Basic: Animation Layer & Avatar Mask
With animation Layer we can override or add an entire animation set over other one. You can mask your layer so it only affect part of the body by using an Avatar Mask.
At this example, we've create an additive layer for breathing.
Stamina is consumed as the player moves. When stamina is low, player's breath is faster then in rest. A script updates stamina value into Animator using based on "Forward" and "Right" parameter.