In this case, you would use a proportion. This means
Number of Males who do something / Total Number of People who do something.
For example, if you have 40 males that exercise and 60 females, your male proportion would be
40 / ( 40 + 60 ) = 40 / 100 = 40%
and your female proportion would be
60 / (40 + 60 ) = 60 / 100 = 60%.
If you give us a more complete picture of what you are trying to accomplish, we could give you some more precise details.
Hope this helps,