No benefit from excessive high-intensity exercise

New Research Sparks Call for Guidelines Around High-Intensity Interval Training – Jun 2018 – Source Newsroom: Les Mills

New research has for the first time set a recommended upper limit of High-Intensity Interval Training (HIIT) at 30-40 minutes working out at above 90 percent of the maximum heart rate per week.

At first, I misread this and assumed they were talking about 30-40 minutes in one day, but I’m shocked to see this amount as the maximum for a whole week.  

The study findings – presented by Associate Professor Jinger Gottschall at the 2018 American College of Sports Medicine (ACSM) Annual Meeting this month – provide evidence that any more than 30-40 minutes of HIIT in a maximum training zone per week can reduce performance and potentially result in a greater risk of injury.

Currently there are no guidelines concerning the greatest amount of HIIT people should do in a week for the optimal the training effect,” she says.

Given the extreme intensity* involved in this kind of exercise, it’s imperative that maximum guidelines are provided in the same way that minimum guidelines have been in the past.  We hope this study will be instrumental in helping make these recommendations official.”

Bryce Hastings, Head of Research at Les Mills – who worked in collaboration with Professor Gottschall on the research – says: “What our research findings tell us is that there is only so much HIIT a regular exerciser can do in one week before the effects are compromised.

“The findings have scientifically established that less is more when it comes to HIIT and that any more than 30-40 minutes working out at above 90 percent of the maximum heart rate per week doesn’t help achieve transformative effects. In fact, too much actually hinders.”

Just as with any other treatment, therapy, or regimen, an excess of normally beneficial actions usually leads to damage – literally “too much of a good thing”.

The key lies in the nature of HIIT itself. By pushing the body into its maximum training zone for short periods, a positive stress response is triggered that creates bio-chemical changes in the body that help build new muscle and improve fitness.

This can be measured effectively by examining cortisol and testosterone concentrations in saliva samples.

“In scientific terms, what we’ve observed by measuring the stress response in the saliva of our study participants is that those who do more than 30-40 minutes of HIIT per week are unable to produce a positive stress response,” says Gottschall.

“If you want to get the best possible results from HIIT, our recommendation, based on these findings, is to balance your weekly HIIT sessions with other, less intense cardiovascular and strength workouts. It’s also imperative that you let your body recover properly after a HIIT session.  

This way, you’re likely to perform better when you do your HIIT workouts and benefit from the positive results.”

* High-Intensity Interval Training typically involves periods of extreme exertion where you push your heart rate to greater than 85 percent of your maximum capacity followed by periods of rest.

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