It is a well-known fact that smoking reduces fitness. It does this in a number of ways, chiefly by reducing the amount of oxygen available in the body. Since oxygen plays a major role in energy production, even a minor depletion has an impact on physical performance. Carbon monoxide in the blood also reduces the amount of oxygen that is released from the blood into the muscles. Smoke inhalation has an immediate effect on respiration, increasing airways resistance and therefore reducing the amount of oxygen absorbed into the blood.
Smoking increases the heart rate for a given level of exercise.
Once it leaves the lungs, oxygen is transported in the blood by attaching to the haemoglobin within red blood cells. Oxygen has a great affinity for haemoglobin. Therefore, as the level of carbon monoxide in the blood increases, the level of oxygen decreases. Raised levels of carbon monoxide in the blood also impair the release of oxygen from the blood into the cells. This has a significant effect on heart and other muscle cells where there is a high demand for oxygen.