My headlamp illuminated yet another snow patch, this one close to 30 feet across, looming out of the shadows to completely swallow the trail. Even on a path this narrow, contouring along the side of the valley at night should have been easy, but these intermittent snow fields were killing me. Ollie, my hiking partner, barely slowed, stamping footprints into the crust, but I hesitated. I couldn’t trust my malfunctioning left leg to negotiate the steep and icy traverse, certainly not with a runout that disappeared into darkness. I grunted, turned, and began scrabbling up the muddy incline above the trail, my useless limb trailing behind me. By the time I’d climbed high enough to skirt the snow patch and slide back down to the path, I was filthy, exhausted, and frustrated. In the 14 hours since breaking camp, we’d averaged one mile per hour, taking our grand total over the last two days to 26. Out of 501.

I’d wanted to hike California’s Sierra Nevada for over a decade, my greedy eye fixed on a classic north-south traverse along the Pacific Crest Trail. Geologically, the range runs from Lake Almanor in the north to Tehachapi Pass, near the Southern California desert town of Mojave, but I was only really interested in the highest, most spectacular section. After playing around with a PCT distance calculator the previous year, I’d discovered that the route between Donner Pass and Walker Pass never fell below 5,000 feet and ran for exactly 501 miles, one mile over the minimum requirement for a permit. I loved the thought of breaking 500; It was 2022, I would turn 50 the following spring, and the challenge of hiking ten times my age intrigued me. Everything had fallen nicely into place. Except for one thing.

In 2019, I was diagnosed with multiple sclerosis (MS), a neurological disease in which the body’s immune system attacks the protective myelin sheaths around the nerves in the brain and spine, exposing them to damage and resulting in a poorly functioning central nervous system. Effectively, the signals sent by the brain to the rest of the body are interrupted.

The first evidence of the disease cropped up in 2017, when my legs started going through periods of uncontrollable twitching, contracting violently every couple of minutes. It was impossible to sleep during these attacks, or drive, or sit watching television. I was referred to a neurologist, who diagnosed me with restless-leg syndrome (RLS), and I now take a drug called pramipexole three times a day to prevent the spasms from driving me insane.

Then, in 2018, my left foot began to drag when it got tired. This would have been problematic for anyone, but hiking has been my primary obsession for over three decades, so the inconvenience was tinged with panic. I was born in the UK but moved to my adopted home of Sydney, Australia, in 2009. I’ve walked all over the world, from the Andes to the Alps to the Himalayas. Then there was trail running. I’d won an ultra in my time, and was only the second recorded person to run the full 43-mile circumference of Easter Island. I’d just started training for the 100-kilometer Ultra Trail Australia when the dragging began, and that was the end of that.

I like to think I’m a level-headed individual. I didn’t rant or damn God or even cry when, via an MRI scan and spinal tap, my neurologist diagnosed me with MS. What I did was ignore it as best I could and carry on with my life. That first summer, as planned, I walked the UK Coast to Coast path, the Haute Route in Switzerland, and Corsica’s GR20 back-to-back, a total of 442 miles. I called it the European Triple Crown.

Such feats meant I could pretend this slow-motion car crash wasn’t happening. The disease became my secret shame, known to only a handful of people: my doctors, my wife, and select colleagues. I felt embarrassed that my body was failing to do its job, as if it were somehow a moral weakness. To friends who caught me limping, I spun a lie about a rolled ankle. I couldn’t face their sympathy, and that unintentional look of pity behind the eyes. As far as my family was concerned, I didn’t want to worry them. Even today, five years after my initial diagnosis, I haven’t told my parents.

As I began planning the Sierra traverse in late 2022, my condition deteriorated rapidly. I went from breezing through multiday hikes to being unable to walk for half an hour without my left leg dragging behind me, like a sandbag attached to my knee.

There was no question of postponing the hike, though. The most common form of MS is called relapsing remitting, sufferers of which can sometimes live a relatively normal life between episodes of catastrophic disability. The other form, primary progressive MS, with which I am blessed, steadily worsens over time, a constant downhill slide into neurological oblivion. I can’t afford to delay anything today that I may not be able to do tomorrow.

