Fast Talk Episode 168: How Much High Intensity Training Do We Need?

Thanks Steve - I’ve seen that somewhere before but had forgotten about it. very handy!

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To be honest, I do not think the published research from my lab or any of the other awesome labs I know of can give you a black and white answer here. I think we have at least managed to move the needle away from “intensity only” towards “intensity x duration” when discussing the stimulus for adaptation we create with HIIT training. As Trevor and Chris have discussed on Fast Talk, the physiology is complex but the training prescriptions can and should be pretty simple. So, to be honest, I would think in these terms:

  1. 2 weekly HIT sessions are probably enough at our age, maybe any age, so that is a reasonable set of guardrails on the training planning process. These weekly hard/high stress/high recovery demand sessions can take different forms, structured intervals, organic intervals inserted into a longer training session, or as training races IRL or on a virtual platform like Zwift.
  2. Do not let the 7-day week force you into a rhythm or training structure that is “almost but not quite sustainable”. We like to nail down the training routine BUT, 7 day cycles are tricky to manage. In an ideal world, perhaps the repeating cycle length would be 10days, or 14 days (for triathetes I would for sure use 14days if I were a coach). Sticking to 7 days is fine, but be ready to let yourself do 2 HIT sessions one week and only 1 the next week, if that works best. OR, you can try blocking the stimuli a bit and do more HIT followed by more volume within 14 day cycles. Don’t be afraid to mix it up a bit and remember that you will train about 300 times this year, so the key is staying healthy and being able to come to most of those sessions with the right level of freshness/fatigue for the task at hand.
  3. Based on our research, a 4-week block of the same kind of interval sessions (for example 2x weekly sessions of 4x8min) is generally well tolerated, but after that, you probably stagnate. So, no matter what, rotate the HIT sessions periodically.
  4. Personally, I think there is value in doing “organic” HIT sessions. Given the parameters you wrote, I would do one structured interval session and one session where I know that the goal is to work hard that day, but I am more flexible as to how that work emerges. It can be repeated climbs, a progressive ride, team tempo training, etc. You can end up with some “short” surges lasting 3-4 minutes and some longish tempo bouts all in the same session. That is the reality of cycling when 2 or more men ride together, so embrace it and use that “squirrel chasing instinct” with intent once a week. Then be disciplined enough to NOT use it the other days :slight_smile:

@stephen.seiler thank you so much for your reply!

yes, there has been a lot of “just do it”, “no pain, no gain” with the HIIT crowd. and as Kaggestad once said “the 4x4’ almost ruined a generation x-country skiers”. really like your idea of organic intervals (fartslek?) .

perhaps an idea to start with 1x red/week and 1x amber/week, see how one tolerate it and then 3x red every two week period, using the 2 week cycle period, rather than sticking to the 7 day period.

my challenge will be late fall, when going to the gym again and doing “heavy” sets and combining that with the HIIT - burnt once, twice shy…

take care and have a great day!

@steveneal Thanks! this is a fascinating chart that I’ve been looking at. I’m curious, in your experience, in general (generalizations are hard) do you find that athletes see better adaptations with the “quality” durations/reps vs the “quantity” or a bit of both?

Do you ever prescribe both in a block, as in 1 day of quality, 1 day of quantity per week? Or do you like to progress duration or reps of one style? Ex: 4x4 → 4x5 → 4x6 or 3x 13x30/15 x3 → 4x 13x30/15

@stephen.seiler One thing I’ve been curious about is when do we ADD intensity instead of duration? I get that we could progress 4x8 to 5x8 to 6x8 (doing the 8-min at the same wattage). However, is there ever a reason to do the interval(s) at a higher power than previously completed? Or does extending duration generally lead to better performance adaptations?


