I also figured out that my breathing rhythm was part of the problem. I was exhaling at the finish, breathing in and out again during the recovery, inhaling at the catch and breathing out during the drive. Basically, I was taking too many breaths.
Now instead of getting that quick breath in before the drive, I breathe in during the drive. Meaning I exhale at finish, breathe in during the recovery, exhale at the catch, breath in during the drive.
I applied the changes during a 15 mins session today, and it felt much better. I didn't cover as many meters, but I have probably been going too lightly on the power front now, correcting too much in the other direction. I'll try to find the sweet spot in terms of power applied during the drive, and will then work my way up to 30 minutes. I can work on getting faster later down the line. Still worked up a real sweat!
Today's session:
15 mins, 3176m, avg 2:21/500m, avg 123W, peak 178W, avg 20.7 spm, avg HR 154, avg peak 482N, avg work 356J
Previous session:
15 mins, 3314m, avg 2:16/500m, avg 139W, peak 178W, avg 14.4 spm, avg HR 149, avg peak 693N, avg work 580J
Thanks for the advice, I'll make sure to check out those videos. Yeah, I think for now I'll just be happy if I get to a point where I can row for decent lengths of time, without compromising too much on power. 30 mins to start with, then hopefully towards 60 mins. If we take a running analogy (I used to run a long time ago, but my knees won't allow it anymore), I'm at the stage where I'm working my way up from the run-walk-run-walk kind of beginner sessions.If you have less than 5 hours or so to work out then do whatever you enjoy doing. Just about any training plan will work.
NOTE: cardio improvements come slow, and stay a long time. You can build for years with improvement.