Question: If an average man competes with a hundred random women in muscle strength tests - how many from that hundred would he expect to beat?
Answer: All of them.
- Because only about one woman per thousand is stronger than the average man.
(Subject to caveats below)
Until a few days ago, I did not realize that the difference between strength in men and women was quite so extreme, so qualitative.
I came across this fact referenced in a review-theory paper about sexual selection: "...less than 10% overlap between the male and female distributions, with 99.9% of females falling below the male mean."
WD Lassek, SJC Gaulin. Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity. Evolution and Human Behaviour 2009; 30: 322-328.
I checked out their main references. This paper was the most striking:
RW Bohannon. Reference values for extremity muscle strength obtained by hand-held dynamometry from adults aged 20 to 79 years Archives of Physical Medicine and Rehabilitation 1997; 78: 26-32.
This has tables of muscle strength, with force expressed in Newtons (N) for different movements, men and women, and different age bands, dominant versus non-dominant side.
If we look at the results for dominant arm elbow flexion ('biceps' strength, more or less) - mean force in Newtons plus standard deviation in brackets - we find:
Men age 20-29 - 285 (38)
Men age 70-79 - 237 (40)
Women age 20-29 - 155 (21)
Women age 70-79 - 130 (27)
And similar results are found for other muscle groups.
What is striking is that at 20-29 the difference in average strength is 285 - 155, which is 130 Newtons difference - or that, in round numbers, men are nearly twice as strong as women. (ie. 130 is nearly as big as 155)
And the standard deviation for women is just 21 - which means that there are about six standard deviations difference, which is a huge difference and means near zero chance of overlap in strengths between men and women.
Indeed, the Men aged 70-79 were much stronger than the women aged 20-29: 237 - 155 = 82 Newtons, which means old men are still roughly half as strong again as women (i.e. 82 is about half of 155) - or young women are only about two thirds as strong as old men.
Now, these numbers are presented as reference values; but like almost all real-life reference values they are not truly representative of the general population, because they are (and this is clearly acknowledged in the methods section) based on a 'convenience sample' of 106 men and 125 women selected on the basis of different ages. And these subjects are not athletes in training, body-builders, or anything of that sort.
Since subjects had to go to a lab and perform strenuous tests - this sample would include only volunteers; and exclude those too ill to come to the lab or too lazy to make the exertions.
This could be significant - for example, a high proportion of men aged 70-79 would be unable to do these tests (being too ill, demented, institutionalized, or whatever) - so the reference value at best refers to that subset of ambulant old men able and willing to do these lab tests.
Nonetheless, the take-home message is clear: the statement "men are much stronger than women" is not just true on average, but is close to being true as a generalization (at least among un-trained subjects).
I have tried this fact out on a few people, men and women, and most - like me - were surprised at the high degree of difference in strength between men and women and especially the lack of overlap.
Since the average civilized men and women do not compete physically at full strength in the course of everyday life, and seldom go head to head on the kind of objective measures of strength being used here, the scale of sex differences in strength is consistently under-estimated - probably due to the factors discussed here: