 What is a long run? A long run for you if you're a beginner might be 5 miles. If you're a marathon runner or an ultra runner it could be anything between 15 and 30 miles. Your long run should be done slowly. You should be able to carry out a conversation during your long run. If you're into heart rate zones you should be working in zones 1 or 2, certainly not in zone 3. Run your long run once a week or at least once every 2 weeks consistently in your training block. Your long run helps to build cell mitochondria and capillary blood vessels. These are responsible for the storage and transport of oxygen and energy to your muscles. Not only will this help your stamina and endurance over long distances stopping you hitting the wall in a marathon but it will also vastly improve your speed over short distances like 5 and 10k.