raise and a hanging/ suspended/ tractioned one. They are done seated on an elevated surface. Usually the hands are placed on the surface (or arm rests) and bear some of the body’s weight to lessen the weight borne on the buttocks and increase abdominal recruitment.
This exercise can be done using weights, such as wearing ankle weights or weighted boots, holding a dumbbell between the feet, or slipping one’s feet through kettlebells. These weights are also affected by the increased leverage of a straightened knee.