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Cardio controversy

Cardio controversy
Unfortunately as with most things in life, everything isn’t black and white. This article is going to look at some of the cardio controversy and interesting facts about cardio that is going around the internet.

If you haven’t already read my article on getting into fitness, please do so here, as it also explains what cardio is.

Cardio controversy?

If you are looking to do cardio, your build, goals, type of cardio and time you do your cardio may alter its benefits and affect other processes within your body due to those factors. But I would also like to say that depending on your current physical abilities, just about any type of sensible active activity or exercise is better than none.

So what effect does cardio have on your body?

Early morning cardio

This is probably one of the most debated subjects on the net in terms of whether you should be doing cardio in the morning, specifically on an empty stomach. Let’s start by saying that research has been done that shows that doing cardio in the morning on an empty stomach does encourage the body to dig deep into burning its fat energy stores. It stands to reason that if you haven’t eaten for sometime then the energy must come from somewhere and that somewhere is significantly from body fat, as during the night your glycogen stores are significantly depleted.

There are some good reasons to do cardio in the morning, as not just the fact that body fat can be burned easily, but your metabolism can also be elevated for sometime after an early morning workout and continue to burn body fat throughout the day. A good workout in the morning can release endorphins that improves the mood for the day. You are also likely to do your workout, as doing it later may end up not happening, due to you being too tired, busy or become lazy later on in the day.

However, one of the notable bits of controversy with morning fasted cardio, is that some research actually shows very little change in the total amount of fat burned during a day than that found working out later in the day, after you have eaten. This is because it is believed that your body uses its energy stores in a balanced way i.e. if it uses more fat or carbs during a workout, it will swap around to using the other source when resting and in recovery.

Another bit of controversy is when the body starts to burn not just body fat and any leftover stored glycogen when fasted, but also starts utilising protein as an energy source to reserve the other stored energy sources. Cortisol levels can also be elevated and so you can become catabolic, with it all leading to the breakdown of muscle.

The bottom line for doing cardio or not in the early morning is that if your main goal is to burn body fat then by all means do what is required to burn as much stored energy as possible when it is most convenient to you. If your goal is to build or retain muscle then losing muscle is the last thing you want to do. Therefore you should do any cardio you like later in the day, limit the amount of time doing cardio to twice a week and with a maximum of 30 minutes steady state or 15 minutes HIIT per session and add weight training to your workout plan.

Cardio and low calorie diets

Too much steady state cardio on a low calorie diet may help initially with fat loss but it also leads to muscle loss, making it even more difficult to lose fat, due to the fact that muscle actually burns fat calories, even at rest. Those that then try to reduce calories further end up in a vicious circle, those that give up, gain more fat due to a slowdown in their metabolic rate. Another problem with low calories and cardio is that some say that training can become tiresome with a low amount of energy for your workouts and therefore lead to unproductive workouts and less progress.

Cardio and low carbohydrate diets

It has been shown that being glycogen depleted can lead to more fat cells being burned. It also increases adrenaline that helps burn even more fat, releases more human growth hormone, increases testosterone production and lowers insulin. All sounds good, however like low calorie diets, a lack of carbohydrates can make you sluggish in your workouts. It has also been shown to put you in a catabolic state, reducing muscle hypertrophy (growth), of which again leads to a slower metabolic rate.

Cardio and cortisol

Does cardio significantly increase cortisol levels, some say yes, some say no. First what is cortisol? it is a stress hormone, that causes inflammation, stops the body getting to its fat stores, increases ghrelin (hunger hormone) and reduces leptin (hunger suppressor). It makes you want more sugar, suppresses growth hormone and testosterone. Whoever is right with regards cardio increasing cortisol, you in any case need to keep stress down to keep cortisol down, so don’t over train. As a side note cortisol from exercise will gradually reduce as your body get’s use to the stress put upon it. However it is still created and of course if you are placing new stimuli on your body in order to keep progressing it will still increase the stress and hence more cortisol will be released.

Steady state vs HIIT

So which one of these is best for burning fat?

Steady state

Firstly, yes steady state (aerobic) workouts use mainly fat for energy, while HIIT (anaerobic) uses mostly glycogen from the carbohydrates you eat.

One thing to consider is that most of the time we use our aerobic system to do most daily tasks. So for increasing your health for normal daily use, steady state cardio is definitely worth doing. It also can increase lung capacity and therefore makes a more efficient lung, which leads to a lower resting heart rate. However be aware that for fat burning, steady state cardio while it does burn mainly fat at the time you do it, it takes a long time to burn a significant amount of that body fat.

High Intensity Interval Training (HIIT)

HIIT does have the ability to burn more body fat over a period of time after your workout. This after burn can last for as much as 24-48 hours after working out. However one controversial aspect of this is just how much extra fat is burnt really still needs to be researched, as so far the amount may not be as much as people think.

It is however more time efficient for busy people and in fact also uses the aerobic system to regain oxygen debt. HIIT will place more stress on the body than steady state due to the higher physical demand placed on it.

One other thing to take away is that HIIT especially when done with bodyweight style training can increase muscle mass more than a steady state workout and therefore will translate to more calorie burning muscle. A good metabolic boost.

Why not do both?

HIIT pushes the body, while the body adapts quickly to the low stress of steady state cardio exercise which it has the potential to have much less of an effect. HIIT will increase performance more and you can keep increasing your intensity in-line with your progress. But both provide different benefits and doing both can give you great results in fitness and weight loss.

