An erg, short for ergometer, is a machine used to simulate the action of watercraft rowing for the purpose of exercise or training for rowing. It is also known as a rowing machine and is designed to mimic the rowing motion that a person creates when in a watercraft but operates on land. The term "erg" is used to refer to Concept2s Indoor Rowers, SkiErg, and BikeErg, which are all ergometers that measure work performed by the rower. Ergs are often used as a fitness measurement to see how strong or fast an individual is, isolating their performance and displaying metrics in a way that isn’t possible in a shell on the water.

The breakdown of effort when using an erg should be 60% legs, 20% core, and 20% arms, and targets the hamstrings, calves, and glutes along with pecs, arms, abs, and obliques. Rowing on an ergometer requires four basic phases to complete one stroke: the catch, the drive, the finish, and the recovery. Some standard indoor rower ergometer tests include the 250 m ergometer test, 2000 m ergometer test, 5 km ergometer test, 16 km ergometer test, and the 30-minute ergometer test.

In summary, an erg is a machine used to simulate the action of watercraft rowing for the purpose of exercise or training for rowing. It is also known as a rowing machine and is designed to mimic the rowing motion that a person creates when in a watercraft but operates on land. Ergs are often used as a fitness measurement to see how strong or fast an individual is, isolating their performance and displaying metrics in a way that isn’t possible in a shell on the water.