What are atheists' biggest fears?

It depends on the person.

What are A-santa-ists biggest fears? What are a-tooth-fairy-ists biggest fears? Those groups are so vast and their lack of belief in the existence of Santa or The Tooth Fairy don't have a huge amount of impact on the rest of their values.

There are homophobic atheists, there are gay atheists, there are conservative atheists, there are liberal atheists, there are atheists who are artists, there are atheists who hate art, there are atheists who spend their entire life doing charitable work and living on minimum wage, there are atheist oligarchs.
I'm training for a long distance trail race. If I go for a long hike of X miles one week, how many miles should I subtract from my planned running for that week?

You've got the right idea. It's best to backwards plan. I like to break things down into phases (see periodization). First phase could be a strength building phase. It could be high reps resistance training for 4 weeks. Phase two would be less resistance training and more cardio for 4

Can you tear a muscle?

Yes.  In medical and sports terminology it is usually referred to as a muscle strain or pull.  When someone says they pulled a hamstring it usually involves some amount of tearing or damage to muscle fibers.  Muscle injuries have grade levels to gauge the level

How to lose 20kg in 4 months

Well there are many many unscientific and unhealthy ways to loose weight but i am mentioning only those points which help you loose weight quickly:Drink water instead of energy drinks: Energy drinks and juices has some calories so to make it ineffective during weight