Your High Intensity Cardio Prescription

In last week’s blog post I discussed the role of high intensity cardio and why I think high intensity cardio is important but not as important as low intensity cardio. I can’t stress enough that low intensity cardio should be prioritized first over high intensity cardio. Having a solid aerobic base from low intensity cardio allows you to get the most out of your high intensity cardio.

High intensity cardio is “the icing on the cake” of your exercise programing!

If you are at the point where you are ready to start incorporating high intensity cardio into your exercise programming this blog post will explain exactly how to do that!

Just like when we were talking about how to implement low intensity cardio, we have three variables we can manipulate when it comes to high intensity cardio, intensity, frequency and duration. In addition because high intensity cardio is typically done over the course of 2 or more rounds there is a fourth variable we will talk about and that is rest duration.

Let’s start with intensity, because when it comes to how hard to work, the answer is pretty simple.

Intensity

AS HARD AS POSSIBLE WITHOUT HURTING YOURSELF!

I don’t mean kind of hard, I mean truly as hard as you can go.

While saying “work as hard as you can” is an easy thing to say, it does help to have some kind of metric to quantify if you are truly working hard.

As with low intensity cardio, I think heart rate is the most accessible metric to most people as to how hard they are working during high intensity cardio as well. That said we need to figure out what heart rate or heart rate range you should target to achieve during your high intensity cardio.

A VO2 Max test is the best way to figure out this answer. The heart rate zone you would target if you have performed a VO2 Max test would be zone 5. This usually occurs from the last push upwards in breathing frequency up to the max heart rate seen during the test. Here is an example of my zone 5 from my VO2 Max test.

Obviously not everyone has done a VO2 Max test nor should they, so what does everyone else do if they don’t know what their zone 5 heart rate is?

The next best proxy would be to do some kind of all out test and look at what your max heart rate is during that test. For example, you could hop on a rower and do an all out 2k row or you could do what’s called a Cooper Run Test. Do the test and take whatever the max heart rate is during that test and subtract 5-10 beats from it. I would target that heart rate zone for your high intensity cardio. For example, if you did a 2k row and you hit 180 BPM during the test, I would target a zone of 170-180 for your high intensity cardio exercise.

Another option is to use a rating of perceived exertion (RPE) scale. I like to use a 1-10 scale like this

I tell clients I want you at a 9-10 on the scale.

You can also combine the RPE scale with heart rate as well. In other words, the first time you do your high intensity exercise, work at that 9-10 effort, and pay attention to your heart rate. Find the max heart rate you hit during the workout and take 5-10 beats off it. Now you have a heart rate zone to work with going forward.

Duration

This brings us to the topic of duration, how long should high intensity cardio workouts last?

In general high intensity workouts are going to be relatively short. There is no set duration to prescribe because this is going to depend on the person.

There is evidence that HIIT protocols that last about 30 seconds of work for a total of about 5 minutes can elicit changes in VO2 Max in as little as 4 weeks [1]. What would that look like in practice?

You could do two 30 seconds all out efforts 2 times a day once in the morning and once in the evening for 5 out of 7 days a week and meet that requirement.

See where the time benefits of high intensity cardio come in?

Want a more extreme example of how short of a work interval you can do and still see changes?

Here you go..

In another study[2] participants exerted maximal effort on a bike for 4 seconds for 30 rounds with 10-15 seconds rest between each round. They did this 3 times a week for 8 weeks. That comes out to 2 minutes of work per session for a total of 6 minutes a week. After 8 weeks participants saw a 13.2% increase in VO2 Max and a 7.6% increase in blood volume. Not bad for 6 minutes of work a week.

Perhaps the most famous high intensity cardio protocol is the Tabata Protocol. The Tabata Protocol is very specific, you do 20 seconds of work followed by 10 seconds of rest at an intensity that makes you quit by round 7 or 8. The original study[3] done using the Tabata Protocol showed an average increase of 7 ml.kg-1.min-1 in participants VO2 Max executing this protocol 5 days a week for 6 weeks If you add the total time participants spent exercising per week it comes out to a maximum of 4 minutes a day or 20 minutes per week.

OK so what is the deal with duration? Should we stick with short bursts of all out work or longer duration of 30s or more?

Unfortunately I can’t give you a good answer because there isn’t one ideal protocol. What I can offer instead are some guidelines on how to find the right dose for YOU!

When I program high intensity cardio, I always give my clients specific instructions on when to bail on the workout. Yup I give them an out! The reason is because high intensity exercise is all about quality rather than quantity….the benefits come by reaching your maximal effort, and if you can no longer do that, you are no longer getting the benefits.

For example, workouts I program might include a qualification that if they can no longer reach a certain wattage for a given duration, the workout is over….whether they hit the prescribed number of rounds or not!

With that guideline in place I am not sure it matters what high intensity protocol you select. If you pick 4 second all out efforts like they did in the study above it might take 30 or more rounds before your performance drops off. If you pick a 2 minute all out effort it might just take 1 round before you call it quits.

Here is a practical example using this guideline. Say you were my client and I said I want you to do 8 rounds of 30 second intervals on the bike while not dropping below 200 watts. If on round 5 you were only able to average 175 watts during the 30 seconds and on round 6 you only averaged 150 watts, I would want you to call it quits after round 6 even though I told you to do 8. This is because you are not able to maintain the maximal effort I wanted you to hit during the interval.

It helps to have some kind of metric like watts, speed, or distance covered in order to know when to stop the workout. When you start to not be able to maintain the goal, wattage, speed, or distance the workout is done.

Rest Period

I mentioned above that we have an additional variable at play when it comes to high intensity cardio. The additional variable is the rest period.