Week 1: 4x8 min @ 325w
Week 2: 4x8 min @ 335w
Week 3: 4x8 min @ 345w

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A question for @stephen.seiler, @trevor. Not sure if this is the right spot but I think it’s certainly related. Having 13-14 years of consistent training under my belt at the age of 54 and training typically 12-16 hours/week or the occasional overload into the 20-25 hour/week category, it is tempting to quickly progress from Zone 2 (56-75%FTP) into Zone 3/Tempo (76-90%FTP) in the off season, often due to lack of time or sheer boredom.
Typical Off Season:
Monday: Strength Train
Tuesday: 1-2 hours (Base/Tempo, Cadence Drills)
Wednesday: 2-3 hours (Base/Tempo). Once/month HIIT.
Thursday: 1.5-2 hours (Endurance with FTP bursts)
Friday: Strength Train
Saturday: 3-5 hours (Endurance/Tempo)
Sunday: 3-5 hours (Endurance/Tempo)

It would seem logical that one can get all the adaptations from training at long slow distance (at or below AeT/VT1/LT1/BLa <2mmol/l/s/FatMax) by doing more moderate intensity (medio, tempo). My races are MTB Marathon distance (4-7 hour) with typical long tempo climbing. If I have 2 hours to ride on a weekday or more on the weekend, wouldn’t the adaptation be greater if I spent that time doing more tempo work as long as the neurologic stress is managed/monitored? For my level it has been shown that a 2 hour Endurance/Base ride will do nothing. I need to ride 3 hours + if it is going to have an impact. Isn’t an Endurance/Tempo ride for 3 hours where you spend 45 min-90 min at Tempo have a much greater effect than doing 3 hours LSD? It’s been said the 3 hour tempo would equate to a much longer LSD ride. Am I missing out on an adaptation that only occurs with the long slow steady/distance? Or is it purely an issue of the added autonomic nervous system stress?

Hi @josemd,

Thanks for the question. I’ll give you my personal take from a mix of the science, listening to the experts and experience. The short version is no, I don’t think you’ll get additional gains from doing those rides at tempo vs zone 2 (in a five zone model.)

What I’ve seen is that the gains are effectively the same. What’s different is the fatigue that’s generated and the greater need for recovery when you do the rides harder. I think that’s part of why athletes feel a strong urge to go that pace. You’re certainly more tired after three hours at tempo and “feel” like you did more. But the problem is you increased the autonomic stress, not the training stimulus. Doing those rides easier will allow you to be ready for full training quicker and do your hard rides harder. So the net (when you look at it over a week to 10 days) is better when you keep those rides easier.

So I don’t agree that a 45 minute tempo ride is equal to a 3 hour LSD ride. I like to use the analogy of cooking a turkey when I explain this to my athletes. If the instructions say to cook a turkey at 250 degrees for 4 hours, you don’t get the same thing if you cook it at 500 degrees for 2 hours. What you get is a burnt bird that’s under-done at the core.

A couple other suggestions I’d offer based on the week you’ve mapped out. First, I’d include at least one HIIT session per week (not per month.)

Second, I’d strongly recommend a recovery day where you don’t train. I noticed you have two days off the bike where you lift weights. Remember that weights are not a recovery day. In fact, weights are more damaging than any ride. I personally have my athletes do weights on rides day often doing their HIT and strength work back-to-back on the same day. Make the big days big and the easy days super-easy.

Hope that helps!


Thank you for your reply @trevor. So just to clarify, if I have maybe 1.5-2 hours max to ride before going to work (Tues or Thurs) and ride either on the trainer (weather-dep) or outside and it’s an easy day, my day is better spent just riding at base intensity and keeping it easy and the gain will be the same as compared to a harder tempo ride? Thinking back to the 2010 study that showed no improvements after 2 hour rides at base intensity (from one of your articles).
Also, being older and being a mountain biker, the strength training is important to me (I work with RevoPT), so I do like to maintain the twice/week schedule. Although I’d love to get in 2 workouts/day and do an HIT session plus weights, life gets in the way…
Thanks again for your time…

So @trevor says this during the episode:

Trevor Connor 27:18
Right. So, it’s more if you look at somebody who’s been training for years and looked at their VO2 max at the peak of each season, it’s probably going to be about the same, you’re not going to see a budge that much

