Diastasis Recti is a common problem, not only in pregnant women or women who've been pregnant before, but also in overweight individuals. It is also a problem in some athletes who train incorrectly.
Your abdominal muscles are composed of three major groups: your internal and external obliques, your rectus abdominis (what you're seeing when you have a six pack), and your transverse abdominals. Sometimes a gap can form between the rectus abdominis making it literally impossible to have a flat stomach. This gap can also lead to major or minor back issues due to the lack of support down the mid-line of the body.
The linea alba is a fibrous structure that runs in between your "abs" down the mid-line of your body from the bottom of your sternum to your pubic bone. It is the connective tissue that runs vertically between your rectus abdominis muscles (your six pack). If a larger than normal gap forms between your rectus abdominis muscles, the linea alba will stretch to accommodate the separation. This means the mid-line of the stomach will no longer be supported by muscle, but instead it will be supported by the much more elastic linea alba. As a result, your organs can bulge or protrude from the stomach, pressing against the linea alba. (Muscle is much better at holding in your organs than the connective tissue of the linea alba.)
As I mentioned earlier, this condition is common among pregnant women and women who've been pregnant before. This is usually the reason why women tend to get a "mommy pooch" after having kids. Even after their uterus shrinks back to its normal size, they still appear to have a belly bulge because their organs are protruding through the linea alba. This condition can last a lifetime if not treated. Moms with this condition, will oftentimes hit the gym concentrating on their core in an effort to regain a flat tummy. They will usually spend a lot of time doing crunches/sit-ups, cross over twists, "V" ups, and planks to tone their abs. What they don't realize is that these exercise and exercises like them can actually make the problem worse! It is important that they heal the separation between the rectus abdominis muscles first, before doing crunches/sit-ups, planks, and other similar core workouts.
This problem is not only experienced by women who've had children, but it can also happen to people who've gained a significant amount of weight around their midsection. Excess fat in the abdomen puts pressure on the rectus abdominis muscles and can lead to a separation. In these cases, it is essential to implement a fitness program and diet that addresses the excess body fat and heals the separation of the abdomen.
Surprisingly, many athletes who are in excellent shape can find themselves with diastasis recti. The diastasis recti is a result of incorrect form while training. In fact, Joseph Pilates himself had a diastasis recit that got larger as he grew older. Although many of his famous Pilates exercises target the core, they can actually lead to or exacerbate a diastasis recti. If you look up photos of Joseph Pilates in his later years, it is clear to see that he has a noticeable separation between his ab muscles. ( http://www.pilateswithpaige.com/joseph-pilates.html )
So how do you know if you have diastasis recti? When testing for this, if you find that there is a separation, you want to determine how far apart the separation is and how superficial the linea alba is. The closer the linea alba is to the surface of your skin, the easier it will be to repair the separation. To test for diastasis recti, lie on your back with your knees bent. Place your fingers on your belly button pointing down towards your feet and lift your head (not your shoulders) a few times as you press slightly deeper. You should be able to feel the edges of the rectus abdominis muscles coming up when you press. If there is a separation between them, determine how many fingers fit in the space between them. If the separation is only a half of a finger in width, then there is no diastasis. If the separation is a finger width or more, then a diastasis has occurred and needs to be treated. To determine how superficial the linea alba is, see how deep your fingers can go into the gap. If you feel a pulse, then the linea alba is deep and weak. This means treatment may take longer.
When training, it is important to concentrate on pulling your abdominal muscles in towards your spine. This activates your transverse adbominals. The stronger your transverse abdominals are, the less risk there is for diastasis recti to occur. It is also important to focus on pulling your abs to your spine when passing a bowel movement, sneezing, coughing, getting up from a lying down position, and sitting in a chair. Doing these everyday activities correctly will help to protect your body from diastasis recti. If you have diastasis recti, it is important to let your trainer know so that they can modify the workout for you and give you exercises that will heal the gap. It can also be helpful to wear a support belt while you heal the gap.