Most people with livestock have no love for mountain lions. Especially when you see one kill one of your livestock, and the wildlife officials literally call you a liar. A mountain lion is very capable of killing an animal well over 1,000 lbs.
If one does attack you, go for their eyes. Yes, they almost always attack from behind so be watchful.
This video gives you an idea of the strength of a mountain lion. IMO, pound for pound a cat is a very strong creature - stronger than any human.
WARNING - This video is graphic with a mountain lion killing a mule deer buck.