NEW YORK (AP) — Michael Phelps is the latest athlete to use a hyperbaric chamber to aid his recovery from training.

The 16-time Olympic medalist said Wednesday he had been sleeping “at 8,000 feet every night” for almost a year. The 26-year-old swimmer noticed he bounced back from workouts better when he trained at altitude, so he’s trying a device that simulates that.

“We’ve been able to realize after going to Colorado Springs so many times that it is something that helps me recover,” Phelps said. “That’s something that is so important to me now being older. I don’t recover as fast as I used to.”

He said the chamber looked like a fish tank: “Imagine, like, a bed with a box around it.”

“It’s kind of strange, but it’s good,” Phelps said during an appearance for sponsor Head & Shoulders. “I don’t mind it. There’s a giant door at the end of my bed.

The worst thing is trying to watch TV in it. I’ve got to watch it through Plexiglas — it’s blurry.”

Phelps is preparing for what he says will be his final Olympics this summer in London. He won a record eight gold medals in Beijing in 2008.

Hypoxic or hyperbaric tents and chambers are used by many athletes to replicate high-altitude conditions and boost levels of oxygen-rich red blood cells. They have become popular with NFL players trying to speed their recovery from injuries.

In 2006, the World Anti-Doping Agency’s ethics committee ruled that such chambers enhance performance and violate “the spirit of sport,” but the executive committee refrained from adding them to their list of prohibited substances and methods, instead asking for studies to look further into health implications.