Stop Doing Leg Pull In Knee Up Like This (Read This First)

You want that deep, burning contraction in your lower abs, but instead, you feel a sharp pinch in your hips or a dull ache in your lower back. If that sounds familiar, you aren’t alone. The leg pull in knee up is one of the most effective, yet frequently butchered, core exercises in the gym.

It looks simple enough—sit down, pull your knees in, extend them out. But simplicity often masks the technical nuance required to actually target the core rather than just yanking on your hip flexors. Let’s fix your form and get the tension where it belongs.

Key Takeaways

• Primary Target: The move specifically targets the lower region of the Rectus Abdominis.
• The Secret Sauce: Posterior pelvic tilt (tucking your tailbone) is non-negotiable for safety.
• Common Error: Leading with the feet instead of the knees shifts tension to the quads.
• Equipment: Can be performed on a flat bench (greater range of motion) or the floor.

Understanding the Leg Pull-In Muscles Worked

Before we fix your mechanics, you need to understand the engine driving this movement. Many lifters ask about the leg pull-in muscles worked because they feel it everywhere except their abs.

The Agonist: Rectus Abdominis

Specifically, this move targets the lower fibers. While you can't completely isolate the "lower abs" (it's one long muscle sheet), you can emphasize the lower region by moving the legs toward the torso while stabilizing the upper body.

The Synergists: Hip Flexors (Iliopsoas)

This is where things get tricky. Your hip flexors are designed to lift your legs. In a leg pull knee up, they will work. However, the goal is to make them the secondary movers, not the primary ones. If your abs are weak or your form is loose, the hip flexors take over, leading to that tight, snapping feeling in the front of your hip.

The Setup: Bench vs. Floor

You can do these on the floor, but I usually recommend a flat bench. Why? Clearance. On the floor, your heels often drag or clip the ground, causing you to unconsciously hike your hips or arch your back to compensate. A bench allows your legs to drop slightly below hip level, increasing the stretch on the abs.

Execution: The "Accordion" Technique

Don't think about moving your legs back and forth. Think of your torso and thighs as an accordion closing.

1. Sit on the edge: Position yourself on the edge of a bench. Grip the sides of the bench behind your hips for stability.
2. The Tilt: Lean back slightly (about 45 degrees). Crucial step: Tuck your pelvis under. Imagine trying to pull your belly button through to your spine.
3. The Pull: Exhale forcefully as you pull your knees toward your chest. Do not just lift your feet; drive the knees in.
4. The Squeeze: At the top of the movement, your lower back should round slightly as you crunch the abs.
5. The Release: Inhale as you extend your legs out. Stop just before your lower back starts to arch off the bench.

Common Mistakes That Kill Gains

The "Back Arch"

If there is a gap between your lower back and the hypothetical backrest, you are in the danger zone. This puts shear force on the lumbar spine. If you can't keep a neutral or slightly rounded spine, you are extending your legs too far out.

The Momentum Swing

Bouncing out of the bottom position uses elastic energy, not muscle tension. Pause for a split second when your legs are fully extended. If you can't stop the momentum, you aren't controlling the weight of your legs.

My Personal Experience with Leg Pull In Knee Up

I have a love-hate relationship with this movement dating back to my early garage gym days. I remember doing these on a thin yoga mat on concrete, and the first thing I noticed wasn't the ab burn—it was the raw friction on my tailbone.

I realized quickly that I was balancing directly on my coccyx (tailbone) rather than the meat of my glutes. It was excruciating. The fix wasn't more padding; it was changing my center of gravity.

I learned that by leaning back an extra two inches and actively rounding my lumbar spine, I could roll off the sharp bone and onto the upper glute. Another thing the textbooks don't tell you: the "hip pop." For weeks, my left hip would make a distinct click on every rep. It didn't hurt, but it was annoying. I found that slightly widening my knee path—pulling them toward my shoulders rather than the center of my chest—silenced the clicking instantly. It engaged my obliques slightly more and stopped the tendon from snapping over the hip bone.

Conclusion

The leg pull in knee up is a staple for a reason, but it requires respect. It is not just a "finisher" to be rushed through at the end of a workout. Treat it with the same biomechanical focus as a heavy squat. Control the eccentric, mind your pelvic tilt, and stop if your lower back starts to scream. Your core will thank you.

Frequently Asked Questions

Why does my lower back hurt during leg pull-ins?

This usually happens because your core has fatigued, causing your anterior pelvic tilt to increase (arching the back). When the abs stop stabilizing the pelvis, the heavy load of your extended legs pulls directly on the lumbar spine. Stop the set immediately if you feel this pain.

Can I add weight to this exercise?

Yes, but proceed with caution. Once you can perform 20 strict reps with perfect control, you can hold a light dumbbell between your feet. However, ensure you don't sacrifice the "crunch" at the top for the sake of moving the weight.

Is the leg pull knee up better than a hanging leg raise?

It isn't necessarily "better," but it is more scalable. The hanging leg raise requires significant grip strength and shoulder mobility. The seated leg pull-in removes those variables, allowing you to focus purely on the abdominal contraction, making it ideal for hypertrophy (muscle growth).