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Complete Guide to Interval Training

By Greg Brookes

Interval Training has been around for many many years now. No matter what your goals, whether they are to lose fat, improve your heart and lung capacity, complete a marathon, increase your lean tissue or improve your insulin sensitivity, interval training is far superior than long steady cardio training.

In fact this type of ‘short burst’ training is so effective at improving your health I’m surprised that more people aren’t doing it!

Complete Guide to Interval Training

What is Interval Training?

The concept of this type of training is simple, simply intersperse short periods of hard exercise with periods of rest.

So a very simple example might be:

  1. Run hard for 30 seconds
  2. Rest for 2 minutes
  3. Repeat 4 – 8 times

Often this type of training is called HIIT or High Intensity Interval Training, the reason for this title is because the periods of exercise needs to be very challenging.

How challenging you may ask?

Well usually hard enough for you to reach your anaerobic zone or the zone where you no longer use oxygen to fuel your energy system. Just for reference:

Aerobic means with oxygen and Anaerobic means without oxygen

I’ll get into exactly how hard to work and ways to monitor your intervals later.

8 Benefits of Interval Training over Long Steady Cardio

When I talk about Long Steady Cardio I’m referring to what most of you will understand as regular cardio exercise, this is the stuff that lasts for 20 minutes or more and the intensity doesn’t really change.

You will probably understand it as what most people do at the gym e.g. running on a treadmill, sitting on an exercise bike, using the elliptical, going up and down on the stepper etc.

OK, so here are some of the advantages of keeping things short and intense rather than long and steady:

1 – It’s Quicker

Interval training is fast. Based on the example I have given above your actual time exercising hard will only last 2-4 minutes. The rest of the time you will spend warming up, resting in between intervals and then cooling down.

Most steady cardio will last 20 – 40 minutes and you get less results for your time investment.

2 – More Fat Burning

You actually burn more fat in the long term than with steady cardio. Once you stop your steady cardio then the fat burning stops but when you stop your Intervals you continue to burn fat for up to 24 – 48 hours depending on what research you read.

Following your hard interval workout you get what is called an EPOC effect or Excessive Post Oxygen Consumption.

What EPOC basically means is that hard workouts disrupt your body’s natural homeostasis (balance) and this takes a lot of calories to repair and restore.

So you shouldn’t just look at the impact of the exercise during the workout but the consequences of that workout afterwards.

Research by Laval University in Quebec discovered that:

Intervals Burn Up To 9 Times More Fat

3 – Less Cortisol Production

Exercising for long periods produces more of the stress hormone cortisol. Cortisol in turn raises your blood sugar levels which stimulates the production of insulin which is not ideal for improving insulin sensitivity which is a huge problem today.

The release of cortisol also suppresses your immune system and leaves you more vulnerable to attack from all sorts of infections. People who over-exercise often get sick!

Cortisol is also Catabolic by nature so it breaks down muscle tissue. This is the reason why bodybuilders do not run long distances, their muscle mass is far too important to be jeopardised by muscle eating cortisol.

It is also important to note that muscle tissue is highly metabolic. So in other words, it requires a lot of energy for muscle to function so the more you have the more calories your will burn at rest.

4 – Improve Heart and Lung Capacity

In order to improve the capacity of anything you need to push it or expand it. With interval training you increase your heart and lung capacity very quickly because the workouts by their very natural push your capacity.

With long steady cardio you do not challenge your capacity to the same degree. In fact, after the initial shock of the first few weeks of long cardio training your capacity levels even out and very little improvement is made.

More importantly short bursts of exercise build up a reserve capacity for your heart and lungs. What this means is that you have a naturally safe buffer. If your heart rate is suddenly raised then that is OK you have the capacity to handle it.

Now compare this to steady cardio. The buffer you build is not very large because you don’t push to develop it. Now what happens when your heart rate is quickly raised? Is your heart capable of handling it?

5 – Increase in Growth Hormone

Intense exercise like HIIT releases your ‘Human Growth Hormone’ HGH unlike any other form of exercise. We all need HGH to repair bones, muscles, and other soft tissue quickly.

Research from the Journal of Sports Medicine discovered that:

exercise intensity above lactate threshold and for a minimum of 10 minutes elicits the greatest secretion of HGH

Another study by the Department of Exercise and Sport Science, University of North Carolina also discovered that there is a:

linear relationship between the magnitude of the acute increase in growth hormone release and exercise intensity

6 – Less Overuse Injury

This is one area that is often overlooked with regards to long steady cardio. The average person will perform 1000 steps per foot every mile when jogging. That is a lot of bouncing on just one leg.

