Misunderstood as a cosmetic issue, many women don’t realize they can fix their mom pooch — and lower back pain — in 12 weeks.

Nearly 40 women packed into an Athleta clothing store last Sunday in San Francisco to learn the secret to solving “mummy tummy.”

If you’ve never heard the term “mummy tummy,” it’s the soft pooch that falls below a woman’s belly button after she has a baby.

Leah Keller, a personal trainer and mother herself, has developed an exercise called the Dia Method to get rid of the condition within 12 weeks in only 10 minutes a day.

But those 10 minutes are going to be intense.

In the back of the store, 15 minutes into a series of ab exercises that demonstrated the move in different positions, I was squeezing my abs to the back of my spine so hard that I was shaking.

“This should be hard. If it’s not hard, you’re not squeezing tight enough,” Leah explained, rhythmically coaching us through the breathing and muscle activation sequence.

“Tight, tighter. Tight, tighter,” she coached the room of women, faces tense with focus, trying to pull their abs to the back of their spines further and further, with only tiny inhales for relief.

This exercise isn’t just a way for women to change the way they look — this is something much more critical to their well-being.

“People think of it as a cosmetic issue, because it has an undesirable cosmetic effect, but it’s a real health concern,” Leah said of the mom pooch, which is actually a medical problem called diastasis recti.

The bulge occurs when the abdominals stretch sideways, and the connective tissue running down the midline of the torso, called the linea alba, becomes overstretched and weak.

While the spine in the back of the body gives support, we only have our abdominal muscles in the front for support. When someone develops a diastasis, only the thin connective tissue is supporting the back and organs — and not doing it well, according to registered nurse, certified childbirth educator, and personal trainer Julie Tupler.

Tupler developed the Tupler Technique to help women prevent or correct diastasis recti, coaching celebs like Elle Macpherson and Jewel during their pregnancies.

Pregnancy is the main cause of diastasis recti, and the majority of women — 60 percent — have one during pregnancy. The gap between the muscles, which Keller and Tupler measure in finger-widths approximate to a centimeter, can be anywhere from 2.5 cm to 10 cm in severe cases.

Hormones released during pregnancy help the connective tissue relax, making room for the baby growing underneath the under abdominal wall, stretching it forward.

However, the diastasis doesn’t necessarily go away after giving birth. One year after having a baby, 32.6 percent of women still have a mummy tummy.

Diastasis recti affects women in everyday life. Weak support compromises the back and core, is linked to pelvic floor health, digestion issues, and urinary and stress incontinence.

The condition also leaves a woman vulnerable at the same time she’s actively taking care of kids. “Women with diastasis are at risk. If a kid has a temper tantrum and kicks them in the stomach, it can tear the connective tissue. That would expose your organs and require surgery,” Tupler warned.

Tupler discovered the need for abdominal strengthening when she was a nurse “preparing people for the marathon of labor.” She found that women who physically prepared by strengthening their abs experienced easier labor and smoother recovery.

“They could use their abs after giving birth and maintain their sutures,” she explained. A large diastasis also puts a woman at risk for cesarean delivery, according to Tupler. When the abdominal muscles separate, the top of the uterus tips forward, driving the cervix into a sideways position — which means the baby can’t come out.

Unfortunately, many women don’t know that their mummy tummy is a medical issue. They assume there’s nothing they can do to change it, and don’t connect it with the uncomfortable side effects.

Or they try to whip themselves back into shape and end up making their diastasis worse with exercises like crunches, bicycles, or double leg lifts. A serious spreading of the abs can result in major abdominal surgery to fix the diastasis.

Keller met Geeta Sharma, an OB-GYN at Weill-Cornell Medicine, because they had a patient in common. After training with Keller during pregnancy, the woman delivered her first baby in 15 pushes. Sharma was impressed.

Using Keller’s exercises, Sharma conducted a pilot study on 63 women to see if prenatal and postnatal exercises could prevent or correct diastasis recti. They found that all 63 women were able to completely close their diastasis in an average of 11.25 weeks with the Dia Method.

They also found a significant improvement in urinary and stress incontinence, which 41 percent of women who’ve had a baby report. Only 10 percent of the women who completed Keller’s 12-week program had incontinence issues.

This study could be the first in much-needed science on which exercises can fix diastasis recti. NPR reported that the American College of Obstetricians and Gynecologists (ACOG) recommends ab workouts during pregnancy, but “don’t provide details — such as which exercises work best or how often women should do them and for how long.”

That leaves many women doing exercises that make their mummy tummy worse. Allison Rapaport started working with Keller during her first pregnancy because she was nervous about what type of exercise was safe.

“No one, including my doctor, had great answers,” Rapaport told Healthline. “I also did prenatal Pilates thinking it was gentle, so that it must be safe. I quickly realized after working with Leah Keller that many moves I was doing regularly could cause diastasis.”

After Rapaport’s baby was born, she bounced back incredibly fast with no mummy tummy to speak of. “I also didn’t experience any issues my friends were having related to incontinence or aches and pains,” she credited to the workouts, which she called “challenging, but very rewarding.”

“It’s so powerful,” Keller said of the exercises and their ability to change women’s lives.

Both Keller and Tupler had diastasis rectis — before they ever became moms — from being a fitness instructor and professional dancer. They said that the condition is actually somewhat common in athletes, Pilates buffs. and yogis, who are doing a lot of ab workouts that cause their stomachs to bulge forward, creating microtears over time. With yogis, positions that flare the ribs contribute to the issue.

“You still look like you have flat abs, but you lose your waistline,” Keller revealed. She was able to reverse her diastasis within a few weeks, and didn’t have one to resolve after she gave birth to her daughter.

On the other end of the fitness spectrum, beer bellies can give someone a diastasis. “They develop deep visceral fat underneath the abdominal wall, which pushes forward and splits the muscles apart,” Keller explained.

Back at the Dia Method class, we went through the core exercise in several different positions: sitting crossed-legged, standing in a lunge, on all fours, or in bridge pose. Although every position was challenging, I found that it was a lot easier to feel the core compressions while on all fours, and therefore focus on executing the tiny movement correctly.

At the end of class, Keller checked women for diastasis rectis. The severity varied by width and depth, but Keller found most women had a diastasis that was three to four fingers wide, which is in line with the study.

She offered them words of encouragement. “I’ve helped women in their 50s, 60s, and even 70s dramatically improve their diastasis and gain core strength years after they’ve had their own babies. It’s never too late.”