Although several simple machines exist for casual home use, there are three major models: RowPerfect, WaterRower and Concept2. Of these the Concept2 is the most popular, and is generally considered the standard training option for world-class rowers. Each machine consists of a flywheel connected to a chain and handle. The rower pulls the handle, causing the flywheel to spin. The flywheel has a damping mechanism applied (using either air or water) that is intended to simulate the feel of an oar moving through water. Depending on the machine the rower either moves back and forth as part of the rowing action, or the rower remains stationary and the flywheel mechanism moves. The machines where the rower remains stationary are generally considered to better simulate the feel of a boat.
Each machine features a digital performance monitor that can display the athlete's work output in watts, calories, or notional "metres" that are roughly calibrated to correspond to the speed of a four-man boat on the water.
Concept2 organize several national competitions, as well as a world championship held in Boston, USA. Concept2 organize several national competitions, as well as a world championship held in Boston, USA. This event is known as the CRASH-B sprints ('Charles River All Star Has-Beens', based on the Charles River in Boston). The usual distance for competition is 2,000 metres, although until 1996 the CRASH-B and other indoor rowing events were 2,500 metres. The usual distance for competition is 2,000 metres, although until 1996 the CRASH-B and other indoor rowing events were 2,500 metres.