I am pushing through first weeks with Garmin + Stryd to track it. I noticed that my power zone 2 running results in running in HR zone X calculated on your calculator for threshold HR delivered by my Garmin fenix 5. Would it be a clear sign that I overstated my threshold Power?

Is alignment (on rather flat terrain) of 1-2 power zones with 1-2 HR zones sign of properly defined zones?





Great question. Because HR is easily influenced by external factors, Power and HR will only ever align under ideal conditions, and is also why Power and Pace are superior measures of intensity.

Using an automobile as an example is helpful in this regard. A car can measure horsepower, speed, and temperature very accurately. Horsepower is an output, speed in an outcome, and temperature is an indicator. Sometimes these measurements line up perfectly and predictably, but often they do not. We can be traveling at 65 miles per hour at 250 horsepower with an engine temperature of 180 degrees Fahrenheit OR traveling at 30 miles per hour at 200 horsepower with an engine temperature of 230 degrees. We can’t really use temperature (an indicator) to accurately judge intensity (an output).

When we train, we have similar options. Power is our output, Pace is an outcome, and HR is an indicator. HR is not actually measuring any kind of result, it is simply indicating how our body is reacting to the stress we are applying. And, all kinds of environmental factors play into how the heart responds to exercise, including:

– Temperature
– Time of day
– Indoors vs. Outdoors
– When you last ate
– Chronic fatigue
– Stress
– Sleep

As a result, we can perform the exact same workout with the exact same power output and get completely different HR results. I once witnessed a test with a runner on a treadmill locked in at 6:00 per mile in a room maintained at 70 degrees Fahrenheit. The average HR was 160. A week later the same runner, same room, same treadmill, same speed (and therefore the same power output), but the temperature was maintained at 95 degrees. Average HR was 185 in the second test.

Pace is obviously influenced by terrain, but that is the only practical limitation, and Power is not influenced by terrain nor the pitfalls of HR.

In summary, the 80/20 HR Zones were created based on ideal conditions. I would say that most runners on a rest week, with good sleep, in the morning, on an empty stomach, outside on a flat surface, with low humidity at 65-70 Fahrenheit would have 80/20 Power, Pace, and HR zones all line up nicely. Because we probably won’t train ideal conditions, the most consistent results will come from Power and Pace.

HR still has it’s place as a secondary measure. For example, if you don’t have a running power meter, HR is very helpful in hilly terrain where Pace becomes invalid.


Matt and I periodically publish anonymously your inquiries to us, particularly when the answer may benefit the community. Have a question about 80/20 training or training in general? Feel free to e-mail me. David W.

Hi Matt,

I just finished reading your book 80/20 Running. I liked the basic idea and I also have experienced my biggest fitness gains with mostly slow exercising. But I have one question that I did not find an answer – but maybe there was..

As a triathlete I currently do hard and slow workouts in all three sports, but how should I schedule them. I mean if I do 5 runs, 4 swims and 3 bike rides a week, if I do high intensity workouts in each of them, that could mean that I either do 3-4 ”hard days” (meaning there is a high intensity in some of the sports) or I do hard swims and hard runs on the same day and maybe only have 2 hard days per week. Now I usually have a hard bike on tuesdays, a hard run on thursdays and hard swimming on wednesdays and sundays. But according to the 80/20 philosophy: what is optimal?

And one ”common knowledge” is also that one can do more high intensity in swimming than in other sports, but according to you that is false.

Thank you for good books. I also have the Racing Weight books from you.


Dear TE,

Thanks for reading 80/20 Running! Matt and I expect to publish the book 80/20 Triathlon sometime next year which will address your questions as well.

To answer your direct questions, the 80/20 intensity distribution measured in elite athletes has always been observed at a macro level. Some days or even weeks might vary from 80/20, but over a given season the best athletes maintain that ratio. Therefore, you do not need to do high intensity in each sport each day, in fact that would be discouraged, as it interferes with the necessary recovery to continue high intensity on another day. In general, our triathlon plans follow a hard/easy approach with 3-4 days of workouts that include intense intervals, and 2-3 days of workouts exclusively at low intensity. Our plans target 80/20 distribution for each week.

Swimming, as you point out, is an exception. We target 75/25 when swimming by distance. We also allow for much more frequency of swim session that include intense swimming because of the recovery issue. While our plans almost never include an interval bike and run on the same day (excluding race-specific bricks) we often have an intense swim on the same day as an intense bike or intense run.


Matt and I periodically publish anonymously your inquiries to us, particularly when the answer may benefit the community. Have a question about 80/20 training or training in general? Feel free to e-mail me. David W.

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