Weird animation after add rigidbody

I make a spearman in blender with animation and export to unity. The attack animation i make in blender was spearman will turn from 0 to 90°, attack, then 90° to 0
Here is the problem:
1. Work well in blender and unity but after add rigidbody to spearman, the animation wont turn properly(maybe just turn 20°/30°)
2. Try and error, i found out if turn on extrapolate will work but what is that. Can someone explain because i new in unity.
Anyway to fix this? Thx

 

And also will extrapolate reduce performance in mobile? Because I going to add a lot of spearman in the game