The best thing a runner can do to improve his or her performance is to run longer distances instead of focusing on speed.
Running longer distances is gentler on the cardiovascular system and allows the body to adapt its metabolism.
"In everyday life, the body mostly burns sugar to produce energy," explains Ingo Froboese, head of the Centre for Health at the German Sport University in Cologne.
However, "in terms of energy, it would be better to draw from fat reserves," Froboese says. In order to burn fat, the body needs to have enough oxygen, which means it's counterproductive for runners to get completely out of breath.
This is why Froboese recommends a moderate, slow pace for about 80 per cent of training, so runners can remain at an oxygen-rich level.
It is also important to run regularly. Froboese recommends three times per week, 45-60 minutes per training session.
Once runners can cover longer distances without trouble, they can slowly increase their pace and introduce interval training, for example by climbing a small hill or sprinting for one minute in the middle of their run.