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Cortisol, stress and exercise

Cortisol is a steroid hormone that is released into the bloodstream by the adrenal glands in a natural rhythm with our body's sleep cycle. It peaks in the early morning helping us bounce out of bed and gradually falls, reaching a trough at 3 or 4 am when we should be soundly asleep.

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What does cortisol do?

Cortisol has a vital job as one of the body’s stress hormones, released as part of the fight-or-flight reflex. It shuts down less critical functions like reproduction and immunity to focus on fighting the immediate physical threat and breaks down tissue to provide the energy necessary.

The functions of cortisol are supposed to be immediate and short lived, enough to see off any physical challenge. This was great for cavemen fighting sabre-toothed tigers -but less ideal in modern lives when stress can be psychological and constant.

The positive role of cortisol in your body

Cortisol has a vital physiological role. By raising plasma glucose levels at times of stress, cortisol provides the body with the energy it needs to face bodily attacks from injury, illness or infection. It has potent anti-inflammatory effects easing irritation and pain.

The negative effects of too much cortisol

Too much cortisol for too long can have serious, negative effects. The tissue breakdown, reduced protein synthesis and conversion of protein to glucose can decrease musculature and increase abdominal fat, not an ideal result! It also suppresses levels of growth hormone and sex hormones, which can reduce libido and fertility. It lessens glucose usage and increases blood levels potentially predisposing to diabetes and its effects on calcium can increase osteoporosis.

So it is clear that moderating cortisol levels is important for the maintenance of our health and wellbeing.
 

Exercise, stress and your cortisol levels

Exercise is perceived by the body as a form of stress and stimulates the release of cortisol. In general, the more your fitness improves the better the body becomes at dealing with physical stress. This means that less cortisol will be released during exercise and also in response to emotional or psychological stresses.

However, research shows that the time and intensity of exercise can affect the level of cortisol release. When it comes to exercise, more may not be better. Training for more than 60 minutes, even at a low intensity will burn up the body’s glycogen stores and stimulate cortisol release. A study confirmed that long-term cortisol exposure was significantly higher in endurance athletes.

Short high intensity exercise such as sprints, HITT or weight training cause less of an increase in plasma cortisol concentrations. However, the levels tend to surge if rest periods are short and work levels are high. This is particularly significant if exercising when starved or nutritionally depleted and was also increased by training in the early morning when cortisol levels are naturally higher and the response to exercise can be more.

What you can do to maintain healthy cortisol levels when training

It is possible to enjoy the undeniable benefits of exercise while minimising the impact on cortisol concentrations:

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