[ELI5] Why do we loose muscle mass if we stop training?

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I know that muscles are a good protein source and if we don’t eat enough protein our body will take it from our muscle mass.

However, regardless of how good you eat, after a year or so with no training you will see a reduction in size.

I’ve also noticed that to maintain current muscle size you don’t really need to keep intensive training, as long as you keep active and use said muscles and eat properly you won’t lose muscle mass.

So why is it that your body gets rid of muscle mass if you don’t use it even with proper eating?

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3 Answers

Anonymous 0 Comments

Your body is made to survive in a world where resources are scarce. So it doesn’t want to waste resources maintaining fitness you don’t need. It’s not just that it’s scavenging protein, it’s that maintaining larger muscles, more aerobic capacity, etc. requires resources even if you’re not using them.

Anonymous 0 Comments

Muscle is more costly to maintain, physiologically speaking. Your body isn’t going to waste resources maintaining muscle that you don’t use, so if you stop training it will slowly cannibalize the existing mass and divert that energy to other things like fat stores. When you start needing to use muscle again, it will build it back up.

Keep in mind that, evolutionarily speaking, we are adapted for what life was like 20,000 years ago. Food was scarce, so rationing nutrients was paramount for the body. Any nutrients that were going to waste were diverted to fat to get you ready for the inevitable lean times when you didn’t get enough to eat. Wasting that energy on unused muscle wasn’t a luxury we could afford and still survive.

Things are different now, but our bodies have not had enough time to adapt.

Anonymous 0 Comments

Muscle tissue takes energy to maintain, even if you’re asleep.

Humans evolved in drought-prone central Africa where energy was sometimes hard to come by, so we’ve evolved a number of energy-saving measures to survive long periods of poor food quality.

One of these adaptations is min-maxing your muscles. Muscles that you don’t use regularly get scrapped so that they’re not wasting energy.