Optimized Aerobic Prescription

Most of the amateur bike racers I know are limited by time available to train. I think this is a relatable limitation to all of us… So wouldn’t it be nice if an amateur endurance athlete could optimize the time they do have available to train, by establishing a minimum effective dose for eliciting adaptations.

How to the Pros Spend their Time?

We know how elite athletes spend their time, when time is not as much of a limiting factor.

Interestingly, maximizing recovery time in between training sessions becomes the limiting factor at high training volumes.

Stoggl & Sperlich in a 2015 Review article established that “the majority of studies [of elite endurance athletes] present a ‘pyramidal’ Training Intensity Distribution (TID) with a high proportion of high volume, low intensity training (HVLT).”

Stoggl & Sperlich, 2015
The trainingintensity distribution (i.e., percentage time spent in zone 1: < first ventilatory threshold or steady-state lactate at ~2 mM; zone 2: at or near lactate threshold (~4 mM) or second ventilatory threshold; zone 3: high-intensity training above lactate or second ventilatory threshold) in welltrained to elite endurance athletes in retrospective analyses during (A) preparation phase, (B) pre-competition phase, (C) competition phase, and (D) seasonal analysis.
The training intensity distribution among welltrained and elite endurance athletes
Front Physiol. 2015;6:295.

This means that many elite athletes spend the majority of time at low intensities, with decreasing amounts of time spent at increasingly higher intensities.

However we also know that Polarizing training between high and low intensities, and avoiding ‘moderate’ or Threshold intensity seems to offer greater potential benefits (Hydren & Cohen, 2015 & Seiler, 2010).

So we can we smarter than the Pros in how we spend our limited time by avoiding time in the moderate/threshold zone. But there’s a reason why even the Pros can’t spend hours at high intensity.

Limited Volume at High Intensity

We can understand intuitively that we are limited in how much work we can do at high intensity, either in a single exercise bout or during a training block. So we can quickly establish a maximum effective dose for the high intensity portion of our training plan.

In a Review article, Seiler (2010) established that “about two HIT [High Intensity Training] sessions per week seems to be sufficient for inducing physiological adaptations and performance gains without inducing excessive stress over the long term”. The studies he looked at found only equivocal benefits and clear signs of overtraining resulting from 3 or more HIT sessions per week.

Seiler, 2010

There are a few specific cases in which more than 2/wk HIT workouts can be beneficial, but these cases require very specific planning, adherence, and monitoring and so I’ll leave them out of the current discussion for now..

Otherwise, this seems to concur with typical popular training protocol, and I’m happy to limit my training plan to two HIT workouts per week for logistical convenience.

How much Aerobic is Enough?

The more indeterminate prescriptive element is the minimum effective dose for Aerobic training, to fill out the ‘easy’ portion of our Polarized training plan around our two HIT workouts per week. When time is limited, how do we know whether we’re accumulating enough Aerobic training load to elicit positive adaptations?

One simple answer would be: after I’ve accounted for my two HIT workouts, I should just spend as much time as possible training under my Aerobic Threshold!.. That would probably suffice, but we can try to optimize our time further.

Despite the idea of long slow distance as the “traditional” Base training structure, it was surprisingly difficult to find conclusive literature investigating adaptations to low intensity Aerobic training..

(although I’m not claiming to have done a comprehensive review of the past 60+ years of endurance physiology research, so I’m sure I’ve missed things)

One article I encountered on post-exercise hormonal response to low intensity continuous running (Tremblay et al, 2005) found that changes seemed to occur only beyond 80-minutes of steady activity.

Although the implications of these hormonal changes were unclear, with the study concluding that “Beyond 80-min of running there is a shift to a more catabolic hormonal environment, although whether this will ultimately have negative or positive consequences is debatable”. So something seems to be happening after 80-minutes of low intensity.

Tremblay et al, 2005

These and other findings were called back on by Seiler (2010) to reaffirm the descriptive findings that elite endurance athletes “achieve excellent results when accumulating a high training volume by emphasizing frequent exposure to 60-180min bouts performed at [low intensity]…”

best practice prescriptive summary
Seiler, 2010

How Frequent is Frequent?

