Cobb County, Ga. (CNN)-- Every time Robert McCune steps out of the hyperbaric chamber he feels free of aches and pain.
"I feel refreshed. Sometimes, I have a headache and I get in there and when I come out, I swear to you my headache is gone," he said.
The retired NFL linebacker for the Baltimore Ravens is using hyperbaric oxygen to treat headaches and tremors caused by 10 years of repeated concussions he suffered on the field.
"It's probably been hundreds, where I have just blacked out, lost my vision, not really knowing where I was," McCune said.
McCune is among a growing number of athletes using hyperbaric oxygen as a concussion treatment, with hall-of-famer Joe Namath being one of the biggest names leading the charge. Namath said the treatments have improved his memory retention.
Injured body tissue needs increased oxygen to heal, so the hope behind hyperbaric is that pressurized oxygen is restoring brain cells damaged by traumatic brain injuries.
Dr. Louis Hilliard runs the Atlanta Hyperbaric Center out of Smyrna where McCune gets his treatments.
"This is a non-toxic, non-invasive form of treatment that can get sick people well very easily just within a matter of weeks to months," he said.
A session costs between $75-100 for up to two hours.
Hilliard - himself a former football player - said it's so popular among athletes that he created an NFL outreach program that he runs with McCune.
"There's so many other players that are out there that are starting to realize the positive, wonderful effects of what hyperbaric is," he said.
Concussion treatment has developed into a multi-million dollar industry from universities to the Department of Defense scrambling to find ways to prevent and treat head injuries. And with concussions on the rise - Hilliard's timing seems spot on.
The NFL reported a 58 percent increase in concussions in 2015 with 182 cases reported, up from 115 in 2014.
But not everyone is convinced it works.
Dr. Gerald Zavorsky, an associate professor in respiratory therapy at Georgia State University studies concussions. He said while hyperbaric is used to treat burn victims and carbon monoxide poisoning, the science is sketchy when it comes to concussions.
"People think that this extra high pressure oxygen allows for more blood to have this oxygen to be carried to the brain well that is not really true," he said.
Part of the problem, he said, is figuring out whether it's the pressure or the oxygen affecting damaged brain cells.
"It's just really hard to separate whether it's high pressured air versus high pressured oxygen, and in these studies the high pressured air is thought to be a placebo effect because you're not actually getting more oxygen to the brain," Zavorsky said.
And, said Zavorsky, that placebo effect is what may have athletes like McCune believing they feel better - although there's no scientific evidence to support it.
"I think as scientists and researchers we shouldn't take testimonies for granted it needs to be backed up with research," he said.
Hilliard says the skeptics don't bother him or hurt his business. He's been selling a lot of chambers -- the most expensive price tagged at 20-thousand.
"I don't care what people think. When I see the miracles happen in my office and the people that are coming in here with various ailments," said Hilliard. "We don't treat anything all I do is just give them a breath from God."