Shownotes

Guido's background

02:24 -

• I started studying in Utrecht back in 1988. I was interested in medical biology — that’s what it was called then, nowadays it’s biomedical sciences.
• I began studying with a special interest in exercise physiology. I also did research in molecular biology, so that really built the scientific base of my education.
• But I didn’t want to end up just in a lab. I wanted to work with athletes and help them become better. That’s when the idea of studying medicine came into view. The first two years of medical biology and medicine in Utrecht are quite similar.
• But medicine wasn’t an open program — I had to get in through an application, and I didn’t succeed the first year. So I continued with medical biology. In my fourth year, I got into the medicine program.
• So I ended up completing medical biology and then continued with medicine because my goal was to become a doctor in sports medicine and exercise physiology.
• I succeeded — after finishing medicine in 1997, I started a four-year specialization in sports medicine and exercise physiology, which I completed in 2003.
• That was a lot of studying. And then I started working — but I couldn’t really find a place where I could do exactly what I wanted. So, what do you do then? You start your own business.
• It was really small at first — just an afternoon a week in a health and sports centre, working as a sports doctor. It was nothing at the beginning.
• But it grew, and over the course of five or six years, it became a successful sports medicine practice. I worked with a colleague, and we really specialized in endurance sports — mostly runners, cyclists, and triathletes.
• The practice kept growing. In 2011, we moved to the city of Amersfoort because we had the opportunity to join the University of Physiotherapy, where I now lecture on exercise physiology.
• That helped everything grow even more. Amersfoort is a larger city, so many athletes started coming to me for exercise testing and injury consultations.
• But things got too big. From 2010 to 2011, I also started working as a coach. That was my passion. By 2019–2020, I had around 40 to 50 athletes that I trained and coached — on top of running the sports medicine practice.
• It was just too much. My wife was the manager of the practice, and we were both overwhelmed — certifications, staff getting sick, so much to deal with. So we looked for someone to take over the business and found a good person.
• Now I still work in the same sports medicine center, but only one day a week. For the rest of the week, I’ll be a full-time coach, working with triathletes, mountain bikers, cyclists, and runners. And it’s a lot of fun. Five years later, I’m really happy with this setup.

Guido's interest in being a coach

07:36 -

• That came later. For the first 10 years, I was just a sports medicine doctor. But one of the main things I did was exercise testing — prescribing training zones, and helping athletes improve performance.
• It wasn’t just injury treatment.
• So from that side of exercise physiology, I started training myself in coaching — getting certifications from the triathlon union, and learning the craft. I enjoyed it a lot, and my athletes were happy with my work, so I stuck with it.

The most common issues in sports medicine practice

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• A lot of injuries — especially from endurance sports. Most injuries were from running, which is the most injury-prone of the three disciplines.
• So I saw a lot of ligament injuries, Achilles tendon issues, knee problems, foot injuries — all common running-related injuries.
• It wasn’t often that I had to refer people to an orthopaedic surgeon. Usually, the prescription was about adjusting their training — switching from running to cycling or swimming or doing strength training during recovery. That was the largest group of cases.
• It’s tough to know whether something is just a small pain that will heal or the beginning of an injury.
• Many athletes try to ignore pain. They warm up and feel fine, but the next morning they wake up stiff and sore. It’s difficult to judge.
• One rule I use is: if you have pain for two days in a row, that’s a yellow flag — tell me. Ideally, tell me the first day. But two days in a row is the point where we take it seriously. If it’s three days, that’s a red flag — we need to reassess or maybe stop running.
• I also tell my athletes to always report how training went and whether they felt anything unusual.
• And this is where I have an advantage — I’m not just a coach, I’m a doctor. I can make better decisions about whether something is serious or not.

Guido's coaching methodology

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• I always want to understand how the athlete’s performance system is built — especially their energy systems.
• How strong is their aerobic system? How strong is their anaerobic system? Do they need a good sprint system for their goal events?
• For example, in a long-distance triathlon, you don’t need to worry about the sprint system as much, but I still never ignore the anaerobic system.
• In my opinion, all energy systems need to be trained — not equally, but all should be addressed because they influence each other.
• When I start working with an athlete, the first week is about getting to know them: understanding how they respond to training, and whether they interpret my sessions correctly.
• In the following weeks, I begin to include specific testing within the training.
• I use power a lot — power tells me about energy production over time. More power = more energy per second = better performance.
• I look at their power-duration curve — the best 2-minute, 5-minute, 10-minute, 20-minute, 40-minute, and 60-minute efforts.
• Some athletes have high short-duration power but drop off quickly. Others have a slow decline — these are more aerobic.
• I look at power not just in cycling, but also in running. I want to make athletes more efficient and build a strong engine.

