while it is def not possible to "outrun" a grizzly bear, there is still a low chance of getting away. if you are in a heavily forested area, you can zig zag through trees and areas which are too narrow for a grizzly bear to go through. bears might be able to accelerate and move faster but humans still take the cake for coordination.this can buy you precious time in which many options can be taken. you can climb up a tree, hide in some bushes, jump in a lake, or even find a big brnach and fight for your life.