For years, we’ve bought into the myth that sit-ups target the upper abs, while hanging knee raises hit the lower abs. Heck, I’ve written about “upper-ab exercises” because I bought into it too.
But like many training myths that float around the gym floor, this one has enough legs to run.
The six-pack muscle might look like separate muscles divided at the belly button, but that’s not the case. You can’t switch off the top half while firing up the bottom half like you’re choosing burners on a stove.
However, not every ab exercise affects the Rectus Abdominis the same way. The exercise you choose and how you perform it can shift where you feel it and which part of the muscle it emphasizes.
That’s where the distinction between isolation and emphasis becomes important.
That’s the nuance we’ll dig into rightnow. Because as you’ll see, the answer isn’t as simple as “upper and lower abs don’t exist.”
Let’s dive in.
Why We Think We Have Upper and Lower Abs
Suppose you’re lucky enough to see your abs. They don’t look like one continuous muscle, but a stack of individual muscle blocks running down the front of your torso.
However, looks are deceiving.
“Anatomically, we don’t really have separate ‘upper abs’ and ‘lower abs’ in the way people often talk about them,” explains Gareth Sapstead, author of Ultimate Abs: The Definitive Guide to Developing a Chiseled Six-Pack.. “The rectus abdominis is one paired muscle running from the pelvis up towards the ribs/sternum, with the tendinous intersections creating the six-pack appearance.”
But don’t swing too far the other way either, because here’s where this discussion gets interesting. Once people learn that the RA is one muscle, the pendulum often swings the other way completely:
Upper and lower abs don’t exist, so every ab exercise trains the entire rectus the same.
Sapstead doesn’t buy that explanation either.
“I think the fitness industry sometimes swings too far the other way, saying there’s no such thing as upper and lower abs, so exercise selection makes no difference.”
“I don’t think that’s quite right either,” says Sapstead.
Although the rectus abdominis works as a unit, different movements can shift where the greatest muscular demand occurs, Sapstead says. You cannot switch on your upper or lower abs, but that doesn’t mean exercise selection and execution are irrelevant.
“I prefer the term ‘bias’ rather than ‘isolate,’” explains Sapstead.
That’s the distinction we’ll use throughout here.
To understand how bias versus isolate works, we first need to look at what the rectus abdominis does.
What the Rectus Abdominis Does
Its obvious job is spinal flexion—bringing your rib cage and pelvis closer together. During a crunch, you’re moving your rib cage toward your pelvis. In a properly executed reverse crunch, you move your pelvis toward your rib cage. Both are spinal flexion.
But why does it matter in our upper-versus-lower discussion?
That’s important because the direction of movement changes, but we haven’t switched from one abdominal muscle to another. Instead, we’ve changed which end moves and how the muscle is challenged.
“The rectus abdominis still functions as a unit,” explains Sapstead. “But we can alter where the exercise places greater demand.”
But flexion isn’t its only job.
The RA resists excessive spinal extension. During an ab-wheel rollout, for example, gravity wants to pull your lumbar spine into extension as your arms move farther from your body. Your abs must create tension to prevent your lower back from arching.
Creating tension also matters outside direct ab training. A strong core connects the upper and lower body, letting you transfer force while squatting, deadlifting, carrying, throwing, and doing other athletic movements.
The rectus abdominis also helps control your pelvis and rib cage position. When it contracts, it can contribute to posterior pelvic tilt—think about tucking your pelvis under you.
Now let’s get to a question that might be circling in your head: If the rectus abdominis functions as one muscle, can you actually isolate the upper or lower portion—or are we simply changing the emphasis?
Can You Really Isolate One From the Other?
You should know the answer. No, you cannot isolate your upper or lower abs, no matter what you have been told before. But exercise selection still matters.
“Exercise selection, loading direction, and pelvic/trunk movement can alter regional recruitment enough that talking about an upper or lower ‘bias is still useful,” explains Sapstead.
That word—bias—is the key.
That is why trainers such as Sapstead doesn’t dismiss someone who says they want to target their lower abs; he changes how the spinal flexion movement is performed. For him, the big difference-maker is posterior pelvic tilt.
“The rectus abdominis attaches onto the pelvis, so if I want an exercise to have more of what people would perceive as a ‘lower abdominal’ bias, I want the pelvis actually moving towards the ribcage rather than flexing the hip.”
That distinction matters with leg raises and hanging knee raises because moving your legs isn’t the same as moving your hips.
“You can perform hanging knee raises all day long by flexing and extending at the hip, “ explains Sapstead. “The legs move, but the pelvis doesn’t. At that point you’ve created a very different exercise.”
Sapstead has a fix: “Imagine trying to bring your belt buckle towards your ribs.” Now you’re adding posterior pelvic tilt rather than relying on hip flexion. Hello abs, do you feel that?
But the upper rectus didn’t shut down, and the lower rectus didn’t suddenly become an independent muscle.
You’ve changed the movement to alter the emphasis—not created isolation.
Next, we will see if the science backs this up.
What the Science Says
This is where the upper-versus-lower ab debate gets more interesting, because science doesn’t provide a clear answer. Mixed evidence is another reason “bias” fits better than “isolate.”
One older study compared a curl-up with a posterior pelvic tilt and found greater upper rectus abdominis activity during correctly performed curl-ups. Among participants with higher overall abdominal activity, the posterior pelvic tilt placed greater demands on the lower rectus than the curl-up did.
But technique mattered because these differences weren’t noticeable in people who did it wrong. That’s an important detail when we’re arguing over which exercise trains which part of your six-pack.
Another study of 25 healthy participants found that the reverse curl produced the greatest lower ab engagement among five ab exercises.
But not every study finds a difference.
