Podcast, Science and Physiology

Finding the line between enough and too much training with Filip Larsen, PhD | EP#340

 May 30, 2022

By  Bernardo Gonçalves


Filip Larsen - That Triathlon Show

Filip Larsen, PhD, is Associate Professor at the Swedish School of Sports and Health Sciences as well as Chief Science Officer at Silicon Valley Exercise Analytics (SVEXA). In this interview, we discuss research conducted by Filip and his team on finding the line between enough and too much training using various physiological and cellular markers, and how to take these findings from the lab and apply them in the field.

In this Episode you'll learn about:

  • Effects of intensified training on performance and cardiovascular parameters
  • Effects on mitochondrial parameters, including impaired mitochondrial respiration
  • Effects on glucose tolerance and substrate utilisation
  • Effects on glycolytic pathway and muscle glycogen adaptations
  • Implications for training, including when and how to do high-intensity training, how often to plan in rest cycles among load cycles, and more

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Filip's background

03:45 -

  • I am an associate professor at the Swedish School of Health Sciences in Stockholm, Sweden.
  • I am also a Chief Science Officer at Silicon Valley Exercise Analytics. I have been working with the National team for a couple of years as a physiologist and nutritionist.
  • My research focuses primarily on endurance sports from a muscle physiology perspective.
  • I have been training primarily in endurance sports. I started with orientating as a kid and did it on a recreational level only for fun.
  • I did it until my teenage years (15-16 years old). Then, I switched to athletics, doing middle-distance races most time, and in my 20s, I switched to triathlon.
  •  I started with sprint triathlons and moved to longer distances, doing Ironman.
  • I got three kids, and now, I am a recreational commuter athlete, mainly doing cycling and ultra-endurance races.

Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy individuals.

Hypotheses Filip wanted to access in this study

06:12 -

  • It sounds very complicated and technical, but in the projects we are doing right now, we want to have the athlete's perspective on what is happening in the muscles.
  • The starting point for this project was that the more you increase the training load, the more you get better. However, you might reach a breaking point where you no longer get any benefits from increasing your training load.
  • If you do that, you can become overreached and develop an overtraining syndrome.
  • Therefore, we wanted to find the optimal training dose and understand what happens when you train more than your optimal training dose.
  • You start to get maladaptations, where you do not get any positive effects anymore.
  • Thus, our focus was on this breaking point. 


07:45 -

  • It was challenging for our subjects. We took recreational athletes with some training background but without structured training.
  • We took five biopsies each week.
  • We did a baseline test, and the first week was less demanding.
  • The second week focused on moderate training. At the end of the third week, we wanted athletes to be at the optimal training load, so we tried to design the best training to provide the best stimulus.
  • By the end of that week, they were significantly tired and feeling the need for some rest.
  • After, we gave them this overtraining week, where we had almost daily intense sessions. At the end of that week, they were having the symptoms of someone that has trained too much. (lack of motivation, muscle soreness, lower maximum heart rate)
  • We took other biopsies and did more testing.
  • Then, we let the athletes recover with light training for another week. Therefore, it was four weeks of progressive, demanding training and one recovery week.
  • These athletes did not have any experience in interval training. We did 4-min or 8-min intervals supposed to be all-out.
  • We told athletes to give their best and produce the best power output possible.
  • The first week was about 1-2 sessions, the second was three, and we progressed until six high-intensity workouts in the overtraining week.
  • One crucial part of the protocol is that we did not give them any low-intensity sessions. (only high-intensity training)


12:30 -

  • First, we evaluated the cardiovascular adaptations (Vo2max, lower lactate levels, lower heart rate for the same power output).
  • We did not see striking differences compared to other studies when we did those measurements. As the training load increased, they got higher and higher Vo2max.
  • According to the theory of positive adaptations to the training load, the lactate levels and heart rate at submaximal efforts decreased.
  • After the overtraining week, the only thing that was impaired was their performance, as they did not see improvements with more training. However, these students had experienced good performance improvements from week to week.
  • VO2max and lactate levels kept improving over the overtraining week.

