The newest fitness trend has people wearing strange-looking masks.

And do they really work?

It’s been a big year for fitness trends. People are training like vikings, doing military-inspired workouts called rucking, exercising with face yoga, and even laying on their sweaty backs and taking selfies of their “sweat angels”.

Now, a new trend has been popping up everywhere. We’ve noticed people wearing them on the street. Ruby Rose has been pictured sporting one, and you’ll regularly see footballers training in them. So what on earth are these masks?

Apparently, they’re designed to simulate what it’s like to workout at higher altitudes by limiting oxygen intake. So, if you’re anything like us, you’re probably thinking, why are people using them if they make it harder to breathe?

“The best indicator of a solid workout would be your breathing patterns, but factors like the weather and altitude can affect your breathing. The main reason people use training masks is to help them train to breathe more easily in different conditions, and to improve overall endurance levels” says Ali Cavill, a personal trainer and owner of Fit Fantastic.

The masks can be customised for the wearer so that they can train for different environments or altitudes.

The little plastic discs you see on the masks allows the user to choose the difficulty to match the elevation they require. Most of the masks come with three different valves, which mimic training altitudes of 3000ft up to 18,000ft. (Post continues after gallery.)

Through the different altitudes, the masks restrict oxygen intake during exercise. According to one manufacturer of the masks, Training Mask, as your body adapts to the resistance, your lungs will be trained to take deeper breaths and use oxygen more efficiently.

“The masks do strengthen and train your breathing muscles. I think anything to do with improving breathing muscles and maximising strength is a great thing,” Cavill says.

Altitude training is not uncommon in professional sports training programs. Since 2005, Collingwood Football Club has been sending its players to Flagstaff, Arizona, similarly, Carlton Football Club have altitude training rooms for their players.

And with more and more celebrities and sportspeople we see wearing them, we suspect we’ll be seeing more scary-looking people running past us in the street.

But before you go and buy one (most of them retail around the $120 mark) it’s recommended that you have relatively high fitness levels and consult your doctor before using one. Using an elevation mask without proper training can result in rapid brain oxygen loss that may lead to the swelling of blood vessels in the brain, or even death.

So yeah, it’s not something you want to rush into.

This post originally appeared on The Glow.

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