In the addendum to my last post, I mentioned the lengths to which the Olympics are going this year to separate the men from the women. While it's generally agreed that women are at a disadvantage [full disclosure: I put in age and gender classes in the Fab 5 series only to increase participation], no one's been able to say just why men run faster than women. Here's the various theories.
Size theory: Men are larger and have larger hearts and lungs
The problems with this theory are many. A friend of mine thinks races should have height divisions and that, being a foot shorter than me, she has to take 50% more steps in any race than I do and that's why I'm faster. Sprinters do tend to be tall, but it's been shown rather elegantly that size is a disadvantage in the marathon. Men's hearts and lungs are in the same proportion to body size as women's - volumetrically, smaller is more efficient; this might be why small children seem to be able to play forever.
Untrained men do average higher maximal oxygen uptake levels than untrained women and the measurements among elite athletes show similar differences. This might account for some of the differences in racing, but not all; those with the highest VO2max readings are not the best runners (actually, the highest are in skiers) and oxygen uptake is irrelevant in sprinting, where men are still faster than women.
Composition theory: Women have less muscle and more fat
This is an easy, attractive theory, but doesn't withstand scrutiny. Female bodybuilders are very muscular and some in contest shape have had almost no body fat, but they aren't very good runners. Gayle Olinekova, a Canadian marathoner and bodybuilder, was the only cross-over of which I can think. The most muscular men don't win races, nor the ones with the least bodyfat (though, of course, bodyfat is dead weight and does slow one).
Heat transfer theory: Women dissipate heat less efficiently
I've never seen this discussed, but I think it's interesting. Men sweat more than women and women often supplement sweating by skin flushing, which isn't as efficient. Moreover, men sweat most from the chest, forehead and back (protecting vital organs), whereas women sweat most in the underarms (used for sensory signaling - there's some interesting data here I won't go into).
If this were all-important, then women would excel in cold weather races and do much worse in hot weather races. Though there is some anecdotal evidence for this, there's no good evidence.
Brain chemistry theory: it's all hormonal
Hormone differences do make men more likely to take risks and to compete harder as a result. This can be overcome by training and experience.
Multivariable theory: it's all of the above (and more)
While none of the theories above are sufficient to explain the differences between men and women, some say that each has a role and together they explain it. This is much harder to disprove, but one can do multivariable analyses; thus far, it's inconclusive.
Social theory: Girls are dissuaded from competition
In most societies, women running is not as acceptable as men running. I've heard many women claim that their running has been hampered by societal influence. The beauty of this claim is that it is completely untestable. If society is to blame, then societies that are more restrictive to women should have greater differences between the sexes; the number of great Algerian, Moroccan and Ethiopian women runners refute this. Though there is scant evidence, the difference between identical female twins raised separately is not substantially different from identical male twins raised separately.
Statistical theory: Fewer women run
This was a favored theory forty years ago. In any population, there is a bell curve distribution in abilities. The best times are in the extreme ends of the curve. Smaller populations have fewer numbers in the extreme ends and so the most extreme case (world record) is less likely to be as far from the median.
The problem with this is that the medians are different and the number of women running is almost the same as the number of women, unlike even a generation ago.
What a theory needs
Any theory trying to explain why men run faster than women needs to consider the following: 1) Boys and girls compete about the same until puberty. 2) The difference between men's and women's records is about 10% at every distance. 3) The difference between the median men's time and median women's time is also about 10% in many large races.
The difference has to be anatomical, independent of speed or distance. The difference has to be greater between the sexes than within either sex.
My theory: inefficient hip angles
Boys and girls hips are similar. Women's hips differ from men's in order to more easily bear children and this difference leads to inefficient hip angles. This difference would affect every step, so it would be true from sprints to ultras.
No study has been done. Casual observation does show that faster women tend to have narrower hips than slower women, but this is largely a matter of fat deposition. The best women runners do seem to have boyish hips, but again, the actual angle measurement can't be eyeballed. I knew one national class woman runner who had quite wide hips - her brother was also a national class runner, so she might've just lucked out on every other measurement - but she also had a broad back and shoulders, so the hip angle might have been slighter than it appeared.
I have no opinion as to why men are better bowlers or race car drivers. Nor do I care.
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