How does HIIT change our body?

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Photo by Victor Freitas on

If you’re new to HIIT training then working out and feeling like you’re going to pass out probably go hand in hand. For those of you that have been training for a while you have probably seen first hand some of the impressive benefits that HIIT training has to offer (see 7 benefits of HIIT training).

HIIT is characterised by repeated sessions of brief, intermittent, maximal effort with periods of rest or low-intensity exercise for recovery. Popularity of HIIT workouts have increased year on year especially among busy professionals with limited time away from the work place

For those of us participating in HIIT classes this article will talk you through and explain the physiological changes that occur during the class.

Ever heard of Phosphocreatine?

Not many people have but it’s the high energy molecule used by your muscles to fire you up for the first 10-20 secs of an explosive HIIT session.

Here comes the burn….

Huge energy demands depletes the source of phosphocreatine at around 20 secs into a HIIT session. As a result the body enters a period of anaerobic glycolysis and lactic acid production. Increasing levels of lactic acid build up and are used as fuel. It’s probably around this time that you can feel your heart thumping and you want to stop and die all changes mainly related to changes in blood pH.

Time to breath and settle into a steady rhythm…

When our bodies are working hard during a HIIT session the demand for oxygen outstrips supply and we enter anaerobic metabolism. During anaerobic metabolism we are unable to get enough oxygen to the muscles that are working maximally so we have to eventually reduce intensity for efficiency. This unique evolutionary process allowed our Neanderthal ancestors to escape sabre tooth tigers and us to hit snooze a few too many times and still make it into the office on time.

Time to recover…

During the rest period the body becomes enters aerobic metabolism again and lactic acid is broken down.

Following an intense HIIT session hormones such as cortisol, growth hormone, testosterone, endorphins, adrenaline, noradrenaline and aldosterone have all been shown to increase. These hormones play a crucial role in stimulating physiological changes that lead to improved health and fitness.

Published by Dr Chris George

NHS doctor working in General Practice.

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