Breathing hard during exercise brings oxygen to your muscles, which the process release energy to fuel your workout.

oxidation

Explanation:

From the moment we perform body movements, there is a greater demand for oxygen. This is due to the need for oxidation of energetic substrates such as free fatty acids and circulating glucose. Thus, aerobic metabolism is potentially increased to supply the energy required by muscle contractions, whatever their intensity. From this we can say that breathing hard during exercise brings oxygen to the muscles, which helps the oxidation process release energy to fuel the workout.

oxygen +1 most likely