With a follow up from @stephen.seiler

Dr. Stephen Seiler 28:05
So, VO2 max tends to peak pretty early, and people tend to overtrain it, that’s where we get into all this interval training. They do a lot of work to keep trying to pound that VO2 max, but it’s just not going to keep climbing. Then you go to these threshold type developments and those take longer because you’re building mitochondria, you’re building capillaries and so forth, efficiency, it seems from the literature, from case studies and so forth, perhaps takes even longer, meaning that we see slow gains in efficiency over time, over several years of training

I guess I have a couple of questions:

  1. Sebastian W. Says during a recent podcast higher training volume = higher VO2MAX. Something like 10h = 60, 15h = 65, 20h = 70. If training volume dictates VO2MAX, then shouldn’t the question be, “how much volume should we do”

  2. If most of the things we as endurance athletes want to develop take months / years as Stephen S. Says and high intensity adaptations are chemical which ramp up quickly and fade quickly then what should we be focusing on for those longer term adaptations? More ~fatmax the better? What’s the point of ever doing intensity outside the couple week race prep window needed for those chemical adaptations?

I really like the 85% map range 15-21 intervals when I use this type of intensity. So it falls somewhere between I guess. Have had great success with this.

With intermediate or better athletes during this type of intensity training block the other session a week would be more like a workout I use (that the same guy from the chart showed me years ago.)


3 sets of 3x 40/20 2m recovery between each set
3 sets of 3x 30/30 2m recovery between each set
3 sets of 3x 20/40 2m recovery between each set

Ultimate Plus

9x 30/30
1m rest

8x 25/35
2m rest

7x 20/40
3m rest

6x 15/45
4m rest

I tend to do blocks of months of endurance and tempo training, then weeks of intensity training.

While doing the tempo training I would test 1-5m power.

While doing the intensity training, I would test tempo ability of fatmax.

Hope that helps a little.


Hello! My first post.

I enjoyed this podcast very much. But, I was a little disappointed it didn’t actually answer the question: How much high intensity do we need?

I understand there are minimal gains doing 3x instead of 2x high intensity sessions per week. But what about doing, say, just 1x high intensity session per week?

Or, given that the seven-day week is an arbitrary construct, what about 1x high intensity session every four days, or five days, or six days?

Since polarized training indicates that 80/20 is optimal, one might think that doing 1x high intensity session every five days is ideal.

Does anyone have any thoughts on this? Or any research I can look at to draw my own conclusions?

Thanks in advance, and please keep the thought-provoking podcasts coming…!!


Well for a first post, I would say it gets right at the heart of the challenge of translating research-based “best practice” into individually optimized and sustainable methods. As you allude to, using a 7-day cycle as a fixed unit of training organization immediately creates lots of headaches when trying to program the right balance of high recovery demand vs low recovery demand sessions (yes, I am using this terminology to keep us from just thinking HIIT vs everything else).

From my perspective, you have 2 choices. One choice is to stretch the 7 day cycle to 9, 10, or maybe 14 days. For example, with a 10 day cycle, 2 hard sessions per cycle gives you that 80:20 ratio. (while 2 hard sessions per 7 days is 70:30 assuming you train every day). So, this can create some “air” in the program and often solves some problems of feeling “not quite recovered”. Another approach is just to be more flexible and stick with the weekly cycle (since it corresponds to weekend group rides, family obligation variation, etc.). BUT, then you allow yourself to do the one hard session on one week, and 2 the next week, or otherwise “flex” with the cycle so that over time, you are staying in balance and feel like you can fully mobilize on the hard days.


OR, it just may be that 1 hard session per week works well for you and the math is quite simple. BUT, then you have to trust that and also remember to give yourself the extra recovery when temptation pulls you into an extra hard Zwift race, or a Saturday long group ride gone ballistic. It is kind of like eating an extra large dessert. Sometimes you just gotta have some fun, but it should not become a habit or the effects will become visible over time :slight_smile:



This is a great question and just the fact that we are asking this question now is real progress from my perspective. As with all great questions, the answer is not black and white. I do not have research data to throw down here other than a lot of data demonstrating the total accumulated duration is an important part of the mix when driving adaptations from HIT in already well-trained athletes.

I think of HIIT prescription as a stair-case build. I want to go from one level to another and I have to manipulate both rise and run to get there, with “rise” being intensity manipulation and “run” being total accumulated duration “at working intensity”. Using both allows for quite subtle and smooth progression, and more “successful” HIIT sessions over time.

