SAN JOSE -- The heart attack was six months ago. But Dan Clark still wears the plastic hospital bracelet on his wrist.

"It's tattered and frayed," he said. "But it reminds me to be grateful that I'm alive."

Clark was a San Jose State football defensive lineman in the mid-1980s who later carved out a pop-culture niche as the cocky, Spandex-clad character "Nitro" on the American Gladiators TV series. And Saturday he brings back to San Jose his Gladiator Rock 'n Run, which deftly has caught the growing wave of obstacle-course racing.

But in December, Clark thought he might be dying after suffering a heart attack while working out -- a shock for a fitness buff.

Dan Clark demonstrates  the "Beast," which is the final obstacle for his Gladiator Rock’n Run obstacle race at Joseph D. Grant County Park
Dan Clark demonstrates the "Beast," which is the final obstacle for his Gladiator Rock'n Run obstacle race at Joseph D. Grant County Park in San Jose, Calif., on Thursday, June 26, 2014. (LiPo Ching/Bay Area News Group) ( LiPo Ching )

"I thought I was bulletproof because of my lifestyle," said Clark, who lives in Southern California and turned 50 in May. "But that's exactly why cardiovascular disease is the No. 1 killer. We just don't understand the risk factors. But I learned how everything can change in a heartbeat."

Or when a heartbeat nearly stops.

Surprising health scare

Friends always thought Clark lived a charmed life. A brief professional football career morphed into his role as a 260-pound "gladiator" combating amateur athletes. Years later, he's an adventure-race entrepreneur.

"He's never really had a real job," said Frank E. McFadden II, a college roommate who has remained good friends with Clark. "But everything he does, he's successful at it. He's just this little, playful puppy who has never realized that he's really a Rottweiler. He's the happiest guy that I've ever met."

But that wasn't the case last December. Clark was in the gym -- where he trains five days a week. Clark experienced shortness of breath, chest pains and a cold sweat.

"I was shaking my left arm and that's when I thought, 'This is a heart attack,'" Clark said.

An electrocardiogram confirmed his self-diagnosis after a friend drove him to an urgent-care center.

"Suddenly, you're that guy everyone is looking at, on the gurney, with an IV in your arm and an oxygen mark over your face," he added. "I remember they kept talking about nitro in the ambulance. I thought they were talking about my Nitro character until I realized they were talking about giving me nitroglycerin."

Clark underwent emergency surgery for a blood clot in one of his arteries and had a stent implanted.

"I definitely thought that I might lose one of my best friends," McFadden said. "But when I got to the hospital, he already was out of surgery. And I had to tell him to settle down and rest because he wanted to walk around."

Family history is a strong risk factor for heart attacks, and Clark's father had suffered one. But less clear is what role anabolic steroids might have played.

Five years ago, he published an unflinching tell-all called "Gladiator: A True Story of 'Roids, Rage and Redemption." He wrote of how steroids helped him get a football scholarship, play a few games in the NFL and buffed his chiseled physique. But his body also began to break down as he added more muscle than his frame could handle.

Heart problems are a side-effect of steroids, according to the National Institutes of Health. But Clark said he long ago stopped taking them, was closely monitoring his body chemistry and had shown no symptoms before that day.

"It would be easy to point the finger and say that 20 years ago you did this, and now this is the result," Clark said. "But I just don't know. I haven't read any literature about linking past usage to current problems like this."

New fitness boom

Today, he is focused on his Gladiator Rock'N Run series. The idea came to Clark in 2009 when he ran the popular San Jose Rock 'n' Roll Half Marathon with former San Jose State teammate Bob Frasco.

"I felt such a sense of accomplishment," Clark said. "But I started looking for something more than just running around on pavement. I wanted to design something that was fun and could be done by anyone."

That year, according to The New York Times, there were just a few of these extreme events. But now Clark is part of a boom that includes 250 companies operating obstacle-course events. The Tough Mudder and Spartan Race series, which are the young industry's giants, each are expected to draw 1 million participants this year.

"I call it a flame-leaping, mudslinging, Spandex-clinging run from hell with beer," said Clark, who is holding events in eight cities this year. "You're going to get dirty. But you'll have a smile on your face."

Over the six-kilometer course at the Joseph D. Grant County Park on Mt. Hamilton Road, competitors will navigate obstacles such as a waist-deep pool of icy water, a mud pit, an 8-foot wall and crawling through underground trenches. Clark said they are expecting 7,500 people, including between 3,000 and 4,000 participants.

Meanwhile, his health is back to about 95 percent of what it was before the scare. Last week, to mark six months into his recovery, Clark tried another potentially heart-stopping activity. He went sky-diving.

"I just thought that it was a good way to celebrate life," he said.

For more information about Saturday's event, visit www.gladiatorrocknrun.com