Now consider the average jogger who has a weak core and / or weak glutes. Every step and contact with the ground will force a misalignment up through the body or kinetic chain.

Want to know why most people get bad knees when they run?

It’s not bad shoes that are the problem, it’s weak hips and core muscles that cannot stabilise foot placement and energy transference.

Interval Training involves less repetition. Sprints involve less than 100 steps. Full body circuits can be dispersed across movement patterns. Yes Intervals will be more explosive but there is less chance of wear and tear to the joints as repetition is kept to a minimum.

7 – Continue to Get Results

Fat is vital for survival and actually the body’s favourite source of energy. Without fat we would have never evolved to be in the place we are today. So naturally the body is very protective of its fat stores and hence why many people struggle to lose fat.

When you perform lots of long steady cardio you are telling your body that it is going to need a lot of fat for energy. As you persist with your long cardio workouts the body becomes more efficient at making fat available.

Although you do burn some fat with these long workouts if you stop then most people pile on the pounds quicker than they took them off. This process is totally natural and the body’s way of simple looking after its own survival. Remember fat was scarce through our evolution and physiologically the same principles still apply today.

8 – Increases Mitochondria

Interval Training stokes up your fat burning furnaces. Pushing yourself with more intense exercise increases human growth hormone and subsequently the number of Mitochondria, the small fat burning furnaces held within your muscle tissue.

The more Mitochondria you have the greater the fat burning potential. Although slow cardio will have a small effect on your mitochondria it has nowhere near the same impact as interval training.

Examples of Interval Training

OK, so now you have an understanding of the benefits of this intense training lets take a look at how it’s done.

As mentioned earlier all you basically need to do is choose an activity that increases your heart rate and gets you into that Anaerobic (without oxygen) Zone.

The more muscles you use during an exercise the more energy is required so you will want to focus on big full body exercises like:

  • Sprinting or Running Quickly
  • Airdyne Bike Sprints
  • Rower Sprints
  • Swimming Sprints (although be careful in deep water)
  • Hitting / Kicking A Punch Bag
  • Kettlebell Swings
  • Complex Barbell Circuits
  • Bodyweight Circuits
  • Dumbbell Circuits
  • Jump Rope or Skipping

This list could go on and on. Basically anything that gets you seriously out of breath quickly can be a method for interval training, so use your imagination 🙂

How Intense To Work

We are all at different fitness levels so one person’s intense can be another persons stroll. It is important that you decide your own level of intensity.

My Client Example

I trained a client a few years ago that was morbidly obese. We used intervals in her training very effectively.

How did I do it?

We basically used a hill on Hampstead Heath and just walked up it in short bursts. I divided the hill up into intervals marked by benches or trees and then we took it one goal at a time. So we walked to the first bench and rested. Walked to the next tree and rested etc.

Was this interval training for me? No. But for the client it was serious training.

Using a Rate of Perceived Exertion (RPE)

A really simple way to determine how intense you are working is by grading your intensity on a scale of 1 – 10.

  • 10 = Full Speed / Can only maintain for a few seconds
  • 9 = Working Very Hard
  • 7 = Working Hard
  • 5 = Could Hold a Conversation
  • 3 = Walking Pace / Warm Up
  • 1 = Relaxed

So with this type of intense training you want to be looking to achieve an intensity of somewhere between 8-10.

Basically if you can chat to your friend while exercising then you are not working hard enough.

It’s fun to see how many people you can spot at the gym that are exercising and chatting. What does this tell you?

Using a Heart Rate Monitor for more Accurate Readings

My favourite method for interval training is to use a heart rate monitor. For most of my new clients I buy a heart rate monitor and then teach them how to use it.

By monitoring the heart rate you can get a much more accurate account of how hard you are exercising. This method does have an advantage over the Rate of Perceived Exertion (RPE) method because it keeps you honest and doesn’t allow for human error.

Often guessing how hard you are working when you are new to this type of training can be very difficult.

Here’s a quick example of how to use Heart Rate Training:

  1. Establish your Max Heart Rate
  2. Work at an Intensity of 85% – 95% of Max
  3. Rest until Heart Rate Drops to 65% or less of Max
  4. Repeat Interval 3 – 8 times

There are some very sophisticated heart rate monitors these days but all you really need is the ability to monitor your current heart rate in real time.

Performing Interval Training Workouts

So by now you should have chosen your interval training method (eg. Jogging up a hill), and you also know how to monitor the intensity (eg. Perceived Exertion or Heart Rate Monitor). Next you need to know how long to work for and how long to rest for.

