system
Given the following post, respond as if you're commenting on Reddit:
human
Does locking your knees while standing actually cause you to pass out?

And if so, what is the scientific explanation for this?
gpt
Sortof. Strictly speaking it isn't locking the knees, it's standing in a rigid unmoving position for long periods. Standing knees locked means your muscles don't have to work to support your weight.

What happens is that the blood flow coming back up from your feet is assisted by natural muscle movements squeezing the veins, and little one way valves in the veins that act to pump blood back up the legs. No muscle movements means your circulation in general is worse, and that leads to an increased risk of fainting.