I'm replying to the original post in a direction I have not seen another take.. somebody who works out their legs regularly and is in good shape should NOT get leg pain when bowling in my strong opinion.
You may be used to it, but likely you are sticking on the approach and too much of your forward momentum energy is being absorbed by your joints on your slide leg.
Look into a better pair of
shoes that will let you slide more freely through your shot.
If that does not help, see a doctor about it, you may have a medical condition in the joints that can be rectified.