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Happy Monday! The family had a great time celebrating this past weekend. I tend to fall into the trap of opening up the computer 7 days/week as there is ‘always something to do’. This past weekend, I don’t think I opened up the computer on Saturday and spent very little time with it on Sunday, and it was honestly pretty nice. I certainly felt more recharged this morning and similar to running rest days, there’s probably some utility in having true off days to keep all aspects of life sustainable and maximally enjoyable!

The article today is technical and an extension of last week. If you are uninterested, I don’t blame you and feel free to skip to race recaps :)!

As promised, we’re going to discuss how to think about and apply heart rate using a 5 zone model! If you missed last week, you can find the website blog entry here. I will try to update this weekly when I send out the newsletter so that you all can access previous newsletters!

To summarize, last week we defined zones 1-3 with a 3 zone model. Easy (zone 1) was anything below aerobic threshold. Moderate (zone 2) was between aerobic and lactate threshold. Hard (zone 3) was anything harder than lactate threshold. In the 5 zone approach, we’ll say ‘easy’ is zones 1 and 2, ‘moderate’ is zones 3 and 4, and ‘hard’ is zone 5. You will see some zone 4 ‘cutoffs’ slightly above threshold HR, but that’s really not terribly important if it is or isn’t.

Now… everything that follows is looking through the lens of a 5 zone model (as I don’t want to have to specify each time :) )! Additionally, people will have slightly different cutoff points for different zones (i.e. different percentages of threshold/VO2 max/max HR). These zones are simply a way to try and understand how sustainable a certain intensity is. The ‘accurate’ way to do this would be to measure blood lactate levels throughout exercise, but that’s obviously rather invasive and a HRM is more accessible. It’s tempting to strive for ‘perfection’ by hitting ‘zones’, but this isn’t a perfect approach and there is no need to be strict.

Zone 1

Zone 1 has gotten a lot of attention recently as Kipchoge and Kilian training write ups have somewhat focused on how much both of these athletes spend in this zone. As a relative ‘effort level’, I’ve heard zone 1 described as being able to nose breathe and is an ‘all day sustainable’ output. The HR that represents this zone is roughly 50-60% of max heart rate (MHR) or 65-75% of lactate threshold HR (LTHR).

Activity spent in zone 1 is targeting the most aerobic metabolic systems. You’re primarily utilizing beta oxidation to create energy from stored fat and running in zone 1 is either very slow for most of us or somewhat impossible depending on the level of training (i.e. it is possible that running will automatically exceed the threshold for zone 1 work).

Zone 2

Similar to zone 1, zone 2 is primarily aerobic. You are still primarily burning ‘fat as fuel’, but you are increasing the rate of both oxidative and non-oxidative glycolysis (burning a higher rate of stored or exogenous carbohydrate). This happens at roughly 60-70% of MHR and 75-85% of LTHR.

Zone 2 work isn’t as sustainable as zone 1 given the metabolic demands (as you burn a higher percentage of carbohydrate as fuel source, the sustainability is limited by endogenous or exogenous carbohydrate fueling). Most racing efforts are occurring in zones higher than zone 2. However, the longer you go, the more time will be spent in zone 2 (think 6+hr efforts depending on level of training). For the very long distances (100mile+ and even some slower 100ks) you will spend the majority of the race in zones 1 and 2 depending on level of training (let’s just assume everything I mention is ‘depending on level of training’). For example, Kilian will spend time in harder zones at UTMB, but even he is playing with fire given how unsustainable this is over a 20 hour race.

Zone 3

Zone 3 is when we start to prioritize carbohydrates as the primary fuel source. We are working harder than our aerobic threshold and that means that we’re also starting to accumulate lactic acid, which leads to fatigue. Zone 3 is defined as 70-80% of MHR and 85-98% of LTHR.

Using a HR zone to pace a race is tricky as training level makes a big difference on what you can sustain and where you should be for a longer distance race (2+hrs). However, any time you run harder than zone 2, you are making an effort substantially less sustainable and fueling becomes more and more important. In a trail race marathon/50k/50 miler/and even 100k, you can spend time in zone 3 and even zone 4, but this is with the understanding that there will be recovery intervals in zone 1 and 2 as you run downhill or even stop at an aid station. For a road race, a marathon or 50k can largely be spent in zone 3 and even some time in zone 4, but you don’t have the same recovery opportunities.

