An erg is an indoor rowing machine, short for “ergometer.” The word comes from the Greek ergon (work) and metron (measure), so it literally means “work measurer.” In rowing culture, “the erg” is the standard training and testing tool, used by everyone from beginners in their garage to Olympic athletes preparing for competition. It measures exactly how much power you produce with each stroke, making it one of the most precise pieces of cardio equipment available.
How an Erg Measures Your Effort
What sets an ergometer apart from a basic exercise machine is its ability to quantify your output. The most widely used model, the Concept2, works with an air-braked flywheel. When you pull the handle, a chain spins the flywheel, and specially designed vanes push against the air to create resistance. A sensor measures the flywheel’s angular velocity, tracking how fast it speeds up during your pull and how quickly it slows down between strokes. From those measurements, an onboard computer calculates your mechanical power output.
The monitor displays this as a “split,” which is the time it would take you to cover 500 meters at your current pace. A 2:00 split means you’re producing enough power to theoretically row 500 meters in two minutes. You’ll also see total distance, stroke rate, calories, and watts. This real-time feedback is what makes the erg so valuable for training: every stroke is measured, and there’s no hiding from the numbers.
Air, Water, and Magnetic Resistance
Not all rowing machines work the same way. The three main resistance types each create a different rowing experience.
Air resistance is the most common type in gyms and rowing clubs. The faster you row, the more air the flywheel moves, and the harder it gets. This follows a squared power principle: doubling your speed requires roughly eight times more power. That dynamic feel closely mimics rowing on water, where the boat responds directly to how hard you pull. Air ergs are self-powered and need no electricity, though they can be noisy at high intensities.
Water resistance machines use paddles spinning inside a water-filled tank. The sensation is smooth and feels natural, with resistance that also increases with effort. These tend to be quieter than air ergs and are popular for home use.
Magnetic resistance machines use magnets positioned near a metal flywheel. Unlike air and water models, resistance stays consistent regardless of how fast you row. You adjust difficulty by changing a preset level rather than by rowing harder. They’re the quietest option and work well for steady-state endurance training, but the fixed resistance doesn’t replicate the feel of actual rowing as closely as air or water models do.
The Four Phases of the Rowing Stroke
Every stroke on the erg follows the same four-phase cycle. Learning these phases correctly matters, because good technique protects your back and produces more power with less wasted energy.
The catch: This is the starting position. You’re sitting with your shins roughly vertical, arms extended straight, and body leaning slightly forward from the hips. Your weight is loaded onto your feet, ready to push. Think of it as a coiled spring.
The drive: The drive is where all the power happens, and it follows a specific sequence. Your legs push first, which is where most of the force comes from. British Rowing’s technical model emphasizes a “front-loaded, leg-driven stroke,” meaning your trunk and arms stay braced and still while your legs do the initial work. In the middle of the drive, your back begins to swing open. Only in the final portion do your arms pull through. The whole sequence takes less than a second at a firm pace.
The finish: At the end of the drive, your legs are fully extended, your torso is leaning back slightly past vertical, and the handle is pulled to your lower ribs. This is the moment of full extension.
The recovery: You reverse the sequence to return to the catch. Hands move away first, then your torso rocks forward, then your knees bend as you slide back up the rail. The recovery should feel unhurried, taking about twice as long as the drive. This ratio gives you a brief rest between strokes and sets up a clean entry into the next one.
Calorie Burn and Fitness Gains
Rowing is a full-body movement that engages your legs, core, back, and arms in every stroke. That broad muscle recruitment is why it burns calories efficiently. A 155-pound person burns about 252 calories in 30 minutes of moderate rowing, comparable to cycling at a similar intensity. Pick up the pace, and rowing pulls ahead: vigorous rowing burns roughly 369 calories in the same timeframe, compared to about 278 for cycling.
The erg is also an effective tool for building cardiovascular fitness. Research comparing rowing to cycling found that rowers achieved higher peak oxygen uptake (a key marker of aerobic capacity) on a rowing ergometer than on a bike. Younger subjects reached values about 17% higher when rowing compared to cycling, while older subjects saw a 10% improvement. This likely reflects the fact that rowing demands oxygen delivery to a larger total muscle mass than cycling does.
Common Technique Mistakes and Back Pain
Low back pain is the most frequently reported injury among rowers, and it’s almost always linked to form errors rather than the machine itself. A systematic review of rowing biomechanics identified two key problems. First, rowers who experience back pain tend to let their pelvis tilt too far backward at the catch, which forces the lower spine into excessive flexion, essentially rounding the lower back under load. Second, they often overextend through the hips at the finish, creating a repeated cycle of too much rounding and too much arching.
Fatigue makes this worse. As you tire, your lumbar spine flexes more at the catch, and this effect is actually greater on an ergometer than in a boat. The practical takeaway: if your lower back starts aching during a long piece, your form is likely breaking down. Shortening the stroke slightly, focusing on pushing with your legs rather than pulling with your back, and stopping before exhaustion degrades your technique will go a long way toward keeping you healthy.
Ergs in Competition
Indoor rowing has its own competitive scene, headlined by the World Rowing Indoor Championships. Races are typically set at a fixed distance (2,000 meters is the standard benchmark) with rankings based on finishing time, though some events use a fixed time format where the winner is whoever covers the most distance. All competitors in a race use the same make and model of machine to ensure equal conditions. Only machines approved by World Rowing are permitted at the world championship level.
Outside of formal competition, the 2,000-meter test is the universal measuring stick in rowing. It takes most people between 6 and 9 minutes and is widely considered one of the most demanding single efforts in sport, requiring a blend of aerobic endurance, anaerobic power, and mental toughness. Coaches use 2K times to rank athletes, select crews, and track fitness over a season. If you hear a rower mention their “erg score,” they’re almost certainly talking about their 2,000-meter time.