What Muscles Do Leg Lifts Work and How to Do Them

Leg lifts primarily work the hip flexor muscles, especially the iliopsoas (the psoas major and iliacus), along with a strong supporting role from the abdominal muscles, particularly the rectus abdominis. The exact balance between hip flexors and abs shifts depending on the variation you choose, the angle of your legs, and how well you stabilize your pelvis. That interplay is what makes leg lifts both effective and surprisingly easy to do wrong.

The Hip Flexors Do Most of the Heavy Lifting

When you lie on your back and raise a straight leg toward the ceiling, the muscles responsible for pulling your thigh toward your torso are the ones doing the bulk of the work. The psoas major, which runs from your lower spine through the pelvis and attaches to the upper thighbone, and the iliacus, which lines the inside of the pelvic bowl and merges with the psoas to form the iliopsoas, are the dominant drivers. Research using fine-wire electrodes placed directly into these deep muscles found that they are the primary contributors to hip flexion during a straight leg raise, and their activity climbs sharply as the leg gets higher. At around 60 degrees of hip flexion, the iliopsoas reaches over 60 percent of its maximum voluntary contraction capacity.¹

Several other muscles assist, but their contributions are smaller than most people expect. The rectus femoris, one of the four quadriceps muscles and the only one that crosses the hip joint, fires during leg lifts. So do the sartorius, adductor longus, and tensor fasciae latae. However, these synergist muscles do not contribute greatly to the increasing demand as the hip flexes higher. A study measuring all of these muscles during a straight leg raise confirmed that, while synergists are active, the psoas major and iliacus are the ones that ramp up at larger hip flexion angles.²

One interesting detail about the psoas: during an active straight leg raise, the psoas fires not only on the side lifting the leg but also on the opposite side. The iliacus, rectus femoris, and adductor longus are only active on the working leg’s side, but the psoas activates contralaterally as well.³ This suggests the psoas has a dual job: flexing the hip and stabilizing the lumbar spine. That second role matters a lot when you think about why leg lifts can feel so intense in the lower back.

How the Abdominals Get Involved

Most people think of leg lifts as an “ab exercise,” and they do work the abs, but not in the way you might picture. Your abdominal muscles are not raising the leg. They are anchoring your pelvis so your hip flexors have a stable base to pull from. When you lie on your back and lift both legs, gravity wants to drag your pelvis into an anterior tilt, arching your lower back off the floor. The rectus abdominis contracts to generate a posterior pelvic tilt that counteracts that pull.⁴ In practical terms, your abs are working hard, just not to move the legs. They are working to keep your spine flat and your pelvis neutral.

This stabilizing role is no small effort. A comparison of trunk exercises found that the bilateral leg raise produced significantly greater activation of the rectus abdominis than the plank.⁵ That finding surprises people who think of planks as the gold standard for ab engagement. The reason is leverage: two heavy legs extended far from your center of gravity create a massive torque on the pelvis, and the abs have to match it or the lower back takes the load.

The deeper core muscles get involved too. The transverse abdominis, which wraps around your midsection like a corset, and the multifidus, a small muscle running along the spine, both contract to increase intra-abdominal pressure. That internal pressure acts like an inflated cushion supporting the lumbar spine from the front. Research on intra-abdominal pressure during heavy loading tasks has shown that the diaphragm is the most important single contributor to maintaining this pressure, coordinating with the surrounding abdominal wall muscles to stiffen the trunk.⁶ If you have ever felt the urge to hold your breath during a difficult leg lift, that instinct is your body trying to lock the diaphragm in place to boost spinal stability.

The Psoas Works Hardest Near the Top

Not every part of the leg lift taxes the same muscles equally. The movement has concentric (lifting), isometric (holding), and eccentric (lowering) phases, and the distribution of work shifts across them. Researchers who tracked muscle activity through these phases found that the psoas major reaches its highest activation during the late concentric phase (near the top of the lift), during the hold at end range, and during the early eccentric phase (the start of lowering). During these portions of the movement, the psoas was significantly more active than the rectus femoris.⁷

This has a practical implication: if you rush through leg lifts with momentum, swinging your legs up and letting them drop, you skip the portions where the deep hip flexors and core are working the hardest. Controlling the top of the lift and lowering slowly is where much of the exercise’s value lives.

