Over at Five Thirty Eight, Walt Hickey has a piece about cheerleading as a sport and injury rates, which is both a nice look at the way to use stats to measure the real danger level of an activity, and the sort of small details that can be teased out. The piece includes a table of injury rates for a wide variety of sports, seen above as the "featured image" and reproduced below. I don't really have anything much to say about cheerleading, but one thing did jump out at me from the table, leading to the question in the post title.
this table show concussion rates in competition and in practice and includes both boys' and girls' sports ("boys" and "girls" rather than "men" and "women" because they're looking at pre-college sports). There are several sports that are single-gender (football and wrestling don't have female analogues, field hockey and cheerleading don't have male analogues, and while there are definitely girls playing ice hockey, I suspect that the number of programs may be too small to pass whatever statistical threshold went into assembling this table), but also some that are paired, and they tend to be sort of close together on the table. Lacrosse, basketball, track, and swimming are all in the same approximate place on the table for both boys and girls.
The exception is soccer. Girls' soccer has a concussion rate that's nearly double that for boys. I find that both surprising and puzzling-- there's no significant difference in the rules or equipment for boys and girls, so why would girls' soccer be more dangerous than boys'? It doesn't really fit with the other paired sports, either-- in lacrosse, the rates are very similar, despite significant rule differences, but the same is true of basketball, which like soccer has very little difference between genders in terms of rules or gear.
It's also hard to square with the other table in the article, showing rates of severe injury in various sports, where boys' soccer ranks higher than girls'. Those are measuring different categories of things, though, using different types of stats (rates per participant vs. rates per game/practice), so maybe the comparison isn't that straightforward.
I have no idea what's up with this, but it jumps out as the biggest oddity of that table (other than the practice thing relating to cheerleading that's the actual point of the story, anyway). Are boys better at hiding soccer-induced concussions? Is there something weird about the rules for girls' soccer that I've never noticed before? Is this just a pure statistical fluke?
Leave your favorite theory in the comments, if you like.
It's probably due to boys hiding concussions during games - the rates for girls is higher in competition for other comparable sports - basketball, softball/baseball. I bet the true boys' lacrosse number should be higher.
I don't know anything about sports other than soccer, but in soccer you're supposed to hit the ball with your head, and if you do it wrong it's easy to get hurt (and doing it wrong is more likely for the young and inexperienced). Women have usually significantly slenderer necks than men, which also means less muscles there, so a similar impact with the ball could lead to stronger head movement and hence harsher hit on the brain.
The "boys hide injuries" seems a bit weak since it should apply to all sports, not just soccer.
I find it somewhat plausible that soccer provides more opportunity to hide injuries, given the large field, large number of players, small number of officials, and the continuous nature of the game. You don't have a lot of stoppages where coaches or refs get a good look at a player who might have sustained a head injury.
I'm a little dubious about the skinny neck argument, because we're not talking about randomly selected girls, but girls who play competitive soccer. They're a self-selected group who you would expect to be better than average at hitting balls with their heads. But it might be part of a mix of factors.
Maybe girls' neck muscles, etc. are weaker than boys' at taking the force of those impacts from headers in soccer.
I think it may be due to soccer being the most aggressive sport women have an opportunity to play, so it tends to attract the more aggressive girls. The more aggressive boys tend to go for football or hockey.
I'm vaguely surprised that the rates for girls' field hockey is so low, because those girls are nuts.
There is much less contact in girls lacrosse vs. boys lacrosse - players don't even wear helmets in girls lacrosse, just goggles and mouthguards. So, those sports aren't really paired.
I would tend towards the neck muscle theory. At least, it sounds like a plausible theory. It's much harder to come up with a theory for why girls suffer ACL tears at a much higher rate than boys do, like 5 times as often. The latest thinking is that it has to do with running and jumping technique, though as far as I can tell, training with that in mind doesn't seem to have slowed down the rate of ACL tears in women's basketball, which I follow.
My guess is that most concussions in soccer come from head collisions, heads being hit by elbows and shoulders, and by heads hitting the ground and/or the post. I don't think neck muscles are the issue here. Instead I would look for a difference in behaviour between girls and boys when two people jump up for a header. If the girls play "fair" and keep their arms down, there maybe a bigger chance of knocked heads. Boys may push off more (and the infamous creeping upward elbows) to make space, and keep the number of head collisions down.
This is only a guess, however. (The closest I ever came was when I got tackled from behind. The closest I ever came to giving a concussion was with a clearance straight into a guys head. He was ok but I knocked his contact lens out and naturally felt terrible. )
My initial hypothesis - Girls are particularly prone to mistaking other girls' heads for soccer balls - seems to be a non-starter.
More plausibly, there is some threshold for a coach to decide that an event was serious enough to call for a medic to check out a player, or to require that a player make a prompt appointment to see a physician. Could the threshold for boys' coaches be higher than that for girls' coaches?
Consider this also: If the boys are just a bit more likely to minimize or hide their injuries AND the boys' coaches have just a slightly higher threshold for taking action, then those two factors could have an unfortunate resonance - Neither factor might be large by itself, but put them together, and...
