Rowing machines simulate the feel of sweep rowing, working your arms, back, legs and core. While rowing machines are used by competitive rowers for training, they're also found in many commercial gyms and can be a part of any cardio and strength training regimen. The different types of rowing machines are categorized by the way they produce resistance.
Magnetic-resistance rowing machines use electromagnets to provide braking resistance on a flywheel. This type of resistance tends to be quiet and smooth, and can be accurately measured through electronic components. This allows for digital displays that provide detailed information on distance, calories burned and other data. Resistance on these machines is fully adjustable but, because they have a rigid central rail that cannot be folded up or collapsed, they typically take up a lot of room and therefore may not be ideal for home use in smaller spaces.
Air-resistance rowing machines have a flywheel that resembles a cylindrical fan blade. When you pull on the handlebar the blade spins; the harder you pull, the faster it spins and the more resistance you feel. Some air-resistance rowers have a lever you can use to adjust airflow -- and thus resistance -- to the fan blade; and some air-resistance rowers also provide digital displays that show your workout data. This style also has a rigid central rail, so it tends to take up lots of space; and the fan blade can get noisy.
Water-resistance rowing machines feature an enclosed tank of water with paddles suspended inside. As you pull the handlebars the paddles spin, using the water to provide a type of resistance that most closely simulates the feel of actual rowing. Like the air-resistance models, this style provides more resistance the faster and harder you row; resistance can also be adjusted to some degree by adding or removing water from the tank. Water-resistance rowers are also relatively large and rigid and, because of the water tank, they are very heavy. They are not as noisy as the air resistance models, but noisier than the magnetic versions.
Piston-rowing machines feature pairs of hydraulic pistons that are connected to separate handlebars. These pistons provide the resistance and are often adjustable, but most machines of this style provide more of an arm workout than a leg and full-body workout. This is partially because the handlebars on this style of machine are fixed, which provides a less-natural stroke, and partially because piston-resistance machines are designed to be compact, usually featuring a fixed seat position and shorter range of motion. Advantages of this style include compact size and relative affordability compared to other models. Many piston rowers can be folded up and slid underneath a bed for storage.