"Rowing, indoors or outdoors, at any exercise level of intensity, requires a greater exercise expenditure than any other aerobic activity. Calories are burned in relation to the number of muscles used and the intensity and duration of the exercise. Rowing with a sliding seat uses a very large muscle mass since the upper, lower and trunk muscles are used vigorously"
Dr C Everett Koop- Former US Surgeon General
Working 84% of the muscle mass, more than any other exercise, rowing recruits all major muscle groups. Maximize gain, while minimising time; rowing can burn in excess of 1000 calories per hour. Importantly rowing does so with a far lower perceived level of exertion than other aerobic exercises.