In the quest for strong abdominal muscles, you might be crunching and planking your heart out regularly. Yet every day when you climb back onto the floor to go after it again, you’re still finding abs exercises incredibly challenging. What gives?

No, this doesn’t mean your abs are inherently weak. But it might be a sign that your workout needs some fine-tuning.

Why form is key to strengthening the abs

The abdominals are stabilizing muscles made up of four main muscle groups—the transversus abdominis, rectus abdominis, and internal and external obliques—running along the front of your torso from the ribs to the pelvis. While many people try to strengthen their abs through old standbys like sit-ups and planks, these moves often result in the recruitment of other core muscles to “help,” says Kristie Larson, CPT, a body neutral strength coach in New York City.

“Factors like body positioning and the mobility of your hips and spine can make a big difference in which muscles are being developed,” says Larson. “If someone feels like abs exercises are never getting easier, my first recommendation is to pay attention to where you are feeling the work. If a plank is harder on your quads and shoulders than it is on your abs, then the problem isn’t strength, it’s positioning.”

One of the most common mistakes when doing abs exercises is tilting the pelvis forward, says Sherry McLaughlin, MSPT, CSCS, founder of the Michigan Institute for Human Performance. “People with overarched spines tend to have a hard time with abs exercises,” McLaughlin says. Instead, your pelvis should be in a neutral position—if you lie on your back with your knees bent and feet on the floor, neutral is the position in between having your back arched completely and having it flat on the floor. (Many trainers will tell you to aim to have just enough space for a blueberry to fit underneath your lower back.)

Tight opposing muscles can also neurologically weaken ab muscles and throw off your form, says McLaughlin, pointing out that one common culprit is the hip flexors, or psoas muscle. “This muscle tends to be tight in people who sit a lot or walk with their toes pointed out,” she says. Tight quads can also cause your pelvis to tilt forward.

Other common form mistakes are over-using the hip flexors doing floor exercises like crunches, and lifting the hips or tipping into the shoulders in plank positions, says Larson. “People also over-prioritize duration over intensity. An effective plank position should feel challenging almost immediately and it may be very difficult to maintain a strong plank for longer than 30 seconds. A longer hold does not equate to stronger abs if the tension and position are not maintained,” she adds.

Are you doing the best exercises for your abs?

While you may recall countless sit-ups in grade school gym classes, that’s not the most effective way to build abdominal strength, says McLaughlin. “Because the abs are primarily a stabilizer, they should be worked in that way. Though crunches serve a purpose in strengthening the abdominal muscles, the abs rarely do this move in real life,” she says. “There is generally no need for muscles to flex the trunk when you are upright and moving around.”

Instead, McLaughlin and Larson recommend strengthening abs through moves that closely mimic actions we perform in everyday life. “To improve your ab strength, do exercises that use your whole body weight or add external load. Heavy carries, hanging knee raises, and rotating med-ball slams will improve your ab strength more than crunches will,” says Larson. “Externally loaded exercises like farmer carries and cable woodchoppers are generally more effective for ab training than floor-lying work because you have to stabilize dynamically to keep your balance.”

Exercises you might not even associate with your abs like squats, overhead presses, and deadlifts are also very good at increasing ab strength, advises Larson. Just be sure to only lift appropriate amounts of weight if you’re a beginner—don’t overdo it.

Perfecting your squat form can also activate your gluteus maximus, which can help keep the hip flexors from taking over, says McLaughlin. “If you start to have even mild low-back discomfort [doing planks or crunches], stop the exercise and try to do something that activates the quads or glutes—squats and lunges are a great place to start—and then retry the abdominal exercise,” she says.

The real way to tell if your abs are getting stronger

If you’re looking in the mirror and not seeing a six-pack in the reflection, that doesn’t mean your abs aren’t getting stronger. Because the abs are stabilizing muscles, progress can be tricky to pin down, but there are some telltale signs to look out for.

“It is difficult to quantify improvements in ab strength because your ab muscles don’t work in isolation in the real world: They work with your limbs and the rest of your core musculature to stabilize, rotate, flex, and extend the spine to keep you upright through movement,” says Larson. “So maybe you can hold a plank longer or do a few more sit-ups, but where ab strength improvements really can be felt is during heavy lifts when you are able to maintain torso positioning under load.”

Overall, the best gauge of increased ab strength won’t be felt in the gym, says McLaughlin. “You will be able to tell if your abs are getting stronger if other things are getting easier: squatting, lifting from the ground, lifting overhead, throwing, etc.,” she says. “You will notice an absence of back pain or knee pain. All of these are signs that your abs are working.”