Are HIIT workouts bad for your body? The heart-thumping exercise could be making you more stressed and tired
Fitness experts fear training in this way can have a negative impact on your health and wellbeing
IT’S the heart-thumping exercise loved by thousands of time-poor fitness fans looking for fast, impressive results.
High Intensity Interval Training (HIIT) involves repetitions of short bursts of intense, 'maximum effort' exercise, like sprinting, cycling or rowing; usually for anywhere between 20 to 40 seconds.
It has gained mass appeal – even David Beckham, Britney Spears and Gwyneth Paltrow are advocates – because, by working out at the top level of exertion, you burn more calories in a short space of time.
And, studies show that your metabolism stays in a heightened state for up to 24 hours after you've finished.
But, is the HIIT phenomenon actually bad for your body?
“People are falling apart from this exercise,” Max Lowery, author of The 2 Day Meal, told The Sun Online. “Short term your body can deal with it, but when you’re doing it regularly over time, your body will slowly start to breakdown.”
He says there is often no focus on form or technique in HIIT classes, which can lead to chronic pain, muscle problems and injury.
Max Bridger, founder of LDN Muscle, said: “In general, HIIT isn’t performed correctly. It’s jumped on by so many ‘experts’, but it can mean anything from a circuit class to general interval training.
"The issue is simply that people are doing workouts that they're not conditioned for. There is no emphasis on flexibility, mobility or activation.”
While most people exercise to de-stress, Bridger says HIIT can actually make you feel more frantic. “
"It’s very high stress,” he said. “Too much HIIT training can mimic stress, stop you sleeping and ruin your appetite. HIIT, if it’s your sole source of training, will increase the risk of burnout.”
Lowery added: “The word ‘smash’ is always related to workouts at the moment. It’s that attitude you have to be destroyed at the end of the class.
"Sometimes that is needed for specific results, but sometimes the last thing you want to do is ‘smash’ your body, when it’s already feeling stressed.”
HIIT, according to Lowery and Bridger, should not be done more than three times a week, because it is so strenuous. It puts a strain on your nervous system, joints and muscles; especially if you are overweight and unfit.
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Lowery said: “Overtraining is a real danger: it can ruin your immune system, cause insomnia, affect your appetite and release cortisol, which in turn can make you more likely to put on fat.”
Office workers are at risk. Sitting at a desk for eight hours a day can cause all sorts of joint and muscle issues. “If you’ve been sitting at a desk, all day, for five days a week, you’re going to have a lot of imbalances,” Lowery said.
“What HIIT does is make those imbalances worst. If you’ve got a weakness anywhere, for example a posture problem, HIIT will make that even more ingrained.”
A 2017 study published in the found instances of a condition called rhabdomyolysis - the breakdown of muscle - among new HIIT fans. The condition is usually associated with military training camps.
The muscle breaks down and leaks into the bloodstream, which can cause severe pain. If left unchecked, it can lead to kidney damage.
Bridger also says HIIT is problematic for women who are anaemic or going through the menopause.
“A woman can lose 20% of their bone density in five to seven years when going through the menopause,” he said. “It would be more beneficial to focus on resistance and weight training because this can increase bone density and stall the decline. HIIT won’t have that effect. It’s more likely to result in damage to ligaments and bones.”
He added: “Women who suffer from anaemia should also do HIIT around their menstrual cycle. When you come onto your period reduce intense exercise because it could cause stomach pains and you’ll fatigue quicker.
"If you do have white blood cell deficiency or anaemia it’s not a great time to be putting your body under high stress.”
HIIT can have impressive results. It's an effective tool for increasing cardiovascular fitness, sculpting your physique and increasing metabolic rate - but it should not be done in isolation.
Lowery said: “There’s no one size fits all rule when it comes to the ideal exercise regime. As a rule, if I was getting someone into general fitness for the first time, I would say three general sessions in the gym.
"Each session would be 15 minutes of mobility work, then strength and then at the end I’d finish off with some conditioning and cardiovascular work.”
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Max Bridger is a personal trainer and co-founder of . Follow Max on