eli5 Why/how do muscles shrink?


You get sore muscles when you train, because you muscle strings rip and when they heal, your muscles grow. As far as I know. So why and how do they shrink?

In: 213

Muscle naturally degrades, but when you work out or use your muscles regularly, you are promoting protein synthesis. If you work out enough you are synthesizing protein at a faster rate than it’s degrading . But when you are sedentary they degrade faster than you can synthesize them. *why* this happens is not entirely understood and there are many contributing factors

Complicated things take more energy to maintain than simple things do. If you’re building an elaborate sand castle on the beach, it will probably not fare as well when a wave hits it as a mound of sand would.

Muscle is more complicated than fat because it has to constantly do things: contract, relax, heal itself, etc. Fat basically just sits there being fat until your body tells it to either add more because you have a surplus of energy or release some because you have a deficit of energy. So having one pound of muscle on your body takes more energy to maintain than having one pound of fat.

In prehistoric times, humans often would go weeks or months without sufficient food. If you had a lot of muscle, you would find yourself starving much sooner than someone without a lot of muscle. So we ended up evolving so that our muscles degrade pretty quickly when they are not being used. If there is a famine, you can just sit around, your muscles will atrophy, and you will need less food to survive until times of plenty again.

Your body is constantly trying to economize and manage what it considers to be limited resources. Muscle is expensive to maintain, so, if you don’t keep making sufficient demands on your body to build and use that muscle, your body will consider it an unneeded expense and allow it to degrade.

The fact that most of us have enough food available to maintain a lot of muscle is a very new concept to evolution, which is geared to prevent us from starving to death.

Muscle mass uses a LOT of energy for your body to maintain. If you aren’t regularly using it, your body will gradually break that muscle down to save energy. But some remnants of that original bulk remain, so it’s easier to rebuild lost muscle than to gain it in the first place.

Other people have mentioned the muscles degrading. With that said, the most noticeable shrinking from someone who quit working out isn’t from a loss of muscle. The most noticeable shrinking is losing glucose storage in your muscles, resulting in less water storage in the muscles.

Also, if you are actively working out, your muscles are in a prepared state to lift heavier objects. Your muscle fibers are slightly firing in their preparedness state; this makes your muscles appear larger. After a short time of quitting exercise, they will shrink because they are no longer in that state.