When you train the first three parts of your rectus abdominis muscles, you can halve the size of your belly within a year.
When you train your oblique abdominal muscles and calf muscles, you can theoretically burn 70 kg of fat per year. But whether you actually lose that much weight depends on whether you can get the yo-yo effect under control.
In late 2025, American doctors observed that people who lost weight with the help of diabetes medication lost more muscle mass than fat mass. They thought that this had something to do with the medication.
In the first six weeks of 2026, I lost 1.5 kg per week. According to my scale’s app, that was 500 grams of fat and 1 kilo of muscle.
At the beginning of 2026, I was 60 kilos heavier than in 1979. According to my scale’s app, that was 20 kilos of fat and 40 kilos of muscle.
For about 10 years now, we have had access to second-generation digital scales capable of calculating body fat percentage. This gives us access to information we did not have before. Initial results seem to indicate that, whether losing weight or gaining weight, two-thirds of the change in weight is attributable to a change in muscle mass and only one-third to a change in fat mass.
This means that the yo-yo effect is likely caused by the mechanism that also determines how much fuel airplanes need to carry. Airplanes need to take off. This means that fuel consumption is determined not only by distance but also by weight. Not just the weight of the airplane, but also the weight of the fuel.
A few years ago, I read in an article that a Boeing 747 weighs 200,000 kg. For a certain distance (London-New York?), it requires 90,000 kg of fuel. But now the airplane has become much heavier, so it needs an extra 40,000 kg of fuel to transport that 90,000 kg. Plus 15,000 kg extra extra to transport that 40,000 kg. Plus 6,000 kg extra extra extra to transport that 15,000 kg.
It works the same way for humans. We use muscles to move around. When we gain weight, we need extra muscles to move that extra weight. But muscles themselves also have a considerable weight, so we need extra extra muscles to move the weight of the extra muscles.
So for every kilo of fat you store, your body builds two kilos of muscle to move the weight of the fat plus the muscles.
When you lose weight, your body has to get rid of all those muscles again, but that is where a problem arises. Your body does not know which muscles are the regular muscles and which muscles are the extra and extra extra muscles. So it employs a trick.
If you walk 500 meters or more daily at a brisk pace while you are losing weight, you need a little less muscle today than yesterday because you have become lighter. The muscles you do not use today are broken down. Exactly as intended.
But if you cycle to work five days a week and don’t cycle on the weekend while losing weight, there are a number of muscles that you only use when cycling but don’t use on the weekend. So they get broken down. On Monday, those muscle groups are subjected to a heavier load than they are used to, because part of the muscle group has been broken down. Your body reacts to this by blocking fat burning and prioritizing muscle building.
This applies not only to cycling but to any activity where you use muscles that you do not perform seven days a week. So if you play football or dance or go to the gym once a week. Or if, while losing weight, you do a major clean-up and walk to the outside container ten times. In all these activities, the body alternately proceeds to build and break down muscle mass.
It turns out to be even worse.
A few months ago, I discovered that I have two techniques for standing up when I am sitting on the toilet. Sometimes I use one technique, sometimes the other. But both techniques use different muscles. So if I switch while I am losing weight, that affects my weight.
Then there are injuries and illnesses that prevent you from exercising temporarily, causing you to lose weight and gain it back when you start again. You have vacations where you do different things than usual and use different muscles. In the first six weeks of 2026, due to an injury and bad weather (I fell on slippery roads in 2008 and broke my hip), I cycled and walked less than usual. So I only trained the first three parts of my straight abdominal muscles and my oblique abdominal muscles.
As if all that weren’t bad enough, by the end of May 2026 I reached the point in my fitness program where, to get thinner, I need to train the fourth part of my straight abdominal muscles. The exercise is very easy but of course, it does mean that I am building muscle mass.
So people who work on their fitness have to make a choice. To lose weight, you must train as few muscles as possible and be completely consistent in your muscle use. But to get thinner, you must train the muscles that pull your intestines into your abdominal cavity.
How to get thin Exercises