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.

Dear David W,

I’m going to buy your plan for the level 3 half marathon plan. I have a race (in Madrid, Spain) on April 8 which by my calculations will have me starting Dec 31/Jan 1… I had a bike wreck in a triathlon a few months ago that resulted in broken bones, concussion, etc. So I’m just now starting to get back into where I can work out 4-5 times a week. So I’m on pace to be at least to the proper starting place for your program.

I am a gadget guy. I supported Stryd on Kickstarter and upgraded to the footpad at the first opportunities. I record my power on my runs, but it is just another interesting bit of data that I review at the end of some of my runs. So I’ve never really done much with it. That is why I’m so intrigued by this [the 80/20 power-based run plans].

So that leads me to my questions: When should I do the power test? I would assume fairly close to the start of the program so that my numbers are pretty accurate for that time. As my training increases and my thresholds change, will I be doing more tests during the training plan?


Dear DH,

I wish you the best of luck on your recovery.

You are exactly right, particularly where you are coming back from low fitness, your power thresholds will constantly change (improve). The run plans have RT (run tempo) workouts scheduled every recovery week, which is every 3rd or 4th week. Those RT workouts are designed to confirm or re-establish your zones. Therefore, you’ll be testing regularly anyway with an 80/20 plan.

It would be good to do a test before your start your regular training. We have a suite of tests in our Intensity Guidelines for Running document on our 80/20 Resources page. Some of the tests are brutal (30-minute time trial) and some are easier, if slightly less accurate. I would do the easy test at first. Make sure to see the section on RT workouts at the bottom of that guide.

Also consider that HR zones will change very little. Your output for a given HR will, but early on, consider using HR as a secondary (or primary) measure of intensity until your power zones level off.

Finally, we offer a Level Guarantee. If you buy the Level 1 plan and find that 8 weeks later it is too easy, come back to me and I’ll get you the L2 plan for free. This applies to leveling up or down on all of our plans.


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 David,

I hope you are well. I was excited to receive your email about the addition of 80/20 ironman plans with running power targets. I’m currently using the level 3 Pace and Power ironman plan, but would love to try the power and power plan. Is there a way to get access to this without having to pay the full price of the new plan? Perhaps I could pay half, for the addition of the running power structured workouts?

Also I was wondering if you had any guidelines/advice in regards to electrolyte supplementation during an ironman (e.g. an hourly electrolyte target during)? I’m 62kg, 174cm, I think an average to high sweater, and my exercise clothes do generally have white salt marks after a session, particular when it is hot. Any advice/guidance you can give me would be greatly appreciated.

Warm regards,


Dear LH,

Great to hear from you. I’m really pleased that we have these triathlon Run Power and Bike Power plans available. All of your 80/20 plans allow for a complimentary switches between levels and intensity types, so you can have this one for free. Please use coupon code [redacted] for a 100% discount off of the IM L3 Power and Power plan.

Regarding electrolytes, I have a short answer and a longer answer. Short answer: 300-500mg per hour on the bike is a safe dose. The electrolytes in your nutrition probably already have something close to this and additional supplementation may not be necessary.

Longer answer: There is no empirical evidence that electrolyte supplementation is helpful for endurance athletes, and no evidence that it reduces the risk of cramps or improves performance (see http://tri-talk.com/74/). There is also no evidence electrolytes in moderate doses are detrimental, so feel free to try it.

To illustrate, attached is an example of electrolyte concentrations and IM performance. In this particular study, there was no statistically significant difference in electrolyte concentrations between Ironman crampers and non-crampers (controls). Also consider Tim Noakes phenomenal book, Waterlogged for more on the subject.


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 David

I am looking at following the 80/20 ironman training plan (probably level 2) and have downloaded the free Ironman plan

I have a few questions:

1. When cycling I noticed I can keep in zone 1-2 for heart rate but when I analyse I see my power is spread more over all zones including 4-5. Is power a better measure and more preferred way for cycling?

2. What kind of performance gains would you expect during a 4 week period? If there is no improvement in pace and power would that indicate an issue in my training?

3. Does the plan contain longer cycle and runs towards the end of the plan?

Thanks, C

Dear C,

Thanks for looking into our plans! Responses below.

1. Power is commonly recognized as a superior way to measure intensity. Heart rate (HR) is affordable and convenient, but HR has several disadvantages. The root of these disadvantages is that HR is an indicator not an output. Like your car, your engine temperature (an indicator) might be directly related to your horsepower (output) and speed (outcome), but often they are not in sync at all.

Your power zones are also most likely not yet calibrated correctly, almost certainly too low. Consider our Intensity Guidelines for Triathlon document for some protocols on how to retest your power zones.

2. This is tough to answer. I regret that genetics plays such an out-sized role that the results are all over the map. What I can comfortable say is that the best athletes in the world use an 80/20 intensity distribution, and you’ll have the best chances of success with that format. If I were to commit to a “typical” triathlete without a strong background in cycling, I often see a 10-15% percent improvement in the first year, another 5-10% the second year, and diminishing but continued returns from year 3-5. The monthly improvements would be some fraction of those annual estimates. Genetics could double or half those “typical” results. Be patient, sometimes you’ll go months without seeing an improvement, and then you’ll get a 5% bump overnight.

3. Yes, the free plans are just the first two weeks of each plan. We use the empirically proven method of progressive overload in all of our plans, the weekly volume caps out at 2-3 times what you see in the first 2 weeks.


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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