I have a relative who recently took up cross fit competitions. Her arms are huge and muscular and she brags about her 6 pack. She wears spandex most of the time when she's not at work, and tight shirts to show off her muscles. She likes to compete with the guys, and often beats them.
My husband and I were discussing this today, and he said that he's thinking about telling her that all of her muscles are working against her chance of finding a husband, because no man wants to be scared that he could be outdone by his wife. To which I replied, "Well, when I'm out in public with her, I can't help but notice how many men take a second look. What is that saying about those men?" To which he replied- "Those men aren't looking for a wife, they're looking for some temporary fun." He also said that women who work out all of the time don't do it just because it feels good- they do it because they are seeking some sort of recognition for it- i.e. the lustful glances, the compliments on how toned she is, etc. What he says is true. It makes me very sad for her.
I agree with what some others have said- I don't think I could go as far as to say it's a sin for a woman to ride a motorcycle- but the way she rides a motorcycle or plays sports could cause her to sin against modesty. Motorcycles, I'm afraid to say are often times, at least in American culture, immodest for both men and women. Men (and women) like to soup them up with loud motors to grab attention, etc. You go to somewhere like Kampala, and you'll see motorcycles being used in a completely different fashion by men and women- to get around in an economical way.
I enjoy being active, but not competitively. My husband and I will throw balls back and forth for fun, play tag, etc. And the only time I ever win at tag is when he lets me win. :) I find I get plenty of activity tending a very large garden and doing other yard work, going on walks, running errands, and cleaning house.