Are Sit-Ups and Crunches Safe?

Are Sit-Ups and Crunches Safe?

Sunday, March 7, 2017

Written by: Cora Tomowich

Calling all men and women across the globe! Whether you are an avid fitness enthusiast, a victim of low back pain / pelvic dysfunction, or a new mom in postpartum recovery, you are likely spending a fair bit of time thinking about your core. Many of us have been told that we have a weak core, that we need to improve our core stability, or that our core muscles have poor/flabby tone.

So, many of us will consult with Nurse YouTube or Doctor Google to find the best exercises that solve our core issues. Unsurprisingly, a plethora of different exercises targeting the six-pack abdominal muscles will pop-up with promises of a flatter, sexier, healthier tummy, which is awesome, right? Who wouldn’t sign-up for those?

Truth is, many of those exercises can actually work against us. There’s one in particular that has been the source of much debate and misinformation: the abdominal crunch. After dozens of studies, experts have found that abdominal crunches or sit-ups can actually oppose the core benefits we are trying to achieve.

Why Crunches DON’T Work

1. Abdominal Crunches Target The Wrong Muscles

The abdominal crunch exercise aims to strengthen and tone the six-pack abs but is that all it does? No. With crunches, we actually put a lot of strain on our neck and chest muscles, as well as, a little-known muscle called psoas. Psoas is responsible for hip flexion; and lives in the low back region originating from the anterior aspect of the lumbar vertebrae and crossing over the pelvis to attach onto the front/inner thigh.

Strain of the psoas muscle will cause or worsen low back pain, pelvic misalignment, a snapping sound with hip movement, and pelvic floor dysfunction. So, unless you are aiming to develop these issues, abdominal crunches are not for you.

2. Abdominal Crunches Hurt The Pelvic Floor

During the abdominal crunch motion, there is a lot of extra intra-abdominal pressure being forced downwards upon the pelvic floor muscles. With repeated exposure to this high pressure, the pelvic floor is forced to give-way in order to allow the crunch to occur. Over time, the pelvic floor muscles will become strained and/or weakened against any small or large increases to intra-abdominal pressure. This means that our pelvic floor will no longer be able to withstand the simple demands of our daily lives (i.e., holding our reproductive organs in place while we walk, or preventing urinary leakage when we cough or sneeze).

In my practice, I see many men and women who regularly perform abdominal crunches and consequently experience pelvic floor dysfunction. Without first properly developing good core strategies, they will tend to experience higher incidences of pelvic organ prolapse, urinary or fecal incontinence, pelvic heaviness, and/or longstanding issues of pelvic pain.

3. Abdominal Crunches Can Ruin The Piston System

Quick physiology lesson: the diaphragm is the primary muscle associated with breathing and plays a huge role in core function. It is located along the base of the ribcage, which is designed to be in line with the pelvis. When properly aligned, the diaphragm and the pelvic floor muscles move through their normal excursions together as we breathe. During inhalation, for example, the diaphragm moves downward to allow air to enter into the lungs and the pelvic floor moves downward to compensate for this natural intra-abdominal pressure change. During exhalation, the diaphragm moves up to push air out of the lungs thus normalizing intra-abdominal pressure and causing an elastic recoil or lift of the pelvic floor. When picturing this, think of the diaphragm and pelvic floor muscles moving like a car’s piston as they rise and lower together in synchronicity… hence the term “Piston System”, which I first heard from Julie Wiebe, a Sports and Pelvic PT in the U.S.

Here is a quick video to further explain the Piston System:

When working properly, this piston system allows for a healthy movement of blood flow into and around all of our abdominal organs; it regulates pressure and gases within our system; and it gently massages each organ with the natural movement of air. Most importantly, this piston system helps to generate a co-contraction of the other two deep core muscles to effectively create a solid foundation upon which the rest of the body can function – this is deep core stability. As we have already discussed, repeated crunches cause a weakening of the pelvic floor, but also a restricted downward movement of the diaphragm during inhalation. In order to adapt to this restricted breathing pattern, we are forced to breathe up into our chests, effectively straining our neck and shoulder muscles.

The loss of our beautifully tailored piston system ultimately causes a loss of our deep core stability. So, how do we compensate for this? Imagine that a house had no frame or foundation, eventually the outer-facing bricks would be the only things holding the house upright! Well, the same thing happens in the body. We start to overuse and grip our superficial low back and abdominal muscles in order to maintain core stability in our daily activities (i.e., sitting or standing upright). I see this in my practice all the time and most people don’t even know they are doing it!

4. Abdominal Crunches Worsen a Rectus Diastasis

A rectus diastasis (RD) or “Mummy Tummy” is a natural separation of the six-pack abdominal muscles that occurs during pregnancy, but does not self-correct within the first few weeks postpartum. Consequently, many women are left with a bulging or protruding tummy; and will do anything to bring those abdominals back together again. Well, I am here to tell you that abdominal crunches are quite literally the worst exercises you can do to promote this “togetherness” as they only widen the gap.

In the case of a rectus diastasis, studies have repeatedly shown that a separation of any size is not dangerous as long as there is good, healthy tone across the abdominal wall to provide a counterforce to the internal organs that may otherwise herniate. The trouble with RD occurs when we are unable to achieve good tone and are left with a high potential for herniation. Some women have a tiny separation but poor tone and tend to herniate on a regular basis; while other women with a large separation and good tone, do not.

Studies have also shown that the best and most important way to achieve good tone is through the establishment of a strong piston system, and thus the proper co-activation of all deep core muscles. Crunches, as we’ve learned, work against us as they weaken our greatest ally in the struggle against “Mummy Tummy”: the pelvic floor. Conversely, a strong pelvic floor and a well-functioning piston system generate the ideal co-contraction of all deep core muscles; thus, promoting good core stability and producing the necessary tone across the abdomen, keeping our insides inside.

In my practice, I see many women with an RD, who also report feeling highly self-conscious, easily fatigued, light-headed, and have difficulty staying in upright positions for prolonged periods of time. When we start working on developing a strong pelvic floor and good core strategies during activity, healthy abdominal tone is achieved. I’ve also noticed that when tone is optimized, the separation tends to correct itself, regardless of initial size.

How to Avoid Accidental Crunches

I hope you now have a clear understanding of why crunches or sit-ups do not serve our core stability or functioning in any way. Please also keep in mind that pseudo-crunches can sneak in to our daily activities, and below is a list of the most common ways this can happen:

  • Sitting straight up in bed from a lying position
    • Instead, turn onto your side and gradually push yourself up into sitting
  • Doing “Hundreds” or “Bicycles” in Pilates
  • Doing “V’s” or “Boat Pose” in Yoga
  • Any form of leg-raising exercise while in a lying or dangling position
    • Once again, this overworks psoas and can lead to new or worsened low back pain

What You CAN Do

Now, you are probably wondering: “what can I do if I’m not allowed to do crunches?” Since everyone has a unique core strategy, it is difficult to answer with certainty what your specific exercise regimen should be. I recommend having your pelvic floor, posture, and breathing pattern checked by a qualified physiotherapist so that we can determine your core needs and the best ways to address them.

If it is your primary goal to be amazing at crunches, I will say this: ONLY when you’ve successfully done all of your pelvic floor exercises, achieved good strength and co-activation in the deep core muscles, are breathing properly, and your pelvic floor is able to withstand the repeated increases to intra-abdominal pressure, can we slowly add crunches back into your life.


  1. Julie Wiebe, PT: Piston Science [Online Course and Embedded Video]
  2. 2. Pelvic Health Solutions [On-site Courses Level 1 and 2]
  3. Photo:

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