If you’ve ever done straight leg raises and thought, “This should be easy, right?”—you’re not alone. At first glance, it looks like one of the most basic ab moves out there. You just lie down, lift your legs, and boom—core gains. But here’s the thing: even simple exercises can mess you up if you don’t do them right.
I’ve seen a lot of people—myself included—make the same mistakes when doing this move. And trust me, your lower back and hip flexors will let you know if you’re doing it wrong.
So let’s walk through the 3 most common mistakes in straight leg raises, why they matter, and how you can fix them. These small tweaks can help you get the most from the movement without jacking up your lower back or wasting reps.
What Are Straight Leg Raises?
Before we dive into the mess-ups, let’s make sure we’re on the same page. Straight leg raises are an ab and hip flexor exercise that you do lying on your back. The idea is to lift both legs off the ground while keeping them straight, hold briefly, then lower them back down.
Sounds simple, but there’s more going on here than you’d think.
When done right, this move fires up your core, especially the lower abs. It also works the hip flexors, which are key muscles that help you lift your knees and stabilize your pelvis. Plus, it can help with posture and balance.
Mistake #1: Arching Your Lower Back
This one’s a biggie, and almost everyone does it at some point.
When you lift your legs, your abs are supposed to keep your lower back pressed into the floor. But a lot of people let their lower back lift off the mat—especially when their legs get close to the ground.
Why it matters: When your back arches, your core checks out and your spine takes on the load. That’s not what we want. It can lead to lower back pain, strain, and basically turns the exercise into a hip flexor stretch more than an ab move.
How to fix it:
- Focus on keeping your back glued to the floor the whole time.
- If you can’t do the full movement without arching, try bending your knees a little or only lowering halfway.
- You can also place your hands under your glutes for added support (but not under your back—don’t cheat).
Personal tip: I like to exhale slowly as I lower my legs. It helps keep my abs tight and my back flat.
Mistake #2: Using Momentum Instead of Control
I get it. It’s tempting to swing your legs up and down just to get through the set. But when you start kicking your legs or dropping them too fast, you’re not really engaging your abs anymore.
Why it matters: Using momentum turns this from a strength move into a swing fest. You’ll feel it less in your core and more in your hips or even neck, especially if you’re straining your head off the ground.
Plus, you’re putting extra pressure on your lower back again (yep, that back’s not gonna be happy).
How to fix it:
- Slow it down. Like, real slow. Try a 3-count up and 3-count down pace.
- Keep your core braced the whole time—like someone’s about to punch you in the stomach.
- Don’t let your legs hit the floor between reps. Hover just an inch or two above to keep tension going.
Extra challenge: Add a light ankle weight or resistance band if you want more burn without speeding up.
Mistake #3: Not Engaging the Core Properly
Sometimes we think we’re working our abs, but we’re really just going through the motion. If your abs aren’t actively pulling your legs up and down, you’re missing out on the whole point of the exercise.
Why it matters: You’ll end up overworking your hip flexors and under-training your core. That means slower progress, less definition, and maybe even that annoying pinch in the front of your hips after leg day.
How to fix it:
- Pre-engage your core before you even lift your legs. Take a breath in, and then tighten your abs like you’re bracing for impact.
- Try doing the move with your hands on your abs so you can feel them working.
- Keep your neck and shoulders relaxed. You don’t need to curl your upper body up—just keep your focus on the midsection.
Helpful hack: Try adding a posterior pelvic tilt. That means slightly tucking your pelvis under and flattening your lower back before you lift your legs. It helps lock your abs in from the get-go.
Straight leg raises are awesome when done right. They build lower ab strength, help with core stability, and even prep your body for harder stuff like hanging leg raises or toes-to-bar. But only if your form is dialed in.
If you’re making any of these three mistakes—arching your back, using momentum, or not engaging your core—it’s time to slow down and reset. Just a few form tweaks can turn this from “meh” to “whoa, I actually feel my abs now.”
Next time you do straight leg raises, think less about how many reps and more about how you’re doing them. Your core (and your back) will thank you.