How Long Should Each Interval Last?

The length of the interval will vary depending on your current fitness level and the activity you choose.

So the ultimate goal is to reach your Anaerobic Zone which is found at 85% – 95% of your max heart rate or approx. 8-10 on your RPE scale.

Some exercises will get you to this level very quickly like a full blown sprint (especially up hill) and some exercise will take a little longer like Kettlebell Swings.

Ultimately the more effort and the more muscles required the less time it will take to reach the Anaerobic Zone.

Here is a guide to some Interval Training Exercises and where to start:

Beginners (60 secs per interval)

  • Begin slowly and work harder and harder throughout the minute
  • Try Brisk Walking
  • Brisk Cycling
  • Brisk Boxing Pad Work

Intermediate (30 – 45 secs)

  • Again build up to maximum exertion at the end of the interval
  • Try Brisk Jogging
  • Jumping Rope / Skipping
  • Dumbbell Squat and Press
  • Kettlebell Swings
  • Rower Sprints

Advanced (20 – 30 secs)

  • Maximum exertion from the start
  • Try Hill Sprints
  • Jumping Exercises: Squats, Lunges
  • Sled Pushing or Pulling
  • Battling Ropes

A Quick Note About Energy Systems

The harder you work within each interval the less amount of time you will be able to last.

For example when I train clients and we have performed hill sprints I know that by around 20 seconds there is very little explosive energy left and the effort begins to slow as they switch to different energy system.

The reason for this is the primary energy system over the first 20 seconds is ATP or Adenosine Triphosphate and this is responsible for explosive power, like sprinting.

Once all ATP has been used up then it switches over to the Glycolytic System until approx. 2 minutes and then finally the Oxidative System from 2 minutes onwards.

100M Sprinters Will Never Leave the ATP Explosive Energy System

It is important to note that no one system works independently they all work together for the production of energy just some are more productive during certain times of exertion.

How Long to Rest After Each Interval?

The length of your rest period will have a direct correlation with your overall fitness level. The fitter you are the quicker your Heart Rate will return back to a resting level again.

So Beginners will take longer and more Advanced athletes with take less time.

If you are using a heart rate monitor then this is easy to monitor. Simply perform your interval and then wait until your heart rate drops to around 65% or less of your max heart rate before repeating another interval.

If you are not using a heart rate monitor then you will have to wait until you feel you are at a RPE of about 3-5 before repeating your interval.

2 minutes is generally a good guide for sprints. You will have to adjust your rest periods especially as your fitness improves.

You will also notice that as you perform more intervals your length of rest will increase this is why having the same rest period each round is not a great idea. For better results your rest periods should taper up like this:

  • Interval 1 / Rest 60 secs
  • Interval 2 / Rest 75 secs
  • Interval 3 / Rest 90 secs
  • Interval 4 / Rest 105 secs

If you use a heart rate monitor and time how long each rest period takes for your heart rate to come down you will see this tapering effect happen.

How Many Intervals to Complete?

The secret here, like all exercise programmes, is progression. Start off slow and build up. Here’s a simple progression you can use:

  • Week 1: 3 Intervals
  • Week 2: 4 Intervals
  • Week 3: 5 Intervals
  • Week 4: 6 – 7 Intervals
  • Week 5: 7 – 8 Intervals
  • Week 6: Change Interval Exercise
  • Repeat from Week 2

5 Interval Training Programs for You to Try

This type of training although very effective is hard on the body so you should limit its use to only 2 – 3 times per week and allow a few days rest in between. So Monday, Wednesday and Friday are good choices.

A Word of Warning – Develop Base Conditioning First

Before beginning any Intense Cardio training like the ones below you should first ensure you have at least 4 weeks of base cardio conditioning first.

You can develop base cardio either by a simple jogging program, swimming program or, my favourite, bodyweight circuit training. Diving into training that is very intense is never a great idea so ease your way in gently.

1 – Treadmill Workout

I want to start by saying I’m NOT a great believer in treadmill training unless you have no other option. You are always far better to get outside and run in a more natural environment. Regardless of whether you use this programme indoors or outdoors the method is still the same.

  1. Run for 3 minutes at a conversational pace of about 5 RPE
  2. Increase the pace for 2 minutes at about a 7 RPE
  3. Increase again for 1 minute at about 9 RPE
  4. Return back to the 3 Minute Pace and repeat for a total of 3 circuits

This program is good for those new to interval training but have some running experience. You will find the hardest transition is from running hard at a 9 RPE and then returning back to a steady 5 RPE pace again. You will want to stop but you should try to just keep doing even if the pace is very slow.