When I’d revealed my plans to my neurologist, a man of measured understatement, his eyebrows had risen a good inch. He’d recovered well, though, suggesting a series of exercises to strengthen my hip flexors—the muscles that bring our legs up when we walk. When these are malfunctioning, I can trip over the tiniest crack in the pavement. Something like a fallen log presents a major impediment, as I have to use my arms to physically lift my legs over it. Nevertheless, I’d stubbornly declared that whether it took me eight, ten, or twelve hours per day, I would go the distance. Little did I know that twelve hours would be my minimum daily slog.

Ollie, an Aussie mate now relocated to San Francisco, had offered to join me for the first few days, after which my wife, Gerda, and brother-in-law, Mike, would accompany me as far as Yosemite. Then I’d be on my own. Ollie and I had hiked together before, and although I’d forewarned him I might have issues, he would never have expected to be babysitting the mess I’d soon become.

June 25 was a bluebird day, but from the first step we had to navigate entirely by GPS; the winter of 2022 to ’23 had dumped over 200 percent of the normal snowpack, and we only occasionally snatched glimpses of the trail as it peeked out from beneath the crust. Unused to such conditions, I slipped repeatedly, slid down snowbanks, fell off traverses, and generally found ingenious new methods of becoming horizontal.

If the first day was challenging, the second was like going ten rounds with the Abominable Snowman. Drifts formed a succession of frozen waves across the trail, creating an unrelenting series of short, sharp crests. Intersecting tree wells several feet deep sculpted knife-edge snow ridges that had to be negotiated in crampons. In due course, I tripped over a pine needle and fell straight into one such hole, fortunately managing to twist and land on my backpack. I was unhurt, but I caught the look on Ollie’s face. Up until then he’d been cheerfully boasting about my 500-mile mission to any hikers we encountered like it was a foregone conclusion. I’d smile, but cringe inwardly, painfully aware that the chances of my actually succeeding were slim. The tree-well incident lifted the veil from Ollie’s eyes.

“I’ve got no problem helping you,” he said, “I’ll help you all day, but I really don’t think it’ll be safe for you to hike alone.”

“Yeah,” I sighed. “I know.”

This dismal performance was exactly what I’d been fearing. I’d originally planned my trip around an average daily distance of 15 miles, which, six months before departure, I could cover with ease. My final training hike, however, in the Blue Mountains west of Sydney, had been an unmitigated disaster. My leg gave up very early on, but I managed to drag it up and down hills, over boulders and fallen trees, for 11 miles. On the second day, I managed only five miles before shortcutting back to the car.

When I’d revealed my plans to my neurologist, a man of measured understatement, his eyebrows had risen a good inch.

I was so demoralized that I resigned myself to giving up hiking forever. The Sierra traverse was to be my swan song. I planned to sell off all my hiking gear when I returned, focusing on kayaking instead, where my traitorous legs couldn’t hinder me. Even further down the road, when they ceased to work at all, I would take up paragliding. I decided all this in a detached, logical way, because I knew that should I seriously consider the reality of being imprisoned in a wheelchair forever, I’d break down completely.

My spirits were low the morning after the nighttime traverse. I’d half-limped, half-crawled into camp at 10 p.m., feeling very sorry for myself, and for Ollie. We were behind schedule and slowing, and would be at least a day late reaching South Tahoe, where Gerda and Mike were waiting. That afternoon, I was heaving myself to my feet after yet another tumble when one of my trekking poles snapped. The surrounding trees rang with the expletives that erupted from my lips. I’d been struggling with two poles; with one, I’d be a bad joke, a shuffling caricature. Trail name: Keyser Söze.

