CARDIO: HIIT vs STEADY STATE vs ZONE 2

7/9/2017

Cardio used to be simple; the most complicated decision you had to make was which machine you preferred. But it turns out that cardio is not a one-size-fits-all approach and should be tailored to each individual and their goals.

Learn about the different kinds of cardio and how to include them in your training regime.

*All nutritional and fitness info must be discussed with your doctor before any changes to diet or exercise regime are implemented.

HIIT

HIIT cardio has become one of the main tools in the fat-loss-toolbox, and for good reason. HIIT, High-intensity Interval Training is basically any activity you can perform at a maximum level for a short period of time, followed by a short rest period.

In order to maximize the benefits of a HIIT workout, studies show that you need to reach between 80- 100% of your Heart Rate Max (HRM) during your high intensity intervals, then go down to around 50-60% during your rest periods.

A great example is sprinting; sprint at 90% of your MHR then rest, enabling your HR to go down to 50-60% of your MHR. The exact timing of each work/rest interval depends on your goals; a shorter work period (10-120 secs) targets your ATP and Anaerobic systems, perfect for sprinters, weight lifters, high intensity sport athletes, (hockey, baseball etc), whereas a longer work period (2mins+) will target your aerobic system, perfect for long distance runners and endurance athletes. Tabata-style HIIT workout would be 10 sec work, 20 sec rest, total work volume 4 mins, whereas a HIIT workout is generally longer: 30-60 sec work, 60-120 sec rest, 10-30 mins total. Either one, done properly, can help with fat loss and aerobic capacity goals.

So why is HIIT better for fat loss?

Burn more calories per minute: The often quoted “burn 9 times more fat with HIIT vs SS” has been basically de-bunked, and even the more accurate “burn 3 times more fat with HIIT” is not very compelling as studies show very little actual fat loss difference in terms of grams (yes, grams, not even pounds). However, due to the explosive nature of the workout, HIIT will definitely burn more calories per minute than SS. Your total calorie expenditure over the course of the workout might not actually be greater (due to the short nature of the workout), however, if you are looking for more bang-for-your-buck so to speak, HIIT wins over SS.
It also wins in the post workout calorie expenditure by increasing your Resting Metabolic Rate (RMR): Working at this level of intensity for a short period of time means that you will be using primarily the fast twitch fibres in your muscles. These fibres are anaerobic, meaning “without oxygen”; performing anaerobic exercise means that your muscles are working at a level where they cannot rely on oxygen for energy and need to tap into the glycogen stored in your muscles for energy. These fast twitch muscle fibres are great for fast, explosive movements, but they tire more easily. Their use of glycogen means that at some point the glycogen will be depleted, causing lactic acid buildup. The depletion of glycogen also means that it will need to be replenished in the muscles; when we consume our post-workout meal of protein and carbs the glycogen will be replenished and this process uses energy ie. burns calories. This increase in RMR after exercise means that our metabolism will essentially be increased for up to 24hrs following the workout. (Read more: Insulin: Friend or Foe? And: Our Metabolism: Can We Change It? and: Post-Workout Nutrition)
Increasing our muscle mass also helps to increase our RMR. Steady state (SS) typically uses more slow twitch fibres which cannot grow very large, however HIIT uses fast twitch fibres and the process of “breaking” them (by working them) and then “building them” (with nutrition and rest) causes them to grow. It is this use of the fast twitch muscle fibres that can actually help build our muscles as we do cardio.
Increase in Leptin: Leptin is a hormone release by our adipose tissue (fat cells) that inhibits appetite and increases energy expenditure. HIIT has been shown to increase leptin production, although only in the absence of insulin so to benefit from this increase in leptin, perform your HIIT in a fasted, or protein only state (read: Fasted Cardio: Pros and Cons).
Improved aerobic capacity: Exercising at the intense level of HIIT can actually increase your aerobic capacity. Studies show that HIIT can increase your VO2 max, the maximum rate at which your body can consume oxygen during exercise. Forcing your body to rapidly reach a high heart rate helps it grow stronger, and this stronger heart pumps oxygenated blood more efficiently to your muscles. This increased capacity will help you get better at not only HIIT, but endurance cardio also. To quote a meme I once read: “long distance running makes you better at long distance running; sprints make you better at everything”. It worked for me: read: Running: Is it for Eveyone?
Mobilise fat stores: As HIIT workouts are explosive and intense in nature they will use more of your fast twitch fibres, which means that you will be tapping into your glycogen stores (as seen above). Once your body has depleted its stores of glycogen it looks around for the next available source of energy: stored fat. In order to use this stored fat as energy it has to move the fatty acid from its storage in our fat cells into the blood stream. Once there it goes through a process called the Krebs cycle where the fatty acids are turned into acetyl sugars and released into the blood stream to be used as fuel.
Burn more fat during rest periods: as your body switches from high intensity intervals performed at an anaerobic level, to an at-rest aerobic level you will start burning more fat. Our body uses a higher percentage of fat while at rest so these rest periods are essential for fat burning.
HIIT is less adaptive: Yes, your body will adapt somewhat to HIIT and you will become better and more efficient at it. However the HIIT workouts are easy to adapt to your new level: shorter rest periods, different activities, increased workloads ie. incline, load etc. These adaptations will help keep your body in a state of energy (calorie) burning vs energy conservation.