2 – Simple Sprints

This method of training is very simple but highly effective. I have used it many times with clients looking to rid themselves of that final few inches of fat.

  1. Warm Up thoroughly
  2. Run hard for 30 seconds with RPE 9
  3. Rest 2 minutes or until heart rate is down to 65% of max
  4. Repeat 3 – 8 times

Please be aware that as you are sprinting hard the risk of injury increases. Ensure you warm up thoroughly first and pay special attention to those hamstrings, they are particularly vulnerable during sprints. You can make things even harder by running up hills. For those less conditioned simply jogging or walking up hills can be an option too!

3 – Kettlebell Swings

This method is not only effective but great for people with little space or who need to keep joint impact to a minimum. So if you suffer from knee problems then this could be an option for you.

  1. Warm up your hips and hamstrings
  2. Swing Kettlebell for 30 seconds
  3. Rest 15 – 30 seconds or until heart rate is down to 65% max
  4. Repeat 3 – 8 times

There are lots of varieties you can use with this kettlebell program. For example one handed swings, two handed swings or double kettlebell swings.

Another variation that I have used successfully is to decrease the kettlebell weight as you progress through the intervals, this allows for the fatigue that is generated:

  • Intervals 1 & 2 = 32kg
  • Intervals 3 & 4 = 24kg
  • Intervals 5 & 6 = 20 kgs

Here’s a Video Tutorial of the Kettlebell Swing:

4 – Rower Intervals

Using an indoor rower is a fairly safe way to work on your cardio intensity and it utilises a lot of muscles so its very effective.

There are lots of options you can use including the Workout # 1 protocol above but here is one of my favourites:

  1. Set the damper to between 7 – 10
  2. Warm up with 3 minutes of easy rowing
  3. Perform 20 Hard Stokes
  4. Row for 2 minutes at 5 RPE for recovery
  5. Repeat for 3-8 circuits

I used this simple program to enable me to break the 7 minute barrier for 2000M. Give it a try I think you will like it.

5 – Bodyweight Circuits

Using just your bodyweight in various ways can seriously elevate your heart rate and is a great interval training option.

Here’s one simple option:

  1. Following a full mobility warm up
  2. High Knees – 30 seconds
  3. Rest 15 – 30 seconds
  4. Burpees – 30 seconds
  5. Rest 15 – 30 seconds
  6. Repeat 3 – 8 circuits

Here’s how to do the High Knees exercise:

And the Burpee with modifications:

How Should this Intense Training Feel?

These types of intense workouts only really work if you push into that anaerobic zone.

The trick here is find the correct balance between working hard and not producing too much lactic acid.

Once you start to hit the higher end of your anaerobic zone then you will start to feel sick because the bi-product of producing energy without oxygen is lactic acid and this will build up in the system.

If your mouth starts to taste unusual and your saliva thickens then this is generally a sign of lactic acid build up.

With time your lactic acid tolerance will improve and you will be able to push harder and for longer without feeling sick. To start with take it easy and get used to how it feels.


So there you have my guide to Interval Training. There are lots of great benefits to be had and the results will speak for themselves.

Just start off slowly and get used to working hard and then resting. Enjoy the workouts but most of all warm up well and progress gradually. Good luck!

Do you use Interval Training? Got Questions? Share them below:

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    1. Peter Everett Avatar
      Peter Everett

      Always something to gain from your articles/blogs Greg, thank you very much.

      One of my favourite HIIT routines is:


      30 sec left handed snatch
      15 sec slingshots
      30 sec burpees
      15 sec slingshots
      30 sec right handed snatch

      repeat for 3x left hand and 3x right hand snatches totally 6xsnatches and 6xburpees.

      Cooldown 2 minutes

      20 Sec Globlet Squats
      10 sec Halos
      20 Sec kettlebell lunge with rotation
      10 sec Halos

      repeat for 4x goblet squats and 4x rotation lunges

      10 x Turkish Get Ups


      I tried to incorporate all 3 planes of movement as you suggest and have begun using this as a basis for compling HIIT routines with the aim of keeping the variety. I tend to do around 4 per week and try to throw in the odd jog, swim, or activity day with the kids 🙂

      Your HIIT advice has enabled me to tailor short, beneficial routines with enough variety to keep it interesting and keep the body on its toes 😀

      (as mentioned before, I do alternate day fasting, so on fast days if I want to train, I keep it to 20/10 HIIT with low resistance/high anearobic effort bodyweight routine such as jumping jacks, press ups, fast mountain climbers)

      Happy for any feedback if I’ve got it wrong anywhere!


