For anyone who is interesting in an exercise on the Concept II machine that is great for building power (and is really f-ing tiring), listen up.
I rowed for my university all last year, and I've heard we have one of the most intense winter training schedules of any school in the sport. We did many days of 80+ minutes of rowing, but nothing kicked my butt as bad as these did:
What you do is set the units on the machine to Watts/hr, and the time for 10 seconds. Set the rest for one minute, as you need to fully recover after every one of these. The gist is to basically see how high you can get the Watts/hr in the 10 second interval. You do this of course by pulling like your life depends on it, and you want to get the flywheel spinning as fast as possible. You'll probably have time for 4-6 strokes in ten seconds. Do anywhere from 10-20 of these at one minute intervals, and you'll see what I'm talking about.
An average of 500-600 is pretty decent. Anything around 800, and you're definitely a haus. Above 1000...maybe you should do this for a living.