I know, for example, that eyes get worse when strained but biceps for instance get stronger. Why is that?
In: Biology
Skeletal muscles are very different from organs. They have much more capacity to grow, and the adaptive healing is what makes them stronger.
The only organ inside your body that is good at regeneration is the liver but it still doesn’t become “stronger.”
So first off – when you strain your biceps, they get weaker. If you try and do another set an hour later, it’ll be significantly harder than your first set. BUT it’s only temporary, which is where the interesting bit comes.
Getting weaker when overworked is just the natural outcome – we should expect almost everything to have that problem. And for the most part, things do – healing up over time if they’re not overworked, but as long as they keep being overworked they’ll keep deteriorating. Even your muscles will keep deteriorating if you don’t take a long enough break to let them heal back to full health.
Muscles, however, have a neat trick – when they heal from the damage, they grow a bit bigger for next time, so it’ll be harder to overwork them. This allows animals that are forced into new circumstances, or that take lingering injuries, to adapt to the tasks that they are now doing by growing the muscles they need for those tasks and letting the muscles that they no longer need as much shrink.
This feature is more strongly expressed in humans than in many other animals because of how adaptible we are, and how much we seek out and conquer new environments, and learn new ways of doing things.
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Now, why don’t other, non-muscular, organs also take this “grow back stronger” approach? Things like the Heart and the Diaphragm do, but those are still just muscles at the end of the day.
Your bones do too – they get stronger from exactly the same exercises that strengthen your muscles. If they didn’t, you might get strong enough to break your own bones without needing Adrenaline pumping into you, which would be bad. You should only break your own bones when the alternative is you (or a loved one) dying.
And, oh, the brain does, if you work your brain hard it hurts things and then they come back stronger – the parts you use the most become strengthened, making you better at tasks you do often.
The immune system does – if something is hard for your immune system to fight off, the type of cell that *was* effective will get more copies of it produced.
Your liver does – if there are specific toxins you injest regularly, your liver will adapt to better filter them out of your bloodstream. This can actually be a problem when you’re on long-term medications, as your liver doesn’t know that *those* poisons are being taken on purpose.
So for the most part, your organs *do* get better at dealing with the problems they’re commonly faced with. There are a few exceptions, where either there was no pressure to adapt in our evolutionary history, or adapting was just too difficult and never managed to evolve in our lineage, but in general our organs are pretty adaptable.
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So why do we think of muscles as a special case? Well, in every case when something “grows back stronger” there’s a cost to it. If it didn’t cost anything we’d just have the strongest possible version at all times.
Our muscles have a relatively simple cost that we don’t really care about much – they require more food. If you’re living in a first-world country this is probably not a problem – hell, if you’re overweight it could even be considered the solution to a problem. The muscles can happily get bigger on the outside of our body, just under the skin, and not run into any other organs. The Heart and Diaphragm could conceivably run into problems from pushing on other organs, but honestly those two organs are so *absolutely vital* that there’s never an issue with it, we have evolved to give them enough room to do what they need to do.
For most other organs they’re limited by space – your liver can’t get bigger without pushing on your digestive system and your bladder, your brain just plain can’t get bigger at all because your skull won’t let it, your immune system is hosted inside your bones – so rather than growing bigger they have to specialise; if you drink a lot of alcohol your liver will adapt to be better at processing alcohol, but it will become *worse* at everything else that you need your liver for. Which quickly becomes a problem.
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