Smoking decreases the body's ability to absorb oxygen
Even a modest amount of carbon monoxide in the lungs decreases your body’s ability to absorb oxygen. It also decreases the amount of oxygen your body transports to your muscles. Moreover, tar coats the lungs and makes it more difficult to breathe. If that’s not enough, smoking causes a swelling of mucous membranes in the lungs, which also affects breathing.
During exercise the heart has to work harder if your smoke
A smoker’s heart rate is elevated. Thus, when exercise is attempted, the effort seems more arduous and the heart rate speeds quickly. In all, your heart will have to work harder to do the same amount of work a non-smoker does. And, you’ll feel less comfortable doing it. If you’re prone to high blood pressure, smoking makes it worse.
Increased fatigue during and after exercise as a result of smoking
You’ll also find that smoking increases your fatigue level during and after your exercise session. Endurance is reduced and physical performance may not improve as much as if you did not smoke.
With all the above negative effects, it’s easy to see that smoking and fitness do not mix.
Got this from this link -
http://www.thedietchannel.com/Smoking-Effects-On-Workouts.htm