Some protocols, like Tabata, have very specific rest periods, others do not. Again, I don’t believe there is one answer to what the optimal rest period is. In my opinion, the best rest period for most people is one that allows you to fully recover so you can go as hard as possible in the next round. The goal of high intensity cardio is not to fatigue you quickly, it’s to go all out at max effort. If that means you need to rest for 3 minutes between rounds, rest for 3 minutes.

There are a couple of indicators you can use to determine if you have rested long enough and are ready to go again. The best indicator is your breath. Once you can breath through your nose again, you are probably ready to start the next round. If you have a heart rate monitor you can also correlate that with a heart rate. In other words, once you can breathe through your nose again take a look at what your heart rate is. Now you can use that heart rate to know when you can begin your next round.

Frequency

Next is frequency…how many times in a given week should you do high intensity cardio?

Again I can’t give one answer for everyone.

Many of the studies that look at high intensity exercise have participants solely perform high intensity exercise and nothing else. However, as I discussed above there are more important forms of exercise that I think should take priority in your exercise programming.

For the average person I suggest strength training at least 2 days a week, with 2 days of low intensity cardio….so how many days do you have left for high intensity cardio? For the average person that’s probably 1 day at most, because remember you need to recover from the high intensity exercise as well before you do it again.

Now again, depending on how stressful each session is you may be able to do it more than once a week. If you need to do 30 rounds of 4 second intervals you might choose to split that up across multiple days in the week rather than doing it all in one session. In other words, there is some flexibility here to make it work for YOU.

You might also be thinking that since you are “only” doing one day of high intensity cardio a week, it’s probably best to try to avoid skipping it.

Actually, when I need to sacrifice a day of exercise in my clients programming, the high intensity day is the first day I get rid of!

Why?

It has to do with why we are switching their training to begin with. In almost all cases I am adjusting their training due to a life stress, so why would I add additional stress by keeping the high intensity day and taking away something that might be lower stress for them? It makes no sense. For example, if they had to skip a day of exercise because their kid was up all night sick and they didn’t sleep all night, why would I keep a high intensity exercise session in their training if what they needed was something more rejuvenating?

If they go a week without doing a high intensity cardio session, it won’t be the end of the world!

Modality

You may also be wondering what modality to use for your high intensity cardio training….do you run, bike, row, swim, jump rope?

Again the modality does not matter either, anything will work, it’s all about getting your heart rate up!

There are certain considerations to keep in mind though.

Running can be hard on people due to the impact forces plus the potential for injury. In addition if you have strength or hypertrophy goals, running can impact your legs which may impact your resistance training. So for that reason, running at a high intensity should be done with some forethought.

If you are not training specifically for some event that would require you to run you might want to consider another modality.

If you just enjoy running but don’t enjoy the way the high impact feels you might want to consider doing uphill sprints. Due to the incline it results in less impact on the body, so it might make your joints feel better.

I also personally tend to push clients towards a modality that is low impact and has a low chance of injury. A bike or a rower are great options.

So to summarize how to implement high intensity cardio, here are the basic guidelines

  • During the work period you should be going all out, a 9-10 RPE, close to your max heart rate (use zone 5 if you know your heart rate zones)
  • Pick a duration to work, start small to begin with, the smaller the duration the more rounds you may have to do, the longer the duration the less rounds you will do
  • Rest period should allow you to fully recover. Once you can breath completely through your nose you are probably ready to start the next round. You can correlate this to a heart rate and use that heart rate to know when to start the next round
  • Repeat for as many rounds as you can until you can no longer sustain the effort for your set duration. If your speed, wattage, or distance starts to drop off a cliff, you are done!
  • Most people will only need to do high intensity cardio once a week

Below is an example of a high intensity cardio session I did using the above guidelines. This was more of an advanced protocol but it serves as a good example. In these sessions I did 5 rounds of 500m rows at my 2000m PR pace of 1:49 min/500m. I have been doing this workout once a week for the past 6 weeks.

The light blue secontion is my warmup, the reddish section is the 5 500m intervals and the dark blue section is the cooldown.

The dark green line is my heart rate, the light green line is the oxygen consumption at my thigh muscle, and the pink line is my breathing rate.

In this workout my goal was to maintain my 2000m PR pace for each 500m interval. At the point I could no longer maintain that pace I called it quit, that was round 5. My rest between each round was dictated by my breathing, heart rate, and because I had access to it, muscle oxygen at my thigh. I could usually return to nasal breathing at a heart rate of 83 BPM. That happened to correlate with an oxygen saturation at my thigh of around 60%. Once all things lined up I began the next round. Excluding the warmup and cooldown the session took about 15 minutes.

I hope this blog post gave you a good idea of how to best incorporate high intensity cardio into your exercise routine. If you have any questions, or need additional help feel free to leave a comment below!

At this point in my cardio exercise series we have covered a lot. For most people this series of blog posts provides all the information you need to properly incorporate cardio into your exercise routine and reap all its benefits! However there is one more piece to the cardio story we have not covered. I have talked about low intensity cardio, and high intensity cardio, but what about everything in between? That type of cardio often gets a bad wrap, however there are some use cases for cardio that are submaximal but not super easy. To find out when it is useful, sign up for my newsletter using the form below and I will send you an email once the next blog post is available!

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  1. (2019, January 29). Effects of different protocols of high intensity interval training for …. Retrieved April 18, 2022, from https://www.jsams.org/article/S1440-2440(18)30919-8/fulltext
  2. (n.d.). Four-Second Power Cycling Training Increases Maximal Anaerobic …. Retrieved April 20, 2022, from https://pubmed.ncbi.nlm.nih.gov/34310498/
  3. (n.d.). Effects of moderate-intensity endurance and high-intensity … – PubMed. Retrieved April 22, 2022, from https://pubmed.ncbi.nlm.nih.gov/8897392/

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