Not sure exactly what you mean by laps on the HR monitor, but I normally just hit "record" which starts the monitor and don't mess with it again until the workout is complete. I have a Garmin Forerunner 405 and it allows you to go in and set up different workouts. I'm sure there is a better way than what I do, but if I am doing an interval workout, I'll set the desired zone to 4, set the time of the workout and then hit "Do Workout". I track the time of the interval manually (I look at the clock on the rower for example) and use the watch to remind me when I am in the correct zone. Of course when I am on the two minute recovery period, the watch is yelling at me telling me I am not in the desired zone. But my method works well with, say zone 1 or 2 workouts. If it is a 1 hour zone 2 ride, I'll set the desired HR to zone 2, the time to 60 minutes, and hit "Do Workout".
As far as your heart rates being too high or low, what you are really interested in the amount of power you can output at lactate threshold. This is why using a power meter is extremely useful in measuring fitness progress. For example, lets say on your first LTHR test your average HR was 189 (which it was) and you maintained an average wattage output of, say, 200 watts. The next time you do the test, the thing you want to look for is the average watts you were able to maintain at threshold. Hopefully the next time your wattage output will improve to 210 watts (or whatever). Your lactate threshold heart rate will not necessarily be any different and not an indication of improved (or worse) fitness levels. The really nice thing about the rower is your average power output is recorded. Go back and look at what you pulled and write it down.
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