A few guidelines:

  1. Probably not much point in going beyond 60minutes of accumulated duration for an interval session. If you can accumulate more minutes than that, then I think you will get a better stimulus from just doing a continuous load. Is there a “sweet spot” for accumulated duration on these interval sessions that are clearly above threshold but not “anaerobic”? I would say 30-40min. So, 10x3min, 8x4min, 4x10min, 5x8min, etc. all fall within that range. I think this limit also ensures that you or your athlete will not fail at the end of a HIIT session due to glycogen depletion.
  2. First extend, then intensify. Let us say you have a goal of averaging 350W for 3x8min. after a 4 week cycle of HIT sessions, you hit this goal. Well done, now what? I would prescribe 4 x 8min at 350W, then 5x8min at 350W. When you have consolidated and EXTENDED your HIT repeatability out to 40min of accumulated work load, then I would increase by 2-4% (3% of 350W is 10.5W).
  3. I think a 4 week cycle of doing the same HIIT prescription is enough. Unload after 4 weeks of concentrated effort, and mix up the prescription. There is no one magic HIIT session (4x8min for example).

@stephen.seiler thank you for indulging me in such a thorough reply. I love the stair analogy you used, makes complete sense.

I’ve found that just focusing on extending duration ends up eliciting gains in overall max power. For example, I did a 3 week intensive VO2 block in May as a prep to my first race. I focused on 3-5 min intervals around 90% of MAP with a goal of extending TiZ @ 92% of HRmax from 10-minutes to 20-minutes. A good proper “VO2max” block.

It took me a good 2-3 weeks AFTER this block to realize those gains, but I ended up smashing my season PR @ 2-min on a short steep climb this weekend. From 478w to 492w. Not all that impressive, but a testament to extending duration and how it can yield raw power gains, even if/when that’s not the goal.

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@steveneal this is very helpful, and gives me a whole new set of workouts to add into my library. I’ve mostly steered clear of these short-short type sessions since they can be hard to execute in the flatlands of Minnesota (you need A LOT of uninterrupted road to do them), but they sound like excellent trainer workouts.

Thanks for the detail, again, very helpful.

Great questions. I think this is where we run into those time ceilings with many athletes. And then what’s our choice at that point? Seemingly that we add some intensity to help those gains with additional overload. I would think those gains would likely not be as high as if we had another 5-10+ hours per week of consistent volume. Seems to be just a reality at a certain point, so it’s this balance of the training and managing recovery to maximize the adaptations. I think @stephen.seiler said it so well above, extend and then intensify. It seems that once we hit our peak volume, the option then is to strategize on how and when we apply those “high demands” sessions.

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I guess where I’m a bit confused now. If high intensity (AMPK) signals short term adaptations, then I’m seeing this more of a “what is the least I can get away with to maintain” and/or “what’s the point except in the ~weeks before a race”? Or did I misinterpret what was said? Can high intensity also lead to long term adaptations? E.g. when paired with two a days to boost calcineurin pathway?

@smashsquatch, I think we’re on the same page. I can’t speak to how long you would hold onto an adaptation from boosting a particular pathway, but thinking in terms of performance, athletes generally can’t hold those performances for a long time after high intensity training. The training residuals are different for high intensity vs. aerobic training. When you say ‘long term adaptation,’ how long are we talking?

I’m not sure. From the episode

Dr. Stephen Seiler 28:05
So, VO2 max tends to peak pretty early, and people tend to overtrain it, that’s where we get into all this interval training. They do a lot of work to keep trying to pound that VO2 max, but it’s just not going to keep climbing. Then you go to these threshold type developments and those take longer because you’re building mitochondria, you’re building capillaries and so forth, efficiency, it seems from the literature, from case studies and so forth, perhaps takes even longer, meaning that we see slow gains in efficiency over time, over several years of training

So the things S.Seiler is talking about (Mitochondria, capillaries, efficiency), what drives those changes? What are we trying to do with high intensity and what is the minimal amount (not maximal amount) needed to build and also maintain that?