Train the anaerobic system for long-distance triathletes

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• Courses aren’t always flat. For example, the Almere triathlon in the Netherlands is very flat, but most races aren’t.
• When you hit a hill, you can’t just downshift and spin slowly — you need anaerobic power to push over it effectively.
• Also, if you want to surge or catch someone, or handle changes in pace — that requires anaerobic energy. And even for the run, having an anaerobic “tank” helps with short surges and recovery.
• For professionals, racing is fast and dynamic — they might have to close gaps after a bad swim or push the pace strategically. They need anaerobic capacity.
• For age-groupers, it’s usually more about pacing themselves and avoiding blowing up. Most are focused on finishing strong, not reacting to race dynamics.

Swim training principles

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• The technique is always the most important. I’m not a swim coach myself, so I refer athletes to technique specialists if needed.
• Also, don’t just swim in a pool. You must train in open water, especially if you’re racing there. Some swimmers are great in the pool but get anxious in dark, cold, choppy open water. That kills performance.
• And for workouts, I use Critical Swim Speed (CSS) and do training around that. Intervals like 50s, 100s, 200s — some faster than CSS, some right at it.
• For 50-meter intervals, I prescribe 105–110% of CSS with 10–15 seconds of rest.
• 100s are at 100–105%, 200s and 400s at 95–100%.
• Main sets typically take about an hour — around 3–4 kilometres, depending on the swimmer.

Cycling principles

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• Biking is my favourite. First, you must have a power meter. It gives me all the data I need.
• I also start with a lab test (CPET) unless the athlete has good historical data. I want to know VT1, VT2, VO2max, and define zones accordingly.
• Then I plan intervals based on those markers — VO2 max intervals at 110–120% of FTP, or sometimes 1-minute reps with short 15-second rests. These are hard but very effective.
• One thing many athletes don’t like — but I think is very important — is torque training. Basically, low cadence, high resistance riding.
• It’s like strength training on the bike. It helps you push harder, especially in the TT position where you can’t rely on high cadence all the time.
• When you exaggerate low cadence, you develop strength, and later you can convert that into speed or sprint power.
• So if I think an athlete needs more strength, I include torque training.
• It’s not power-based — it’s based on torque in Newton meters per kilogram. For a strong athlete, I target 1.0 Nm/kg.
• Let’s say the athlete weighs 80 kg. Multiply by 6.28 (2π), you get ~500 watts at 60 RPM. That’s the target power.
• So the session would be:
  • 1 minute seated at 500 W, 60 RPM
  • On a 5% gradient hill
  • Then turn around, roll back, repeat.
  • Eventually progressing to 2, 3, even 4-minute reps — always seated. It's tough!
• I also like combining intervals with fatigue. For example:
  • Ride 2–3 hours easy
  • Then do your high-intensity intervals.
• This simulates race fatigue. Many athletes only do intervals fresh, after a 30-minute warm-up. But in racing, you have to perform when already tired.

Run training principles

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• I use power in running too — specifically with Stryd foot pods. I monitor running economy and efficiency.
• Efficiency is how much power you need to run at a given speed. Good runners have low energy costs.
• I look at this in flat conditions to remove wind/elevation as variables.
• I use VO2 max intervals (2–3 minutes at 110–120% of Critical Power) and threshold intervals (e.g., 5–8 minutes at 100–105%).
• Building toward races, I also prescribe long steady race-pace runs, especially after 1–2 hours of easy running.
• For example, 20–30 minutes at goal pace after a 90-minute easy run.

Improving running efficiency

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• It’s hard to improve — it’s very individual and based on how someone runs.
• Stryd gives lots of metrics. Many athletes take long strides and run at a low cadence (160–165). That causes high vertical oscillation and energy loss.
• I encourage them to increase step frequency to 175–180. At first, it feels unnatural and tiring, but over time it becomes more efficient. Ground contact time drops and the economy improves.
• Especially for triathlon, where you’re running off the bike, efficiency seems key.
• You might run well when fresh, but after biking, you need to reduce force and impact. If your form is inefficient, it will fall apart late in the race.