One of the remaining questions to the recommendation for low intensity Aerobic training focused around the ~2-hr duration is that, many sports have shorter and more frequent training bouts than cycling:

Rowers, swimmers, triathletes and other endurance athletes often train twice a day, or as Seiler (2010) notes “Numerous descriptive studies of [elite] endurance athletes [converges on] training 10 to 13 times per week…”

Seiler, 2010

With more frequent training bouts, again recovery between bouts becomes more important in facilitating continued quality of training. This might help explain why pure cyclists, who typically train with a single extended training bout on the bike per day, commonly exceed the 2-hr duration recommendation.

As to the question of minimum frequency, Hydren & Cohen in their 2015 review of the literature on Polarized Training provided a “sample” pre-season Polarized training plan consisting of 2-3/7 (per week) HIIT workouts, and 3/7 Aerobic rides of 2-hrs or less, for  5-6/7 total rides and a net total 7-8 hrs/wk.

Hydren & Cohen’s (2015) sample pre-season Polarized training week, based on at least 5 key studies demonstrating consistent superiority of Polarized training for athletes of all training levels across multiple endurance sports

That may be achievable for time-constrained athletes and demonstrates that you don’t need to devote massive hours to gain the benefits of Polarized training. The priority is the two weekly HIIT workouts, then filling in whatever your remaining time is with steady Aerobic riding.

Coming to a Conclusion… For Now

Despite the questions remaining as to minimum effective dose for Aerobic adaptations, at this point I would recommend the following features to consider as part of your time-constrained training plan:

Optimized Aerobic Training Plan

    • Polarize your training: Spend most of your time at low intensity, under Aerobic Threshold, and a small but important amount of time way above FTP, around VO2max or ANaerobic intensities. Minimize moderate intensity, including Tempo, Sweet Spot & Threshold.
    • Aerobic training bouts should last at least 80-min to accumulate enough training load for significant adaptations.
    • Two high intensity interval workouts per week is sufficient to optimize adaptations. More than two often results in fatigue and overtraining, and diminishes training quality for very little benefit
    • More frequent Aerobic training bouts are better: there doesn’t seem to be a minimum frequency, but more frequent may be more beneficial than fewer longer bouts (although see why I still think including a long Stamina Ride in your training can give you an adaptive edge)



References (not comprehensive)

11 thoughts on “Optimized Aerobic Prescription

  1. Hello Jem,
    A perfect review as usual.
    I will start base period next week. I plan on practicing polarized training this year even if I applied the pramid training plan last year. And I think that it is absolutely necessary to study weight. How can weight studies be planned? Before or after HITT training? Or should I definitely put a day between the HITT workouts and weight training?


    1. Thanks Sefa, and great question! I haven’t done as much research into weight training, but what I have come across suggests Lifting should be part of every Endurance athlete’s routine at least at some point during the training cycle. Might be a topic for a future post 🙂

      The Prep and Base phases are the perfect time to include some kind of Lifting. For the most part, Lifts should be considered high intensity, so they will contribute to fatigue. For that reason I wouldn’t recommend Lifting on “recovery days”, as I used to do!

      I personally prioritize my bike workouts – my VO2max & HIIT workouts, so I want to ensure I’m fresh for those days. For that reason I tend to schedule my own Lift workouts *after* my HIIT workouts, either on the same day or the following day. The downside is that I’m fatigued for the Lift workout, but that’s a sacrifice I have to make to ensure maximal quality on the bike. Then I’ll give myself one or two days of low intensity Aerobic riding to recover before going into my next bike HIIT workout as fresh as possible.

      Just my opinion for now, but hopefully that gives you somewhere to start!


  2. Where does aerobic threshold sit in relation to FTP, or is it measured with HR? I’m new to cycling and this idea is intriguing. It seems simple. 2 HIIT per week, the rest below aerobic threshold? No more crazy SST complicated plans? Just 80/20? I keep hearing that those low intensity miles are called “junk miles”. Thanks for the references, and especially for a fantastic blog!


