A man suffering from anemia cannot get large amount of oxygen and energy will not be produced sufficiently inside the body. Due to lack of enough energy the person feels tired even in short walk. 

Hemoglobin is an iron-rich protein that helps red blood cells carry oxygen from the lungs to the rest of the body. If you have anemia, your body does not get enough oxygen-rich blood. This can cause you to feel tired or weak. Having anemia can make you feel tired and weak. There are many forms of anemia, each with its own cause. Anemia can be temporary or long term, and it can range from mild to severe

People who are anemic most often experience fatigue. While it's normal to feel tired after a long day at work or a heavy exercise session, when you're anemic, you feel weary after shorter and shorter periods of exertion as your body's cells become starved for oxygen.If you aren't getting enough iron, this can limit oxygen flow and anemia may develop. If you show up at the doctor's office looking pale, especially around the eyes, and complaining of constant chills and exhaustion, your doctor is likely to test for iron deficiency.