Periodization

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• It depends on the athlete and their goals. I don’t follow a rigid 3-weeks-on, 1-week-off model.
• I base it on feedback — how fresh the athlete is, how they’re recovering.
• I also use some recovery data, but mostly I read comments and adjust. I have a long-term plan toward the goal, but where recovery weeks fall is based on how things are going.
• Life happens — athletes get sick, and work trips pop up. Sometimes the week that was meant to be easy is actually perfect for a big training week. So I adjust accordingly.

Manage intensity over the year

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• I don’t start with only aerobic work. I always include some high intensity, even in the early phases — maybe just short efforts like 10x30 seconds with 3-minute breaks.
• As we approach races, the intervals become more race-specific, and those sessions take up more time in the week.
• The biggest training weeks happen about 2 months before the race.

Metabolic testing

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• I do lab testing (CPET) once a year. That’s enough because I get plenty of data during the season from power meters in training.
• The lab test is important to establish a baseline — and for health screening. It includes a medical checkup, EKG, bloodwork, lung function, plus the exercise test.
• That gives me the athlete’s performance profile and flags any health risks.
• I’m starting to do more field testing now. There are new portable CPET devices like the VO2 Master and SpiroFit.
• VO2 Master only measures oxygen, but SpiroFit measures both oxygen and CO2, which is even better.
• This lets me see metabolic data outdoors — while running or riding outside — and assess real-world efficiency. That’s critical in long-distance racing.
• There’s a great study by Peter Christensen done before Magnus Ditlev’s Roth world record. It shows how powerful field testing and simulation can be.
• For example, he was riding at 320 watts with just 4 litres of oxygen uptake — very efficient.
• That’s the benchmark I show my athletes. If you can do that, you can win.
• There is a new version of the VO2 Master coming with CO2 and That’s been talked about for a few years, but it’s still not widely available. I know Gustav Iden and Kristian Blummenfelt have tested it. But it’s not on the market yet.

Set training targets from lab vs field data

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• I use both. I always know approximately where an athlete’s VT1 and VT2 fall.
• In the lab, I also check how much metabolic energy is needed to produce mechanical power.
• The goal is to become more efficient — needing less oxygen for the same power.
• You can track that in the field too, but only with a CPET device.
• I use the critical power model a lot — including a dual-model approach. One model for short durations (2, 5, 10 minutes), another for longer durations (20, 40 minutes).
• The short efforts tell me about anaerobic capacity, while the long ones show aerobic strength.
• Professor Charles Dauwe at the University of Ghent developed this approach. I also use terms like “supercritical power” — above which you burn through your anaerobic tank quickly and fatigue fast.
• I use all available power data — especially from the past 90 or 365 days. I pull the top efforts for 2, 3, 4, 5 minutes, etc., and fill them into the model.
• From that, I can calculate things like W’ (anaerobic work capacity), and see where critical power is — for example, 330 watts, and how long the athlete can hold that.
• Then I use that to guide intensity targets — for VO2max work, we go to 120% of critical power.
• Some athletes enjoy testing and will go hard for 20 or 40 minutes. Great — I’ll take that data.
• But for most, I just use what they produce in races or hard sessions. Maybe a 20-minute climb or a good race effort. I rarely prescribe 20-minute tests specifically.

W’ to define athlete profiles

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• For example, I coach some under-23 mountain bikers and elite women. For them, W’ is crucial.
• They need to attack, climb explosively, and recover fast.
• It’s ideal to have both a high VO2 max and high lactate production — which is difficult. But I try to balance both in their training.
• For mountain bikers, a good anaerobic capacity is around 30,000 joules. For critical power, five watts per kilogram or more is ideal for elite males.
• In intervals, I can calculate the anaerobic energy used — like 40 seconds at 300 watts above CP, then 20 seconds recovery. I look at how long they can sustain those efforts before emptying their tank. It’s quite predictive — especially for structured efforts. Recovery is a little trickier to model, but it works well for things like individual pursuits or structured intervals.

