Anyone who has spent any amount of time in the Army has experienced the mind-numbing, painfully long formation where you are forced to stand at the position of parade rest (or attention) for long periods of time, often under the hot sun. Before the event, the phrase “don’t lock your knees” will be uttered over and over again by NCOs and the E4-Mafia like a meditative mantra. In these long formations, someone will invariably pass out, spilling over onto the floor in dramatic fashion. Then a soldier or two will drag the victim to the back of the formation where he can’t be seen and left to recover, while the rest of the formation snickers at his misfortune with whispers of “shouldn’t have locked his knees.”
As a young soldier, I had no reason to disobey the orders of my more experienced NCOs, so whenever I stood in a formation, I made a conscious effort not to lock my knees. “Locking my knees”, as I understood it, was standing in a manner in which my legs were completely straight, the knee joint “locking” back so the bones of my lower and upper legs support one another, requiring no “work” from the muscles of my body to maintain balance and position. Locking the knees somehow disturbs the blood flow process, resulting in the fainting solider phenomenon.
It turns out the medical science behind “don’t lock your knees” doesn’t exactly hold up. While the advice to avoid locking knees is widespread – even outside of military communities – the actual cause of fainting is usually loss of blood flow to the brain which can be brought on by any number of things, but the act of locking ones knees has nothing to do with passing out. While the act of locking ones knees and maintaining a rigid, completely unmoving position for a long period of time may interrupt proper blood flow, the act of locking the knees alone does not by itself cause fainting spells.
As this very scientific YouTube video demonstrates, locking your knees can interfere with proper blood flow from the legs, which in turn might result in less blood flow to the brain and ipso facto a soldier passes out.
I can remember foolishly standing in formation, trying my best to maintain a “knees slightly bent” position (as the position of attention calls for, after all) and feeling my knees “hover” inside of my pants as I awkwardly tried to maintain a good-enough but not-quite straight position. For sure, it kept me occupied, and maybe that mental occupation is what prevents fainting spells. I remember another occasion though, while deployed to Iraq, where I was standing in a change of command ceremony and started to feel nauseous and dizzy. I started having a cold sweat and I felt like I was going to pass out. I knew not to lock my knees and wasn’t, but it didn’t matter. Thankfully, the formation ended before I took an embarrassing spill, but thinking back on it, the likely cause was dehydration, as just about everyone had the shits at the time.
Like most Army myths, this one will continue to spread – and I have a feeling that some will aggressively defend it as fact, despite the lack of hard scientific evidence. While locking your knees might affect the flow of blood, there is no evidence that says that it actually does. Thankfully, I’ve spoken with a few NCOs who have privately confessed that they’ve been locking their knees in formation for years – because it’s easier – and they’ve yet to pass out.