smoking is pretty bad. I've been smoking since 13, and around half a pack a day since 18. I quit once three years ago for one solid year, just to see if I could do it. Wasn't that hard. It's hard for a week, and then it isn't as difficult. The trick is to find somethign to take the place of the habit, like pushups or something.
Anyway, smoking is bad, but it's really not as bad as the groups make it out to be. They consider a light smoker 1-4 packs a day. 1 to 4! 4! I smoke about one every hour and a half. Figuring that a person is up about 16 hours a day, a 4-pack-a-day smoker is smoking 5 cigarettes per hour. A cigarette takes about 5 minutes to smoke, ~10 if it's an american spirit cigarette. So, at their maximum they consider a light smoker someone who smokes a cigarette, waits 5 minutes and then smokes another one, OR someone who chains american spirits all day long with breaks for the bathroom and eating.
Not to mention that industrial cities have so much carbon in the air that there are thousands of cases of lung cancer from people who don't even smoke.
Now, the reason I lead into this post by saying "smoking is pretty bad" is because while I don't believe it is as detrimental as is proclaimed, it does impede growth. Nicotine restricts blood flow as a stimulant, and it's a diuretic, which means that the normal nutrients you would be getting from food, etc isn't getting effectively absorbed. In that scenario, it makes maintaining fitness problematic, and can indeed lead to getting sick, malnutrition, and put a block in front of any workout regime or training that you do.
Not to mention that the worst of it is probably the smell you put off.
Essay Pro