Women's upper body muscles respond to strength training just as well as men's

The extent to which women can strengthen the muscles in their upper body through strength training is the same as the extent to which men can do this. However, this does not imply that women can easily reach the strength level of men who work out.

Study
In 2016, Brazilian sports scientist Paulo Gentil published a study in which he got 44 male and 47 female students to do a full-body workout twice a week for 10 weeks.

The workout consisted of basic exercises such as leg press, leg curl, chest press and lat pulldown. The subjects did 3 sets of each exercise with a weight that allowed for 8-12 repetitions. The subjects rested for 2 minutes between sets.

Before and after the training period, the researchers determined the torque that the test subjects could develop during a biceps curl. 'Torque' is what athletes in the gym often refer to as 'force'.

Results
In absolute terms, the men gained more strength than the women [left in the figure below]. But in relative terms, in terms of progression over the strength already present before the training program began, the progression of the men was similar to that of the women [bottom right].

Conclusion
"Despite the physiological and hormonal differences between sexes, women demonstrated the same relative strength gains compared to men [...]", writes Gentil.

"It appears there is presently no evidence of a need to design different resistance training protocols to men and women. [...] One should not expect to find limitations in upper body strength development in women."

Reference: PeerJ. 2016 Feb 11;4:e1627.