You've got to tell them, but realistically, unless things are career ending, you should be fine. The military will spare no expense to take care of its own medically, as long as you are an asset.
Never hide anything, or be dishonest, it's not worth it. As long as it is legit, they will bend over backward to accomodate your needs, but try to pass something off and your a$$ could be nailed to the wall. Just say that you know the military encourages physical fitness and you were trying to comply with those policies.
Now if you get hurt riding a motorcycle and your command has put out direction not to, then you might need to be worried.