Four Masai hunters running through bush holding spears, Masai Mara National Reserve, Kenya, East Africa, Africa

Sanderling (Calidris alba) sprinting across a shallow film of water on sandy beach, with a reflection of itself below. Soroby. Argyll,. Scotland, UK

Sanderling (Calidris alba) sprinting across a shallow film of water on sandy beach, with a reflection of itself below. Soroby, Argyll,, Scotland, UK

Two nurses running down corridor in hospital

Mixed Race woman running in park

Runners starting, Olympic Games, Sydney, Australia

Tartan track of a sports field, starting blocks for sprinting disciplines, lane markings

Tartan track of a sports field, starting blocks for sprinting disciplines, lane markings

Athletics, woman sprinting, start from start block, Germany, Europe

Athletics, woman sprinting in the curve, Germany, Europe

Man, athletics, sprinting, Germany, Europe

Meg Oster trail running in Hope Valley outside of south Lake Tahoe in California.

Panorama of slow pan of sprinting cheetah (Acinonyx jubatus), Serengeti, Tanzania

Woman running on a track; Wellington, New Zealand

Jogger on rural trail

Woman running