Smoking makes it harder to get fit, even if you are young. In fact, teenagers lower their exercise performance levels with smoking, according to a study by D. Louie in the 2001 Canadian Respiratory Journal. When you smoke, you harm your exercise tolerance and physical endurance several ways.
Vascular System Effect
Smoking adversely affects your vascular system, or the network of blood vessels in your body. The nicotine and carbon monoxide from smoking raise your fibrinogen, which is a blood-clotting factor, while lowering your HDL, or "good" cholesterol, according to John Buckley's "Exercise on Prescription: Cardiovascular Activity for Health." When your fibrinogen levels get too high, your blood gets more "sticky" and allows lipids to accumulate. This plaque causes narrowing of your arteries. Narrowed arteries reduce the blood supply to vital organs, such as your heart, and to your muscles.
You need a healthy vascular system to meet your body's energy demands during exercise, according to Brian Mac, performance coach for UK Athletics. The blood vessels in your muscles dilate during exercise, and blood flow increases to boost the oxygen supply to these muscles. When oxygen isn't supplied to your muscles quickly enough, your body can't properly produce the energy it needs for muscle contractions.
Effect on Lungs
Smoking decreases your lung capacity, according to The Diet Channel. It also produces lung-congesting phlegm. You are better able to exercise when your lung capacity is good and your lungs function well. According to an article in Scientific American by Jeremy Barnes, associate professor of health management at Southeast Missouri State University, your body performs exercise more efficiently when it can get oxygen into your blood stream and bring it to your working muscles, where it is used in the metabolic processing of energy.
The carbon monoxide in cigarette smoke reduces the amount of oxygen available in your body, according to Australian sports physiologist David Pyne. Carbon monoxide binds to the hemoglobin within your red blood cells, as does the oxygen needed for transport around the body when it leaves your lungs. Carbon monoxide's affinity for hemoglobin is up to 300 times greater than oxygen's. Higher carbon monoxide levels in your blood make it harder for oxygen to be released from your blood into your cells, affecting your heart and other muscle cells that have a high oxygen demand during exercise. This oxygen transport interference decreases your exercise performance because it hampers energy production in your body.