    1. Thanks Cory! There are a lot of different ways to get fast, and the body definitely isn’t simple! But the literature I’ve encountered seems to be trending toward consensus around Polarized training and a certain minimum volume of Aerobic work for Physiological Training. But yeah, Polarized training is basically just a little bit of very very hard work, and a lot of very easy worK!

      ‘Junk miles’ usually refers to riding in the ‘tempo’ zone or moderate intensity, eg. 75-95% FTP. It’s the kind of intensity that feels “just hard enough” but doesn’t really give you much training benefit. I do think there’s a time and place for Tempo rides, and SST falls at the high end of Tempo.. Actually, I’ve written before about the value of SST as I see it, and I do think SST belongs in Performance Training, but that’s for a future blog post 🙂

      Aerobic Threshold (AeT) and ANaerobic Threshold (AnT, or FTP) are represented as *both* Power and HR thresholds:

      Power reflects ‘energy out’ or how much Work you produce
      HR reflects ‘energy in’ or how hard your body is working to produce that output workload

      So the relationship between both is critical to understand. Joe Friel has a good summary of the different and overlapping terms

      AeT & AnT are measured precisely by lab tests via gas exchange or blood lactate, but they are fairly predictable and AeT can be reliably estimated if you know your FTP. AeT HR usually occurs anywhere from 75-85% of LTHR, and AeT Pwr is a bit tighter, usually right around 75% FTP.

      Hope that helps!

      Liked by 1 person

  3. Hey Jem

    The information provided is valuable and I want to give you a thumbs up for it. I want to say that Aerobic exercises today is recognized is the absolute necessity of healthy living. It is also fit for someone who is trying to lose weight or tone their muscles. The simplicity of an aerobics exercise program extends in its flexibility. It can be done almost everywhere, indoors or outdoors, and almost anytime.


  4. great post, Jem, thank you. After years of 4-5 hours weekend ride, I recently decreased my base ride for shorter base rides, between 1-2 hours, and found in the space of 2 weeks that my normalized power to HR shot up 20%
    It’s in line with what you have posted elsewhere, about runners entering catabolism after 80 min. Running uses more body muscles, so I wonder, every else being equal, if there is a slight shift to longer times with cyclists.
    I asked Fast Talk when was a Seiler base ride enough; when the normalized power started coming down relative to heart rate. They said it depended on the person, and that Seiler was doing research on this.
    What is the tradeoff between adaptation, longer recovery times with longer base rides? What is the goldilocks moment when more riding increases recovery with not much more adaptation? That seems to me to be the holy grail of aerobic sports.


    1. I wouldn’t over-index on the 80-minute statistic I referenced in this article. If I were to re-write this article it would highlight that adaptation to low intensity training will be dependent on how long your training bout is relative to how long your body is “used to” (ie. able to maintain metabolic homeostasis without a stress/strain response). The longer you are able to maintain homeostasis, the longer you will need to go to get the same adaptive stimulus (all else being equal).

      I posted this on the TrainerRoad forum a while ago that probably gives a better summary:

      Let’s say at 65% VO2max, power under aerobic threshold, properly fueled, etc. Everything feels pretty easy for 2hrs. At 3hrs I’m starting to feel tired. At 4hrs I’m gonna be pretty cracked when I get home. That probably means a 90-min ride won’t give me much adaptive benefit. Might be considered a recovery or maintenance ride. 2-3hrs might be where I start to get an adaptive stimulus. And maybe 4hrs gives me a big boost, but also fatigues me so that I need to recover or go easier the next day(s).

      There is an elegant model of how duration relative to TTE (time to exhaustion) affects training load, adaptive benefit, and recovery required.

      Once again, let’s not get too preoccupied with over-precise targets (it doesn’t mean I need exactly 2:15:00 at 189W to get any benefit) And let’s just appreciate that the stimulus (intensity x duration) we need to improve is related to the chronic stimulus that our bodies are currently capable of and adapted to. Might be 75min for some, might be 25min or 125min for others.
      Hofmann & Tschakert, 2017

      Now, I’m actually very interested in your anecdotal finding that “performance” (evaluated by NP/HR) improved considerably after decreasing base ride duration. A colleague of mine has a fantastic meta-analysis (I’m biased, of course) in review right now that finds something similar. Unfortunately that’s all I can say until the meta-analysis is published. But it’s making us re-think how to program our low intensity training volume around HIIT workouts, when optimizing for performance outcomes.


