Locking your knees can cause you to pass out?

[crocoduck_hunter]

I just remembered hearing this when I was a kid in elementary school: we were always told not to lock our knees when standing because you could suddenly lose consciousness. I know a number of the boys in my class naturally tried doing this but nobody actually ever passed out, so I thought I'd ask here if this was something that was actually possible or just a UL.

[erwins]

It's caused by blood pooling in the legs, so there's insufficient return to the heart and brain. Normally, moving one's legs helps to pump blood back to the heart through muscle contraction. Locking the knees makes standing still easier, but reduces use of the leg muscles. In some people, this pooling may lead to hypoperfusion of the brain and fainting, which is essentially the body's way of putting the brain and the legs and the heart at the same level.

There are things one can do to prevent it, like wiggling toes, contracting calves, contracting abs, taking a few deep breaths. These all help with veinous return. It also helps to be fully hydrated. This is also why some people faint and some don't. There are a lot of variables.

A cite: http://www.uamshealth.com/?id=872&sid=1

[Skeptic]

What does "lock your knees" mean. I can't understand what is being discussed.

[Lainie]

Extend the joint fully and keep it rigid.

[Seaboe Muffinchucker]

Anecdote is not data, but when I was in high school I was in the marching band. We attended WSU Band Day in Joe Albi stadium in Spokane (ancient times--before Martin Stadium was built). It was quite a warm day in September, and our uniforms were wool. At least two members of the band almost fainted and a major reason was that they locked their knees because they were nervous about performing there.

Seaboe

[A Turtle Named Mack]

Or maybe, Seaboe, it was because it was a warm September day and they were dressed in wool. My HS band got a chance to march at the opening of the Talladega 500 in mid-August - we dressed in band t-shirts, but we still had to assemble and wait for about a half hour and then march over a mile on the track, where it was over 120 degrees (in the grassy areas outside the structure, it was pushing 100), and we had several members collapse, but not until we were marching. We were marching, so there was no issue of locking knees (we did not goosestep), but it was just too taxing for quite a few to endure that heat.

[Ellestar]

In my philosophy class when I was a first year in college, a young woman who was giving a presentation in front of the class passed out because she locked her knees.

It was fully air-conditioned in that class and she wasn't exerting herself. In fact, her partner was the one talking at the time she passed out. It wasn't nerves, either, she was perfectly comfortable talking in front of the class.

For a few moments, we thought it was some bizarre part of the presentation until her partner started freaking out.

[erwins]

Originally Posted by Skeptic

What does "lock your knees" mean. I can't understand what is being discussed.

To expand on what Lainie said, if you straighten your leg fully, there is a final part of your knee's range of motion where you sort of pull your kneecap up, and the knee moves backward a bit. It sort of locks the joint at the end of its range. Locking one's knees is also not good for the joint.

[Seaboe Muffinchucker]

Originally Posted by A Turtle Named Mack

Or maybe, Seaboe, it was because it was a warm September day and they were dressed in wool.

I'll stick with my explanation, thanks. It was a lot cooler than 100 degrees (probably mid 70s), we had plenty of water and were encouraged to unfasten our coats while waiting, no one fainted while marching, and there's a real chance that these two locked their knees specifically because they'd been told it was a bad idea.

Seaboe

[Hound_Dog]

Actually, shame on me, but I have never heard about it. It's interesting enough to make me wanna try it despite the fact that I am old enough not to :P

[me, no really]

When I was in air force cadets, we were taught to move our kneecaps up and down when on parade for long periods - basically because it was a way of wiggling and moving while still appearing to be stock still on parade.

[Saitaina]

Locking one's knees is de facto for cheerleaders, especially flyers (those in the air). None of us have ever passed out due to locking our knees (other dangers involved in that sport however).

And trust me, when you're a base holding two hundred plus pounds (two or more girls), passing out is the LAST thing you want happening.