Is there a biological reason for women to be weaker then men (in the same weight category)?

Question

Are women weaker then men because of something biological, or cultural, or both? Men do have predispositions to be higher and heavier, but lets compare equal weight categories (a 70kg man against a 90kg man would have problems too).
Cultural reasons that could be making women weaker:

• muscles considered ugly on women (or at least they think so and are afraid to do weight exercises)
• men have a big social pressure to have more strength in both childhood and as a teenager, so they often start to exercise early
• women do the physically easier work when helping out home (the brother helps to cut wood while the sister cleans the house) and this adds up over the years. This continues into adulthood, where men have a higher chance of working in a physically harder job.

Do women gain strength slower with the same intensity of exercise? Lets say there would be two people with identical physique (height, weight, initial strength, age) but of different gender. They both start weight lifting (for example) and they work out with the same intensity and duration and eat the same food. Would they end up equally strong?

Answer 1

According to Rippetoe & Kilgore,

As a general rule, women do not have the same level of neuromuscular efficiency as men. This is probably due to the differences in hormonal profile and the much lower levels of testosterone.

It's also worth noting that a pound of muscle has the same absolute strength in either gender. The mass is distributed differently, leading women to lag in upper body strength:

And, while levels of absolute strength relative to muscle mass are essentially the same in the two sexes, women's upper-body movements suffer from the large relative difference in local muscle mass distribution.

Rippetoe & Kilgore go on to explain that an ideal training program for women looks the same as that for men (with minor differences do to menstrual cycles & the resulting effects on recovery).

Looking a little deeper at the generally-accepted hypothesis that hormonal differences are the cause, this study finds that testosterone increases muscle protein synthesis and protein balance, resulting in greater muscle mass. Furthermore, in-vitro and rat data suggests that ovarian hormone inhibits muscle protein synthesis.

I would posit that cultural correlations result from these physiological differences, rather than causing them. However, it is worth noting that cultural causes of malnutrition (American women tend to be deficient in calcium and iron) can also impact the efficiency of a strength program.

Answer 2

Basically, the difference comes down to testosterone and it's effects on the human body. It creates higher density bones, stronger muscles and other various effects.

http://www.springerlink.com/content/l47235487q162675/

There are a few studies around showing the differences, but not too many modern ones as it has been proven in the past what the effects of hormones are on growth and strength, as well as the continuing effect(s) of those hormones, and many of those studies are not available online.

http://jap.physiology.org/content/83/5/1581.short

That study suggests that while men are stronger in their prime, they tend to "age" faster, and lose more than women in the same measured categories, including faster bone loss in the post menopausal stage. This is probably at least partly due to the loss of hormone production in the post menopausal women, and the way that estrogen limits the effects of osteoblasts, which leech calcium from it's primary storage spot, bone.

As far as iron, that is mainly due to menstruation. Women simply need to produce more blood on a monthly basis than men do, and iron is a critical part of that process.