2. Your Breathing Gets More Efficient
Your lungs become more efficient at getting more oxygen to your muscles not only by better processing the amount you take in during each breath but also by increasing your respiration rate. We actively use our respiratory muscles when we breathe in and relax them when we breathe out.
Inhaling and exhaling through your mouth allow more oxygen to enter your body and fuel your muscles. The quality of your breath can be an indicator of your fitness level or how well your body is responding to the pace and intensity of your run.