Your Exercise Prescription For Cardio Exercise

Welcome to part 4 of my blog post series on cardio exercise!

Over the past 3 posts I have laid out the benefits, the changes to your body that cause these benefits to occur, and at what intensity you need to exercise to see the benefits you are after.

The question now becomes how much cardio exercise do we need to do to see the health benefits we are after, and how to best monitor the intensity of our workouts to make sure we are getting as much out of our exercise as possible?

The answers to these questions, in my opinion, are going to come down to where you are starting from.

For someone just starting out, the amount of cardio they need to do in order to see amazing benefits is going to be very small. On the other hand if you are an elite endurance athlete you have probably maxed out all the benefits you can possibly get and you can spend hours and hours doing cardio and see no improvement in your fitness or health.

This is the unfortunate truth about fitness, as your fitness improves and your body adapts you will have to put in more work and will get less back in return.

That may sound depressing, but it’s virtually true for all forms of exercise, once you max out your adaptations from a given stimulus all you can do is maintain it at that point. In order to get further adaptations you need to change the stimulus.

The good news is that most people will never get to the point where they have completely maxed out their cardio training. However this understanding that there is a ceiling will help frame why in this blog post I suggest you start slow and build from there and also why you incorporate an assessment into your exercise programming. The assessment will help identify plateaus in progress and dictate whether you need to incorporate more cardio exercise to see further progress.

With that said lets jump into the first topic for prescribing cardio exercise…finding the proper intensity!

Finding The Proper Intensity

If you recall from my previous post, aerobic exercise just means exercise at an intensity that allows you to continue to burn mostly fat for energy, it is low intensity in nature. We also discussed several ways to measure intensity to identify whether you are aerobic or not…

  1. We could look at oxygen consumption, both at the lung and at the muscle.
  2. We can look at lactate generation, as the more lactate present in the blood the more we are relying on anaerobic metabolism
  3. We can look at fat vs carb utilization. As long as we are burning more fat than carbs we are likely using aerobic metabolism primarily.
  4. We can look at our heart rate and find out at which heart rate we start to rely on anaerobic metabolism.

All of these are valid options, but they are not all practical. Looking at oxygen consumption and carb vs fat utilization requires expensive equipment and is not something the average person has access to, so those are out.

This leaves us with lactate and heart rate.

Measuring lactate is doable, in fact Dr. Peter Attia suggests this method to all his patients. In my opinion, measuring lactate is not the best option because it can’t be done in real time, you need extra equipment that again is relatively expensive, and it involves pricking your finger.

So that leaves us with heart rate, which is the method I use myself and with my clients. Even the best heart rate monitors[1] on the market are less than $100, and you can find ones much cheaper than that if you would like. When you combine your heart rate monitor and your phone, you have everything you need to measure the intensity you need to exercise at!

Besides being the most accessible method for measuring intensity, heart rate has another advantage in that it is impacted by other lifestyle factors. Sleep, stress, food, immune function…all of these can impact your heart rate. If everything is on point you might be able to do more work without increasing your heart rate as much. Conversely if one or more of those are off, you will have to lower your effort to keep your heart rate in check. Your heart rate can be a very good form of self regulation when it comes to exercise

Once you have your heart rate monitor the only question left is how do you know what heart rate range to target to make sure you are staying aerobic?

If you have had something like a VO2Max test done you can find your aerobic heart rate zone by looking at your fat and carb burn from the test. Your optimal aerobic heart rate zone is from the heart rate at which you burn the most amount of fat calories to the point where you start burning more carbs than fat, also known as your crossover point. Here is what that looks like from my VO2Max Test

The light green line at the top of the graph is my heart rate, the dark green line is my fat usage and the other light green line that intersects with the dark green line is my carb usage (sorry I don’t have control over the colors on the graph).

My peak fat utilization, aka my fat max, occurs at a heart rate of 103 BPM. The point at which carb usage overtakes my fat usage (showing I am more anaerobic than aerobic) occurs at 137 BPM. Therefore if I stay within that heart rate range I am predominantly aerobic and maximize the aerobic adaptations we are after. This heart rate range is also what is commonly referred to as “zone 2”. Training within this heart rate range is referred to as zone 2 training.

This is great if you have done a VO2Max test but most people haven’t and won’t so what do you do then?

The best option, and the option I use with all my clients, is to use what’s called the maximum aerobic function (MAF) formula. The formula is simple.

Maximum Aerobic Heart Rate = 180 – age

So if you want to know the maximum heart rate you can hit before you burn more carbs than fat and become predominantly anaerobic you subtract your age from 180, and the number you get is your maximum aerobic heart rate.

For example, if you are 40 years old, to stay predominantly aerobic during your workout you would want to try and stay at 140 BPM or below.

Is this number perfect?

