The first three parts of the rectus abdominis
The first three parts of the rectus abdominis are the weakest muscles in the body. As a result, very little is needed to keep them trained. A set of eight lift-ups or one or two roll-ups a day is more than sufficient. When the first three parts function properly, they fulfill five essential functions.
First function: Energy storage.
The first three parts of the rectus abdominis fulfill the same function as the spring in an old-fashioned alarm clock. They make it possible to perform the actions necessary to train the rest of the muscles in the body.
Second function: Feedback system.
The first two parts of the rectus abdominis pull the abdomen up half a centimeter 24 hours a day. The weight of the abdomen is determined by the contents of the intestines. Depending on what people have eaten in the last few weeks, or have not eaten if they are experiencing famine, the weight of the intestines varies between 500 grams and 10 kilos. The heavier the intestines, the more fat the first two parts of the rectus abdominis muscles burn as they pull the belly upwards. The more people eat, the more fat they burn. This is the feedback system that has ensured we maintained a low, constant weight since the dawn of humans.
Obese people store fat between their intestines. As a result, the weight of their belly can rise to 25 kilos. However, this does not affect the speed of the weight loss process because the first two parts can only lift 3 kilos.
Third function: A slim belly.
The first three parts pull on the fourth part. They also pull on the oblique abdominal muscles and the back muscles. As a result, the muscles in the torso are pulled tightly around the torso, causing the intestines to be pulled into the abdominal cavity. These muscles burn 12 grams of sugar per day. When these muscles become weak, two things happen. The intestines start to hang out of the abdominal cavity, causing people to become fat. The 12 grams of sugar are stored in the form of 5 grams of fat per day (= 2 kilos per year, 20 kilos in ten years).
Fourth function: Energy supply.
For evolutionary reasons, the oblique abdominal muscles are responsible for the energy supply of our body and of the first three parts of the rectus abdominis muscles. The first three parts of the rectus abdominis muscles keep the oblique abdominal muscles active.
Fifth function: Walking and running.
Naturally, bipedal animals walk by falling forward. But if you are 1.80 meters tall and stumble, your head hits the ground at a very high speed. Humans have an adaptation. We contract the first three parts, pulling the upper half of our torso and head forward. This causes the center of gravity of our body to end up in front of our feet, making us fall forward, while the rest of our body remains upright. As a result, the risk of falls is significantly reduced. As long as the first three parts functioned properly, humans could run at 15 km/h without any effort and sustain this for hours. This made hunting large land animals possible.
The sabotage of the first three parts of the rectus abdominis muscles
Thirteen thousand years ago, the first preservatives were discovered. People who possessed this knowledge no longer had to run after their food all day long. But TV and the internet didn’t exist yet, and having sex all day gets boring too. So after some (hundreds of) years, they discovered sports.
Thirty years before the invention of agriculture, they discovered the sit-up.
The problem with the sit-up is that it works differently than people think. So when children at the start of their growth spurt complain that the sit-up has suddenly become a lot harder and ask if they can do the roll-up, gym teachers think they are being dramatic and forbid the roll-up. (For thousands of years, gym teachers only learned the sit-up as adults).
The technique of the sit-up
When you perform the sit-up, the muscles on the front of your abdomen swell up. So you might think that these are the muscles that lift the torso. But in reality, the first three parts of the rectus abdominis are absolutely not strong enough for that.
There is another muscle group involved: The oblique abdominal muscles. The oblique abdominal muscles contract in a horizontal direction, and in a vertical direction, they are the broadest muscle group in our body. They are just as wide as the rectus abdominis are long. At the bottom, they are attached to the fourth part of the rectus abdominis, and at the top, to the rib cage. This makes it possible to use the oblique abdominal muscles vertically like a cable.
When people perform a sit-up, they contract the fourth part of the rectus abdominis. This pulls on the first three parts at the front and on the side on the oblique abdominal muscles, which function as a cable.
In adults, the first three parts account for 5% of the torso weight, and the oblique abdominal muscles 95%. Children are lighter, meaning the first three parts are proportionally stronger and account for 15% of the torso weight.
The weight of your torso is 60% of your body weight with a minimum of 30 kg in adults. 5% to 15% of the torso weight results in overloading of the rectus abdominis muscles, causing them to swell.
This works throughout our entire lives except during the first six months of the growth spurt.
The problem
During the first six months of the growth spurt, muscle lengthening is faster than bone lengthening. One consequence of this is that children become gangly. They have to contract their biceps further than they are used to in order to lift their forearm.
The other consequence is that the total length of the four parts of the rectus abdominis muscles becomes longer than the distance between the sternum and the pelvis. During this period, children can contract the first three parts of the rectus abdominis muscles, or they can contract the fourth part. However, they cannot contract all four parts simultaneously.
With the roll-up, they train the first three parts.
With the sit-up, they contract the fourth part. This pulls on the first three parts, but nothing happens there because the muscles are too long. The fourth part pulls on the side on the oblique abdominal muscles, which function like a cable and lift 100% of the torso’s weight.
So children rightly feel that the sit-up has become 15% harder and complain about it.
But gym teachers who only learned the sit-up as adults forbid the roll-up. As a result, the first three parts of the rectus abdominis muscles were not trained for six months.
The consequence
Muscles are well-trained, strong, short, and thick. Or they are poorly trained, flabby, long, and thin.
After the first three parts of the rectus abdominis muscles have not been trained for six months, they have become flabby, long, and thin. So by the time bone length growth catches up with muscle length, the total length of the four parts of the rectus abdominis muscles is still longer than the distance between the sternum and the pelvis. Making it impossible to train the first three parts.
As a result, the feedback system stagnates. The rectus abdominis, oblique, and back muscles become weak, causing the intestines to hang out of the abdominal cavity and the body to store 5 grams of fat per day. And children are no longer able to run at 15 km/h.
Twelve thousand years ago, this meant that humans were no longer able to hunt large land animals. They couldn’t hunt small animals because of rabbit starvation. Therefore they were forced to start eating plants.
The solution
According to Google AI, the knowledge regarding which muscles need to be stimulated to reactivate the feedback system has been known since the 18th century. However, the device required for this was only put on the market in the year 2000.