Flat Bum After Pregnancy? – Why You Should Care

Have you ever noticed that women lose their bums after having babies? Maybe you’ve seen this in other mothers. Or maybe it happened to you. There is actually a really good reason for this, and more importantly, it matters for a lot more than aesthetics.

Why does it matter if you have a flat bum?

The shape of your bum is related to two main things: body fat and muscle. You don’t have much control over the shape of your body fat or where your body chooses to deposit it. If you seem to lose weight from your bum before all else, there isn’t a whole lot that can change this. It is largely due to genetics.

On the other hand, you have much more control over the shape of the muscle in your bum. The major muscle responsible for its shape is called gluteus maximus. It’s the largest muscle in the human body, which means it is a pretty big deal. It has important roles in strength and stability, and it interacts with a lot of other muscles.


There is actually a ton of research on glute max (GMax) because of its significance. To keep things simple, I want to highlight two particular articles. (But feel free to do your own browsing. There is a LOT to pick from.)

The first article highlights the link between low back pain and the size of GMax in women. The size of a muscle is an indication of strength, where smaller muscles are weaker than larger muscles. Feel free to read the article in its entirety, but in short, the smaller the muscles of your bum the more likely you are to have back pain. You can also find more information on postpartum back pain here.

The second article demonstrates a link between gluteal muscle performance and risk of falls in older adults. If you don’t already know, falls can lead to a sequelae of negative events the older you get. This article concludes that the less function in your glutes, the more likely you are to fall. And falls can have a significant affect on quality of life, especially as we age.

So, if you weren’t motivated already to grow those glutes, hopefully, this helps you see that a flat bum has a effects that go beyond aesthetics.

Before we take a look at what happens during pregnancy, let’s make sure we understand the basics.

A very, very short anatomy lesson on hips

The hip is a ball and socket joint, where the ball is the top of the femur (or thigh bone) and the socket is at the outer aspect of the pelvis.


Unlike the knee or elbow, which are hinge joints, the hip is capable of far more mobility. It can move forward and back—when looking at someone from the side. It can move out and in—when looking at someone from the front. And it can turn inward and outward—when looking at someone from the top down. For the purposes of this discussion, we’re going to focus on the forward and back motions and on the out and in motions. It’s not that the turning isn’t important. It’s just that I’m trying to keep things simple.


There are LOTS of muscles around the hip that help it to move in all these directions, but the ones that contribute most to the shape of the bum are the gluteals. You can think of them like the big sister (GMax), the middle sister (gluteus medius), and the little sister (gluteus minimus). From here on out, we’re really going to focus on the first two. (Sorry to any of you little sisters out there.)

How pregnancy causes a flat bum

What happens to Gluteus Maximus (GMax)

You are probably familiar with what pregnancy does to a woman’s abs—they get super stretched out. Because each muscle has an ideal length, they can’t contract well if they are too long. This is exactly the scenario when a woman’s abs are stretched over a growing baby. Even if you are someone who was able to workout throughout your entire pregnancy, you still lost some ab strength. It is unavoidable because of the degree of stretching. And for most of us, we lost A LOT of ab strength.


The reason this matters in a discussion of bums is that GMax is basically the counterpart of the abs. As GMax stabilizes your pelvis from the back, the abs pull up on your pelvis from the front. With your foot on the ground, your abs are a counterforce that allows GMax to push your hip past your foot. This contraction of GMax is a big part of how we create forward motion.

If your abs do not pull up from the front—because they are too busy stretching over that gorgeous baby you made—then they are not giving GMax the opportunity to work. And without this opportunity, GMax gets weaker during pregnancy. Just like your abs. At least in part, because of your abs.

What happens to Gluteus Medius (GMed)

Now, that you understand how GMax stabilizes from the back of your pelvis, let’s take a look at how GMed stabilizes from the side of your pelvis. In our anatomy lesson above, GMax provides backward motion for the hip. In a similar way, GMed provides motion out to the side.


The counterpart to this outward motion is, of course, inward motion, and this is the role of a group of muscles, collectively called the hip adductors. There needs to be a balance between GMed and the hip adductors for the hip to function without excessive motion in either direction.


An important point, here, is that hip adductor function is closely tied to pelvic floor function.

(Have you ever crossed your legs when you need to pee? This is why. Crossing your legs tightens your hip adductors, and also, improves your ability to squeeze your pelvic floor.)

And just like the abs, the pelvic floor goes through a lot of changes with pregnancy. The short explanation of this is that hormones, postural change, and the pressure of the baby can cause significant stretching and weakness of the pelvic floor.

When the pelvic floor weakens with pregnancy, GMed often does as well. This is due to the balance needed between the hip adductors and GMed as well as to relationship between the pelvic floor and the hip adductors.

As a side note, GMed will often try to compensate for a weak GMax. When this happens, you might NOT end up with a weaker GMed after babies. Instead, you change the way you move to accomplish the same task. And in this case, your familiar workouts might not get the results they did before babies because you use different muscles to accomplish them.

How to reshape that flat bum after pregnancy

In the middle of cluster feeds, sleepless nights, or toddler rage, the shape of your bum might seem like a silly thing to concern yourself with. Or maybe, you really liked the way you once filled out your jeans, and it doesn’t seem like too much to ask to have that back again. Rest assured, either way, you are justified. Hopefully, you are now armed with several reasons why the shape of your bum changes.

But now, you also know that the shape of your bum is a reflection of the interplay between several groups of muscles. Function in your abs, your pelvic floor, and your inner thigh can all impact glute strength, shape, and performance.

Abdominal separation, incontinence, pain or pressure in your pelvic floor, or a feeling of being disconnected from your body are all common experiences after having a baby. The best way to solve any of these is to see a pelvic floor physical therapist. They can give you customized advice to help you reach your goals in the most efficient manner.

On the other hand, if you are not having any of these issues and you would just like to grow a bum again, the best path forward is to contract your abs when you contract your glutes. Stronger abs make for stronger glutes. And vice versa. The best place to start is with the connection between your brain and your muscles. When your brain can consistently find the right muscle, you will see faster progress and less substitution.

And if you need more information on how exactly to achieve this with YOUR body, don’t hesitate to check out my Mama Made Strong program. It will help you understand your current function and then guide you through how to make the most effective change to reach your goals. It is like the user’s manual that should have come with your body after babies.

4 thoughts on “Flat Bum After Pregnancy? – Why You Should Care”

  1. Seth Petry-johnson

    I love these blogs. A little tongue-in-cheek at times and ASStoundingly informative. The anatomy lessons are useful even for us guys 🙂

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