No.

Is it a good enough approximation?

Yes!

And this brings me to another VERY important point. IF YOU GO OVER YOUR MAF HEART RATE IT DOESN’T MEAN YOU GOT NOTHING OUT OF YOUR WORKOUT!!!!

Let me repeat this again for those of you in the back….

IF YOU GO OVER YOUR MAF HEART RATE IT DOESN’T MEAN YOU GOT NOTHING OUT OF YOUR WORKOUT!!!!

You still got like 95% of the benefit if not more, it’s not the end of the world, this is not an exact science!!! DO NOT STRESS ABOUT IT!!!!

I am going to throw one final option at you with regards to finding the proper intensity for your aerobic training. If for whatever reason you do not want to buy or use a heart rate monitor there are two no cost ways to self regulate your training that will likely keep you in your aerobic training zone.

If you can breathe only through your nose or can hold a conversation while you are doing your cardio then you are most likely aerobic and not anaerobic. For nearly everyone staying true to either of these will keep them aerobic, however I know for myself I can breath through my nose and my heart rate can approach 150 BPM. Again, I have been training for a long time and built up that ability. In reality, most people who have built up to that point have likely bought a heart rate monitor by that point anyways. So if you are looking for a no cost option to make sure you are in your aerobic training zone try either of those.

Duration and Frequency

With the intensity piece in place the next question becomes how much cardio training should you do?

When it comes to exercise I always think in terms of the minimal effective dose.

I find it useful to ask “What is the least amount you can do to get the most benefit”?

For aerobic training, since intensity is pretty much fixed, the volume is your only lever to increase the adaptations you are after so it’s better to start lower than higher in this case. You don’t want to go all out from the beginning because you will have no room to make additional changes.

There are a number of opinions on the optimal amount of aerobic training you should do per week. In Dr. Peter Attia’s podcast on zone 2 training, his guest Iñigo San-Millán suggested that doing an hour-long session 3-4 times a week would be optimal. Dr. Andrew Huberman suggested that you shoot for 150-180 minutes per week of aerobic training which ends up being roughly the same in terms of total volume.

My opinion to answer the volume and frequency question depends on the person, where are you starting from and what are your goals?

If you are coming from the couch, going for a 10-20 minute walk a day is going to be plenty.

If you are a seasoned endurance athlete you might be able to do 1hr or more every day of the week.

For the average person I think working your way up to 1hr to 1.5hrs a week is a pretty reasonable goal and will get you many of the benefits. If you have endurance goals that number will clearly have to go up, but again for an average person just looking for the health benefits getting 1-1.5hrs a week should be fine and doable.

You can split this up however you would like. Maybe you do three 20 minute sessions a week or maybe you try to do it all in one session. Again if you are a beginner, start easy, 10 minutes 3 times a week for example and build from there.

Yes this is a lot less than what Dr. Attia and Dr. Huberman recommend but there is also something else that I want you doing that is going to contribute greatly to your cardio exercise…walking!

In addition to your formal cardio exercise, I prefer you also be walking 7-10 thousand steps per day and despite what you may believe this contributes greatly to your overall cardiovascular fitness! This amount of walking in addition to the formal cardio exercise you do should be plenty of stimulus for the average person to get the health benefits from cardio exercise.

What Is The Best Modality?

With intensity and duration nailed down, we now need to discuss what modality of cardio exercise you should use.

This question is hard to answer because nearly everything will work. You can run, cycle, swim, hike, row, cross country ski, snowshoe, ruck, get on the elliptical, it really doesn’t matter, just pick something you like!

It can even be a combination of multiple modalities, if you want to do 20 minutes of running, 20 minutes of biking, and 20 minutes on the rower across a week…awesome!

The one thing I would encourage you to consider is the eccentric nature of the exercise modality you choose. All this really means is you should be mindful of modalities that have high impact forces because you can get quite sore from them if you are not used to the impact forces.

For example running involves more load being placed on your leg every step you take, doing this over and over again can be acutely damaging to your leg muscles.

Does that mean it’s bad?

No!

It just means it might take time to adapt to those impact forces and you might be more sore than if you did a modality with less eccentric load like cycling or swimming.

Tracking Progress

For many people it’s important to track whether you are making progress with your cardio exercise. As I mentioned above, by tracking your progress and identifying whether you have reached a plateau you can determine when/if you need to add more volume to your cardio exercise routine.

If you don’t care, and are doing cardio because you love it, that is fine too, but if you want to make sure you are moving the needle in the right direction having some kind of assessment or metric you can use is helpful. It would be nice if we could track things like blood lipids, capillary density, oxygen exchange, mitochondria function etc in real time, but that is not practical, so we need another metric to use.

