I’d Track Output and Effort, Not Ergo Calories

I wouldn’t use the calorie total to judge a session on the rowing machine. I’d look at the split or watts, then make a note of how hard it felt to hold them. That gives me something useful when I’m deciding what to do next.

The Concept2 calorie display is an estimate. It uses your output and standard assumptions, including body weight. It hasn’t measured your personal energy expenditure, however definite the number looks on the screen.

And the work you put into the flywheel isn’t the same as the energy your body uses doing it. Your body uses more. Much of the difference ends up as heat.

The units matter here. One watt held for an hour gives 3.6 kilojoules of mechanical work, or about 0.86 dietary calories. A dietary calorie is a kilocalorie, roughly 4.184 kilojoules. If you then assume 25% efficiency, you’re assuming a quarter of the energy used reaches the flywheel as useful work. You haven’t measured the rower’s efficiency. You’ve chosen a value for the calculation.

So you can’t just treat kilojoules as dietary calories and multiply again for efficiency. Wrong units. Quite a lot of arithmetic to end up with an estimate anyway.

Take a 90kg rower and a 60kg rower holding the same split for 30 minutes. Same power, same monitor calorie estimate. The lighter rower is producing more power per kilogram, but that doesn’t tell us who used more energy or who found it harder.

I wouldn’t correct the display by deciding it felt harder, so I must have burned more. Effort and energy expenditure are related, but they aren’t interchangeable.

That’s why I’d keep output and effort separate. Two hundred watts is still two hundred watts. Split is another way of following that output. Neither tells me exactly what it costs you to hold it.

Heart rate can help with the effort side. So can noticing your breathing, or whether the stroke starts falling apart as you tire. But a heart-rate monitor’s calorie figure is still an estimate, even with your details entered. A different screen doesn’t settle it.

For your next steady session, put split or watts on the main display. Keep the effort where the session calls for it. If chasing a calorie total makes you push harder, leave the total alone.

Afterwards, write down the output and a short note about how it felt. Nothing elaborate. If that same output starts feeling easier over time, I’d want that in the notes.