HIIT downside:

HIIT is glycogen depleting, as is weight training. If your goal is to build muscle – as it should be, even while working on fat loss – then you will have to be careful how you schedule your HIIT workouts. Performing HIIT before lifting might impact your strength; fewer reps and/or sets and/or less weight is detrimental to building muscle. Your HIIT workouts also require you to rest in order to recover, so you will need to keep this in mind and not overdo it; more is not always better. If performing both in the same workout it is advised to do weight training, then HIIT, and not more than 2-3x per week.
HIIT and weight training both put a stress on your Central Nervous System (CNS) and if you are performing both you need to moderate how much HIIT you are doing so that it does not impact your strength training.
HIIT is hard! If you’re a beginner it might not be a good idea to try a workout that gets your muscles screaming and your lungs exploding (figuratively!) right away; working on SS cardio first can help build your aerobic capacity and VO2max enough to get you started, then you can work on HIIT to take you to the next level. As the saying goes, “you have to be fit to run, not run to get fit”.

Steady State

This is the traditional approach to cardio, get your heart rate up to a certain level and maintain it for 20-30 minutes, or more. In order to get cardiovascular benefits your HR should be between 60-85% of your maximum heart rate (MHR), depending on your fitness level.

The formula most often used to calculate your MHR is 230–your age (recently revised from 220-your age). You would then calculate your desired HR zone of 60-85% of this number.

For someone who is 30yrs old it would look like this: 230 - 30 = 200. 60% = 120   85% = 170.
Therefore, their heart rate should be between 120 and 170 bpm.

This formula however is based upon averages and not specific to you and your fitness level. The more fit you are, the higher your MHR can go. The most accurate method to determine your MHR is in a laboratory testing your oxygen output, and even that can be flawed.

Even if you determine what your goal HR should be based upon your MHR, you will need to use a HR monitor, which in my experience is not reliable (sometimes mine shows my HR going down to 30 bpm in the middle of cardio!).

Then there is the Lactate Threshold factor: this is the level of exercise intensity at which the blood concentration of lactic acid begins to increase exponentially, usually at around 85% of your MHR.   When exercising above the LT you will feel the lactic acid build up as muscle fatigue (increasing to muscle screaming!); while exercising at or below the LT any lactate produced by the muscles is removed by the body without it building up. As we’ve read in Cardio: Before or After? and Fast Twitch vs Slow Twitch Muscle Fibres, SS cardio generally recruits more of your slow twitch, aerobic muscle fibres; this means that they use oxygen for energy vs glycogen, thereby not producing much lactic acid. You can feel this when you do SS cardio for a long period; you feel physically tired – lungs, muscles – vs the muscles screaming in pain making you stop. This means that you are staying below the LT, and generally staying below 85% of your MHR and keeping you in the SS, aerobic zone.

Complicated, right? And is it necessary to keep all these factors in mind while performing SS cardio?

Going old-school, and using the Rate of Perceived Exertion (RPE), for most purposes is not only easier but generally as accurate as using a HR monitor to determine your level of activity.   While this method may be old, it is still used by trainers and athletes as a reliable training performance guide.

One of the first guides was the 20 point exertion scale designed by Borg in 1982, but even that was perceived as too complicated and it was revised to 10 points:

Using this guide you can determine your HR level:

Using a RPE of no more than 7 means that you are staying below the LT, keeping in the aerobic zone and using your slow twitch fibres.

So why is this a good thing? At a first glance HIIT seems to be superior; lose more fat while improving your aerobic capacity. What more do you want?

SS benefits:

Burn calories: while HIIT will burn more calories per minute than SS, and provides a greater post-workout metabolic increase (read: Metabolism: Can We Change It?), you can maintain SS for longer, potentially burning a greater number of calories. If you are just starting out on your fitness program, SS can be a great way to help you lose some initial body fat, as well as help get your muscles and cardiovascular system prepared to handle more as you progress.
Recovery: performing HIIT is more akin to weight lifting than SS; both are anaerobic activities using a lot of fast twitch muscle fibres and depleting your glycogen stores. While you may feel that you cannot get too much of a good thing (right?), you can, however, if it impedes your recovery. The recovery portion of training is just an important as the training portion, and without adequate recovery you will not see any results. SS however is aerobic, so it does not deplete your glycogen stores in the same way, meaning easier recover.
Cardiovascular endurance: As you build up your aerobic capacity to SS Cardio you will be increasing your cardiovascular endurance. As your body adapts to cardio activity it becomes more efficient, granting you a greater ability to handle intense exercise. As your heart becomes stronger it is more able to pump blood throughout your circulatory system, delivering oxygen to your working muscles. By making your heart stronger you are also reducing the risk of multiple chronic diseases, like coronary heart disease and multiple cancers (lung, breast, colon to name a few). The stress relief brought upon by the release of endorphins – triggered by exercise - can help lower cortisol, elevating your mood and ultimately aiding with fat loss and muscle building.

