eli5: how come we cant actually be perfectly still?


We can be pretty still, and ALMOST perfect, but…not quite. There’s still those little slight movements we all have even when trying our hardest to stand/sit still

What causes those uncontrollable subtle movements exactly? Hope this question isn’t too dumb lol

In: 2

We’re… Floppy. We can only sit or stand upright because of our muscles tensing. Muscles tense when ordered to, they can’t freeze in place, our joints can’t just lock. This means we cannot just be passively rigid, like a block of stone or rubber or something, we have to actively keep upright. While this means that we can actively, purposely resist being knocked over, this lack of inherent rigidity also means that any slight relaxation or twitches of our own muscles also have to be corrected for.

Consider just the ankles. Because they’re not inherently rigid, any imbalance in how the muscles tense results in you tilting at your very base and needs to be corrected for. This means continuous small movements. The only way this could be eliminated is if our muscles could literally freeze solid and remain that way, but they cannot.

Some of the stillest people in the world can’t stay perfectly still even when supported by the ground. Military snipers have to compensate for their heartbeat when they fire and ensure the bullet is fired between heartbeats. This is because the human body is filled with a bunch of tubes with changing pressure. They expand and contract slightly with each cycle of a heartbeat.

Every beat of your heart can push outwards on your blood vessel wells with 1lbs of force per square inch. It’s not much, but it’s enough and it’s fast enough that your muscles can’t compensate for it effectively.

1. Your muscles need to constantly work to keep you standing or sitting. Otherwise, you’d just fall down like a ragdoll.
2. Your body is constantly producing minute movements (pumping blood, breathing, moving your digestive system).
3. You’ve never perfectly balanced. Your center of mass is always at least a tiny bit off your center of balance, even by just a tiny amount, so gravity tends to flip you sideways, so your muscles need to correct against that.