May 19


Interval Training & Fat Burning | Ultimate Guide to Improve Cardio Fitness

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Designing interval training sessions is part art and part science. By this I mean it takes a blend of experience, instinct, trial and error. Likewise, we need to observe what works and keep records.  But, as a starting point, you can't beat some basic concepts. If you're looking to begin or enhance your current interval training program, then this is the article for you.

Below we'll look at different structures for interval sessions designed to develop speed, fitness, and performance. Think of each as a recipe with a certain layout.


Like all good recipes, interval training sessions can be tweaked and adjusted as required.

What you'll end up with is a truly customised personal interval training program that works.

Developing Speed with Interval Training

If you're in good shape or not-so-great shape, you may want to begin with speed play. This even works if you've never tried interval training before.

It's easy to experiment with speed play.

In this type of interval training, you increase cardiovascular effort for various amounts of time and follow with adequate recovery. For example, if you're running you might speed up a little until you reach a marker. Something like a stop sign or a tree that is several hundred metres away. Similarly, you can do the same while cycling or walking outdoors.

The 30-seconds or so of effort is followed by 3 times as much rest, or 90 seconds of easy recovery.

You can play as many times as you like and you get to choose the intensity.

Key point: Speed play works whether you're highly fit or deconditioned. This is because you can keep the training intensity relative to your current fitness level.

Using Interval Training to Improve your General Health and Fitness

These health and fitness intervals have a broad and clear application to most exercise enthusiasts.

This type of interval is more structured than speed play intervals. Additionally, you can use either the aerobic or anaerobic procedures. In short, the goal is to work from somewhat hard to very hard on the RPE scale.

Use the modified Borg 1-10 RPE scale to monitor intensity and effort levels during interval training sessions

Use the modified Borg 1-10 RPE scale to monitor intensity and effort levels during interval training

General Aerobic Health and Fitness Interval Training Sessions

You don't necessarily have to have high fitness levels to perform aerobic intervals. After all, you determine your own level of intensity, and the effort remains moderate (steady-state).


1:1 effort to recovery, also known as a work-to-rest ratio


  • 3 to 5 minutes for effort interval
  • 3 to 5 minutes for the recovery interval

The length of effort and recovery may vary from 3-5 minutes. However, keep the 1:1 ratio of effort to recovery for each cycle.


You are always in control

  • Effort intervals: 4-6 on RPE Scale
  • Recovery intervals: 2-3 on RPE Scale


The number of cycles you accomplish depends on how much time you have available and your current fitness level. That is to say, make the session work for you.

Anaerobic Fitness Intervals

Once you have moderate-to-high fitness levels, you might like to attempt the anaerobic fitness sessions.

During anaerobic fitness intervals, we use a 1:3 effort-to-recovery ratio. Using this ratio, a one-minute effort interval precedes a three-minute recovery interval.

Generally, it's best to perform anaerobic effort intervals for 90 seconds or less. If you're performing at the correct intensities, less than 90-seconds effort will ensure your anaerobic system receives a conditioning challenge.


1:3 effort to recovery


  • 30-90 seconds effort
  • 1.5 to 4.5 minutes recovery interval

Duration of effort and recovery can vary within the above guidelines. However, aim to keep the 1:3 ratio of work to rest for each cycle.


You remain in control of how hard you work.

Effort intervals: 7-10 on the RPE scale

Recovery intervals: 2-3 on the RPE scale


The number of cycles you accomplish again depends on how much time you have and your current fitness level. You just need to make sure that during each recovery, you reach an 'easy' level before going for another interval.

Comparing Aerobic and Anaerobic Fitness Intervals

In either method, you ultimately determine your own workout intensity. That being said, I encourage you to push your effort so that it lines up with the recommended RPE rating.

Everyone's perception will be different, but the end goal is the same. You want to work the interval at a higher level of effort than you would normally do. Aim to correspond your effort with the descriptive ratings on the 1-10 RPE scale.

Improving Fitness and Performance with Interval Training Methods

Performance intervals are a great way to enhance and improve already good cardiovascular fitness.

You might find these interval sessions useful if you're:

  • a competitive athlete or sportsperson;
  • a runner looking to increase speed;
  • already well-conditioned and looking for a new challenge;
  • bored with your current workouts;
  • wanting to take your cardiovascular fitness to the next level.

These are generally the most structured interval training sessions. Additionally, they're examples of classic, high-intensity interval training, or HIIT session.

Before progressing to these sessions, make sure you're already well-conditioned and properly motivated. You should be ready to training in the structured and physically intense environment of performance interval training.

