The Effect Of Exercise Intensity And Duration On Your Stress Hormone Cortisol

Cortisol is a stress hormone which is released due to any type of stress. Whether this be from your boss shouting at you at work, being stuck in a traffic jam, watching a scary film or from exercise.

The purpose of Cortisol being released is to break down stored glycogen (from muscle and fat, the percentage of each varies person to person) in order to give you a quick burst of energy to cope with the stressful situation. This is known as the ‘fight or flight’ response. This response was needed thousands of years ago so you could either fight or flight from wild animals attacking you. However, even though we don’t need this response to deal with present day stresses, this response still occurs.

Luckily we have the capability to override our natural instincts so we don’t run from our boss or punch him if he shouts at us. But because we override our natural instincts and don’t act through fighting or flighting then we are left with unnaturally high Cortisol levels. As long as our liver is functioning optimally then the liver can mop up the excess Cortisol, however, if it is overburdoned with other jobs such as detoxification, then Cortisol is then mopped up in the greater omentum. The greater omentum is an organ which sits just behind the rectus abdominis (six pack muscles) and through having to mop up excess Cortisol it enlarges which gives you the pot belly look.

So how does Cortisol relate to exercise intensity?

Exercise is a stress on the body which means exercise produces Cortisol to be released. However, the exercise intensity and duration determines how much Cortisol is released whilst at the same time exercise intensity and duration determines the other hormones which are released alongside Cortisol.

A lot of people when trying to lose weight do moderate intensity long duration exercise. This type of exercise includes running and cycling as well as exercise classes such as spinning, body pump and body combat. This type of exercise leads to high amounts of Cortisol being released for an extended period of time with a very little amount of other hormones released. In some people who break down glycogen to be burned from there fat stores and who have clean livers they will lose weight, but those people who don’t have clean livers or they burn a higher percentage of muscle will struggle to lose weight and can even gain weight. Those people who don’t have clean livers may end up getting a larger stomach due to the Cortisol being mopped up in the greater omentum instead of the liver and those people who break down a higher percentage of muscle may end up losing muscle and slowing down there metabolism. Because of these effects, moderate intensity exercise can easily lead to weight gain instead of having the intended effect of weight loss. This doesn’t mean you should necessarily cut out moderate intensity cardio from your training regime completely; you just need to be careful with how often you do it.

For those people who don’t have clean livers or those who burn a higher percentage of muscle they should do high intensity exercise for short durations instead of moderate intensity exercise. The reason for this is that through doing high intensity exercise for a short duration you will produce less Cortisol, however, you will also release other hormones which will aid fat loss.

You may be thinking surely by working at higher intensities it is a larger stress on the body so it will produce more Cortisol. The answer to this is yes, it does produce a larger initial spike, but because the workouts are far shorter, overall it produces far less Cortisol. It is impossible to workout out at high intensities for a long period of time, which is why it will always produce less Cortisol. If you do exercise for a long period then you will have moved back into moderate intensity training so you can last longer.

The main benefit of the short duration high intensity exercise over long duration moderate intensity exercise is that unlike moderate intensity exercise, high intensity exercise leads to other hormones being released which aid in fat loss. These other hormones being released due to the high intensity exercise is your body’s natural response to carrying out the fight or flight response. Because fighting or flighting is a high intensity activity, doing high intensity exercise releases the same hormones as what fighting or flighting would. These hormones include adrenaline, testosterone and human growth hormone.

Without going into too much detail adrenaline is released to break down stored glycogen even faster than Cortisol to prepare you for the intense burst of exercise and then testosterone and human growth hormone are released to help you to become leaner and stronger so you can cope with the situation next time. This is the natural response to fighting or flighting because you need energy instantly so adrenaline breaks down sugar far quicker than Cortisol. Then because of the stressful situation your body realises it needs to adapt so it can cope better if the same situation occurs. Testosterone is released to help you build muscle so you become stronger and human growth hormone is released so you burn body fat in order to become leaner so you can move faster. If this natural response didn’t occur when fighting or flighting then people wouldn’t have survived thousands of years ago as they wouldn’t have had the energy to fight or flight from wild animals and they wouldn’t have adapted to cope with the situation better next time.

Because of the natural response of high intensity exercise, it is far more effective for fat loss and getting a lean toned body than moderate intensity exercise such as running, cycling and exercise classes.

Because fighting or flighting can only be sustained for a short period of time and often occurred in bursts then this is how you should train. Short bursts of intense activity repeated for a short duration of ideally 20 minutes. If you can last longer than this then this is a sign to work even harder during the time rather than increase the time frame as increasing the time frame will have the wrong effect on your hormones.

If you are currently doing moderate intensity exercise such as running and cycling or exercise classes such as spinning, body pump and combat and aren’t losing weight or are gaining weight, then you would be far better off doing high intensity interval training for 20 minutes as it will release the correct hormones to help you lose weight. The other benefit is that it will save you a lot of time as well.

The final kind of exercise intensity is low intensity exercise. Low intensity exercise is great for lowering Cortisol. This is because low intensity exercise isn’t a stress on the body so it doesn’t produce a Cortisol spike. The other benefit of low intensity exercise is that you actually burn the highest percentage of fat during this type of exercise. During moderate and high intensity exercise you burn high percentages of sugar to give you energy fast, however, during low intensity exercise you don’t need instant energy so you burn energy from your fat stores far easier. Low intensity exercise is a great combination to be used with high intensity exercise. The high intensity exercise releases the hormones to help you burn fat and the low intensity exercise allows you to burn the fat whilst lowering your Cortisol level to prevent any negative effects.

Low intensity exercise includes walking, mobility exercises, stretching and restorative yoga (intense yoga is a stress on the body and bikram yoga is a stress on the body due to the heat which leads to Cortisol being released).

If you combine high intensity exercise for short durations with low intensity exercise for longer durations then you have the ideal combination to lower your Cortisol levels and to burn fat at the same time.

Now you know the effects of exercise duration and intensity on your Cortisol levels which influences your results, how will you change your exercise routine to start seeing results?


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Shaun McGill

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