The Hanging Leg Raise Is a Different Animal

When people move from a supine leg lift to the hanging version, the demand on the abdominal wall jumps dramatically. Hanging from a bar and raising straight legs to horizontal (or higher) produced rectus abdominis activation above 130 percent of maximum voluntary contraction in one study, with external oblique activity reaching about 88 percent of maximum. That same study measured roughly 3,000 newtons of spinal compression during the hanging straight leg raise, compared to under 2,500 newtons in the body saw, another challenging core exercise.⁸

Values above 100 percent of maximum voluntary contraction happen when the muscle is working even harder than the maximal effort researchers measured during testing. This occurs because the testing position and the exercise position create different leverage conditions, and it tells you the hanging leg raise is genuinely extreme ab work. It also means the exercise creates substantial compressive forces on the spine, which is worth knowing if you have a history of disc issues or lower back pain.

Because you are dangling from a bar, the hanging version also recruits your grip, forearms, lats, and shoulder stabilizers just to hold you in position. The obliques get more work than in the supine version because there is no floor preventing rotation, so your trunk muscles have to fight both flexion and twisting forces simultaneously.

How to Perform a Supine Leg Lift

The basic supine (lying-down) leg lift looks simple, but execution matters. Here is the standard single-leg version:

• Starting position: Lie flat on your back on a firm surface. Legs straight, arms at your sides or hands tucked just under your lower back for tactile feedback on pelvic position.
• Brace first: Before moving your legs, press your lower back gently into the floor by engaging your abs. You should feel your pelvis tilt slightly backward. Maintain this contact throughout.
• Lift one leg: Keeping the knee straight, slowly raise one leg until it reaches about 60 to 90 degrees of hip flexion. The other leg stays flat on the floor.
• Controlled descent: Lower the leg back down at the same speed you raised it. Do not let it drop. The eccentric phase is where a large share of the deep hip flexor work occurs.
• Switch sides: Repeat with the opposite leg for balanced training.

For the double-leg raise, the same principles apply, but both legs lift together. This version is substantially harder because the combined weight of two legs creates far more torque on the pelvis. If your lower back lifts off the floor at any point during the set, the abdominal muscles have lost the stabilization battle and your lumbar spine is bearing load it should not. That is the signal to stop or regress to the single-leg version.

Common Mistakes and Lower Back Stress

The most widespread error during leg lifts is letting the lower back arch away from the floor. When the abs cannot maintain a posterior pelvic tilt against the weight of the legs, the pelvis tips forward and the lumbar spine hyperextends. The hip flexors are still working, but now they are pulling on a spine that has lost its bracing. Over time, or at high volumes, this is a recipe for lower back discomfort.

A related mistake is performing double-leg raises when you do not yet have the core strength for them. Because two legs weigh roughly twice as much as one, the demand on the abdominals to stabilize the pelvis approximately doubles. Many people who can do a single-leg raise with a flat back will immediately lose spinal position with both legs. The fix is straightforward: earn the double-leg version by demonstrating that your back stays flat throughout the single-leg version under control.

Another common issue is leading with momentum. Swinging the legs up with a quick jerk shifts work away from the hip flexors and abs and into the lower back extensors, which have to eccentrically catch the movement. Since the psoas is most active during the late concentric and hold phases, momentum effectively skips the hardest part of the exercise.⁷

Adding a small neck curl, lifting your head and upper shoulders slightly off the floor, can increase abdominal engagement and help maintain the posterior pelvic tilt. This works because the sternocleidomastoid and scalene muscles co-contract with the abdominals when the neck is flexed, boosting overall trunk stiffness.⁴ If keeping your back flat during a double-leg raise is proving difficult, try adding a chin tuck and slight head lift before you raise the legs.

When Tight Hamstrings Get in the Way

Tight hamstrings can subtly change what happens during a leg lift. The hamstrings attach to the ischial tuberosity on the back of the pelvis, and when they are short and stiff, they pull the pelvis into a posterior tilt. Research has found that hamstring tightness significantly influences pelvic position during forward bending movements because of this attachment.⁹

During a supine straight-leg raise, if your hamstrings are tight, you will reach a point where the muscle pulls taut and limits how high you can lift the leg. Some people compensate by hiking the pelvis or rocking the lower back, which introduces unwanted spinal movement. Others simply cannot achieve 60 degrees of hip flexion with a straight knee, which means they never reach the range where the iliopsoas is working hardest.¹

The practical solution is either to bend the knee slightly, which slackens the hamstrings and allows more hip flexion, or to work on hamstring flexibility separately. Acute hamstring stretching has been shown to increase anterior pelvic tilt and lumbar flexion immediately afterward.¹⁰ So if your hamstrings are limiting your leg lift range, stretching them before the exercise may allow you to access a fuller range of motion where the target muscles are most active.