A pilot study comparing six exercises—including curl-ups, leg lowering, rollouts, and reverse curl-ups—found no significant differences in upper- and lower-ab activation across all exercises tested.
Another study examining several ab exercises also found no significant differences in upper- or lower-rectus activation. So, the evidence doesn’t fully support the idea that crunches activate the upper abs while reverse crunches activate the lower abs.
What the research and the gym lab suggest is more subtle: exercise selection, body position, movement direction, and execution may alter the relative contribution of different regions, but it still functions as one muscle.
“Regional emphasis is plausible. Regional isolation isn’t,” emphasizes Sapstead.
What Training the Lower Abs Really Means
Why does this upper-lower myth keep hanging around and get millions of YouTube views? For many people, “How do I train my lower abs?” really means, “How do I get rid of the fat there?”
Those are two different questions.
You can strengthen and develop the rectus abdominis, but training the muscle underneath an area doesn’t mean you’re burning the fat sitting on top of it.
“I’d also mention that seeing your lower abs is a completely separate conversation from training them,” explains Sapstead. Now comes the part all the sellers of those ab gadgets don’t want you to hear.
“You cannot spot-reduce fat from the lower abdomen by doing reverse crunches,” says Sapstead. “But you can develop the underlying muscle.”
That’s the same spot-reduction myth we’ve busted before, but this doesn’t make direct ab training pointless, far from it.
Your abs are muscles, and progressively training them can make them thicker, stronger, and more developed. So, train your abs to build them—more on that next.
How to Train Your Abs
If the upper-versus-lower debate teaches us anything, it’s that you cannot divide and conquer. Train your core’s functions instead. That’s why a well-rounded program uses varied movements rather than 17 slightly different crunches.
Trunk Flexion
This is the classic ab-training function: bringing your rib cage toward your pelvis.
Good choices: Tall Kneeling Cable crunch, weighted stability-ball crunch, and weighted crunch.
Bodyweight variations are great, but weighted ones require more deliberate effort and focus on form.
Pelvic Stability
The goal is to stabilize the pelvis and produce a deliberate posterior pelvic tilt rather than hip flexion.
Good choices: Reverse crunch, hanging knee raise with a pelvic curl, and stability-ball reverse crunch.
Sapstead’s earlier coaching cue applies here: “Imagine trying to bring your belt buckle towards your ribs.” The height of your knees or feet matters less than what your pelvis is doing.
Anti-Extension
Anti-extension exercises challenge you to keep your lower back from over-arching.
Good choices: Ab-wheel rollout, TRX body saw, and dead bug.
The rollout gets harder as you extend farther because it challenges eccentric strength against a longer lever.
Anti-Rotation
Anti-rotation exercises train your core to prevent unwanted twisting while your limbs move.
Good choices: Pallof press, renegade row, and half-kneeling cable press.
This ability to resist unwanted movement is part of what makes core strength useful beyond the gym.
Anti-Lateral Flexion
Pick up a heavy dumbbell in one hand, and your torso wants to bend toward the loaded side. Your core’s job is to tell it, “Not today.”
Good choices: Suitcase carry, chaos suitcase carry, and side plank.
The suitcase carry pulls the torso laterally, forcing the opposite side of the core to resist lateral flexion.
Remember Progressive Overload
“For physique purposes, I’d also treat the abs like any other muscle,” explains Sapstead. “If you want them to grow, they need progressive overload.”
Progress using load, reps, range of motion, lever length, or exercise difficulty. Sapstead likes manipulating lever length—moving your arms overhead during a crunch or extending farther during a rollout will increase the challenge without adding load.
So forget about building an “upper- and lower-ab workout.”
Build a stronger core by training all of its functions and progressively challenge it like any other muscle group.
Myth Fallout: What Happens if You Still Believe?
Believing you can isolate your upper or lower abs won’t destroy your gains, because let’s face it, you will still be training your abs either way. But it can lead to questionable training decisions.
Exercise Hopping
If you’re always searching for the one magical lower-ab exercise, you’re probably not spending enough time getting stronger at what works. Your abs respond to progressive overload, just like other muscles. Load, range of motion, lever length, reps, and better execution all give you ways to progress.
Hip Flexor Madness
When you try to target those lower abs, you turn every reverse crunch and hanging leg raise into a hip-flexor exercise, with the abs along for the ride. This happens because the goal becomes getting the feet higher rather than controlling the pelvis.
“For the lower rectus specifically,” says Sapstead. “I’d worry less about how high somebody can lift their legs and pay much more attention to whether they can produce and control posterior pelvic tilt.”
Ignoring The Core’s Other Functions
Obsessing over the upper and lower abs can make you ignore everything else your core does. The rectus abdominis gets all the mirror love, but your trunk also needs to resist extension, rotation, and lateral flexion. That’s why exercises such as rollouts, Pallof presses, dead bugs, and suitcase carries belong in the core conversation.
The Final Word
So, after all this talk about upper abs, lower abs, and pelvic tilts, where does that leave us?
Somewhere in the middle.
The rectus abdominis is a paired muscle, and you cannot completely isolate one region while switching off the other. But saying exercise selection makes no difference goes too far in the opposite direction.
Different movements may alter regional recruitment within the rectus abdominis. So, stop worrying about finding the perfect upper- or lower-ab exercise and begin training function.
Train trunk flexion, learn to control your pelvis, strengthen anti-extension, anti-rotation, and anti-lateral flexion. Progress your exercises with more resistance, reps, range of motion, longer levers, or harder variations. Then you’re doing what really matters: training your abs like all other muscles.
And when someone tells you that one exercise is finally going to isolate those stubborn lower abs, remember: You don’t have upper and lower abs—you have abs.
