There are countless reasons why a person might choose a particular exercise machine for his or her cardiorespiratory training. Perhaps the stride length and motion on a certain elliptical trainer just feels right or the person feels more comfortable on a recumbent bike than an upright bike. Maybe a client is recovering from knee surgery and therefore uses an arm ergometer to supplement his or her workouts and burn some extra calories. Or, maybe the third treadmill from the end simply has the best view of the TV show the person likes to watch while exercising.

Source: A Comparison of Energy Expenditure When Exercising on 10 Indoor Exercise Machines – ACE