Welcome to the world of performance interval training

The three performance interval structures that follow assume an already high level of fitness.

Intensity, duration and frequency are set depending on the performance goals. These sessions use both RPE and heart rate to monitor effort and recovery intervals. Ideally, you'll use a good quality and reliable heart rate monitor to keep you accountable.

You'll notice that there are two anaerobic performance examples. The second continues to challenge you as your cardiovascular fitness levels progress and develop. Example 2 not only increases exercise intensity, it also decreases recovery time. Essentially, you're working harder with less rest. As a result, you'll find this makes it a very challenging interval session.

Aerobic Performance Interval Training Session


1:1 Effort to recovery


  • 3-5 minutes effort
  • 3-5 minutes recovery

Again, you can vary the duration of work to rest, but aim to keep the 1:1 ratio for each cycle.


  • Effort intervals: 80-85% of HRR (4-6 on RPE scale)
  • Recovery intervals: 2-3 on the RPE scale


The number of cycles you accomplish depends on how much time you have and how fit you are.

Anaerobic Performance Interval Training Session - Example 1


1:3 Effort to recovery


  • 30-90 seconds of effort
  • 1.5 to 4.5 minutes of recovery

Effort and recovery can vary each cycle but aim to keep within the 1:3 work-to-rest ratio


  • Effort intervals: 85-90% of HRR (5-8 on RPE scale)
  • Recovery intervals: 2-3 on the RPE scale


The number of cycles you complete will depend on your current fitness and how much time you have available.

Anaerobic Performance Interval Training Session - Example 2


1:2 Effort to recovery


  • 30-90 seconds of effort
  • 1 to 3 minutes of recovery

Effort and recovery can vary each cycle but aim to keep within the 1:2 work-to-rest ratio. Don't worry, it's supposed to feel tough!


  • Effort intervals: Greater than 90% of HRR (8-10 on RPE scale)
  • Recovery intervals: 2-3 on the RPE scale


The number of cycles you complete will depend on your current fitness and how much time you have available.

Guidelines for performing interval sessions safely and effectively

  • As with any fitness session, make sure you warm-up for at least 5 minutes before attempting the intervals. Additionally, follow your session with a cool-down of at least 5 minutes. After the cool-down, you should feel like your heart rate and breathing are back to pre-exercise levels.
  • If you feel ready for the next interval, then do it. If you need more time to recover, allow yourself to take it. Remember, common sense always rules. Keep interval training fun, challenging and aligned with your workout goals.
  • Beginners, or unconditioned participants, shouldn't participate in interval conditioning that pushes beyond an RPE of 7.
  • Carefully monitor your exertion level. Exhaustion is not the goal. Interval training should feel enjoyable and, though challenging, shouldn't create lingering fatigue or a negative experience.
  • Remember, how hard you push during an interval is up to you. Even though you are encouraged to exert beyond your comfort zone, listen to your body.
  • Interval training workouts that repeat about 10-12 anaerobic cycles should only be used once or twice per week. Monitor your workouts and make sure you are recovering adequately to avoid overtraining.

Recovery after your interval conditioning efforts

The drawback of anaerobic interval training is that you get lactic acid building up in the bloodstream and working muscles. As a result, it takes longer to recover from working anaerobically.

We account for this by adjusting the ratios between effort and recovery.

Proper recovery duration at the right intensity is crucial after anaerobic effort intervals.

After all, it's during the recovery periods that many of the specific training adaptations occur.

In other words, many of the benefits you're looking for take place during the rest, not the work.

Don't cut your rest periods short. They're just as important as the effort.

Also, active recovery helps speed up your recovery from the interval efforts. During active recovery, submaximal exercise (usually steady-state or lower) continues to help prevent muscle cramps and stiffness. Furthermore, by continuing to move you're actually helping the recovery process.

Active recovery accelerates lactic acid removal from your system, more than rest. Keeping the body moving and the blood flowing is more effective than complete rest, like lying down for example. Easy aerobic exercise may help remove lactic acid due to the increased blood flow it encourages.

The increased availability of blood and oxygen to your muscles allows the lactic acid to be metabolised.

Using interval training to maximise fat burning and calorie usage

There is a lot of confusion surrounding the idea of fat-burning versus carbohydrate-burning.

Should you slow down, go longer or work harder to help you burn fat? Let me clear up a few fat myths.

People have been misled.

Many believe they need to exercise for over 20 minutes and at a low intensity to burn fat.

