Why don’t you just set the character’s Max Walk Speed to your normal movement speed if the backwards movement key is pressed (that you check with that Is Less Than node) using a Branch node after the Triggered pin of IA_Move 
If you want to be able to keep sprinting after letting go of the backwards movement key, then you can also set the Max Walk Speed back to your sprinting speed by checking if the Sprint has been triggered or not with a new bool type variable.
Hope this helps! 