SS downside:

Performing long sessions of SS cardio might give you initial fat-loss results; however, you will quickly lose the effects of these sessions. Our body is adaptive and once you perform a certain activity for a while our body becomes efficient at it, thereby using fewer calories. In order to burn the same amount of calories in each session you will need to increase the duration and/or intensity (speed, incline, resistance). In order to lessen this effect you can vary the kinds of cardio machines you use and do things you are not good at (and therefore not efficient). If you hate the elliptical machine, do it until you love it (or at least hate it a lot less!); if you cannot run to save your life, practice, get better at it (read Running: Is it for everyone? for tips), then switch to the rowing machine….etc….etc…
As discussed in my article Cardio: Before or After LIfting?, performing SS cardio can have a catabolic effect on muscles. As you perform aerobic activity, mTOR, the trigger for protein synthesis and muscle growth, is inhibited, and AMPK, an enzyme that inhibits protein synthesis is increased. Both of these affect your muscles’ ability to be able to synthesise the protein it needs in order to repair itself and grow. As increasing muscle mass is another great tool in the fat-loss-toolbox, performing excessive SS cardio can be detrimental for fat loss as well as muscle growth.

HIIT Followed by SS

As we’ve seen, HIIT is great at mobilising our fat stores and moving them to the blood stream to be used as energy, but what happens if we do not use all this mobilised fat? It will be converted back to fatty acids and stored in our fat cells.

In order to actually remove the fatty acids from our body we need to continue to use this energy now released into our blood before it gets re-stored. SS cardio is great at this as we are now using slow twitch muscle fibres; these fibres use the oxygen in our blood stream for energy, along with any sugars that have been released.

Performing HIIT at a high enough intensity to ensure we have used up our glycogen stores, then continuing with SS cardio is a great way to ensure that we both mobilise and remove fat.

Zone 2

After looking SS cardio and HIIT workouts, we turn to Zone 2 or Low Intensity Steady State (LISS), formerly thought of as the “fat burning zone”.

I remember a lot of talk about doing cardio in the fat burning zone many years ago, which meant keeping your heart rate low in order to burn more fat. At lower intensities we use a higher percentage of calories from fat, 50% vs 35% during higher intensities, however as you burn a higher number of calories at higher intensity, you actually burn more fat calories overall. This has meant that this fat burning, aerobic zone is now pretty much ignored, due to the realization that high intensity, anaerobic exercise will actually aid you at burning a greater amount of fat.

LISS or Zone 2 work can however still have tremendous benefits. While performing SS cardio, most people will stay in the upper end of the aerobic zone, around 70-80% of MHR, or about a 6-7 on the RPE scale. Zone 2 should keep you slightly below this, around 65-70% of MHR, or around 120-140 bpm.

For most people this is an easy pace, like going for a slow jog or brisk walk. This makes it easy to add to our schedule; even on rest days this would be a perfect way to include some “active rest”.

Why is this beneficial?

Zone 2 benefits:

The low intensity level will not be likely to hinder lifting performance: as we’ve seen, both HIIT and SS can have an impact on our performance in the weight room. Zone 2 however will keep us at a level that will not have the same potentially negative impact. If you plan on doing cardio before lifting, Zone 2 work is a perfect way to complete them both in the same workout.
Improve heart efficiency: both HIIT and SS will improve your aerobic capacity and help your heart become more efficient, and so will Zone 2, but in a different way. When performing higher intensity the heart becomes thicker as it focuses on getting the blood back out again as quickly and forcefully as possible. In lower intensity work the blood stays in the left ventricle long enough to stretch it out, this allows for a greater volume of blood to be pumped out with each heartbeat. Working in both HIIT and LISS zones will help your heart become stronger in both ways, leading to greater overall heart health improvements.
Adaptation and recovery: as our heart becomes stronger we are able to perform at greater and greater levels, as well as recover faster. This will translate to increased performance in the weight room as you are able to recover faster between sets thereby performing a greater workload in the same amount of time.

Zone 2 downsides:

Lower calories and fat burning potential: If Zone 2 cardio is the only form of cardio you include in your training you are missing out on the fat burning ability of HIIT and the potential to burn more calories with SS.
Cardiovascular benefits: as seen above, performing cardio at a higher intensity has heart-strengthening benefits so performing both high and low intensity will give you the best heart possible!

How do you apply this knowledge to your training regime? An ideal training program will enable you to mobilise and release fat stores while building muscle mass, so performing a combination of all three types on cardio (on different days) would be a great way to tap into all the benefits. It would also give you multiple heart health benefits, build your endurance and prepare you to maximize your performance, both on the track, and in the weight room.

*All nutritional and fitness info must be discussed with your doctor before any changes to diet or exercise regime are implemented.

Change nothing and nothing will change; without change, there can be no progress!

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CARDIO: HIIT vs STEADY STATE vs ZONE 2

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