The acronym RPM stands for rotations per minute. Exercise machines that have arms or pedals that must be moved in a loop or circular fashion are devices that track RPM to help gauge speed, intensity and how hard you are working on the machine. The three most common devices that utilize RPMs are arm ergometers, elliptical machines and stationary cycles.
An arm ergometer is a device that has two hand attachments that attach to a flywheel and arm crank. The goal of the exercise is to rotate the crank against resistance set by the machine. Rotations per minute for an arm ergometer lets you know how many times you have completely spun the flywheel around during that time. The exercise is performed from a seated position and is low impact. Arm ergometry is suitable for individuals with lower-body impairments and may be used after a broken arm has healed to help return strength to the affected arm and mobility to the shoulder joint.
An elliptical is a low-impact piece of exercise equipment that typically requires both your arms and legs to move in tandem to produce movement. The foot pedestals are connected to a circular flywheel that provides resistance during the circular movement of the pedestals. Ellipticals can be pedaled forward or in reverse. The calculation of RPMs for an elliptical stems from how many times the elliptical flywheel has made full clockwise or counter-clockwise rotations per minute. The American College of Sports Medicine notes that the elliptical's low impact can make it a suitable alternative to walking.
The stationary bike also uses RPM to help gauge exercise tempo. Stationary bikes require the user to push pedals with their legs to spin a wheel. Two different versions of stationary cycles are available -- a seated bike and a recumbent bike. The seated bike requires you to push the pedals, located below you, from a seated position. The recumbent bike requires you to push pedals located on the same horizontal line as the rest of your body. The motion is very similar to riding a regular bike but without the movement. Rotations per minute on a stationary bike are calculated by determining how many full turns are made from the flywheel that is attached between the pedals per minute of exercise.
Although RPM is one way to determine pace during exercise, it is only one part of the picture. You must also consider the resistance level at which you've set the piece of equipment you are using to determine how fast you are going. Typically, resistance multiplied by the RPM by the length of the flywheel dictates how fast you are going. Exercising at the same RPMs with different resistance setting means you are not performing the same amount of exercise.