Age groupers with limited training time

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• I ask them to realistically define how much time they have — not fantasy hours squeezed in late or early. What do you really have available?
• Most say 10–15 hours per week.
• If someone wants to do an Ironman for 10 hours a week, it’s possible, but we’ll need a period where they can do more — like during vacation or training camp.
• I also help them decide where to invest their time. Some athletes swim five times a week unnecessarily when they’d benefit more from more cycling or running.
• Adding more hours often comes at the cost of recovery. If you train late at night and early in the morning, your recovery suffers.
• It’s not enough to say, “I rest at work” — that’s not true recovery.
• If they’re already a good runner, we might spend more time on the bike.
• For example, if they run a 2:48 marathon but are weaker on the bike, we shift time toward cycling — maybe five to six hours there, three on the run, one or two in the pool.

Age group common training mistakes

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• Overtraining without enough recovery. Many believe more training = better performance but forget recovery is part of the equation.
• If you go from 10 to 15 training hours, you also need five more hours of recovery. That’s often overlooked.

Advice for older athletes

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• Strength training becomes more important as you age.
• You don’t have to lift super heavy or do explosive work, but you should train all major muscle groups.
• Maintaining muscle mass helps you maintain performance.
• It’s important for everyone. But recovery also gets harder with age.
• If you do a hard session at 50+, it might take longer to recover than when you were 30.
• So yes, it’s worth starting earlier — especially for building resilience and injury prevention.

Good progression for new triathletes

1:02:06 -

• It reminds me of how running a marathon used to be the big goal — now it’s an Ironman.
• Some people hear about it at a party and think, “I want to do that too,” so they sign up.
• I get those requests, but it’s not my favourite kind of coaching. I prefer athletes who love the sport and want to improve, not just tick off a bucket list.
• Usually, I recommend starting with sprint or Olympic distance. Learn to train, race, and improve.
• Then move to a half-distance, and after a year or two, maybe a full Ironman.

Pacing strategy

1:04:00 -

• I pace with power. Let’s say you know your functional threshold or critical power:
  • For a half Ironman: aim for ~90% if you’re strong on the bike, 85–90% if not.
  • For a full: 80%, or maybe even 75–78% for more conservative riders.
• Heart rate shows internal load — it can reveal if heat or dehydration is affecting you.
• If HR is too high compared to normal power, it’s a sign something’s off. You might need to back off or improve hydration.
• For running, I also use power. Same rule — 90% of CP for half, 80% for full.
• You can use critical speed too, but on hilly courses, that’s tricky.
• Just like in intervals, you might hit 120% of CP, but not of speed — especially over longer intervals.

Overrated things in triathlon

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• Definitely — supplements. Athletes sometimes act like supplements are the solution to everything.
• But if you’re not eating properly, they won’t help. Good food is the base.
• Supplements like caffeine, bicarbonate, creatine, and vitamin D are well-studied. But many others promise 5–10% improvements with no solid proof.
• Also, recovery gadgets — boots, ice baths, etc. They’re okay, but sleep is still the best (and cheapest) recovery tool.

Underrated things in triathlon

1:09:29 -

• Efficiency. Everyone talks about VO2 max, but efficiency is just as important — especially in long-distance racing.
• For example, try a few pairs of shoes to find the most economical one for your stride.
• Or do aerodynamic testing or a proper bike fit. That can save way more time than buying some tiny upgrade that gains 2 watts.
• You spend hours on the bike — comfort and fit matter a lot.

