How should I calculate my heart rate zones?

Heart rate zone training is a widely used endurance training method, but many athletes don’t fully understand its nuances. You’ve probably heard people throw around the term “zone 2”, but ask five different people how they calculate their zone 2 heart rate and you might get five different answers.

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So what is the real answer? In this post I will break down the three main ways to determine your heart rate zones and help you understand which approach makes the most sense for your training.

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Maximum Heart rate (MHR) Method 

The MHR method starts by estimating an athlete’s maximum heart rate to establish zones. This can be done in a variety of ways, but the quick napkin math approach is to take 220 and subtract your age. For example, I am 30, so my estimated max heart rate is 220-30 = 190bpm. It’s worth noting that this is merely an estimate - studies show that there is a +/- of 15bpm margin of error for this formula.

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Once you have determined your max heart rate (via the method above, or some other method) you can calculate your training zones based on a fixed percentage of max heart rate. The zones are as follows:

• Zone 1 = 50-60% MHR
• Zone 2 = 60-70% MHR
• Zone 3 = 70-80% MHR
• Zone 4 = 80-90% MHR
• Zone 5 = 90-100% MHR

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While this is the most accessible calculation for heart rate zones, these zones are highly generalized and can be inaccurate for some people. For example, two athletes could have the same max heart rate and thus the same heart rate zones, yet very different lactate thresholds, which means that training at the same heart rate could have very different training impacts.

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Heart Rate Reserve (HRR) Method

The heart rate reserve method refines zone calculations by accounting for your resting heart rate (RHR) in addition to your max heart rate. Heart rate reserve is the difference between your max HR and your resting HR (max HR - resting HR). 

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This formula uses these heart rate datapoints and your desired workout intensity in percentage form to calculate what heart rate you should be targeting for a given workout. The formula is as follows:

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Target HR = RHR + (MHR - RHR) x (intensity percentage).

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To put this in context - let’s say I want to train at 60% intensity for my light workouts. Here is the data I would use to figure out what heart rate to work out at:

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Target HR = 50 + (190-50) x (0.5) → 134 bpm would be my 50% intensity.

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Zones using his formula are calculated using intensity percentages, the same as the MHR method. Those percentages are:

• Zone 1 = 50-60% intensity of HRR
• Zone 2 = 60-70% intensity of HRR
• Zone 3 = 70-80% intensity of HRR
• Zone 4 = 80-90% intensity of HRR
• Zone 5 = 90-100% intensity of HRR

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The benefit of using both resting heart rate and max heart rate in the calculation is that these zones are more personalized than straight MHR calculations and take into account baseline fitness (via RHR). This method still relies on an estimate of max heart rate however, so there can be limitations depending on how you are calculating that number.

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Lactate Threshold Heart Rate (LTHR) Method

The LTHR method bases your training zones on your lactate threshold heart rate. Rather than using a percentage of maximal heart rate, this method bases zones on a physiological point that is unique to you.

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Your lactic heart rate threshold is the heart rate at the transition between predominantly aerobic and anaerobic metabolism. Lactate threshold, AKA the anaerobic threshold, is the effort level at which lactate begins to accumulate in the blood faster than it can be cleared. To find lactate threshold heart rate, athletes typically perform a time trial or test in a lab. There are also some wearables that will estimate it for you. 

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Once you have your LTHR, training zones are calculated as a percentage of this threshold value rather than as a percentage of max heart rate. These zone calculations are as follows:

• Zone 1 = 80% LTHR or lower
• Zone 2 = 80-90% LTHR
• Zone 3 = 90-93% LTHR
• Zone 4 = 93-99% LTHR 
• Zone 5 = 100%+ LTHR

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Using LTHR is the gold standard for serious endurance athletes for heart rate zones since using LTHR for zones is highly personalized to a given athlete’s performance, which makes it an ideal way to calculate training zones. Max HR is primarily driven by genetics whereas lactate threshold shifts with training which makes it much more dynamic and accurate to reflect your current abilities. The biggest drawback to the LTHR method is the friction involved with determining your threshold. 

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Conclusion

While lactate threshold based heart rate zones are the gold standard, it’s not a requirement that everyone use that to determine their heart rate zones. If you’re earlier on in your training or are more focused on generally building fitness than breaking records, the MHR or HR reserve method are more than adequate.

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