That’s when I caved. I quickly calculated we could escape the next day via the Rubicon Trail and hitch a ride to South Tahoe. I wasn’t quitting, but by missing a 35-mile section, including the magnificent Desolation Wilderness, my traverse would be forever incomplete. Not only was the thread broken, but I wouldn’t hit my coveted 501-mile target. I’d failed after less than three days.

A night in Tahoe did wonders for my mental health. With a new pair of poles, and my wife and best mate by my side, I was ready for another shot. This time though, something was different. A few hours out of Echo Lake, I realized my body had stopped misbehaving. It was still tough going, but for some reason my weak leg hadn’t noticed. Maybe it was strengthening naturally, or maybe there was a psychological aspect. By Carson Pass, two days later, I was unrecognizable, forging ahead instead of lagging behind.

“You’re just like your old self again,” shouted Gerda as she puffed up the slope behind me. “I can’t keep up!”

I motioned to her to keep her voice down, afraid the MS would wake up and kick in, but inwardly I was delighted.

While I was amazed at my own renaissance, as a group we were still traveling far too slowly. From other backpackers, I’d learned of the “ten by 10,” a playful thru-hiker challenge involving covering ten miles by 10 a.m. But some days we couldn’t even manage that distance by 10 p.m. By the time we reached our resupply point at Sonora Pass, it was obvious Gerda and Mike wouldn’t make their flight home if we continued at this pace. After some debate, they decided to hitchhike to Yosemite while I pressed on along the PCT. As much as I wanted to spend time with them, I couldn’t stomach another gap in my route.

The 89-mile stretch from Sonora to Yosemite was the most challenging hiking of my life. The snow was so mushy, it was like wading through soft-serve ice cream, and I spent much quality time on my backside. Up on the drier ridges, I’d trip instead of slip, often falling headlong onto my face. Nevertheless, I celebrated my first day alone by passing the 100-mile mark; I was finally getting somewhere.

In the back of my mind I knew that if my leg reverted to its previous state of dysfunction, there’d be no one to help me. My plan had been to meet other backpackers and form a little “tramily”—one of the pleasures of long-distance hiking—but in reality I saw hardly anyone. Most, it seemed, had stayed away due to the snow. I did cross paths with the occasional northbound thru-hiker, with whom I’d exchange information on trail conditions and upcoming river crossings.

“Oh, the Sierra has slowed me down,” replied one Frenchman when I grilled him about his average mileage. “In the desert I was covering 30 to 40 miles a day.”

I couldn’t believe it. Was this guy some sort of Olympic hero? I remarked that he must have been running.

“Well, my watch told me I was running about 30 percent of the time, but it was more like fast walking.”

My pace suddenly seemed all the more pathetic, and I had a strong urge to explain myself, to make excuses for my slowness.

But I resisted. It was the closest I came to revealing my handicap to anyone.

Because of the record snowmelt in 2023, the rivers were cresting their banks and were by far the most dangerous part of the PCT. Snow bridges were my preferred method of crossing, followed by fallen trees, and then fording. Spiller Creek, running down from Sawtooth Ridge on the northern edge of Yosemite, boasted a solid log poised high above the flow, with several branch stumps protruding along its length. Although they were only a few inches long, I couldn’t bring myself to lift my trailing leg over them, as I didn’t trust the leading one to hold me. Most MS sufferers have a poor sense of equilibrium; I can lose my balance on a level floor, never mind a narrow log. Instead, I bum-shuffled out with my ice ax and hacked away at the offending nubs until they were reduced to rough knots. They ripped the crotch out of my pants as I scooched over them anyway.

Wading, though, was anathema. A strong current was not an ideal situation for me to be in. My next major challenge was Rancherio Creek, where a PCT thru-hiker drowned in 2017. It looked fearsome and impassable when I arrived one afternoon, forcing me to wait overnight for the water level to drop. Fording it the next morning pushed me to the very limit of my ability. I was so careful to ensure my every step had bombproof footing that the crossing took half an hour. When I crawled onto the opposite bank, I was shivering uncontrollably, perilously close to hypothermia—my limbs were ice from the knees down, and my toes stayed numb for months afterwards.

