SAN LUIS OBISPO, California – Trudging up a brier-covered mountain in freezing temperatures with a dying headlamp, Nickademus de la Rosa knew his attempt to finish the Barkley Marathons, a race spanning over 160km in Tennessee, was coming to an end, as it eventually would for most other entrants.

The race has no trail markers, an elevation gain comparable to climbing Everest twice from sea level and a finish rate that hovers around 1 per cent.

Earlier in de la Rosa’s career as an ultramarathon runner, he most likely would have been stricken with an overwhelming sense of worthlessness and shame for not completing a race. But in the Tennessee woods in March, he saw the upside.

“Instead of hitting myself and telling myself how worthless I am, I congratulated myself on what I was able to accomplish,” he said.

“I realised I did not have anything to prove at Barkley. I had no more demons to slay and I was happy to finish early and spend time with my wife.”

It was a significant moment for de la Rosa, who has been grappling with a serious mental illness that has imperilled his running career and life.

In a sport dominated by people in their late 20s, 30s and even 40s, de la Rosa was a prodigy. At 19, he finished Badwater, an infamous 217.26km race across Death Valley in California in the brutal heat of July. When he was 21, he completed 217.26km in Minnesota with temperatures of minus 37 deg C.

The next year, he became only the 13th person to finish Barkley since it began in 1986. And at 24, he placed second in the Tor des Geants, a 330km race through the Alps. During that 76-hour race, he slept less than two hours and hallucinated that his running partner’s intestines were hanging out of his body.

De la Rosa said he always ran races to win them, but he now realises that his motivations were more complex. He spent much of his youth and young adulthood in emotional turmoil, and instead of seeking treatment, he essentially self-medicated by keeping a brutal training schedule and participating in some of the world’s most gruelling races.

In 2019, at 29, he was diagnosed with borderline personality disorder (BPD), which can cause sudden shifts from intense sadness to deep fear to shame or joy. Those with the condition often have an unstable sense of self and struggle to keep jobs or maintain relationships, and many, including de la Rosa, attempt suicide.

The illness affects about 14 million Americans, according to the National Education Alliance for Borderline Personality Disorder. That is twice the number of people who have Alzheimer’s disease and nearly the same number as schizophrenia and bipolar disorder patients combined.

On a Monday morning in May, de la Rosa, 33, and his wife, Jade Belzberg, 31, sat at their favourite cafe in San Luis Obispo, California, where they live.

Belzberg is a formidable ultramarathon runner herself, and they had spent the weekend running in the mountains. The ground covered showed in their sun-tanned faces, weary eyes and the slowness in their steps.

Over coffee and tea, the couple talked about his mental illness, their athletic accomplishments and their future, which they see as closely connected.

De la Rosa is tall and broad-shouldered, with unkempt hair and freckles that bring a boyishness to his face. He said his mental illness was a strength and a crutch.

“It was a superpower in races like Barkley that required gritting it out and going into the storm where any idiot would stop because the conditions were terrible,” he said.

“But this special idiot, because he has BPD, would need validation because this win means so much to me, I will push harder than anyone else.”

Like many people who have BPD, de la Rosa finds it hard to regulate his emotions. He explained the intensity of his feelings on a scale of one to 10. When he tips over a seven, he said, his fight-or-flight response is triggered, and he spirals into suicidal ideations, rage or intense self-loathing. Fears of abandonment and of rejection are two of his strongest triggers.

As his career has stalled, Belzberg, who had not run in a race longer than 10km when the couple met a decade ago, has taken off. When she passed him on a recent run, he responded by hitting himself in the head. He said all of this in a matter-of-fact way that would be easy to overlook if he were not talking about self-harm.

Dr Peter Attia, a physician and author of Outlive: The Science And Art of Longevity, said he suspects that dopamine, endorphins, a need for distractions, an urge to self-punish and a longing for self-esteem are among the reasons some people with mental illness, addiction and trauma are attracted to endurance sports.

De la Rosa, who moved to San Diego with his mother after his parents’ divorce and said he could trace his unhealthy relationship with running to his teenage years, agreed.

“I wasn’t that good at cross-country in high school and was not going to stand out. And then I did a marathon and everyone was like, ‘You did a marathon!’” he said.

As someone who felt worthless and struggled to find his identity, he found all of his self-worth in ultrarunning.

In late 2017, de la Rosa was diagnosed with a heart condition that could have been fatal if unaddressed. He had successful open-heart surgery but later developed pericarditis, a condition that inflames the tissue around the heart.

Unable to train or race at the level he was accustomed to and with his running career in limbo, de la Rosa spiralled out of control. During a run in British Columbia a few months after his surgery, Belzberg was concerned about the worsening weather and wanted to turn back.

De la Rosa said he got extremely angry, shoved his wife in the snow and threatened to push her off the mountain. Immediately overcome with shame and horror, he looked for a cliff to jump off. On the way down the mountain, Belzberg said, her husband alternated between “crying, screaming and laughing maniacally”.

In 2019, de la Rosa shocked the ultrarunning community when he posted on Instagram that he was on high-risk suicide watch. He shared his diagnosis and mostly stepped back from intense training and competition.

Belzberg, who is now a sponsored runner and who represented Canada in the World Mountain and Trail Running Championships in June, is thin, with long, dark, wavy hair and eyes the colour of Arctic ice. When she smiles, her entire face scrunches.

She said there were signs long before de la Rosa’s heart surgery that he was dealing with mental illness. When he could not run because of a knee injury, he tried to drown himself.

Belzberg, who started seeing a therapist after her husband’s diagnosis, said she often plays the role of caregiver.

“It’s me suggesting the residential programme and then it’s me suggesting medication,” she said.

“It has been such a fight each time and it’s very isolating because very few people have a behind-the-scenes look at what is going on.”

Her perseverance and his sometimes reluctant focus on his own well-being have helped. He is on a mood stabiliser and for four years has been in dialectical behaviour therapy, which teaches people how to reframe their thoughts and behaviour and helps them deal with distress.

De la Rosa is now on track to get a master’s degree in sports psychology from the University of Western States, and he and Belzberg have built an online coaching business working with around 70 runners. NYTIMES