In short, the more you smoke the less functional capacity you will have.
Smoking leads to a condition called COPD. People who have COPD will have larger lung volumes such TLC, total Lung Capacity and RV, Residual Volume. This may sound good however it is not. With increased volumes the person is trapping air. They are unable to get the bad air out and the good air in. This will lead to a barreled chest and depressed diaphragm. The longer one goes with hyper-expanded lungs the less they can breath.
Now speaking about functional capacity, the smoker has less functional capacity. Again they cant get the good air in and the bad out. Less air exchange.
I am an Emergency Services Registered Respiratory Therapist (RRT), Certified Asthma Educator (AE-C), a Pulmonary Function Technician, and an Emergency Medical Technician (EMT). I also have a degree in respiratory science.