  5. Great info, I will keep you informed of my anecdotal finding as things develop, and how my NP/HR develops.

    I remember in another post you saying that rather than hyper-dosing and needing days of recovery later, it was better have daily consistency, and to do moderate daily training stimulus.

    I am a layman disciple of Seiler. I am past 60, so I found, after a couple of years of tooling around, that 1x/week of his 4 x 8s worked better for recovery for me than 2x/week, and changed it to 3 x 8s a few months ago, as 4 x 8s, done per his research paper which I have, put me too deep in the hole.

    How “clear fatigue” is defined I don’t know. On a base ride, I can usually go 4-5 hours with feeling much fatigue, keeping HR pretty constant. But of course cardiac drift happens, sometimes a lot of it, so I still don’t know when enough is enough.

    Since the intervals by Sieler are very well outlined, with specific start/stop points, it is the 80% of the ride time that seems to have fuzzy parameters, since HR is pretty constant.

    Fatigue seems to be a very nebulous and subjective approach to go by, and different people experience it differently, perhaps analogous to pain threshold differentials. I’ve seen in some rides a big downward NP/HR shifts in the course of the ride but if I didnt see it would have said I still felt pretty good.

    I hope you post the meta-analysis here. Perhaps in the future HR variability, measuring indirectly hydrogen peroxide levels/ROS can give us a sense for biological fatigue parameters.

    I think I have almost all of the pieces down, except when to stop base rides that maximize adaption without too much recovery time!


  6. Jem, so if you’re making your HIIT workouts VO2max and/or Anaerobic, how are you building your FTP?

    For example, let’s say I just wrapped up a 6-week POL block that focused on the repeatability of my 5-min power. Where do I go from there? Assuming I’ve raised my aerobic ceiling, it would seem highly beneficial to push the floor up with a block of FTP work, no?


    1. Hi Anthony, that is such an important question that really isn’t answered by the literature: in terms of “ok I’ve just performed eg. 6-weeks of POL HIIT training and I’m experiencing diminishing returns. What do I do now?” There needs to be more investigation into longer-term periodization of training programming, and optimizing for outcome measures observed beyond 6-weeks.

      That being said, in general you will see improvements to FTP/CP as well as VO2max from polarized HIIT training. That gain to VO2max is assumedly coming from a combination of central (heart, lungs, & circulation) and peripheral (muscle oxidative capacity, substrate flux) which will also enhance your capacity at both aerobic (LT1/VT1) and anaerobic (FTP/CP) thresholds. However, it is possible to see improved VO2max without concomitant improvements in performance measures such as TT time, max aerobic power (MAP), or peak power on a ramp incremental test (Wpeak). Which I’d argue is what we really care about.

      To a very handwavy first approximation, VO2max (physiological capacity) is more related to central O2 delivery, while FTP/CP (performance, metabolic efficiency) is more related to peripheral O2 diffusion and extraction. The good news is that longer duration HIIT appears to directionally enhance TT performance in addition to VO2max. (https://pubmed.ncbi.nlm.nih.gov/33826121/. Disclaimer: the author is a colleague).

      And if I can speculate from the findings of that meta-analysis, if it appears that duration of an interval is more important than the intensity, as long as the intensity is above CP/FTP, then could it make sense to work for even longer durations (eg. 8+ min) at just above CP/FTP? And doesn’t that start to sound like a ‘Threshold’ interval?

      So I could certainly see value in extending the duration of work intervals performed around CP/FTP to continue to improve ‘threshold’ performance. I certainly prescribe longer duration sustained intervals (20+ min) during specific training blocks. I used to consider these ‘performance training’ instead of strictly ‘physiological training’ (as in, they’re more race- or demand-specific, than they are designed to elicit specific physiological adaptations). But now I don’t think there’s much difference between those categories.

      Hope that helps!


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