I always thought left-wingers were the ones that made a point to contribute to other peoples' well being, and not right-wingers.
Also, in the 21st century, building up your biceps probably has terribly little to do with your ability to contribute to society.
If this study is worthwhile (I don't know if it is because I didn't pay very detailed attention to it) I would take the most likely guess to be that it's because right-wingers are more likely to pursue strict gender ideals. A test for the researchers would be to see if left-wing women are stronger than right-wing women on average.
The article states that they found no link between a woman strength and her political views. That said, I would have like more details on how they determined political views.