Mitochondrial adaptations

14:36 -

  • These adaptations were the crucial measurements. We took the muscles biopsies and isolated the mitochondria because they are the powerhouses of the cells that produce ATP for muscle contraction.
  • Positive adaptations to training correlate with more mitochondria and mitochondria with higher respiratory capacity.
  • In the first weeks, we saw this improvement in mitochondria respiration, but after the overtraining week, we found a substantial decrease in mitochondrial respiration.
  • A unique feature of this study is that you can do it in two ways when you measure mitochondrial respiration.
  • You can take a whole muscle fibre, and then you need to have the mitochondria staying in "one piece" and measure oxygen intake per gram of muscle tissue.
  • On the other hand, we broke the muscle fibres, isolated the mitochondria, and measured their respiration. If you measure respiration in the fibres, you will not know if you have an increase in the mitochondrial content or an improvement in the mitochondria themselves.
  • With the isolation, we can evaluate that parameter much more precisely. 

Glucose tolerance

17:17 -

  • The glucose tolerance test is a diagnostic test to address if someone has type II diabetes. 
  • Athletes came to the lab fasting and got 75 grams of pure glucose in a water solution. After, we measured glucose over two hours.
  • When you drink glucose, your blood sugar increases, and if you are healthy, you will see that it peaks after an hour and start to drop back again.
  • If you have a positive effect from training, you will see that this curve decreases as an adaptation to training.
  • You expect to get higher insulin sensitivity and better glucose uptake in the muscle.
  • After the overtraining week, we found a significant decrease in glucose tolerance. (the glucose curve got bigger)
  • It peaked at a higher level and did not decrease as fast. (opposite to what you expect from training)
  • In the first weeks, this parameter did not change. They were healthy subjects, and you should not expect a decrease if they start at a healthy level.

Substrate utilisation

19:17 -

  • A healthy body can choose between fat and carbs as fuels both at rest and during exercise.
  • Regardless of whether they were optimally trained, the preference for fat increased.
  • Therefore, this parameter does not correlate to what we found on a mitochondrial level.
  • There are theories on diabetes that if you have diabetes, some people think this could correlate to an impaired capacity to burn fat or choose fat as a fuel.
  • However, we did not see that during the overtraining phase. (actually, we found the opposite)
  • We did not want athletes to lose weight and avoid energy deficits.
  • Therefore, we weighed the athletes in every session and made sure they kept the weight. After each session, we gave them recovery drinks and standardised meals to match the energy expenditure.
  • The glycogen levels were at the highest levels during the overtraining phase.

Conclusions from this study

22:43 -

  • We found a physiological measurement of the breaking point, something not seen before.
  • We would not have seen changes if you only measured VO2max, lactate or specific enzymes.
  • We needed to access mitochondrial function and a glucose tolerance test to see when you go from the optimal training load to the excessive training load; these two parameters change.

Why do mitochondrial function and glucose tolerance reflect an overreaching state?

24:01 -

  • In the past, we knew that when we train too much, we produce many reactive oxidant species (free radicals) that potentially can damage our cells if our anti-oxidant system cannot handle them.
  • Therefore, we would explain overtraining as an accumulation of reactive oxidant species that damage the cells, leading to maladaptations on a physiological level, mitochondrial function and glucose tolerance in the cells.
  • We measured oxidative stress, and we found that this did not change throughout the study regardless of how much athletes trained.
  • The body wants to maintain oxidative stress at a stable level to maintain homeostasis. Therefore, our body might shut down mitochondrial respiration to achieve that.
  • The mitochondrial produces many reactive oxidant species, so if you turn down that production, you can "handle" the period of overtraining.
  • The trade-off is that your physical capacity will decrease, and if you continue for an extended period, you might get symptoms of overtraining like hormonal disturbances or sleep disorders.

