We will need a character with three animations: Idle, TiredReference, and Tired. The Idle animation is a normal, stationary idle. The TiredReference animation has no motion and is used as a reference pose for calculating additive motion from the Tired animation. The TiredReference animation can be the first frame of the Tired animation. In the Tired animation, our character is breathing heavily.

You can also go to the Chapter 07 Special effectsRecipe 04 Using additive mecanim layers to add extra motion to a character directory. Open the Example.unity scene there. You will find the same Humanoid character there. If you play the game and press the space bar, our character will start breathing heavily while still playing the Idle animation. You can find all the needed animations in the Rigs directory.