Podcast, Science and Physiology, Training

Training, testing, metabolism and physiology with Björn Kafka | EP#286

 May 17, 2021

By  Mikael Eriksson


Björn Kafka is a cycling and endurance coach at the highest level, including coaching multiple World and European champions. He is also an expert in metabolism and metabolic calculations, and has developed the Aerotune Powertest that gives athletes access to in-depth information about their own physiology. In this interview we go in-depth on the topics of training, testing, and metabolism, and Björn shares his expertise from all of these domains.

In this Episode you'll learn about:

  • How VO2max is related to the maximum number of training hours you can positively adapt to without overreaching
  • How to train VO2max (for different types of athletes)
  • VLaMax: how to use it in training, why lower is not always better, and why it still isn't very widely used
  • Guidelines for using high-intensity interval training
  • Guidelines for using cadence and torque work in training
  • Nutrition recommendations in training, racing, and day to day life
  • The Aerotune Powertest
  • General tips for age-group athletes and mistakes to avoid

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05:00 -

  • Like most people within this field, I have my own background within endurance sport and mine was road cycling.
  • However, I never did study physiology, biology or metabolism in University, instead I initially pursued a career within journalism, I wrote for a sports magazine for quite some time.

    I did, however, become a little bored of this after some years, and together with a friend I started up a coaching business.

    This business did become rather successful and during the time we coached some really high level cyclists.

    Our main ”edge” was exercise metabolism and back calculating metabolic pathways through different tests in order to produce a ”metabolic profile” of the athletes.
  • Anyway, after some years I ended up leaving this particular company and started up my own coaching business and this is where we are now!

The three most common mistakes endurance athletes make in their training

12:30 -

  • The first thing is to eat to little in general or take in too little carbohydrates.
  • Working on ones strengths, one should instead target ones weaknesses.
  • Having a too stressful training-life balance.

VO2max as a determinant of how much training stress you can induce on your body

17:00 -

  • I have developed an algorithm that calculates the theoretically ”optimal” training stress (in terms of total kilojoules of work) based on the athlete’s VO2max.

    It is theorized from protein syntheses processes within the cell and how much stimulus (kilojoules of work) these processes need to adapt as well as how big of an overload they can handle.

    For instance, looking at my table over different VO2max values you can see that for someone with a VO2max of 70, their ”optimal” stimulus is around 2500 kilojoules of work per day, which equates to 15h of training if they ride at an intensity where you produce 1000 kilojoules per h (this is quite high intensity and basically no athletes ride at an intensity where you burn 1000 kilojoules per h on average, hence the ”realistic weekly training volume is probably more like 17-19h).

    The total weekly kilojoules of work is, however, also slightly dependent on the glycolytic capacity (VlaMax) of the athlete.

VlaMax and it’s training applications

31:55 -

  • The VlaMax or glycolytic power is the power produced from glycolytic (carbohydrate) sources and witness about your sprint capacity (the higher the better) but is also a limiter in long endurance events as a high VlaMax also means a constant high utilization of carbohydrates.
  • The big question is, however, of course how this parameter is best used in training.

    The ”optimal” VlaMax number is different depending on the demands of the race, a sprinter should aim to have an as high as possible VlaMax whilst a Classic rider should have a VlaMax in the ”mid-range” (i.e. 0.45-0.5 mmol/l/s) and a long distance triathlete should probably be in the 0.2-0.35 range (”low”).
  • But there are also issues with having a VlaMax that is too low all the time, you get very narrow in what kind of training you can do, especially doing work above threshold in order to develop VO2max is extremely demanding on the body for someone with a low VlaMax, hence one can in periods trick the VlaMax up prior to a VO2max block of training for instance.
  • One of the biggest ”myths” about VlaMax within triathlon in my opinion would be that ”lower is always better”, which is not always the case.
  • Another ”word of precautionary” that I would like to say in regards to having a very low VlaMax is that athletes with low VlaMax tend to go rather fast on their endurance rides and even if they have a large fraction of the energy production from fat oxidation sources, they still consume a lot of carbohydrates at this intensity, hence they must make sure to take in plenty of carbohydrates despite the fact that they have a low VlaMax and many cannot take in the sufficient amount and go into over reaching and/or a state of energy deficiency.
  • For swimming, the importance of VlaMax heavily declines as the technique is greatly more important.

Cadence and torque in training

53:15 -

  • I use cadence when I am trying to decrease VlaMax (low cadence intervals).

    Low cadence work can also be done as strength intervals.


58:20 -

  • Intensity is important in order to develop a big stroke volume (an important part of the VO2max).

    In order to increase VO2max, one must make sure that the athlete is actually reaching the VO2max domain, which takes a bit of time (e.g. one min at VO2max power is not enough to stimulate an increase in VO2max) and this also makes these kind of sessions very demanding.
  • In order to get an adequate stimulus on the VO2max I would say one must do 2-3 VO2max sessions each week (this is hard!).
  • For an athlete with a low VlaMax I would recommend the following design of a VO2max session: 1.5-2min @ VO2max power + 7-9mins @ maximum lactate steady state intensity, which is repeated 3-4 times.
  • For an athlete with a high VlaMax I would recommend the following design of a VO2max session: 5x7mins of 40/20s.

    However, I use to design sessions not to target a capacity (like VO2max) rather than targeting a demand of a race.


01:04:40 -

  • Always make sure to eat carbohydrates - you stay injury and sick free, don’t go into mind fogging and stay a normal people!
  • Make sure to eat during sessions (it reduces risk of overeating post sessions).
  • If you want to lower VlaMax very fast, then you can achieve that by lowering your intake by carbohydrates.
  • If you’re looking to loose weight, then be really diligent and calculate how much you take in and consume and look for a deficit of around 300-400 kcal per day (a little bit depending on body weight).
  • You don’t need to go low carbs in order to stimulate fat oxidation processes, just make sure that you’re blood sugar is rather stable both pre and during session (take in ”slow” carbohydrates before training and make sure to take in energy in a regular manner during sessions).
  • For races, you should aim to take in as mush energy as possible (100-120g of carbohydrates per hour), and this you must train in the weeks leading up to the race so that your digestive system can handle that large amount of energy.

Current area of interest

01:13:15 -

  • Training adaptations, this is a really fascinating subject.

    We are trying to develop a model that is aiming to calculate the best training load (volume, intensity and recovery) for an athlete with a particular VO2max, VlaMax, age, etc.
  • I would like to say that training adaptations are a very ”fresh” commodity, you can gain great additions fast but also lose them really quick, hence I am not a big fan of taking long season breaks.

Aerotune metabolic test

01:19:00 -

  • My company does provide a test service, that calculates your VO2max, VlaMax and also gives recommendations in terms of training volume and intensity .

    You perform a 20s, 4mins and 20mins test either outside or inside and after that you upload the power file to our program and it calculates your values automatically.

    Since it is an automatic calculation (no humans needed), we have very competitive pricing (a test package costs 25€).
  • We also offer aerodynamic testing that you can perform on your own.

Rapid fire questions

01:27:05 -

  • What is your favorite book, blog or resource related to endurance sports? The Internet… My favorite sports science book would, however, be Endurance Training Science and Application by Inigo Mujika.
  • What is your favorite piece of gear or equipment? A gear that would be able to give me RPE… Otherwise I would say the HR monitor.
  • What is a personal habit that has helped you achieve success? Putting family first! Working constantly, and don’t be too focused on specific things (life is no straight line) and this will enable you to take in impressions from different kind of directions in life.


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

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