Fastpacking is a combination of trail running and ultralight backpacking.[1] It is described by writer Clint Cherepa as "hiking the ups, jogging the flats, and running the downs", depending on the gradient, because of the weight carried.[2] Participants carry a light pack with essential supplies, including a sleeping bag and tent, or similar form of shelter, if mountain huts or other accommodation is not available.[3][4] The weight carried will vary but fastpackers aim at no more than 15 pounds (6.8 kg) and some achieve less than 10 pounds (4.5 kg).[5] This activity may be undertaken either unsupported, self-supported, or supported. "Unsupported fastpackers make no use of outside assistance along the route", while self-supported fastpackers will leave caches of supplies along the intended route.
Fastpacking involves covering a considerable distance over several days with a pack, which requires both mental and physical strength. Established, well-traveled long distance trails are used because "with minimal extra food and clothing, getting stuck in the backcountry for an extended period of time can quickly become a dangerous proposition".[6]