Training zone systems are typically generated from percentages of a reference value or values. In the case of heart rate it is typically done by: 1) percentage of Maximum Heart Rate, 2) percentage of Heart Rate Reserve, and 3) percentage of Threshold Heart Rate.
Note, this discussion excludes heart rate based training systems where the zones are determined by values from lab tests, i.e., heart rates at specific physiological break points: VT1, LT2, LT1, LT2, 2mmol/l, 4mmol/l, etc.
- Training Zones: What is the point of training zones?
- Training Zones: The simple 7-Zone Power-based System
- Training Zones: The 3-Zone System
Maximum Heart Rate
It makes intuitive sense to describe the intensity of activity as a percentage of your total capacity. Your Maximum Heart Rate (MHR) is one measure of the limit of your capacity, i.e., by definition, you’ll never see a higher HR number and the number suggests the body can no longer increase cardiac output in response to workload.
Deploying this training zone system is straightforward–zones are defined by percentage of you maximum heart rate. The tricky part is determining your maximum heart rate. The are multiple formulas derived from values found in population studies:
220 – age = MHR
191.5 – .007 x age2 = MHR
201 – 0.63 x age for women = MHR
208 – 0.80 x age for men = MHR
206.9 – (0.67 x age) = MHR
208 – (0.7 x age) = MHR
The alternative is to specifically measure your own maximum heart rate. This is possible, but is often difficult to do accurately in a training setting. Usually it requires a several minute effort at a moderately hard pace, finished with a few minutes building to maximum and ending with a 20-30sec sprint. The ramp tests available in training software platforms like Zwift, Trainerroad and others will work too. Make sure you are well-rested before you attempt your test. It will probably take a few tests to determine your true maximal heart rate. Another approach is simply to analyze your recorded training and racing data and extract the highest heart rate you achieved during a period of time that you know included maximal efforts (and is unlikely to be a measurement error).
If you search on the internet for “heart rate zones” most of the results refer to the zones as a percentage of MHR. The confusing part, is that they use the same percentages listed in the Heart Rate Reserve section, but are not clear whether they are relying on Heart Rate Reserve, or only Maximum Heart Rate. As you’ll see below, the zones will not be the same.
Back in the 1980s I remember seeing a different percentage system based exclusively on Maximum Heart Rate. I’ve also seen the 3-zone system using %MHR values, although it is difficult to determine whether these have been generated from %MHR or the value was identified through other means and then simply described as a percentage of MHR. In any case here are the values for the 3-Zone System:
- Zone 1: 55 – 75% MHR
- Zone 2: 75 – 85% MHR
- Zone 3: 85 – 100% MHR
It would be easy to subdivide these zones to get up to 5 zones by splitting zones 1 and 3 into high & low.
Heart Rate Reserve
Heart Rate Reserve is similar to the system above in that it requires your Maximum Heart Rate, but different in that it incorporates your Resting Heart Rate as well. So, this system takes the idea of your “capacity” a step further and focuses on the operative range of your cardiac output.
You can get your resting heart rate from various trackers (WHOOP, FitBit, Apple Watch, etc.). You can also just take your pulse with a heart rate monitor in the morning before you get out of bed.
Heart Rate Reserve (HRR) = Maximum Heart Rate (MHR) – Resting Heart Rate (RHR)
180bpm MHR, 50bpm RHR
HRR = 180 – 50 = 130
Zones are calculated as percentages of your Heart Rate Reserve and then added back to your RHR.
If my HRR = 130 bpm (see example above), and zones are defined as follows:
- Zone 1: 50% – 60%
- Zone 2: 60% – 70%
- Zone 3: 70% – 80%
- Zone 4: 80% – 90%
- Zone 5: 90% – 100%
then, Zone 2 would be calculated as:
Lower Limit: 130 (HRR) * .6 = 78; 78 + 50 (RHR) = 128 bpm
Upper Limit: 130 (HRR) * .7 = 91; 91 + 50 (RHR) = 141 bpm
Note, googling “Heart Rate Reserve” or “Karvonen” (he published the first study establishing the method), will turn up conflicting results. The method of calculating HRR is the same, but the zone percentages are all over the map. You will also find articles mixing up the percentages for all 3 of these methods. Caveat lector!
Threshold Heart Rate
This method is different than the other two in that it is determined on an actual effort you make in your activity. Your Threshold Heart Rate corresponds to a maximal effort lasting 20-30 minutes. There are multiple ways to establish this value, but a typical approach is to do a maximal 30 minute time trial effort and record the average heart rate for the last 20 minutes. This excludes the first part of the effort where the heart rate is climbing up to a steady plateau. Another approach could be to examine your existing data for your highest 20 minute average heart rate value.
The physiological underpinnings of this approach are a little more complicated than the previous 2 methods. Instead of just identifying the limits of your cardiac activity, this method looks for the heart rate corresponding to a maximal steady state effort you have actually performed. This 20-30 minute effort is a good indicator of your sustainable aerobic capacity, so it is useful to think of other efforts as a percentage of that effort.
Once you have your Threshold Heart Rate (THR), zones are calculated with percentages in a similar way to the other methods (but the percentages are different!). Below you’ll find the zones suggested by Joe Friel:
Zone 1: Less than 81% of THR
Zone 2: 81% to 89% of THR
Zone 3: 90% to 93% of THR
Zone 4: 94% to 99% of THR
Zone 5a: 100% to 102% of THR
Zone 5b: 103% to 106% of THR
Zone 5c: More than 106% of THR
If you are particularly observant you’ll have noticed the percentages used in the graphic are different than the list above. Dr. Andrew Coggan has suggested the numbers in the graphic table. These two systems are different in key ways:
- Friel’s Zone 2 is quite a bit higher
- Friel Zone 2: 142 – 156 bpm
- Coggan Zone 2: 121 – 145 bpm
- HRR Zone 2: 128 – 141 bpm
- Coggan’s Zone 4 actually goes above your threshold heart rate. Intuitively, this seems wrong (if Zone 4 is threshold, why would you do intervals above threshold heart rate), but it is consistent with his power-based Zone 4.
Ultimately, these distinctions may not be overly important. The important thing is that you understand what the zones represent and the impact of choosing a particular system.
So which is best?
The key to remember is that the raw heart rate is what is important. Since the body does not operate in zones and physiological responses are along a continuum, where you draw the lines between zones is somewhat arbitrary. In that sense, speaking of one system as being “better” than another is pointless. All the approaches have pros and cons. Ultimately, no system can claim absolute accuracy on any given day. The body is a complex system that is rarely in exactly the same state from day-to-day. Daily heart rate will vary a little depending on fatigue, stress, and diet. More serious medical conditions and drugs can also have significant effect on cardiac performance. But for the most part, heart rate is a consistently good indicator of how the body is responding to the stress it is under. As such, any of these systems can be useful in directing and monitoring training intensity. The key for the practitioner is consistency and periodic testing to ensure the reference values remain accurate. For example, Maximum Heart Rate will change with age and Resting Heart Rate will change with improving fitness.