Since we're just speculating anyway...
My initial guess is it's more on the social side than physiology/physics side. Some combination or subset of:
- Girls more likely to report
- Girls' coaches more likely to report
- Girls soccer widely popular so the population has not just the self-selected best but more recreational players that might be less co-ordinated and get injured more
- Girls soccer has more aggressive players
Players don't hide concussions or injuries in soccer games. They display them, loudly and dramatically, so as to better catch the attention of the referee and gain free kicks penalties, etc. The _stark_ difference in competition vs practice rates for the sport is telling something here, particularly given that soccer is a very low contact sport.
It's not just soccer. Consider the girls' softball/boys' baseball pairing. The girls are about three times as likely as boys to suffer concussions. There are some differences in equipment between the two sports; in particular, I think (but am not sure) the boys wear batting helmets and the girls don't, which cuts down on beanball injuries to the boys, but I don't think that's all there is to it.
Also, regarding basketball: The girls and boys may have sorted close together in the table, but the girls are about a third again as likely to suffer concussions. Swimming and diving also has a relatively large disparity, but the rates are so low that I don't know if the difference is statistically significant.
Since we are just speculating here, I'll vote with the differential reporting crowd for what the leading cause is. Boys are expected to "take it like a man", girls aren't, so the former only report the more obvious or severe injuries. There may be other factors too, such as training (techniques for avoiding injury in boys might need some modification for girls, and in many cases more resources are made available to boys), equipment (likely in the softball/baseball case, as noted above; less likely for most other sports), and a greater willingness of boys to use hands to prevent head-to-head contact.
Nitpick on the OP: Yes, there are male cheerleaders. Not as many as the girls, but not zero either. And the boys don't participate separately from the girls, which is why there is only one entry for that sport.
Girls softball players wear batting helmets. You're also much more likely to see the pitcher in a girls' softball game wearing a helmet or face mask of some kind, because the pitcher is much closer to home plate than in baseball - the pitching rubber is only 43' away in softball vs. 60'6" in baseball.
My unstated assumption in this was that softball and baseball aren't as directly comparable as basketball and lacrosse, specifically because of the difference in the pitching distance and the size of the ball. That's why I didn't mention those rates in the original post. I think you can easily argue that the distance difference makes it more likely to get concussions from either wild pitches or shots right back to the pitcher, as the time to react and dodge is less.
Lacrosse is an interesting case, because girls' lacrosse uses less protective gear, but has more restrictive rules on physical contact. Those seem to kind of balance each other out. It's the same field and the same ball, though.
One poster posited that soccer attracts the most aggressive girls. I think it is the opposite: soccer is seen as the one sport that "everyone" can play, and is the default sport for non-sports-oriented girls. You get a mix of aggressive girls and those less so, and also girls at highly variable skill levels playing together. That's a recipe for injuries.
Daniel, by the the time a student is in high school, usually it's just the most skilled and athletic girls playing, at least around my area, where the level of play in high school girl's soccer is pretty high. The ones who are just playing for fun have either dropped the sport or just play in recreational leagues.
I immediately thought of the argument that soccer is one of the most aggressive sport outlets available for girls (although this might vary by location). My sister broke her collarbone repeatedly playing high-level competitive soccer both indoors and outdoors (certainly no amateurs playing in her leagues), and she took her competition very seriously. In the US, that kind of drive in boys probably pushes them toward the football/hockey choices.
I immediately thought of the argument that soccer is one of the most aggressive sport outlets available for girls (although this might vary by location).
This is a testable hypothesis. The charts don't include girls' ice hockey, presumably because (as Chad mentioned) it's not available in many places in the US. But it is available in some places, mainly in northern New England and the Great Lakes region of the US, and in Canada. So the test would be whether concussion rates for girls' soccer are significantly lower in areas where the most aggressive girls can play ice hockey (places like AK, ND, MN, WI, MI, VT, NH, and ME, or in Canada) compared to places where they don't have that option (states south of I-90).
Interestingly this discussion is recapitulating the discussion in the refereed literarure, cf http://pediatrics.aappublications.org/content/126/3/597.full#sec-5
My first conjecture was difference in skull thickness - but it turns out that women have thicker skulls, on average, than men, despite some firm assertions on the internet to the contrary - though I have not found out if skull thickness disparity is a consistent function of age, evidently some reluctance to do large homogenous sampling of skull CAT scans of children, for some strange reason
The "aggresive girls" theory might be testable by looking at European countries, where soccer is one of the more major sports for athletically ambitious boys (excluding the UK where they go play rugby, i.e. american football without protective gear...)
I think it might have something to do with social conventions where boys tend to play football (Sorry but I still refuse to call it soccer) with other boys and so therefore may feel they have to do some macho posturing for their ego by not flagging up injuries and in doing so play "through the pain barrier" (see the infamous blood stained Terry Butcher photo) for fear of being mocked. In my view, which may be completely wrong as no girls in my school play football, girls may not have this element of shame in letting people know they are injured hence causing such a wide discrepancy .