How Leg Lifts Work the Abdominals
Leg Lifts Can Vary in Intensity
The Pelvic Tipping Point: Retroversion versus Anteversion
Leg Lifts Can Target Specific Abdominal Muscles
The Basic Leg Lift
The Standard Lift
- Lie down on your back.
- Bring your legs up toward the ceiling.
Variations
- Keep your knees straight or bent.
- Lift your legs to a more vertical or less vertical position.
- Perform the exercise with one or both legs.
- Lift your legs to the front of your trunk or to one side or the other.
- Once you’ve lifted your legs, you can make a bicycling or scissoring movement, draw shapes, write your name, et cetera.
The many variations of the leg lift change:
- The intensity of the exercise
- The abdominals that are worked
How Leg Lifts Work the Abdominals
The first thing that we need to understand about leg lifts is that it’s not the abdominals that lift the legs, but the hip flexors (primarily the psoas, iliacus, sartorius, and tensor fascia latae muscles).
1 • The Hip Flexors Create Anteversion
The hip flexors don’t just lift the legs; the fact that they are attached to the pelvis means that at the same moment they pull the pelvis into anteversion.
2 • The Abs Prevent Anteversion
It’s here that the abdominals intervene to prevent the anteversion of the pelvis.
3 • The Abs Stabilize the Pelvis
The job of the abdominals is therefore to stabilize and fix the pelvis.
Leg Lifts Can Vary in Intensity
Lifting one leg is much easier than lifting both legs. This difference is easy to feel. Trying to lift just one leg is a good way to see whether you can stabilize the pelvis while doing this exercise.
The exercise is also easier if the leg that is not lifted is pushed into the floor. This helps stabilize the pelvis. If you don’t press the supporting leg into the floor, greater abdominal strength is required to lift the other leg.
A leg lift is much easier when the leg is bent rather than straight. If you think of the leg as a lever, the fulcrum is at the hip. Bending the leg essentially halves the length of the lever that the muscles must raise at the fulcrum. Because bending brings the weight of the leg closer to the body, less strength is required to lift it.
But there’s another aspect at play here: Straight legs pull on hamstrings, found at the back of the thighs. The straighter the legs, and the closer they are pulled to the trunk, the more difficult the exercise becomes for the hamstrings, which work in the opposite direction. These muscles are progressively put under greater tension and brake the action of hip flexion. It’s then necessary to increase the contraction of the hip flexors and also the contraction of the abdominals to fix the pelvis.
The angle of hip flexion changes the intensity of the exercise. The lower the leg drops—further from the vertical line of gravity—the more difficult the exercise becomes. We can easily feel that holding the legs just off the ground requires much more effort (for the hip flexors) than holding them in a vertical position. The pelvis is pulled more strongly into anteversion, and so the abdominals must work harder to stabilize it.
With leg lifts, we can start with the easiest variations and move to the more difficult ones.
The easiest variation is to lift just one leg, with the leg bent, to the point where the hip flexes at a ninety-degree angle (so that the leg is more or less vertical), while pushing the supporting leg into the floor.
The most difficult variation would be to lift both legs at the same time, with the legs straight and held very close to the floor.
The Pelvic Tipping Point: Retroversion versus Anteversion
1 • Retroversion
Lie on your back with your knees bent, bringing them as close as you can to your chest. Feel how your coccyx lifts from the floor and your pelvis goes into retroversion.
2 • Anteversion
Very slowly lower one leg toward the floor. On the side of the leg that is lowering, feel how that side of the pelvis changes position: from retroversion, it suddenly rocks into anteversion.
Next, lower both bent legs slowly toward the floor. Feel the moment at which the whole pelvis moves from retroversion to anteversion. This is the “tipping point.” It corresponds to a certain angle of hip flexion. Return several times to that precise point where the pelvis changes position.
Looking at the pelvis, we can say that any movement that occurs before the tipping point is retroversion, and any movement that occurs beyond the tipping point is anteversion.
Retroversion
Anteversion
Why does the pelvis go into retroversion when we bring our knees to our chest? The extreme hip flexion pulls the muscles and the ligaments at the back of the hips. When under tension, they pull the pelvis into retroversion.
Why does the pelvis go into anteversion when we bring our knees back toward the floor? When we extend our hips, the muscles at the front of the hips support the weight of the legs. The contraction of these muscles pulls the pelvis into anteversion.
Leg Lifts Can Target Specific Abdominal Muscles
If we raise the legs symmetrically, the pelvis moves into retroversion and the two sides of the pelvis are balanced. The rectus abdominis is the dominant player here as it retroverts the pelvis.
If the movement is asymmetrical, one side of the pelvis will move toward anteversion. For example:
- If we raise just one leg
- If we drop one or both legs a bit to one side
- If we scissor the legs, draw shapes in the air with our feet, et cetera
In all of these cases, the pelvis will turn to the side that is dominated by the movement of the legs. Therefore, to stabilize the pelvis, we need to suppress anteversion (the work of the rectus abdominis) and also inhibit rotation (the work of the obliques).
The work of the obliques can vary in intensity.
Leg Lifts Can Endanger the Lumbar Spine
1 • Flexion
When we bend our knees and bring them toward our chest (before the tipping point; see The Pelvic Tipping Point: Retroversion versus Anteversion), the pelvis pulls the lumbar spine into flexion. This stretches the muscles and ligaments of the back, which can be helpful if they are tight. It also compresses the disks at their front and stretches them at their back, which can be beneficial if done cautiously. However, this flexion can aggravate existing problems or do damage if the structures in the lumbar area are fragile.
2 • Extension
When we bring our legs back toward the floor (beyond the tipping point), the muscles that contract to hold the legs up (primarily the psoas, iliacus, sartorius, rectus femoris, and tensor facsia latae) pull the pelvis into anteversion—an action that requires an equivalent contraction of the abdominals. If we don’t prevent this anteversion, the lumbar spine is pulled into extension. This contraction creates strong compression of the vertebrae and the intervertebral disks at the back.
3 • Stability
If the pelvis isn’t stabilized when we do various leg lifts, it’s going to move alternately before and beyond the tipping point, squeezing the disks to the front and then to the back, which can put them under a great deal of stress. When adding leg beats (alternately crossing your ankles one over the other while your legs are lifted), it’s very important to keep the pelvis fixed. Modify the range of motion depending on pelvic stability.
In leg lifts, the combination of the movement and compression is hard on the disks.
Protecting the Lumbar Spine
It’s absolutely imperative that we stabilize the pelvis during leg lifts. The pelvis shouldn’t retrovert when we bring our legs into flexion; this requires the back muscles to work. The pelvis shouldn’t antevert when we bring our legs back to the floor; this requires the abominals to work (primarily the rectus abdominis). Yet for someone who has weak abdominals, it’s not only impossible to keep the pelvis stable, it’s often even difficult to feel when the pelvis is moving.
Stabilizing the Pelvis
To stabilize your pelvis, you can place your hands, palm down, under the lumbar spine. Your hands will prevent the lower back from rounding.
You can also work with just one leg (bent or straight).
Bend the supporting leg at the knee and place the foot on the floor. The pressure of the foot on the floor will inhibit the arching of your lower back. With your free leg, you can perform leg lifts of varying degrees of difficulty.
While performing the exercise, you can make it progressively more difficult by:
- Releasing the pressure on your supporting foot, letting the abdominals take over the work
- Avoiding letting your lower back touch the hand that you’ve placed under it, letting the back muscles take over the work