In order to catch Gerda before she headed home to Sydney, I was faced with an 18-mile descent to Yosemite Village, my longest day yet. After a section of beautiful sequoia forest, the final plunge to the valley was a series of vertiginous switchbacks, and despite my recent miracle improvement, long, steep downhills still activated my limp. The Snow Creek Trail was a well-constructed path cobbled with small rocks, every one a tripping hazard. I took advantage of them all.

The farther I descended, the more my foot dragged, until eventually my leg collapsed under me and I crashed heavily to the ground. This time, I stayed down. I’d come to rest quite comfortably, my head below my legs and my body folded neatly around some stones. I remained there for a couple of minutes, experiencing a moment of clarity.

What am I doing? I thought. Am I having fun? Not really, no. So why continue?

It was tempting, but even as the thought formed, I knew I wouldn’t quit. Instead, I made a pact with myself: I absolutely would not trip over again. I simply refused. For the remainder of the descent I adopted a ridiculous gait, lifting my feet exaggeratedly high every step like an enthusiastic clockwork soldier, and by this method I finally made it down to the valley floor in one piece. It had been a horrendous afternoon, the memory of which I obliterated in pizza, beer, and the arms of my wife.

As hard as it was for me to continue alone, I knew it was equally hard for Gerda. She’s never been comfortable with me hiking solo, even in the prime of my life, and she’d be sick with worry until I was out of the Sierra. But she recognized the importance of this journey.

“Go make us proud,” she said, as I gave her a last hug before turning and walking out of the backpackers’ campground, my pace lackluster but steady.

I’d spent most of my day off gazing slack-jawed at the big Yosemite walls. Out of my routine, however, I’d forgotten to take my afternoon tablets and the RLS had erupted with a vengeance. With one foot dragging and the other jerking like a Taser victim, I was the reincarnation of the Minister of Silly Walks. Lurching among the young families and outdoor enthusiasts was the most disabled I’d ever felt in my life. Now back on trail, the amplified RLS didn’t recede. When I stopped for a break, my legs continued walking. Balancing lunch on my lap was to risk one knee or the other catapulting my hummus into the bushes.

As annoying as the twitching was, the dragging of my left leg again receded, and I was able to continue hiking without hindrance. I was clueless as to why this was happening. Was MS actually some temporary annoyance one could just “walk off,” like a hangover? High temperatures are reported to aggravate the symptoms, so it’s possible the snow and near-freezing water were suppressing mine. Or maybe it was the trekking poles. Should I be using them in my day-to-day life? No, I couldn’t. People would stare, and I’d have to always deal with that unspoken question: “What’s wrong with this guy?”

Over Donohue Pass, along Falls Creek, through the Ansel Adams Wilderness I went. The snow patches became smaller, the dry sections longer, and I started to remember why I enjoy hiking. My average daily mileage increased incrementally, and my Fun Type halved from 2 to 1. Somewhere around Silver Pass, I realized I hadn’t fallen headlong for five days. My pact was working! No longer having to concentrate on every single step, I reveled instead in the scent of pine needles, or the staccato rapping of a woodpecker, and I thought less and less about my disease. Some days, I even forgot I had MS at all.

This was a far cry from life back home. While new lesions had stopped appearing thanks to six-monthly infusions of rituximab, an antibody medication used to treat certain autoimmune diseases by suppressing the immune system, those that were already present were still deteriorating. My neurologist had tried to be positive. “Not everyone ends up in a wheelchair,” he’d said. “You might get away with only having to walk with a cane.” Ever since then, I’ve been clinging to that possibility. It’s the best result I can hope for.

In the tiny part of my mind I allow to hold and process my disease, I’m dreading the future. But I refuse to think about it in detail. It’s the only way I can deal with it. Lately, though, it’s getting harder and harder to ignore. The legs are one thing, but a more real and immediate fear is losing control of my bladder and bowels. I can think of nothing worse than incontinence, adult diapers, and public accidents. It hasn’t happened yet, but when my neurologist asked me about “urgency,” I knew exactly what he was talking about. They say you can get used to anything. I hope so.