Short-term intensified training temporarily impairs mitochondrial respiratory capacity in endurance elite athletes

Context of this study

27:04 -

  • From a time perspective, we did this study before the first mentioned. However, we did not write it until the first study got published.
  • A third study showed the same results in untrained individuals who did sprint interval training. (10 days of 10x30s all-out on the bike)
  • We obtained the same decline in mitochondrial respiratory capacity before and after.
  • Elite athletes performed a slightly different protocol. These athletes were strong triathletes and cyclists, and they did a hard training block for five weeks.
  • We found a decline in mitochondrial respiratory capacity. However, these results were unexpected. We thought we would see an improvement in mitochondrial respiration with training.
  • Nevertheless, we were doing extreme protocols. Could overtraining explain these results? As we did not know, we measured other parameters, which led me to design a study that could allow me to do five biopsies. If it were overtraining, not only mitochondrial respiration would decrease, but many other parameters would decline.
  • The primary difference from this study is that we used elite athletes, and it is much harder to overtrain elite athletes than recreational ones because they have a much higher base of training.

Training Protocol

30:22 -

  • Behind the training plan, there is a dietary intervention too. Half of the group that performed this study had a high carbohydrate diet, and the other had a low carbohydrate diet. Our study's central hypothesis was to assess if training with low glycogen is better or worse than training with high glycogen levels.
  • However, we did not see any differences.
  • We did intervals in the morning, and the group with a high carbohydrate diet could eat after that session to replenish the glycogen stores. Then, they did a distance ride in the afternoon. The group with a low carb diet did not get so many carbs.

Notes on the first study and the non-existence of a control group

32:11 -

  • It would be best to be careful when making conclusions about single studies because the topics are more complicated than they seem. (especially if you try to take that knowledge and apply it to real athletes)
  • A control group for these studies would be someone that only rested and continued a regular life.
  • But if we take five biopsies, we will also measure oxygen uptake and mitochondrial respiration, and it will remain stable in a control group.
  • It would not add any value but only show we could do the measurements, which would not be so informative.
  • We have another idea for another study design to evaluate the best approach to taper and perform an overreaching phase. (train hard to drop performance and taper to have a super-compensation)
  • If we have a control group that trains consistently compared to a group that does an overtraining week and then tapers can be intriguing to analyse.
  • However, if we can also train at the optimal training load and skip the overtraining phase and the negative impacts of this phase, would that group perform as well as the group that overtrains before tapering?
  • There is much debate on how hard and how long you should do an overreaching block. Currently, there is no consensus on the best method to train before racing.
  • I do not see any value in reaching an overreaching state. (training until your performance drops) In many cases, the performance drops when athletes are already overreaching for some time.
  • I am pretty sure that you should start recovering before entering that state. And this is not only leading up to a race but also in regular training days.
  • Christophe Perry made a good study, where he did the same training day after day, and he measured the adaptation to training.
  • In this study, you can see the time effects playing a role. You could see the most significant signals of improvement during the first sessions, and then it levels off the whole signalling process.

Key points to consider from these load cycles

38:39 -

  • We look for an objective marker for when to stop your loading phase.
  • Most athletes and coaches do that by feel. They plan a hard week, and when they feel tired, they recover.
  • We will publish a study based on the same data because we found some responses during the training phase.
  • For example, we see that lactate levels drop as the training block progresses. If you are in an overreached state, you cannot push your lactate values up.
  • Therefore, we discuss how much you should allow your lactate values to drop before entering a recovery period.
  • And the same thing with heart rate during the sessions.
  • For example, your regular heart rate is 180 bpm when you do intervals. And after training hard for a couple of weeks, your heart rate is 172 bpm. So it becomes harder and harder to achieve a high heart rate.
  • However, we need to determine how much you should allow it to drop before recovering.
  • Therefore, we developed some numbers to find the optimal training load.
  • We have this study submitted already and waiting for approval, and we are now doing an observational study, applying the knowledge we found during this period.
  • By knowing athletes' power and heart rate data, we can model their training load, and we are also using glucose monitors, and Oura rings to measure sleep quality and HR during sleep.
  • We are collecting all this data for one year from 20 elite athletes, and we are looking for patterns of training, performance and physiological parameters. (sleep, glucose, HR)
  • Usually, we would have our athletes in a lab and control most variables. But now, we can better understand the data by using all these devices.
  • Our research aims to apply the lab findings to the athlete's life. (advise them on training and recovery)
  • Moreover, we can now compare data between athletes. For example, we can compare deep sleep time between athletes based on the findings of this study.