Zone 4

This is similar to zone 3 and that’s why the 3 zone model lumps both of these efforts as in the same zone. You’re essentially just running in a slightly less sustainable moderate intensity and it’s defined as 80-90% of MHR and 98-105% of LTHR.

It’s worth noting that these zones are not set in stone. Training approach will move the needle a little bit as to where LTHR is and thus…where all zones fall relative to one another. Additionally, an interesting byproduct of long term running and training is that LT will naturally get closer to VO2max as you become more efficient, but also as you age. So… this value needs to be remeasured at different points in a running career, and even a season as different training modalities will move it around some.

Marathoners, especially elite marathoners, will spend some time in zone 4 during races, moreso in later stages due to cardiac drift and also when some of the actual ‘racing’ occurs. Elite half marathon races are mostly occurring in zone 4 with possible ‘kicks’ in zone 5 at the very end.

Zone 5

Zone 5 is 90-100% of MHR and 105%+ of LTHR. This is the intensity you will possibly spend time in during shorter intervals or VO2 work. 10k races and shorter will at least spend some amount of time in zone 5, but the percentage of time obviously increases as the race distance shortens (and is also dependent on training level).

Using HR zones to pace shorter races isn’t a terribly useful approach (even pacing a marathon using heart rate has some serious limitations). As mentioned above, these zones tend to move around depending on training and your ability to spend more time in harder zones also increases with more training.

To combat this, the idea of critical speed/critical power has recently gained some popularity for developing pacing strategies. The idea of critical speed/power (CP) is also rather complicated, but the CP value falls somewhere between LT2 (where lactic acid starts to increase at a ‘faster rate’) and VO2max. I have even seen it compared to LT2, but this isn’t consistent.

Studies have shown that very trained elite marathoners can run marathons at 96% of critical speed, which gives you a hard set pace (or power output if using a reliable power meter on hilly terrain). This same reference point can be used to pace other fast road races, but when you start to work faster than critical speed, you have a short amount of time utilizing anaerobic energy systems (w’ is used to quantify the amount of time you can spend above critical speed) and spending time at this output requires you spending time below critical speed to ‘recharge’ that battery.

If you don’t understand the above, that’s a-ok as I don’t fully understand it either. There are still questions in the world of running physiology and getting too involved with the ‘perfect pacing or training approach’ is truly a never ending rabbit hole! Additionally, these pacing strategies were largely explored to break records and compete at truly world class levels. This is all very interesting, but there are so many lower hanging fruits for all of us that are worth focusing on more than how to utilize critical speed/power measurements or…what percentage of an upcoming race should be spent in zone 3 vs. zone 4. I don’t think any of us are so close to our maximal running potential that this is the next area worth exploring to move the needle just a bit further, and if so, I’m probably not the right coach for the job :).

Race Recaps:

Ben B. finished his first 100 miler at the Hennepin 100! First time 100 mile attempts make me so nervous as a coach. There is only so much I can prepare an athlete for and it’s practically impossible to have prepared for ‘everything’. There is so much problem solving that happens on race day and I’m always so inspired to hear back about how a day goes and everything that is overcome in the process of getting to the finish!

Matt H. ran the Stump Jump 50k as a training run for a bigger adventure ahead and put together a great run!

Dan C. ran back to back sub-ultra races, which honestly makes me sore just writing that! Running fast for one day tends to leave me a bit wrecked…and layering on that second day is just brutal!

Mitch P. jumped into a local half last minute and completely surprised himself with a really strong race despite no specific work for the run (and also while recovering from a recent marathon)!

Zach H. raced a local 12 miler and had a great day! Zach manages to race a ton during the season and I’m always inspired to get out there more as his psyche is contagious!

Judd L. put together a hard fought finish at the Black Forest 100k, which starts at midnight…! I really can’t imagine starting a 100k race first thing on Sunday and then returning back to the weekly grind right after finishing! Judd didn’t have the day he wanted, but managed to finish strong and put in a solid kick right at the end!

Matt C. had a good run at the Mohican Half, dipping his toes in the world of shorter distance races! We were both commenting after the fact that these races can be so much fun as they’re logistically far more approachable and you can still walk normally a day or two afterwards!

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