    2. Satya Newday Avatar
      Satya Newday

      Thanks Greg, I’m experienced and find your work a treasure. I’m a 66 year old, recently certified trainer with NASM and was trained in RKC system by a martial arts instructor 4 years ago, starting with 15lb KB for swings, snatches, etc, anything heavier irritated my 30 year, rotator cuff disability, although I stayed active and maintained mobility. KB, 30 minutes twice a week remodeled my shoulders and knees at the joints and I could functionally give up bothering with crunches and leg lifts. I increased from 15# to 26, 36, 44 and I can now handle skilfully 53 # without aggravating rotator cuff. Did 6 month training in power lifting recently but that’s a story for another day.

      The 30 seconds rotation doesnt lower my HR at all once I hit 80%. Tabata 4 minute cycle of 20/10×8 swings or snatches have me at 163pm after about a minute (2#6/12kg and I weight @65@5’7″) and takes 2 minutes to return to 65%. Rockport walk test calculates my mad training HR at 172.

      I’ve only had one upper respiratory infection in the last year, so…. Still, If I use 24 or 20 kg kb, by the 4th minute of 30/30 my rate stops falling. With a lighter bell, once it rises my watch/mon doesnt lower. The effect looks like a really high steady state routine 🙂

      What do you think of an 8 minute routine where my heart rate stays above 90% for more than 5 minutes?

      BTW I have started a routine with higher weight and applied reverse pyramid, results with HR don’t very as much as I feel comfortable with with my limited HIIT experience. My he still vets high and stays there.

      Like the vicor said, even for a trainer, I’m not find I g much support for HIIT for older folks.


      1. Greg Brookes Avatar

        Looks like you are in good control of your training Satya, well done. I personally wouldn’t recommend 90% for more than 5 minutes, in fact I would reduce this slightly. As you know speed of recovery is the sign of good fitness so I would work on intervals and allow your heart rate to come down to approx. 65% before going again. Monitor your times over 4 weeks, and see how your recovery improves. Best of Luck.

    3. rachel Avatar

      Here is a rowing HIIT that I use – total time = 8 minutes.

      put pull exertion level as high as you can mange and then:

      2 minute warm up
      20 sec row as fast as pos
      10 sec very gentle recovery row
      repeat until the timer says 06 minutes
      2 minutes cool down

      1. Greg Brookes Avatar

        Thanks Rachel, 8 x 20/10 classic Tabata training, that’s very tough indeed! Thanks for sharing

    4. Rev. Andrew Lindley Avatar
      Rev. Andrew Lindley

      Hi Greg. Thanks for all your very helpful articles. I am a 70 years old retired vicar and have been exercising for the last 50 years to compensate for an otherwise sedentary life style. I am reasonably fit and have tried HIIT but am now doing 30 minutes on an exercise bike or my crosstrainer which includes 20 mins above 70%, 5mins above 80% and 1 min above 90% of maximum heart rate…..is there any problem with this and will I get the same benefits. There also doesn’t seem to be much information around about exercising for older people….most of it seems to be for the unfit to get them moving. Any comments would be helpful. Regards.

      1. Greg Brookes Avatar

        Congratulations on 50 years of exercising. As you know consistency is always the key to success. Sounds like you are going strong. Without knowing more about your exact situation it’s hard to advise specifically but you may want to add in some shorter bursts of intensity throughout the 30 minutes. You could experiment with the Treadmill format that I mention in the article but on your cross trainer or bike.

    5. Robin Jessup Avatar
      Robin Jessup

      As a former runner who developed repeated hip/hamstring issues, I turned to hiit as alternative exercise about 5 years ago. I could no longer sprint without recurring injury. Now over 50 yrs old, hiit is a way of life for me. I have always preferred the flexibility of working out on my own around my own schedule and hiit easily fits that bill. Requiring little space and mostly just my own body weight, it’s easy to exercise regularly. There are a myriad of routine options and thanks to the wonderful information shared online by trainers like yourself, I can keep my workouts fresh and stay motivated with new moves and challenges.

    6. Steve Avatar

      Great info Greg.
      Useful to trainers as well as less experienced people.
      Thanks .

    7. Kel Avatar

      Thanks Greg,
      Best explanation and instruction I’ve seen to date!

      1. Greg Brookes Avatar

        Thanks Kel, pleased you enjoyed it and found it useful. All the best.