First, let's dispel the 20-minute myth.

Even when you're lying flat on your back, the calories your body burns come from both fat and carbohydrate. Technically, your body is working aerobically while at rest and you're using fat.

It's crystal clear that you don't have to exercise for 20 minutes before you begin using fat for energy.

If you're new to exercise, don't be discouraged if you can't last for 20 minutes. When it comes to exercise and activity, something is better than nothing. As you get stronger and fitter, you'll be able to eventually go longer.

Do you burn more fat when you go slow?

The answer is really yes and no, but mostly no.

It's true that as you exercise harder you burn a little less fat per calorie. Conversely, going slower burns a little more fat per calorie.

This seems to support the idea that as exercise becomes harder, your body burns less total fat. In actual fact, only less fat is burned per single calorie.

Here's the rest of the story.

Cranking up the pace and intensity burns more total calories and more fat calories. Why? Well, at the end of the harder workout, you breathe more oxygen. Each litre of oxygen you take in burns about 5 calories. The more oxygen you take in, the more calories and fat you burn overall.

Have a look at the below table to help illustrate the effect of intensity on fat and carbohydrate burning.

Fat and Calorie consumption at two different intensities



Total calories used

Total fat calories used

Less intense - 

30 minutes at 50% HRR

More fat burned - about 50% from fat, per single calorie



More intense - 30 minutes at 75% HRR

Less fat burned - about 40% from fat, per single calorie



This table shows that training at a harder pace burns more total fat than when compared to a lesser intensity. To clarify, this is for a set time period (30 minutes in this example).

Sure, the lower intensity might burn more fat per single calorie, but you won't burn as many calories. And that's the difference.

What's the best level of effort or intensity for burning fat and losing weight?

There are 4 key points when it comes to burning fat and losing weight:

Don't slow down or change how hard you're exercising if you can keep up the pace. 

Exercising as hard as you comfortably can increases the total calories and fat used. You can also alternate this type of continuous aerobic training with low-level aerobic training.

Both help your body become more capable of burning fat.

If the exercise is too hard or limits how long you'd like to exercise? 

Slow down and go longer.

Similarly, if you feel you need to reduce your goal number of intervals, you might be better slowing the pace.

Working both aerobically and anaerobically helps your body fully optimise its ability to burn fat. 

Aerobic training has a different physiological impact compared to anaerobic training. Particularly regarding optimising fat and calorie burning and improving your overall fitness.

That's essentially why you need to do both.

To lose weight, it's the total number of calories you burn that matters. 

Most experts believe the key is the calories you expend during your exercise sessions. More intense sessions burn more calories. Whether you're burning fat or carbohydrate doesn't seem to be important.

Essentially, you don't even have to concern yourself with whether you're burning fat or not. Burn the calories and the fat will take care of itself.

Why interval training maximises calorie burn

Many traditional workouts are designed to accommodate about 30-45 minutes of continuous CV training.

If your goal is to lose weight, you'd be better off working at 80% of your VO2 max or HRR. However, 80% of HRR would maximise calorie and fat utilisation, but it's a more difficult workout.

A more realistic exertion level would be about 70% HRR if you're fairly fit. You're more likely to be able to maintain this intensity level over 30-45 minutes. Don't worry, this level of effort still uses plenty of calories.

What if you find it difficult to maintain high, or even medium levels of continuous cardio? Interval conditioning allows you to accumulate more total exercise. You'll also perform at higher intensities and in more tolerable doses.

For many people, it's much easier to endure relatively short periods of harder work. If this rings true for you, higher intensities eventually allow you to work at higher levels of effort relatively comfortably.

Previously, this same effort would have exhausted you quickly.

If you're deconditioned, you should probably exercise at a level of intensity you can maintain. This will help you optimise fat and calorie burning.

Build your base of conditioning with moderate levels of effort that last 3 minutes or more. Leave worrying about how hard you work until you become fitter.

As your fitness improves, you're encouraged to work out at manageable effort intervals of slightly higher intensities.

The aim is to keep pushing yourself to a state higher than you are accustomed to. That's what fitness is about.

About the author

Paul Stokes

Paul Stokes BSc (Hons) is a Certified Personal Trainer, Accredited Sports Nutritionist, qualified Exercise to Music Instructor, Precision Nutrition coach, Massage Therapist and teaches 8 of the Les Mills Group Exercise programs.

He currently works in the Oil & Gas industry as a Wellness Coach, imparting his vast knowledge and experience to improve the quality of life of several hundred offshore workers.

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