Why Can’t Humans Use The Muscles On The Other Side Of Your Joints As Resistance For Exercising?
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Because we evolved to this form. For our ancestors, there was no need to train like for us today. Their daily lives were training enough. And the ability to use countering muscles gave nobody any advantage to live long enough to procreate.
We can however use for example one arm to train the other to an extent.
There is no reason for your brains/nerves to evolve the ability to “fight” itself like that. There is no situation in the African savannah that would require or incentivize early humans to do resistance training.
We can. The easiest muscles to do it with are the rhomboids and pecs. Stick the arms out to the side and flex the rhomboids. Slowly pull the arms forward, activating the pecs until the hands can be brought together in front while keeping the rhomboids flexed. It can take some practice
It’s worth noting that individual muscle fibres are digital, they are either on or off, constricted or relaxed.
When you move your arm what you are doing is actually a very complex series of controls flicking lots of switches on or off in a useful pattern.
If you hold your arm out in front of you for example, the reason your hand will eventually start to shake is because what you’re actually doing is rapidly turning the fibres on and off to pull it up, relax, then pull up again, and after a while you get tired and that process slows down and becomes visible.
There’s no half measure where a fibre on partially constricts, they want to be pulling full force, you’re just turning them off before they move your arm too far.
The relevance of this is the commands being sent to your arms are really actually quite complicated, a lot more so than the conscious thought. The autonomic functions handle the actual constriction of the various muscle groups, you don’t have much conscious control over them by default.
When you decide to move your arm, you basically start a program that the back half of your brain and nervous system has to carry out.
And your brain is not programmed to activate muscles on opposite sides of a joint, because…well that would lock the limb and risk tearing something (which is what you want to do for resistance training but not what your body wants to be doing). There’s zero reason for that program to exist as it’s useless at best and actively harmful at worse. Arguably a seizure is actually this, when things go wrong and the muscles start firing off in their own.
Now the brain CAN be trained to do a lot of impressive things including taking conscious control over certain things that are usually NOT controlled like that – see those monks that can raise their body temperature or do werid metabolism shit. The brain is surprisingly adaptable like that – even rewire bits of the brain to do different things, like processing visual information in different parts of the brin if the visual cortex is damaged but the optic nerve and eye apparatus is fine (it’s called blindsight, it’s weird).
It would take a lot of training and practice to mentally isolate different muscle groups and fire them in opposition, not sure how you’d go about it. Also not sure it’s *wise* to do that for serious resistance training.
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