Micro-interval training sessions, like 30/30 intervals, have become very popular. And I wrote about the effectiveness of 30/30 intervals here. However, I need to get rid of something: Doing 30/30 intervals might be a complete waste of time for yourself if you fall into a certain group of athletes – think training response.
Now, that might feel controversial to you because I told you to do 30/30 intervals in the first place. Certainly, things are not the way they seem, so please let me explain myself.
The Purpose of VO2max Training
When you just think about the word VO2max, the requirement for this type of work is obvious: If you want to improve your VO2max, you must go max.
Or at least close to max.
Eventually, you want to be out and about an effort that elicits >90% of your maximum oxygen uptake for more than 10 minutes total. So, you end up at VO2max for only part of the workout. Most of the research behind this specific time-at-intensity (10 minutes at 90% of VO2max) was done by French researcher Veronique Billat.
These 10 minutes are the basis for adaptations to happen. Thereby, you will improve your heart’s stroke volume, improving your cardiac output. But the benefits don’t end there.
If done right, VO2max intervals improve your plasma volume, muscle capillarization, and mitochondrial density. Consequently, it improves oxygen delivery to and uptake by working muscles.
Now, a great way to trigger VO2max is micro intervals. However, the key for these to be effective might surprise you.
The Problem of 30/30 Microbursts
For long VO2max intervals (2min and longer) rest time doesn’t affect work intensity that much (at least, when recovery time is not less than 2min or more).
Contrarily, for micro intervals, the work-rest ratio determines the success of the workout. At least for some cyclists.
Or to put it in Dr. Stephen Seiler’s words:
“With short interval prescriptions, physiological responses are highly sensitive to rest duration and work-rest ratio!”Dr. Stephen Seiler
Pause for a moment and read that quote again.
The 1:1 work-rest ratio during the 30/30 intervals might be too long when you reach a certain level of performance. Thus, there’s a big difference in heart rate response and you’re just cruising around the threshold from a metabolic point of view and no gains in VO2max.
The High-Intensity Dilemma
But the dilemma doesn’t stop with heart rate response: The longer break makes higher power outputs possible and likely. However, higher power seems to be bad in this case. Yes, you’ve read that right, higher power numbers are not always better.
Especially, when we want to increase our mitochondrial content. One study looked at the activation of PGC-1α during different exercise intensities. PGC-1α is a critical gatekeeper or regulator for mitochondrial biogenesis.
The exercise protocol was as follows: Subjects did 60/60s either at 73% of Peak Power Output (max aerobic power), 100% PPO, or 133% PPO, with total work (kJ) being the same. Yet, we should take the study with a grain of salt because the rest period was done at zero watts. I mean, no one does that with 30/30s in the field. Additionally, 60 seconds of rest is a long time for micro intervals. You should ride the rest period at least at an endurance pace of around 50-65% of your FTP.
Anyways, back to the study. To get accurate results researchers took muscle biopsies from the subjects.
What they found was that greater activation of PGC-1α results from the 100% MAP. But researchers didn’t stop there. They controlled for differences in muscle activation by using EMG (Electromyography) to measure electric muscle activation. In this case, researchers found that the relative activation was similar for sub-max and max power conditions, but poorer in the supramax condition, as you can see in the image below.
So, if you push power too high there’s an inhibition of PGC-1α response in supramax power. You push hard and feel good but you’re only improving your anaerobic capacity. Hence, your endurance gets worse. After all, we want to avoid that condition by all means.
And that’s interesting when we talk about sprint interval training like 30 seconds all-out. If you want to get faster, you better leave them alone.
How to Create Effective Micro Intervals
To improve our maximum aerobic capacity as cyclists, we need to manipulate that rest period.
So, you could either do 30/15 or 40/20 intervals. And what happens with a 2:1 work-rest ratio is you turn those short intervals into one long interval from a metabolic standpoint. As a result, your heart rate hovers around maximum and even your VO2max reaches close to max.
I use the 30/15s for example, with many of my athletes successfully. Surprisingly, short intervals are mentally easier compared to long intervals for some athletes because you just need to think from 30 seconds to the next. On the other hand, if you increase the off part to at least 50% of interval intensity, you also might counteract that effect. Billat had success when doing this with 30/30 intervals on runners.
Instead of „cruising“ around your threshold and working your anaerobic system, manipulate the rest to make the gains you want.
However, the study cited above found that the right intensity during micro intervals is important. Now, how do you find your maximum aerobic power?
Finding the Right Intensity
Finding the right intensity means two-fold: You want to find the right intensity to do the micro intervals at, and you want to do the right amount of interval sessions per week.
So, to find your maximum aerobic power you have different options. Firstly, you can obtain the data from a lab test. Secondly, you can get the data from a power test in the field. According to Norwegian Researcher Bent Rønnestad doing a 5-6 minute all-out test will get you close to your maximum aerobic power.
Now according to current research, the right amount of high-intensity interval sessions is two per week.
Therefore, stick to one or two VO2max sessions per week during a block of 4-6 weeks. The rest of the training week is just zone 2 endurance training. In the end, if you make the easy days easy, you can make the hard days hard.
Change Your Intervals Without Changing Your Entire Intervals
Alright, let’s review what we discovered so far and figure out some practical takeaways.
- 30/15 and 40/20 intervals work both well, but you need time at least 8-10min per set with 3-5min of rest
- Start with 2x blocks like 2x11x30/15 and build up to 3x13x30/15
- Do some work during 15s/20s off, around 50-65% of your FTP
- Overload the first 5-10sec to accelerate your bike or your run
- 30/30 intervals tend to bring you up to threshold, but not higher. However, you can increase work during the rest period to 50% or more of interval power to counteract that effect and go up to VO2max
- Don’t go too hard – ride at your MAP or slightly above, and do more work in the off part instead
This brings us to the punchline of this article…
The counterintuitive insight from this research is that the best way to improve your endurance and VO2max isn’t always higher power. Instead, it’s best to look deeper and change small things with a big effect.
In the long run, the way to become a faster cyclist is to focus on the right things for the right amount of time.
Ready to Improve Your VO2max?
If you enjoyed this and you want to see training density in practice then try my structured training plans. I base my plans on research and my experience as an athlete and coach. The results? Simple yet effective plans that hold you accountable for long-term progress. Start down below with my base, polarized, or block periodization plans. Enjoy!
- The Block Periodization Plan, 4 Weeks
- The Block Periodization Plan 2.0, 12 Weeks
- The Polarized Training Plan, 10 Hours (8 Weeks)
- Base Plan, 6 Hours + Strength Training (12 Weeks)
- Base Plan, 10 Hours + Strength Training (12 Weeks)
- Base Plan, 15 Hours + Strength Training (12 Weeks)
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Studies Used in this Article
- Training for intense exercise performance: high-intensity or high-volume training?
- What is best practice for training intensity and duration distribution in endurance athletes?
- Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training
- Block periodization of high-intensity aerobic intervals provides superior training effects in trained cyclists
- Tabata training: one of the most energetically effective high-intensity intermittent training methods
- The Scientific Basis for High-Intensity Interval Training
- Is there an Optimal Training Intensity for Enhancing the Maximal Oxygen Uptake of Distance Runners?
- Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and ˙VO2max
- Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration
- Dissociation of increases in PGC-1α its regulators from exercise intensity and muscle activation NBC following acute exercise
- Physiological responses to interval training sessions at velocities associated with VO2max