One of the main impacts of smoking on sports performance is the reduction of the amount of oxygen available in the body. Smoking causes high levels of carbon monoxide, which reduce the amount of oxygen absorbed from the lungs into the blood and consequently to the muscles. This decrease in oxygen will reduce one’s physical endurance, making it more difficult to do well in sports.
How does smoking affect your sporting performance? – http://wiki.answers.com/Q/How_does_smoking_affect_your_sporting_performance