The assessment I like to use is what’s called the Maximum Aerobic Function Test or MAF Test. As you might have guessed, it is related to your MAF heart rate as we discussed above. This assessment is pretty straightforward. The protocol is as follows:

  1. Warmup – this is just 10 minutes to make sure your body is ready to perform the test
  2. Do your chosen form of cardio for a fixed time or distance while trying to maintain your heart rate as close to your MAF heart rate as possible without going over.
  3. Assess how much distance you covered or how quickly you were able to cover a fixed distance.

Let’s make this more concrete.

Say your chosen cardio modality is running. First pick a course you would like to run. This part is important because you want to make sure you pick a course that you can repeat over and over again. In other words, don’t pick something that is an hour away that you won’t be able to get to the next time you want to do the test. For running, the most ideal place is a track.

It is also important that you control for other variables that can affect heart rate as well. That means you want to try and standardize your food, fluid intake, sleep, stress, time of day….you need to replicate things as best as possible each time you do the test or else changes in heart rate could cause the results to be invalid.

Next pick a time/distance you would want to cover. For most runners I would say 30 minutes or 3 miles might be a good starting point.

Warmup for about 10 minutes. This could be a combination of dynamic movements and very easy jogging, just warmup like you would for any other run.

Next start the test. Run at or as close to your MAF heart rate as possible for the set distance or time.

Now assess. How far did you get or how much distance were you able to cover?

That’s it, done!

Now you have a baseline, you can repeat this test every month or so and see how you are progressing. If everything is going well and your body is getting all the adaptations we talked about you should see the distance you cover go up or be able to cover the fixed distance in less time…all while holding your heart rate constant!

If you would like a PDF outlining exactly how to perform a MAF Test I put one together for you that you can get for free here.

There are a couple other metrics you can assess as well, and due to technology these can be pretty accessible to most people.

As your heart becomes more efficient at moving blood around the body your resting heart rate should drop. Fancy devices like the Oura Ring and fitness watches will track this automatically for you. If you have one of those devices you can track that metric over time, it should lower.

If you just have a heart rate monitor you can use the app that came with it and measure your heart rate seated for 1 minute first thing in the morning. Find the lowest it gets during the 1 minute and track that number over time. Again, you should see it trend downward as your body adapts.

If you don’t have a heart rate monitor you can still potentially track your heart rate just using the camera on your phone. The app Instant Heart Rate does exactly that. Again track it for a minute seated first thing in the morning and record the number just like if you were using a heart rate monitor.

Finally you can also track changes in your blood pressure at home as well. There are plenty of automated at home blood pressure cuffs you can buy online that will measure and track your blood pressure. Again it should trend downwards over time as your body gets all the benefits from your training.

Of course you can also get blood work done as well. At the very least you should be getting a basic blood panel done once a year, but you could also go as frequently as every quarter. This will be a good way to track blood lipids as well.

Now you don’t need to use all of these assessments unless you want to. If I was to tell you to pick 1 I would say do the MAF Test or track your resting heart rate.

So with all that said let’s summarize everything you need to know with regards to adding cardio exercise to your routine.

  • In order to make sure you are challenging the physiological processes that are going to provide you the most bang for your buck when it comes to cardio exercise you want to exercise at an intensity that is mostly aerobic. The most practical way to do this for most people is by using a heart rate monitor and keeping your heart rate below 180 – age.
  • When it comes to how often and for how long you should be doing cardio exercise, my opinion is 1-1.5 hours per week assuming you are also getting around 7-10 thousand steps a day. You can split that time into multiple sessions or do it all in one bout if you like.
  • Choose a modality that you enjoy most! Running, cycling, swimming, rowing, hiking, paddle boarding, snowshoeing, cross country skiing, or even the elliptical are all acceptable. You can even combine multiple modalities if you would like!
  • Assess your progress using a MAF Test. If you want you can also track other metrics like resting heart rate, blood pressure, and changes via yearly blood work. Don’t forget about my free PDF on how to perform a MAF Test!

There is one final gap in our series on cardio exercise we need to cover and that is high intensity cardio training. The reason why I have avoided this topic so far is because I know people are more attracted to the harder workouts and will skip over the low intensity cardio exercise and head right to the stuff that leaves them feeling like death. Frankly if your low intensity cardio sucks, you are going to leave a lot on the table when it comes to the high intensity exercise so it’s better to become quite efficient at the low intensity stuff first.

However now that we have outlined everything you need to know about low intensity cardio exercise, we can move on to the high intensity topic. To be the first to know when the next blog post is available, be sure to sign up for my newsletter using the form below and I will send you an email once the next post is available!

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  1. (n.d.). Accuracy of wearable heart rate monitors in cardiac rehabilitation. Retrieved April 6, 2022, from https://pubmed.ncbi.nlm.nih.gov/31275816/

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