Work with Pro triathletes

1:11:29 -

• Menno is someone I’ve known for a long time. I was already the team doctor for the Dutch Triathlon Union back in 2006.
• Menno started with an Olympic-distance triathlon, then moved to long-distance. He’s a great swimmer and runner — very talented.
• But this year, he was getting dropped on the bike — even though he swam with the front group.
• We spoke when he came for a medical certificate, and I asked, “What’s going on with the bike?”
• He wasn’t sure — he felt strong but kept getting dropped.
• So we had a conversation, with his coach Jordi. They’ve worked together for a long time.
• Menno has a great feel for swimming and running, but not for bike pacing.
• A few weeks later, he came back and asked if I could help with the bike.
• This was around May 2024. Frankfurt was on the calendar for August — his Kona qualification race.
• We focused on torque training. He had done some already, but not hard enough — more like 0.75–0.8 Nm/kg, around 400 W.
• We raised that to 500 W seated, and progressed from 2- to 3-minute intervals.
• The hill wasn’t steep enough for 4 minutes, but 3 minutes worked well.
• We also improved his anaerobic capacity — high-intensity intervals, VO2 max sessions, and race-specific blocks.
• Just before Frankfurt, we tested again. I felt confident he wouldn’t be dropped.
• During the race, he had a crash around 80 km and lost the front group.
• But even solo, he held a 310 W average and 330 W normalized — very strong.
• That put him in a good position for the run, even though he was slightly behind.
• He ran incredibly well and finished 5th — just enough to qualify for Kona.
• After Frankfurt, he had a tough recovery and developed pain in his shin.
• At first, it was unclear if it was just soreness, but it didn’t go away.
• We did an MRI and found a stress reaction — no running for 3 weeks.
• We flew to Kona 3 weeks before the race. That first day there was his first outdoor run.
• It was a gamble. We focused on swimming and biking. He executed the swim perfectly, first out of the water.
• On the bike, he stayed in the front group again, averaging the same power as in Frankfurt.
• He held on through the run and finished 5th. Tristan finished 22nd.
• It was both their first time racing Kona.
• Menno now has a T100 contract. T100 is dynamic racing. Menno is a racer — he likes speed and aggressive pacing.
• Long-distance is more about holding back, waiting, and then going in the final 10K. T100 is go-go-go.
• Tristan is different — very controlled and steady, like a machine. You can program him to hold 320 W, and he does it.

Bike training changes Menno and Tristan are doing

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• Now I’ve stepped into more of an advisor role. His coach Jordi is leading, and I provide input when needed.
• At this point, the aerobic base is big enough. We’re focusing on anaerobic capacity and maintaining torque training.
• If he has the strength, he can respond to surges and attacks.
• One session is 30 seconds at 600 W, 30 seconds recovery at 200 W, repeated 5 to 10 times per set, with 3–4 sets total.
• If 600 W is too much, I adjust. Some triathletes don’t believe they can do it, but they often surprise themselves.
• I focus more on intensity. But if an athlete struggles with long sessions — like a 5–6 hour ride — that’s a sign we need to work on volume too.
• Some athletes handle long trail runs easily. For them, we focus more on intensity.

Typical training hours

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• Around 30 hours.
  • Swimming: 7–8 hours
  • Cycling: 15–20 hours
  • Running: 7–8 hours
• That includes training camps, of course.

General Questions

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How do you keep learning and improving your craft as a coach?

I read a lot. I also talk to other coaches. And I stay in touch with researchers. Some are colleagues from the past — I studied with them or worked with them in sports medicine. They’re still doing academic work, and I can ask them questions. But I also learn a lot from my athletes. I try something, get feedback, and adjust. Coaching is always evolving.

What is something that you're focusing on at the moment or trying to learn about at the moment?

That's the field metabolic testing. So I'm doing some testing with the SpiroFit and the VO2 Master. Sometimes people look at me — “What are you doing?” — and then I run around my house or in the forest with a mask on just to see how it works. Is it good? Is it okay? Can I already use it for my athletes. And the other thing is the critical power models, which I'm using.

What is the most influential book you've read?

I’m not a big book reader, but there’s one book that influenced me a lot — Training and Racing with a Power Meter by Hunter Allen and Andrew Coggan. That was the beginning for me. I had a power meter around 2010 and wanted to know how it worked and how to train with it. That book started my whole approach to training and coaching with power. In 2013, I even organized a power clinic in the Netherlands and invited Hunter Allen to my home. We’ve had a close relationship since then, and I’ve learned a lot from him.

What is the best advice you’ve ever received?

Most people know what they’re good at — but it’s more important to know your weaknesses. Sometimes, it’s better to trust other people who are better than you in certain areas. That’s something I’ve taken from both medicine and coaching. As a doctor, you can’t know everything about every patient or problem. It’s better to listen to someone with deep knowledge in one area — they might have a better solution than you.

LINKS AND RESOURCES:

• Guido's website and Instagram
• The Extended Critical Power Model
• Aerobic Energy Turnover and Exercise Economy Profile During Race Simulation in a World-Record-Breaking Male Full-Distance Triathlete - Christensen 2024