Progressions and Where Leg Lifts Fit in a Program

Leg lifts exist on a difficulty spectrum, and understanding that spectrum helps you pick the right version for your current level:

• Bent-knee single leg raise: The easiest version. Bending the knee shortens the lever arm, reducing the torque on both the hip flexors and the abs. Good for beginners and people rehabbing lower back issues.
• Straight single leg raise: The standard rehab and conditioning version. Allows unilateral training, which can reveal and correct side-to-side imbalances.
• Straight double leg raise: A significant jump in difficulty. Both legs create roughly double the pelvic torque. Only appropriate when you can maintain a flat back throughout the single-leg version.
• Hanging knee raise: Moving to the bar adds grip and shoulder demands. The bent-knee version keeps the lever shorter, making it more manageable than the straight-leg hanging version.
• Hanging straight leg raise: The hardest common variation, producing extreme rectus abdominis and oblique activation along with high spinal compression loads.⁸

Side-lying leg lifts deserve a mention because they target an entirely different set of muscles. When you lie on your side and raise the top leg, you are working the hip abductors, primarily the gluteus medius and gluteus minimus, along with the tensor fasciae latae. The hip flexors and abs are barely involved. Despite sharing the name “leg lift,” the side-lying version is a hip stability exercise rather than a flexion and core exercise. If your goal is hip flexor and ab training, the supine and hanging versions are the ones to focus on.

The Psoas and Spinal Health

Because the psoas major originates from the lumbar vertebrae (specifically the bodies and transverse processes of T12 through L5), its role during leg lifts has implications for spinal health that go beyond simple muscle soreness. Every time the psoas contracts to flex the hip, it also exerts a compressive and sometimes shearing force on the lumbar spine. This is why people with existing disc injuries or stenosis sometimes feel worse after leg lifts even when their form looks fine from the outside.

The finding that the psoas activates bilaterally during a single-leg raise reinforces this point.³ Even a single-leg lift loads both sides of the lumbar spine through psoas contraction. For most healthy people, this bilateral loading is actually beneficial because it stiffens the spine and improves stability. But for someone with an acute disc problem on one side, the fact that both sides of the psoas fire during every repetition means there is no way to completely unload the affected segment by switching legs.

If leg lifts consistently cause lower back pain rather than a feeling of muscular effort, the appropriate response is usually to shorten the lever arm (bend the knees), reduce the range of motion, or choose a different core exercise altogether. Exercises that challenge the abs without requiring active hip flexion, such as dead bugs, bird dogs, or the plank, can provide core training while keeping the psoas load lower. The bilateral leg raise data showing it outperforms the plank for rectus abdominis activation does not mean the plank is useless; it means the plank achieves core work through a different loading strategy that may be more appropriate depending on your spine’s tolerance.⁵

Why Breathing Matters More Than You Think

Many people hold their breath during leg lifts without realizing it. This is your body’s reflexive strategy for locking the diaphragm in place to maximize intra-abdominal pressure. That pressure helps stabilize the spine, so the instinct makes sense from a biomechanical standpoint. The diaphragm appears to be the single most important muscle for generating intra-abdominal pressure, and closing the glottis (which is what you do when you hold your breath) helps the diaphragm maintain its position.⁶

For a max-effort set of two or three reps, a brief breath hold is not dangerous for most healthy people. But for longer sets, holding your breath throughout drives up blood pressure and can cause dizziness or lightheadedness. A better strategy is to exhale during the lift (the concentric phase) and inhale during the lowering phase. This keeps some intra-abdominal pressure because the abs are still contracting to push air out, but avoids the sustained spike in blood pressure that comes from prolonged breath holding. If you find that exhaling during the lift causes your lower back to peel off the floor, that is a sign the exercise is too heavy for your current core strength, and you should regress to an easier variation.