Your body is constantly working to adapt to your surroundings and the world in which it lives. The internal pressure exerted by your blood and lungs exactly matches that of the air pressure around you at all times, no matter whether you’re in Denver or hundreds of feet underwater. Similarly, your muscles are perfectly adapted to carry the weight of your body around.
At least, it’s supposed to be.
As your body grows, it also tells your skeletal muscles to exert more strength in order to adjust to the increase in mass. Your weight bearing muscles constantly receive input and mechanical feedback regarding how much you weigh, and thus how much force they’re going to have to exert.
The exact mechanisms underlying this is a little bit more complicated to describe, however. One such way that the body adapts to changing weight is through the expression of certain genes – specifically the one that regulates fast skeletal muscle, troponin T, or Tnnt3. This part of the muscle is a thin filament that regulates the chemical reactions that control how much a muscle contracts and thus how much force it exerts.
As your body grows, Tnnt3 must compensate for the additional mass. To do this, it expresses your DNA in slightly different ways. Now, it’s true that you only have one set of DNA, but it doesn’t always wind up creating the same results, whether by accident or on purpose. This is because there is a complicated series of steps involving mRNA “reading” the DNA to create proteins, and this process can be altered. In fact, it can be altered in 128 unique ways by slight differences in the way Tnnt3 can be spliced. It is the ratio of the abundance of these different slight alterations that regulates how your muscles act and react. It is a constantly changing and delicate balance that your body maintains at all times.
Or at least, it’s supposed to be.
The researchers took rats genetically modified to become fat and tested their levels of different Tnnt3 expression levels. Additionally, they fit some normal mice with specially designed weight vests to mimic obesity in order to rule out any changes that might be caused by the chemicals in the fat itself. What they found is startling.
As the rats began to put on weight – whether from fat or from weights – their bodies slowly began to lose its ability to properly regulate the ratios of Tnnt3. In short, even though they were gaining weight and required more strength from their muscles, their bodies failed to produce the correct proteins and chemicals needed to provide that strength.
The fat broke their muscles.
How many overweight people do you know that simply seem to never have any energy? Exercise isn’t simply bothersome to them , it’s excruciating. Based on this research, it might not be just because they’re carrying more weight. Sure, that’s part of it, but it also appears that their bodies are failing to properly adjust the energy and strength expenditure of their muscles.
And it’s not just a one-time deal. In the mice, the problem became worse and worse as the mice put on more and more weight.
You may think that this is just mice, so it doesn’t apply to humans. However, the same method for regulating the expenditure of muscles is used throughout the animal kingdom, according to a growing body of research. So chances are actually pretty good that this affect will be found in humans as well. Once again proving that it is better and easier to just stay in decent shape rather than let yourself go and try to claw your way back. And it might not just be aging that slows the metabolism; it could be the growing amount of weight wreaking havoc on your muscles.