My confidence grew as I navigated Kings Canyon National Park, crossed into Inyo National Forest, and summited 14,505-foot Mount Whitney, the highest peak in the lower 48. I forded rivers I would never have dared tackle at the beginning: Bear Creek, White Fork—I plowed straight through them even as other hikers turned back. The log over Rock Creek was six feet above the water and pierced with branch stumps, but I sauntered across it without a care. I was unstoppable.

Eventually, the gorgeous Sierra pine petered out, replaced by low, scrubby bushes that scratched my legs and snagged my trekking poles. I found myself with six days to cover the remaining 114 miles to my planned exit at Walker Pass. If it took me any longer, I’d miss my flight home. The snow had all but disappeared under the 100 degree heat of early August, and I was up for the challenge.

By 10 a.m. I’d hit 7.5 miles without even trying. Maybe a “ten by 10” wasn’t impossible after all? The next day I decided to play Hidden Progress, a game of my own devising in which I wouldn’t check my mileage until camp, and I ended up smashing 20 miles for the first time. With just four days to go, I met a middle-aged Polish group doing a week’s worth of the PCT, each with a pack the size of a small grizzly bear.

“How far do you walk in a day?” was their first question. I told them of my new record, and they collectively made noises of astonishment.

“But how old are you?” asked one, with typical Slavic directness.

“Fifty,” I replied.

“Same as us,” said another. “But you are so strong!”

I shrugged off their praise, but secretly I was thrilled. How the tables have turned, I thought. In your face, Frenchman!

Unfortunately, this is where I came unstuck. Straight after lunch, I tripped and almost fell ten feet into a creek. The dreaded toe-bumping followed, and hot on its heels the dragging as my hip flexors failed me. At the mercy of the Southern California heat, my left leg regressed to sandbag mode and my speed collapsed, along with my morale. Having allowed me some respite, the disease had returned to remind me that “walking it off” was nothing but a pipe dream. In this state, there was no way I’d reach Walker Pass in time. My Sierra traverse was disintegrating before my eyes.

If only I hadn’t spent that extra day bagging Mount Whitney, I might’ve …

And then it struck me. This whole time I’d been counting only my PCT trail miles. I’d ignored the 15 miles up and down Whitney. I’d also walked all the way from Tuolumne to Yosemite Valley and back, and over Kearsarge Pass, twice, for a resupply.

I sat on the bank of the Kern River, watching swallows darting in and out of their nests under the bridge, and carefully calculated all the miles I’d actually walked since Donner Pass. I checked and double checked before allowing myself a surge of excitement—upon reaching Kennedy Meadows South the following day, I would actually have done 502.5 miles! Not only that, but I’d learned over the past six weeks that KMS, rather than Walker Pass, is what PCT-ers consider the start of the Sierra. Suddenly I was within spitting distance of both my original goals.

I was ready at 6 a.m. I’d hobbled to a campsite exactly ten miles before KMS, and come what may, I was going to reach that place by 10 a.m. It was the coldest morning of the entire trip, and I set off under a full moon, spare socks over my gloves. By 8 a.m. I was halfway, but slowing, and the next hour produced only 2.2 miles. With 30 minutes and 1.6 miles to go, I was lurching through the desert, feet flopping on the sand, lizards skittering from my path. Ten minutes left, and I redoubled my efforts, finally stamping and staggering onto Sherman Pass Road, chest heaving. Time check: It was 9:54 a.m. I’d done it. The ten by 10, the Sierra traverse, and the 501. I punched the air. Was it too early for a beer?

After a few seconds, the adrenaline ebbed away. In spite of everything—the snow, the rivers, the limping and falling—this debilitating disease hadn’t gotten the better of me yet. As I finally grasped the scale of my achievement, I felt the first tears of relief begin to prick my eyes. I guess I wasn’t going to be selling off my hiking gear quite yet.