Women are indeed statistically weaker than men, but statistical tendencies are often heavily biased by cultural values and norms. The mistake often made regarding female strength relative to males (which is perpetuated by sexism) is that women are weaker BECAUSE they are women, rather than because of cultural values encouraging women to be weaker physically. The same kind of mistake is made about African-Americans, as this demographic has statically lower intelligence. The racist mentality of society encourages the idea that they are somehow genetically dumber, when in fact they are encouraged by society to be less intelligent. Take a look into labeling theory (sociology) and you will see what I'm talking about.
I am not necessarily doubting that men are more biologically strong than women, neither am I affirming it. One could use "sports" as an example of the ultimate limits of women's strength, but such a comparative survey does not escape the sociocultural factors which I mentioned. Women are conditioned by society to be weaker than men, and this socially and psychologically creates a barrier to physical improvements on strength for women, if only unconsciously. Additionally, the stigmas against women participating in sports and lack of social support thereof create a smaller and weaker pool of active participants, suppressing the vast majority of potential that may have otherwise given women a major advantage.
Take for example, how in the Olympics the vast majority of winners come from the United State, then dropping off to the Soviet Union, and other developed nations after that, with less developed nations, despite being physically identical in their abilities, receiving very few medals by comparison. Clearly the environment has a far greater impact on physical fitness than biology. The US has more resources, more leisure, more determination to win in the Olympics, as do developed nations in comparison to less developed ones. In the same way, women have far less leisure, determination, and socioeconomic resources than men, and this has nothing to do with biology.
Both men and women have estrogen and testosterone in their systems, and for the vast majority of people the difference in levels isn't particularly significant. Furthermore, differences in performance, as I have illustrated above, are far more influenced by environmental than biological differences, suggesting that even if men may have a head start, the gap is not significant after accounting for more influential, non-biological factors. Thus, I think there is plenty of room to challenge the common sense idea that men are inherently stronger than women. Perhaps, as the narrowing of the gap between male and female strengthen over the past few decades suggests, the difference in strength is merely the product of sociocultural conditioning making use of simplistic and dysfunctional gender roles masquerading as biological differences.