Additional markers to find the optimal training load

45:26 -

  • We wanted to find parameters that we know coaches and athletes measure daily. We use lactate and HR because we can predict their values, and it is accessible for athletes.
  • Moreover, we have subjective measurements (RPE). You can gather much data by rating how you feel while producing a specific power output.
  • These subjective measurements can also help separate the points where you are overreaching. We also have 6-7 questions where you can see that when you go above your optimal training load, your mood will worsen, and your energy levels and motivation will drop.

Using high-intensity training for performance vs for health goals

47:41 -

  • Our study does not indicate that you should not do HIT because it is time-efficient to improve metabolic health and cardiovascular performance. If you only have one hour of training per week, you should do a more intense session than an easy run.
  • However, you can do too much of it, especially if you are an elite athlete. If you compare distance or threshold training to HIT, most scientific studies favour HIT training as more effective.
  • Nevertheless, all athletes understand that you need a base to adapt to the higher training intensities. However, that base is not a clear concept in the scientific literature.
  • I have not seen answers showing how much low-intensity training we need to adapt to HIT training at a cellular, metabolic or mitochondrial level.
  • Our study shows that you might temporarily hurt mitochondrial function if you do too much.
  • Suppose you look at physiological responses where organisms try to maintain homeostasis and return to the baseline to build back stronger. In that case, there is no real sense in not providing recovery quite often.
  • It will only accumulate fatigue and many damaged processes if you accumulate it for too long.
  • You need to repair damaged cells with protein, replenish glycogen stores to bounce back and push more to improve.
  • In scientific terms, it is challenging to say that short cycles would be better or that you will have mitochondrial dysfunction.
  • I do not have any scientific support but only information from observational studies. For example, we can look at the comparison between three days and three weeks of overreaching.

Three pieces of advice to help athletes improve performance

53:16 -

  • I am amazed by working with professional athletes. However, I do not think they are so unique or genetically gifted.
  • They are doing things differently compared to regular people.
  • The first noticeable thing is the consistency of training day after day. People might think this is boring advice, but I would argue that people cannot be consistent. Do you manage to avoid sickness or injuries?
  • If you train too hard in specific periods, it will punish you, and you will have to get some rest.
  • If you can balance load and recovery week after week, it is similar to what elite athletes can achieve.
  • The second point is sleep and nutrition are crucial points athletes need to be aware of in their daily routine. The simple things are crucial, like going to bed consistently at the same time each day. You should not get stressed before going to bed or staying up late watching horror movies, and get dark curtains, so you do not get exposed to light.
  • The elites get consistent sleep compared to those not on an elite level.
  • I think people make nutrition too complicated. However, the basics are so easy. For example, you should eat enough, do not stress about it or make sure you refuel after intense sessions.
  • Things that are not interesting to talk about are the crucial factors we need to consider.

Rapid-fire questions

56:34 -

What is your favourite book, blog or resource?

Better Training for Distance Runners by David Martin (Author)

What is an important habit that benefited athletically, professionally or personally?

Getting up early.

Who is someone you have looked up to or who has inspired you?

I could not point out a specific person, as many people inspire me.


Bernardo Gonçalves

Bernardo is a Portuguese elite cyclist and co-founder of SpeedEdge Performance, a company focused on optimising cycling and triathlon performance. He writes the shownotes for That Triathlon Show, and also produces social media content for each new episode.

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