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 and will it reduce performance on mobile? Because I going to add a lot of spearman in the game. Can someone explain because i new in unity. Anyway to fix this? Thx