Robinson cites the MRIs, CAT scans and other tests he's taken and that none, to this day, have shown any concussion-related effects. When a test definitively reveals something, Robinson swears, "I'll put my bike down, I'm done. It's not worth it."
But, doctors say, no such test exists.
"We don't have any single litmus test that will tell us with certainty that the individual is OK," Echemendia says about concussions. "Our tests are still relatively crude, and it's possible that some of our tests are saying the person is OK when the person is not."
A thorough biopsy could be performed, Raukar says, but only postmortem. "There's no way to look at the toll until you're dead," she says.
When posed with this notion, Robinson says, "I'll just ride until they find something."
The idea that something could go wrong or already has and that it's beyond Robinson's control may still seem distant to him, although he faced a life-changing event recently that forced him to acknowledge the possibility.
Because one of Robinson's closest friends was Junior Seau.
They met more than a decade ago through Dr. David Chao, the San Diego Chargers' team doctor and the X Games medical staff's lead physician. Chao thought both could light up any room they entered, and that two people like that would be great friends. "Honestly, Kevin is so much like Junior, they're in some ways the same person," Chao says.
Eventually, Robinson joined the board of directors for the All-Pro linebacker's charity, the Junior Seau Foundation, to educate and empower young people and it inspired Robinson to start a similar foundation.
Robinson had scheduled a charity event on May 20 in Rhode Island. Seau booked a plane ticket and sent a text message relaying his excitement to Robinson weeks before.
But in early May, Seau, at age 43, committed suicide by shooting himself in the chest.
Robinson had last seen him a couple of months before at an event in a San Diego resort. He recalled that Seau was in great spirits.
Robinson's charity event went on as planned and about 6,000 attended, he says. Many wore buttons and T-shirts with Seau's jersey number -- 55.
At the end of the night, Robinson stood on stage with Dr. Chao and others. Robinson looked over and saw Chao and Chao's wife and remembered Seau was supposed to be next to them. That, Robinson says, is when it began to sink in: Junior was gone.
Then, with tears and his voice breaking, Robinson handed out a new award that he decided would be presented to someone who goes above and beyond to help their community: the Junior Seau Award of Excellence.
Robinson calls Seau's death a "mystery," but it no doubt devastated Robinson.
"He was so depressed," Raukar says of Robinson, after news of the suicide. "They're both contact athletes. They've both had head injuries. He was looking at his future."
Though many have speculated Seau's suicide was related to years of head injuries, Robinson refuses to.
"I just try to remember him for all the amazing things he's done and the presence he had in my life," Robinson says.
Yet, Robinson acknowledges that he has formed a pact with a close group of friends, some of whom play in the NFL, that if they ever seem to be mentally deteriorating, "We're going to talk, we're going to be open about it, we're not going to hide anything."
What inspired them to make such a promise?
"Recent events," he says, slowly, "definitely made an impact."
An impact. Perhaps one more powerful than any of the hundreds he has suffered.
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baxter.holmes@latimes.com
twitter.com/baxterholmes
