I just got back from the ASCA course, and one of the great things we covered was this french interval system they call The Eurofit Supermax Intervals. Basically using 1-2km row/run to get your max aerobic speed (m/s) you determine your 130% speed. Using this speed you set your distance to cover in 15sec(little bit of maths involved), then basically go flat out for 15sec on 15sec off making sure you make the distance each set. Go for minutes or rounds. I did it on a C2 and we set it for 70m each set and did 1050m. Very taxing on a rower starting and stoping. The course coach was the S&C coach for the Brisbane Broncos and makes them do it once a fortnight or so with running, apparently they hate it.