Smoking has both immediate and long-term effects on several physiological systems used in intense exercise. Intense or maximal exercise requires these systems to be stretched to their full capacity.
Any reduction in this peak capacity will result in reduced performance. Furthermore, there is a temporary drop in immune function following intense exercise, which leaves an ‘open window’ for infection. There’s also increasing recognition that the immune system plays an important role in recognising and killing early cancer cells; therefore the combination of smoking and intense exercise can’t be a good one.
The effects of smoking on the respiratory system are most obvious. After one cigarette, the cilia (hairs that waft phlegm and other pollutants out of the lungs) are suppressed. With long-term smoking, the cilia are removed completely, and smokers have to cough to get pollutants out of the lungs. The risk of infection is greatly increased. Smokers have more frequent infections, and this will get in the way of training. More serious infections such as pneumonia can cause lung destruction on a permanent basis. With smoking, the air sacs (alveoli) in the lungs are progressively destroyed, and smoking eventually leads to reduced lung capacity.
This will lead to reduced respiratory function at all levels of exercise, but will be particularly noticeable with higher-intensity exercise because the higher intensity simply won’t be there.
Immediately after a cigarette the blood vessels tighten (vasoconstriction), leading to reduced oxygen delivery to the working muscles. The heart has to work harder to achieve the same performance, meaning blood pressure rises to meet demand. Normally blood pressure does need to rise during intense exercise in order to improve the perfusion pressure to muscles; but in the context of smoking, the heart is working unnecessarily hard.
In the long-term, smoking can lead to atherosclerosis, a hardening and blockage of the arteries throughout the whole body. The coronary arteries that supply the heart progressively narrow, meaning the heart cannot perfuse itself properly; this leads to a poor cardiac output. Smokers develop angina, heart attacks and heart (pump) failure.
Overall, smoking is associated with innumerable harms for a triathlete, many of which come from smoking only one cigarette.