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The Problem with Leg Lifts

 
By: NCSF  on:  Dec 16 2011
3  Commentscomments
 
 
 
 

Although many exercisers still use them, leg lifts are a contraindicated exercise. The idea that lifting ones legs off the ground for abdominal development is flawed at the biomechanical level. The rectus abdominis connects the sternum to the pelvis. The abdominals do not attach to the femur; therefore the contraction of the abdominal musculature will pull on the pelvis in the supine position – not the legs. The proper contraction of the abdominals in the supine position will cause a posterior pelvic tilt as the pelvis rotates toward the sternum. This is commonly seen during the abdominal curl-up, or crunch as it is better known. The limited range of motion employed, approximately 30° of spinal flexion, is driven via isolated contraction of the rectus abdominis. To the contrary, when leg lifts are employed the abdominals take on only an assistive role as the hip flexors take over as the prime mover. The iliopsoas, or hip flexor, is actually a muscle group comprised of the iliacus and psoas major (the psoas minor attaches to the pelvis). Additionally, the rectus femoris also crosses the hip and serves the dual role of hip flexion and knee extension.

The long resistance arm created by the extended legs during leg lifts creates resistive torques that pull on the attachment sites of the hip flexors. Under this resistance the attachment site of the psoas major pulls the lumbar spine into an arch while the concurrent pull of the iliacus on the iliac spine further increases the lordotic curve due to an increasing anterior pelvic tilt. When in this position, the abdominals cannot serve as a mover until the pelvis moves posteriorly. Therefore, supine leg lifts are a (contraindicated) hip flexor exercise that places unnecessary strain on the structures of the spine. One caveat to the supine exercise is once the legs reach a position that allows for posterior pelvic rotation the abdominals contribute to the movement. Therefore, in a supine position a common adjustment is to flex the knees and hips to 90 degrees as a starting point and the action more efficiently addresses the abdominals, albeit through a limited range of motion.

A better way to properly address the abdominals using the distal load of the legs is to perform the exercise from a hanging position. Again, the movement requires a posterior pelvic tilt, but due to the removal of the forced fulcrum created by the ground, the abdominals gain a level of mechanical advantage. Simply hanging and flexing the hips to 90 degrees is a hip flexor exercise, but once the pelvis rotates backward, the abdominals are responsible for the brunt of the forces. The exercise from the hanging position creates a closed chain environment which increases stability requirements and often explains the “swinging” action in those who cannot properly maintain position. Modification to the hanging requirements are commonly seen when exercisers use elbow supports by a machine or the bar straps which provide mechanical advantage and help reduce the stress placed on the shoulders particularly for those with tight lats. The exercise begins from an extended body position and is completed when the knees reach the height of the chest. Whether using extended or flexed knees the emphasis is placed on pelvic rotation rather than hip flexion. Common errors occur when incomplete movements are used or when momentum is generated from hip flexion or swinging actions dominate the force production through rotational inertia.

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Supine Leg Lifts
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Comments
 
 
 
Rudy Pineda
Date: Jan 9 2012 5:15 PM
 
 
I would agree by saying that the abdominal musculature is activate during the exercise; however the article is correct “the abdominals are not the prime movers for this exercise” The Psoas Major originates from the transverse processes of the lumbar vertebrae I-V (low back) and merges with the Iliacus to form the Iliopsoas. This muscle the runs across the iliopubic eminence into its insertion on the lesser trochanter of the femur (thats how the legs are pulled upward). Clients with the inability (primarily due to weakness) to decelerate the downward movement of the legs, are at risk of increasing their lordotic curvature (as mentioned in the article) and potentially causing additional damage to adjacent structures in the lumbar spine (e.i nerve root compression). There’s many abdominal exercises out there, why do this one? If I was to recommend this exercise it would be only as an Isometric hold exercise.
 
 
 
Joshua Wiltberger
Date: Jan 4 2012 2:18 PM
 
 
Lol Nice ^. I agree with the article, sure you’re not using the rectus abdomens muscles as a primary mover , but as long as your instructing your client to keep a neutral pelvic tilt (back flat on floor) and not an anterior pelvic tilt ( gap between floor and lower back) it’s a great isometric hold for the abdominal muscles. Try it!
 
 
 
Peter Cruttenden
Date: Dec 18 2011 9:00 AM
 
 
But as the old saying goes "The thigh bone is connected to the hip bone....." There is still engagement of the abdominals when doing leg lifts.
 
 
 
 
 
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