"The smaller difference in lower body strength may be due to the fact that during childhood, both males and females frequently exercise their leg muscles during activities like running, walking, and playing. Males, however, are socially pressured to enhance their upper body muscles, leading to a wider difference in upper body strength"
While there probably is societal pressures, to suggest that the difference between male and female upper body strength is solely down to physical activity after birth is ludicrous.
Testosterone is an independent factor in muscle mass and accounts for the majority in strength difference. Also, muscles in the upper body have a higher androgen receptor count and therefore respond greater to serum testosterone levels and physical stimuli.
+1. The few women with high testosterone are also better are building muscle, have higher sex drives, and female babies with high testosterone are less interested in faces than things, much like male babies (Baron Cohen at Cambridge, let me hunt a link if you need it)
Very interesting, thanks. I'm always interested in reading up on things along these lines. At this point the amount of studies that show fundamental differences between the sexes are so overwhelming that it's hard to deny it with a straight face. Culture simply does not have the power that people want to attribute to it.
http://en.wikipedia.org/w/index.php?title=Sex_differences_in...
"The smaller difference in lower body strength may be due to the fact that during childhood, both males and females frequently exercise their leg muscles during activities like running, walking, and playing. Males, however, are socially pressured to enhance their upper body muscles, leading to a wider difference in upper body strength"
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Thankfully this has since been removed.