But will women ever be as fast as men? After two record-breaking performances at the London Marathon, some wonder if there is any biological barrier that humans cannot overcome.
Sawe shatters two-hour marathon goal
Elite endurance: Following record-breaking performances at the London Marathon by Sebastian Sawe and Tigst Assefa, experts are questioning whether there are any biological barriers left that humans cannot overcome. Glossary
Endurance - The ability to keep doing something difficult, unpleasant, or tiring for a long time.
Insurmountable - Too great to be beaten.
Sceptical - To have doubts or reservations. The philosophical theory of scepticism holds that some knowledge is impossible.
Testosterone - The hormone that causes people to develop male sexual characteristics. Women also produce some testosterone.