Some may find it best to split them into different sessions. However some may get benefit from doing HIIT for a short period 5-15 minutes and then do some steady state cardio after. This is because when you do HIIT your body releases fat into your blood stream, but when you stop doing HIIT the excess fat is returned to be stored, but adding steady state after will pick up the fat in the blood stream and use it to provide energy for steady cardio use.

Note: Obese/overweight/health risk individuals need to take care with any HIIT activities unless cleared to do so. Steady state may be best to start with, but watch for potential repetitive injuries also.

Cardio and muscle

Firstly I will say from the start, that I much prefer to do any cardio after lifting any weights or in a separate session on occassion. This is due to the fact that it has been shown in many research, that doing cardio after weights can help burn more body fat and gives you more energy for your weight training session. This I can actually feel, having tried cardio pre weight training. I just didn’t have the energy required to lift the weights after doing any cardio.

However, I’m going to add a small caveat here. Although the general consensus is to add cardio after weights, there is some conflicting evidence that doing cardio before you lift weights can actually increase your testosterone levels for sometime after your workout and doing cardio last suppresses some anabolic effects, with increased protein breakdown and increased cortisol levels putting your body in a catabolic state.

Catabolism is where your body breaks some muscle down and converts it to glucose, why? for survival! it tries to keep as much fat as possible for long term energy use. Therefore while I may have had more energy for my weight training by not doing cardio before my weights session, apparently I may have been putting myself in a catabolic state by doing it after? This does require more research however and for the time being, I’ll carry on doing cardio after weights.

If building muscle is your priority over everything else, including health, then simply limit or don’t do cardio. Cardio will use some muscle tissue for energy, especially if you are on a calorie controlled diet.

Another bit of controversy is the effects of steady state cardio on muscle development. It has been shown that aerobic exercise can convert fast twitch muscle fibres into slow twitch fibres, while strength training does the opposite. The use of resistance training promotes strength and hypertrophy, but reduces mitochondrial density needed for endurance. While steady-state aerobic exercise increases the oxygen capacity of a muscle, but reduces muscle strength. I will add though, that as your body becomes more use to training and more efficient, that both of these can in fact help by allowing each adaption to help each other and negate some of this effect. Basically I believe that doing aerobic activity to increase muscular endurance and cardiovascular ability can translate into improving your overall workout performance when lifting weights and also allow for better recovery by way of the increased capillaries, blood flow and aerobic capacity.


Before I summarise I want to make a few recommendations. However as this is an article on controversy feel free to research and do what you feel is best for YOU and your requirements.

Although I have made some general recommendations, It may have occurred to you that the article isn’t for or against any particular way of doing cardio. There is a good reason for this and that is the fact that each person has a different goal, each person has a different reaction or affected differently by the exercise they do. Research isn’t always clear or correct. This is precisely why there is controversy. There is no one size fits all, nor is there a definitive answer and why it can be so confusing to many.

At the end of the day, just workout out when best suits you. Don’t over think it……….

Lean individuals
If you are a lean person and don’t have enough calories in your diet and also want to build muscle, doing cardio can reduce your ability to build muscle. Why? It has been shown that too much regular steady state cardio can suppress testosterone production in lean individuals and can lead to high cortisol levels. Also when trying to maximise muscle growth you want to set your muscle fibres structure up for that process, not confuse it by creating an aerobic environment for it. If you’re lean, want to build muscle and really must do cardio, do separate sessions for cardio and weights, limit your cardio sessions to twice a week and do short HIIT sessions using low impact exercises, such as cycling and shadow boxing to avoid affecting your recovery from weight training.

Average weight individuals
Do whatever feels best and go by your results, either steady state and/or HIIT. For some it may be best to separate your cardio and weight training days however to avoid what is termed the’ interference effect’. Basically this means that doing two different types of exercise in the same session creates two different types of stimulus and therefore can limit the effects of one another or even have a negative effect on each other.

However if you haven’t got the time to do both on separate days then if your priority is on building muscle, strength and even endurance, then you can add some cardio after your weight training workout.

Overweight individuals
Those that are overweight or obese can benefit from any type of exercise. I don’t really think you need to worry what type of exercise you are doing and when and what order. I do however highly recommend that you do both cardio and lift weights. And as soon as you are cleared and fit enough, use HIIT when possible. The most important thing for you is to actually do something active and do something you enjoy and not find it a chore to have to do.


As you can see there is a lot of overlap, contradictory and confusing information. Experts and researchers will always argue about all aspects of exercise and diet. I also hope I didn’t confuse you too much. It would have been easy for me to just say do this, do that, don’t do this, don’t do that. But I wanted to put my mixed research and knowledge out there for you to go away and make your own mind up.

Finally, as a firm believer in overall health over just muscle gain, I will always recommend you incorporate some kind of cardio activity, whether that be steady state and/or HIIT and add it to a weight training regime. The health benefits are too good to be missed out on. Both steady state and HIIT provides different benefits from one another. Who cares about the controversy, incorporate both. Lastly, learning about the food you eat and its timing may actually be a good place to consider when and how to workout, providing the right nutrients and macros when needed for the task ahead. The nutrition plan.

Please take a look at my combo training article for an idea how I split my training.