Cardio and Dieting


It is something that plays a large role in the lives of almost every competitor, to go from lean, to stage lean cardio is required by 95% of physique athletes.  Now, whilst for the average trainee looking to improve their physique, the most important aspect of their cardio regime may simply be to “get it done”, for those of us who are looking to leave no stone unturned in our quest to present our best possible physique on stage, the details of the cardio regime can be the difference between a competition winning physique and just making up the numbers.

To help decide how to best implement cardio into our routine, we need to understand exactly what we are trying to achieve by doing so.  Put simply, that is to reduce body fat to competition levels whilst having the minimum impact possible on muscle gains.  This is important to understand as most types of cardio activity, with the exception of high intensity sprints, will cause metabolic and muscular adaptions that are quite the opposite of those adaptions caused as a result of intense weight training.  It is therefore required that the trainee can implement their cardio routine without causing the body to start to adapt to its stimulus as those adaptions would prove counterproductive when it comes to the building and maintaining of muscle mass.

With the goal of the contest prep and the increase in cardio being to efficiently burn body fat, it is useful to understand how stored body fat is utilised as a fuel source as there are 3 stages that must be completed before the stored fat is oxidised:

  1. Mobilisation – The first stage is the breakdown of stored fat inside the fat cell.

  2. Transportation – Once released from the cell the fatty acids are transported throughout the blood stream.

  3. Oxidation – The burning of the fat for energy in the cells mitochondria in the tissue that needs it.

These 3 stages though, do work independently and just because a fatty acid is freed from the fat cell and enters the bloodstream, does not mean that it will be burned for energy.  If it is required as a fuel source then it will be, otherwise it will circulate in the bloodstream before being re-stored.

The mobilisation of fatty acids is primarily controlled by hormones and it is initiated in response to an energy shortage.  Regardless of the intensity of the activity the body is currently undertaking, walking, intense weight training or even just having a chat, if energy levels are low fatty acids mobilisation can occur.  Transportation is related to blood flow, so whilst it too can occur at any training intensity, it is important to note that it may be restricted at certain times or to certain areas.  This is often the controlling factor for those who are attempting to lose their “stubborn fat”, such as a lean individual close to competition shape, but storing a little excess body fat on their lower stomach for example.  It is often difficult to lose primarily as a result of restricted blood flow to the area.

When it comes to the oxidation of the fatty acids, this is where the intensity of the activity does come into play as fat can only directly be burned as a fuel source during periods of low intensity activity.  The breakdown of fatty acids can not occur rapidly enough at higher intensities where instead glycogen would be required.

So now we have a better understanding of the processes involved in fat burning, lets take a look at the different methods of cardio that are commonly used, discuss advantages and disadvantages of each as well as seeing how they would fit into your routine to best accomplish the goal of fat burning with minimal impact on muscle mass.

The two most effective types of cardio implemented when the goal is to maintain muscle and burn body fat are either High Intensity Interval Training or Low Intensity Steady State cardio.  Both of these offer different advantages as well as disadvantages and the choice of cardio as well as how it is implemented into an individual’s routine can make or break that competition winning physique!

Firstly though, let me just explain briefly why moderate intensity cardio should be avoided in a programme optimised for burning fat whilst maintaining muscle mass, or even just burning fat in general as maintaining muscle mass is key to keeping the metabolism elevated so is an important consideration even for a heavily over-weight person just looking to get in shape.

Yes, you can burn more calories working at a moderate intensity for 45 minutes than at a low intensity.  But, those calories will come from glycogen stores instead of fat tissue (see part 1 for information on fat oxidation).  If glycogen is not readily available you will end up breaking down muscle tissue in order for amino acids to be used as the energy source.  Long-term, this will have negative effects on muscle mass and hence negative effects on the metabolism.  What’s more the intra-muscular fibre adaptions are opposite to those required for building muscle size.  The body will also quickly adapt to this increased energy expenditure, as well as the reduction in muscle mass through its use as an energy source during activity, muscle tissue will become preferential as an energy source over fat tissue at other times too as the body clings on to its most dense energy source (fat tissue) for when needed to fuel the extra activity it is being put through on a daily basis.  It will also adapt to the extra caloric demands by reducing the amount of the most energy inefficient tissue that the body holds – skeletal muscle! So all in all, excessive moderate intensity cardio will deplete muscle mass, especially when in a caloric deficit, and long-term will actually make body fat harder to shift.


Firstly, by HIIT I mean HIGH intensity interval training! Not go fast for one minute, then reduce pace for a minute, I mean flat out sprinting!  If you are able to perform HIIT for longer than 30 minutes max, then you are not going flat out during the sprints!  In fact 8 x 30 second sprints should be all you need to get the job done!  Anything longer than 30 minutes and what you are performing will be classed as MIIT (MODERATE intensity interval training) and we have already talked about the negative effects of moderate intensity training.

Proper HIIT style cardio should leave you breathless after each sprint, in doing so, you are working at intensities that are comparable to those utilised during your weight training sessions.  The effects are comparable too, providing you have the adequate fuel available for the workouts.  Otherwise, like your weight sessions, they will be counterproductive with skeletal muscle once more likely to be used as a fuel source. Let’s look at some of the advantages and disadvantages of HIIT when it comes to its use when dieting to optimise fat burning whilst maintaining muscle mass:


  1. Will offer a greater net calorie burn due to additional calories being burnt following the activity as a result of EPOC (Excessive post-exercise oxygen consumption).  So your metabolism remains elevated for up to 12 hours following exercise (intensity and duration dependant).

