Heart Rate Zones and Power Zones derived from FTP (Functional Threshold Pace), as used by cyclists and triathletes, are adaptable to Rowing. And there is also the UT1, UT2, AT, TR, AN system calculated from 2k race pace commonly used in Rowing. As well there is RPE or Rate of Perceived Exertion that can be subjectively estimated by the athlete.
Internal and External Load
RPE and Heart Rate are internal measures of workload or, more accurately, of its effect on the athlete. 500m Split Pace or the Average Power registered by your Ergometer Monitor are external measures of mechanical work actually performed.
However, RPE can be a remarkably reliable estimate of external workload when used by athletes that can be honest with themselves and have considerable experience at comparing RPE with other measures. Heart Rate, while internally valid is less externally reliable because of the phenomenon of Cardiac Drift, a steady climb of heartrate over the duration of a workout, and also because of the influence on it of emotional mood as well as of extrinsic conditions such as temperature and humidity. This makes it less useful for setting the intensity of a workout but nonetheless useful for gauging how well you actually coped with an intensity. A comparison of internal load to external load is clearly useful.
Power and Pace
Power is interchangeable with Pace as a measure of intensity on an Erg. And Power or Pace Zones can be calculated either from FTP determined by a 60-20minute all out piece using percentages of critical pace, or from a 2k Race time using a power profile derived from Jensen’s Golden Standard.
Your 2k pace can also be approximately extrapolated from your FTP and vice versa (again according to a standard power profile). Your individual power profile may vary from this, but if you have measured one of these, you can make a fair approximation of the other. A beginner not ready to perform a time trial could even use Rate of Perceived Exertion to establish approximate temporary training zones by extrapolating MAP and FTP from their Easy (conversational) Pace.
Comparing P Zones with H Zones
To make the comparison of a Heart Rate Zone with a Power or Pace Zone meaningful, you need to base your power zones not on average 2k race pace but on vVo2 max, the maximum velocity you require to reach maximum oxygen uptake. vVO2max can also be expressed as Maximum Aerobic Power (MAP).
What makes a comparison of MAP to HR possible is a correspondence between percentage of MAP and percentage of Heart Rate Reserve, the number of heartbeats per minute your Maximum Heart Rate is above your Minimum Resting Heart Rate.
If you have no access to a laboratory test of vO2max but have a 2k Personal Best Time, make a rough estimate of your sprinter/stayer percentage as a starting point, and experiment to see how much it needs to be adjusted to correspond with heart rate and how you feel at various paces.
However, using P Zones and H Zones still lacks one parameter that is crucial for Rowing, and that is Work per Stroke.
Rowing is a strength endurance sport in which Strength and Muscular Endurance play as important a role as Cardiovascular Endurance.
Work Zones
So we need to introduce W Zones that correspond to various percentages of the average Work Per Stroke exerted within a personal best 2k test or race.
Counting the strokes rowed at each pressure within a workout enables you to compare the muscular load of a session to its metabolic load and to estimate the relative muscular stress on different days. There may be days when you need to let the muscular system recover, yet want to continue exercising the cardiovascular system or vice versa.
What provides additional flexibility to regulating work per stroke or Muscular Load in relation to Cardiovascular Load is that you can exert greater work per stroke at a given pace by rowing at a lower stroke rate. Thus, if your 2k Race average stroke rate is 33, rowing at P2 Easy Pace and rating 16 would result in W5 the same number of Jules per stroke as in the race. And a P2 pace at 20spm would result in Firm Work or W4.
A spreadsheet log entry comparing the three zones would look like this: