Designing interval training: 10 things you have to know | EP#139

Do you know how to deliberately structure your interval workouts to achieve specific physiological outcomes and maximise the benefits of the hard work you put in? If not, it's time to get started, and this episode will be your guide.

• The importance of time at VO2max and how much of it do you need?
• Using long intervals to the best effect and optimising their structure. 
• Using short intervals to the best effect and optimising their structure.
• How to manipulate interval duration, modality and intensity to achieve a desired workout nature. 
• How to manipulate recovery interval duration, modality and intensity to achieve a desired workout nature

4:00 -

• Paul Laursen and Martin Bucheit wrote a research review a few years ago on high intensity interval training.
  • High Intensity Interval Training - Solutions to the programming puzzle.
  • Part 1 is called "Cardiopulmonary emphasis"
  • Part 2 is called "Anaerobic energy, neuromuscular load and practical applications". 
• They're now going to turn that into a book. 
• I'll be discussing these reviews in this podcast as I've learnt a lot through reading them and experimenting. 
• This episode is only about part 1 of the review - the cardiopulmonary emphasis.
  • How can you get as much air as possible into your lungs. 
  • Then how can you extract as much oxygen as possible from that air into your bloodstream. 
  • Then how can you get as much of that oxygen delivered to your working muscles as possible. 
• This is the definition of VO2max - it's the maximum volume, uptake and utilisation of oxygen by the muscles.
• This review also only deals with high intensity intervals that are performed above the anaerobic/lactate threshold. 
  • It's close to, or above your VO2max intensity. 
• Improving your VO2max is the main goal here.
  • Think of fitness as a continuous thread, from short durations to long durations.
  • For short durations you can hold a high intensity, but for long durations the intensity drops.
  • This is called the power-duration curve, and is very commonly used in cycling (e.g. using the WKO4 software).
  • If you can bring your VO2max intensity up, it pulls on the continuous string and it brings up the sustainable intensity for the longer durations as well as the shorter VO2max-intensities. 
• For example, say your lactate threshold is roughly 85% of your VO2max, which is a common assumption. 
  • If you increase your VO2max by 3%, your lactate threshold won't necessarily improve by a full 3% but it will still improve. 
• This is why high-intensity VO2max-intervals are so effective. 
• They are the tide that raises all boats - focusing on high intensity intervals doesn't mean your endurance at lower intensities won't improve. 
• In the next few sections I will review some basic concepts that Paul discussed in the interview we did together. 

10:15 -

• Your interval workout can target one, or several of the following:
• Cardiovascular = VO2max.
  
  • Increasing your oxygen uptake capability and oxygen utilisation by the muscles. 
• Metabolic = anaerobic gycolysis.
  • When working at or above VO2max, carbs are anaerobically turned into ATP, which is the basic fuel source of all the cells in the body. 
  • This is a metabolic adaptation because the muscles stores glycogen which are then used to make ATP, without oxygen. 
• Neuromuscular/musculoskeletal = neuromuscular system. 
  • Your nervous system sends signals to your muscles to contract.
  • You also have musculoskeletal strain. 

12:40 -

• Long intervals: longer than 1 minute and done at an intensity that is above 90% of your vVO2max or pVO2max (speed or power at VO2max). 
• Short intervals: shorter than 1 minute usually done at vVO2max or higher. 
• Repeated sprint training: short sprints with short recovery between them. 
  • Not really relevant for triathletes, often used by team sports players. 
• Sprint interval training: all out sprints of 30 seconds, with long recovery (2-4 minutes). 
  • Again not as relevant for triathletes, at least not for improving VO2max.

13:45 - 

• The primary goal of an interval session is to spend a prolonged time at your VO2max intensity. You want to maximise your T@VO2max.
  • This doesn't mean that your cardiovascular system needs to be at 100% of VO2max to gain adaptatons, but it needs to be above 90% of it's oxygen utilisation and uptake capacity. 
• You want to do this while controlling for the level of anaerobic engagement.
  • The metabolic adaptations are anaerobic in nature. 
  • You also want to control for neuromuscular load and musculoskeletal strain. 
• This episode will discuss how to accumulate time at VO2max (T@VO2max) optimally.
  • Although there's no formula for how to do this, we have a lot of indicative studies that show roughly what you can do. 
• I will use running a lot as an example but this works just as well with cycling. 
• I will also talk about vVO2max which is your velocity at VO2max.
  • This is your pace when at VO2max. 
• You need to establish your vVO2max which can be done in several ways:
  • Lab tests, which is good but there are caveats about running on a treadmill compared to outdoors. 
    • It's not always a direct translation. 
    • Also if the stage durations in an incremental lab test are too short, or the step increases on the treadmill speed are too high, this can inflate your vVO2max. 
  • I would recommend using a recent race result or time trial, and plug the values into the McMillanRunning.com calculator. 
    • This will give you your estimated threshold pace and your VO2max pace. 
  • You can also do a five minute time trial.
    • The time to exhaustion at the speed of VO2max is in the 4-8 minute range. 
    • If you do a 5 minute time trial you can use the pace you hold as an estimate of your vVO2max. 
      • This has been shown in studies to closely correlate with lab test results. 

18:20 - 

• For long intervals (1-6 minutes duration), they will be done at 90-105% of vVO2max. 
• For short intervals (1 minute or less), they will be done at 95-120% of vVO2max. 
  • You may well have been going into speeds that are 130-140% vVO2max.
• When you design your workouts:
  • Base them on speed or power, both work well. 
  • Personally, I use speed and/or power on the run, and power on the bike. 
  • Heart rate is not a good measure as the lag is so long so it won't be effective.
• If you can't use speed or power, use your Rating of Perceived Exertion (RPE).
  • This allows you to self-regulate but it requires good self-regulation. 
  • For example, if your workout was 10x400, you'd try and hit the pace that is the maximum you can sustain for all 10 intervals. 
    • Ideally you want to do your last 2 intervals a little faster than the first.
• RPE is essential for hill repeats on the run for those not using power, because you cannot rely on pace. 

Refer to Figures 6 and 8 of the review article for source material. 

21:02 - 

• Short versus long intervals when it comes to attaining time at VO2max has only been studied and compared in a couple of studies: 
  • One example compared long intervals (2 min work/2min rest) to short intervals (30s hard/30s easy - active recovery). 
  • The study showed that there was significantly more time spent at VO2max in the long intervals.
  • However when you change the short interval structure to 60s work/30s rest, then the "time at VO2max effectiveness" was higher than long intervals.  
    • Time at VO2max effectiveness is percentage of time at VO2max as a percentage of the entire interval workout. 
• These studies suggest that long intervals can be more effective than short intervals to accumulate absolute T@VO2max. 
• Short intervals with work/rest ratio significantly greater than one can also be very effective, however. In particular when you consider how relatively short the entire workout needs to be to accumulate a lot of time at VO2max.  

23:11 - 

• Regarding long intervals, the recommendation is to have at least 2 minutes duration.
• Based on knowledge of VO2 kinetics, we know that when you repeat intervals it takes 1min 20s-2min 20s for you to reach VO2max intensity when working close to vVO2max. 
• In your first interval, you probably won't reach VO2max max at all unless it's longer than 3 minutes. 
• There have been experimental studies that have demonstrated this. 
• They have compared 2min work/2 min rest intervals with 1 min work/1 min rest intervals. 
  • They found the runners reached VO2max in the 2 minute intervals, but didn't at all during the session with 1 min intervals.
  • This study has since been repeated and the same results were found. 
• They also showed that extending the intervals to 4 or 6 minutes did not improve the peak-VO2 values. 
  • The percentage of VO2max that was reached during 2 minute intervals was 92%. 
  • During 4 min intervals it was 93% and during 6 min intervals it was 92%.
  • This is probably because the intensity was lowered when the intervals got longer. 
• These studies suggest that 2-3 minute intervals is a sweet spot.
• Ideally they need to be at least 2 minutes or you likely won't reach VO2max at all, unless you make your rest intervals significantly shorter. 

25:57 - 

• You want to maximise your work capacity for subsequent intervals, while maintaining a VO2 that is elevated from baseline so you can more easily accumulate time at VO2max in subsequent intervals. 
• It's easy to assume that active recovery would be better because you keep your VO2 at a higher level so it'll be easy to reach VO2max in later intervals. 
• However, it has also been shown that this can potentially significantly decrease total work capacity.
  • I.e. how many intervals you can do at the required intensity. 
• It can also trigger the engagement of the anaerobic system during the following intervals. 
• In the context of long intervals, it is recommended to use passive recovery when the rest intervals are less than 2-3 min duration. 
• If you chose active recovery, it's recommended to use 3-4 mins at sub-maximal intensity. 
• Personally I think suggesting 2-3 mins for recovery depends on what the session looks like. 
  • There is a chart in the review article comparing different sessions and time accumulated at VO2max for each. See the table under "Example Interval Workouts and T@VO2max" to review T@VO2max and effectiveness of some example workouts. 
  • The best session in this review is 5x3 min at 90% of vVO2max with 90 second passive recovery.
    • They accumulated almost 10 minutes at VO2max, with an effectiveness of 43%

29:09 - 

• Research is limited in this area. 
• Based on what we do know, the accumulated high intensity (i.e. more than 90% of vVO2max or pVO2max) during a typical session has been reported as anything from 12-30 minutes. 
• Example sessions could be 6x2 minutes, 6x600m, 5x3 minutes, 5x800-1000m, 4x4 min, 6x6 min, 4x6 min, or 6x5 min. 
  • This gives you an idea of the total duration. 
• 6x2 mins (12 min total work) seems low. 
  • In most examples the effective time at VO2max seems to be at most 50% or lower. In other words, with a 6 x 2 minute workout you could expect to accumulate maybe 6 minutes at VO2max (although this of course depends on rest interval duration and intensity). 
• I would recommend at least 15 minutes total work duration - if you can get 50% effectiveness you'd already have 7.5 minutes at VO2max. 
  • Many workouts produce 0 minutes at VO2max, often unknowingly, so 7.5 minutes would be great. 
• If you're an advanced athlete, you need to have longer time at intensity, because you need to overload the body to elicit adaptation. 
  • In  other words, you may need to accumulate more time at VO2max to improve it than a beginner athlete. 
  • You may aim for the 25-30 min total work duration workouts to accumulate enough time at intensity. 

32:01 - 

• A study has shown that comparing hill running (6x500m which took 1:40), with a track session (6x600m which took 1:40).
  • Both sessions accumulated some time at VO2max.
  • However the time at VO2max compared to exercise time was clearly higher in the track workout - 44% of workout time spent at VO2max compared to 27% during hill session. 
  • The reason for this is unclear, and the intervals in the hill workouts may not have been long enough to observe the slow VO2max component found in uphill running. 
• It has made me think that you want to prioritise VO2max sessions to flat running.
• Unless you're injury prone, in which case hills may be better. 

33:42 - 

• Now we're getting into short intervals, which are up to 1 minute duration. 
• You should aim for an intensity that is 100-120% of vVO2max.
  • This is a higher intensity than the long intervals. 
  • However many athletes when they do this workout go way beyond 120%.
  • This often means they can't accumulate enough intervals to spend a lot of time at VO2max. 
• Several studies have compared increasing intensity of short intervals from 100-120% of VO2max. 
  • They have found that for athletes that are older or less trained, you will want a higher intensity as VO2 kinetics may be slower. 
  • For higher level athletes, you can keep it at closer to 100% rather than 120%, but the number of intervals will be higher. 
• When you go above 120% of vVO2max in these intervals, studies have shown that the total exercise capacity is impaired.
  • This means the total time at VO2max is typically lower than going 120% or below. 
• The review authors suggest if you split your high intensity workouts into several sets of these intervals it may be effective. 
• As a general recommendation, I would steer you to stay in 100-120% vVO2max range. 

36:17 - 

• There are a few things here that we don't know because they haven't been studied.
  • E.g. How does a 30/30 workout (30s hard, 30s active recovery) compare to a similar total duration workout using 60s work/60s active recovery. 
• What we do know, is when you increase the work duration to rest ratio, going above the 1:1 ratio, the time at VO2max increases significantly.
  • For example, one study investigated in well trained triathletes 30s work/30s active recovery, compared to 60s work/30s active recovery.
  • The total time at VO2max was 9 minutes in the 60/30 workout, and 1.5 minutes in the 30/30 workout. 
  • This shows how important increasing the work to rest ratio in short intervals can be. 
• Older and less well-trained athletes that have slower VO2 kinetics are recommended to use longer work intervals (e.g. 60/60 instead of 30/30). 
• More well trained athletes may need to adapt the total amount of work that they do. 
• For example: a less well trained athlete might do 15 x 60s hard/60s easy, which gives a total of 15 minutes at a hard intensity. 
• A well trained athlete might do 50 x 30s hard/30s easy, which gives a total of 25 minutes at a hard intensity. 
  • This is why you need to know your vVO2max and adjust your intensity accordingly to ensure you can maintain the intensity for all intervals. 

39:07

• A study has shown that during a 30 seconds on/30 seconds off workout, when comparing recovery interval intensities of 50% vVO2max and 67% vVO2max to a baseline of passive recovery, "small" and "very large" time at VO2max improvements were seen, respectively. These same improvements were seen in the workout effectiveness.
  • However, increasing the recovery intensity further to 84% moderately reduced T@VO2max.
• It is recommended to keep recovery interval intensity at ~70% vVO2max.
• If your intervals are of very high intensity (e.g. 120% vVO2max) you may need to scale back the recovery intensity a little bit. 

41:12 - 

• Using different sets in interval workouts is common practice when designing sessions. 
  • By sets, I mean for example doing 3x3 mins at VO2max intensity, then doing an active rest for 5 minutes, then doing another 3x3 minutes. I.e. 2 x ( 3 x 3' / 3').
  • In total you do 6x3 mins but you have an additional active rest in between intervals 3 and 4.
• This has been consistently shown to reduce the total time at VO2max.
• However, there is a time and place for splitting workouts into sets.
  • For example, if you want to do a 30 sec on/30 sec off workout and you want to a total of 30 minutes for your main set (i.e. 30 repetitions). 
  • If you know this is likely to be challenging because of your fitness level, you may aim for 36 minutes but split it into 3 different sets - 3x12 minutes.
  • This would be 12 times 30/30, then 1-4 minutes active recovery, then another 12 times 30/30 etc. 
  • You want to achieve 36 minutes because you have to take into account that when you start a new set it'll take time for your VO2 kinetics to rev up again. 
  • If you don't increase the main work time, you will lose time at VO2max.

43:46 - 

• There should be a very short, or non-existant delay between your warmup and the start of your main work. 
  • Otherwise your time needed to reach VO2max will be longer. 
• Warmup intensity can be around 60-70% of your vVO2max or power at VO2max.
• Finish with some strides/builds/skipping ropes at the end of the warmup. 
• The warmup is important in this context. Just remember not to take a long break between it and starting the work. 

• Interval Training - Science and Application part 1 with Paul Laursen | EP#128
• Interval Training - Science and Application part 2 with Paul Laursen | EP#129
• High-Intensity Interval Training, Solutions to the Programming Puzzle : Part I: Cardiopulmonary Emphasis.
• High-Intensity Interval Training, Solutions to the Programming Puzzle : Part II: Anaerobic Energy, Neuromuscular Load and Practical Applications.
• Scientific Triathlon training camp in the Algarve, Portugal, 20-27 October 2018.
• McMillan Running Calculator

Connect with host Mikael Eriksson

Hi! I'm your host Mikael,

I am a full-time triathlon coach and an ambitious age-group triathlete. My goal is podium at the Finnish national championships within the next few years.

I first started the website Scientific Triathlon in autumn 2015 as a passion project to share my learnings with a larger triathlon audience. Later on, in early 2017 I started the podcast That Triathlon Show. 

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