  2. Providing fuel is adequate, offers muscular adaptions comparable to weight training.  Sprinting uses maximal force, the adaption is to make muscles bigger and stronger so they can improve this performance.

  3. More time efficient – Sessions are shorter and less of them are typically required to achieve the same goal.


  1. Relies heavily on carbohydrates as a fuel source, so adequate fuel must be consumed in order to prevent muscle tissue breakdown.  This raises the question I will address later, as to whether it may be better to just not add the extra calories to fuel the workout in the first place.  As you can already see from the previously mentioned advantages, HIIT can be either advantageous or disadvantageous to muscle tissue depending on the circumstances.

  2. Much harder to recover from and care in the programme setup must be taken when combined with intense weight training.  If you are already training intensely in the weight room 5-6 times a week, HIIT will effect recovery between weights sessions and can lead to acute and chronic over-training.

  3. Although overall calorie expenditure may be greater, fewer calories are burnt during the session and a much lower percentage of these calories will come directly from fat stores.

  4. The activity is very painful!  At least when performed properly!

Low Intensity Steady State Cardio

By low intensities we are talking working in a heart rate zone that will optimise the process of utilising fat for energy.  The intensity can vary and generally the lower the intensity, the greater percentage of calories burnt that will come from fat.  Of course though, the lower the intensity the lower the net total of calories burnt during the session so compromise is needed.  Heart rates for Low Intensity Steady State cardio will generally fall between 50% and 65% of the trainees maximum heart rate.  This is a general guide though as lower will usually result in too fewer calories being burned from the session and higher will start to cross-over into moderate intensity cardio which I have talked about in part 2.



  1. Extremely easy to recover from.  Of course this is specific to the intensity, but if the intensity is kept under control, low intensity cardio can be used with a much higher frequency than HIIT cardio during a diet.  It does not affect the nervous system in the same way and therefore, even daily LISS sessions can be used without resulting in overtraining (rest of the programme dependant).  

  2. Can burn fat directly as a fuel source.  At lower intensities fat can be utilised directly as a fuel source.  The percentage of calories burned from fat will depend on the intensity as well as the amount of glucose in the blood stream.  Performing low intensity cardio fasted will ensure that blood glucose levels are minimal and therefore fatty acid oxidation will occur almost from the onset of the session.

  3. There is no requirement to add additional calories into the diet to fuel the session.  The whole point here is to slightly increase the caloric deficit and as we are aiming to use fat as a fuel source adding extra calories into the diet to supplement cardio that is kept at lower intensities would be counter-productive.


  1. Does not offer metabolic benefits offered by HIIT style training, so 24 hour calorie expenditure will be lower and therefore more is required. 

  2. Time consuming: as mentioned more sessions are required, sessions will also be longer in duration.

  3. Used in excess and if intensity is not right, can result in muscle loss.  As with HIIT, finding the right balance between intensity, volume and optimal inter-linking with the rest of the training programme and diet is key!


There is no one size fits all approach, considerations for when implementing a cardio programme would include:

  1. Genetics, does the trainee hold muscle mass easily?  Do they have areas that tend to flatten out when dieting?  Do they find it easy/hard to shed fat?

  2. Recovery – How frequently is the trainee training with weights?  How frequently do they train larger body parts and in particular legs?  Someone who has been training 6 times per week with 2 weekly leg sessions may quickly over-train with 3 or more HIIT sessions weekly.  But a trainee who has been training only 4 times per week with only 1 leg session per week is likely to be able to handle more high intensity work.  Again though the diet setup as well as other lifestyle factors such as sleep will need to be considered.  Of course, frequency of leg training could be cut back in the first example, but if that frequency has been required to build the muscle, would this really be the best idea especially when adding extra cardio?  Remember, the body adapts to the stimulus it is given!

  3. Does the trainee have a high or low metabolism?  If the trainee has a high metabolism and is already training intensely with weights, will HIIT training be the best approach?  The metabolic benefits offered are less important, they are probably already consuming a lot of calories in order to maintain muscle so the volume of cardio and stress created as a result of the cardio should be kept to a minimum.

  4. Do they have a lot of fat to lose?  The trainee has a deadline for being in contest shape, so what is required to ensure that they are able to reach the required condition in time?  Hopefully they will not be starting their prep in a position where fat loss needs to be rushed, but if this is the case it will affect the type and volume of cardio required.

  5. Do they have a lot of time available?  For a serious competitor, this should not be an issue, they do what they must to look the best they can.  But for many, daily cardio session and especially twice daily may not be an option, therefore HIIT cardio, which is less time consuming may be the best choice.


Another method I like to use with many clients is a combination of both styles of cardio.  As I have mentioned in part 1, training at high intensities will cause fatty acids to be released from the cells and to circulate in the blood stream.  But, at those high intensities they can not be utilised as a fuel source.  One way around this, is to start the session with HIIT to cause this fatty acid mobilisation and then to switch to LISS cardio for the second half of the session in order to oxidise the fatty acids released.

I would also advise any competitor to start with the minimal amount of cardio necessary to reach the required weekly fat loss targets.  This will leave room to increase intensity, duration and/or frequency throughout the prep each time progress slows.  Also, in doing too much too soon and over shooting those weekly targets, energy levels will suffer and muscle mass will be affected.

For more information on cardio and implementing it into your own routine take a look at my members section where you will find a video discussing the topic