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.

The carbon monoxide in cigarette smoke attaches to the haemoglobin in blood cells more easily than oxygen does. Haemoglobin’s job is to carry oxygen around your body to feed your organs. If carbon monoxide hitches a lift, less oxygen is carried to your organs. The more oxygen reaching your organs the more energy you have.

Cigarette smoke also decreases your lung capacity very significantly. It does this by narrowing the airways in your lung each time you inhale. If your lung capacity is lower than it should be, it’s harder to get the oxygen you need from each breath. So, when you exercise, your body is begging for more oxygen than your lungs can deliver, you breath harder and faster and very quickly become breathless.