As part of WIRED’s exclusive look at Breaking2, Nike’s revolutionary attempt to break the two-hour marathon mark, our writer is using the same training regime, apparel, and expertise as Nike’s three elite athletes—including Olympic gold medalist Eliud Kipchoge—to try to achieve his own personal milestone: a sub-90-minute half-marathon. This is the second in a series of monthly updates on his progress.

On Wednesday, January 26, I ran 10 kilometers through a forest in Kaptagat, Kenya, with Eliud Kipchoge, a few of his friends, and some of the scientists from Nike’s Breaking2 project. It was 4 pm and still blazing hot. We were at 8,000 feet of altitude. The atmosphere was jovial. Philemon Rono, a relentlessly cheerful athlete known to his friends as askari kidogu—“Small Police”—cracked jokes at my expense for at least the first 20 minutes. To be sure, little could have been funnier than me, a very hot 6-foot-5 British man, sweating next to Rono, 5 feet 31/ 2 inches of pure runner.

All of a sudden, our curious-looking gang went quiet. Having lost a couple of hard-breathing scientists on the way out, casualties to the altitude, we turned around at halfway. For a brief period, with the sun muffled by an avenue of dense trees, nobody in the group said a thing. The pace gently increased from around 5 minutes per kilometer to a little north of 4:40 per kilometer. All you could hear was the hi-hat beat of sneakers on dust and the straining bellows of an outsized mzungu attempting to hang with the Olympic marathon champion.

At a dusty athletics track, Kipchoge and crew run 12 repetitions of 1,200 meters at roughly world-record pace for the marathon. Cait Oppermann for WIRED

It was during this period that I reflected upon the happy fact that I was not dead. Kipchoge has run whole marathons almost twice as fast as we were moving at that moment. Why had he chosen not to crank up the pace? Why hadn’t he killed us? Kipchoge is polite to a fault. Was he simply humoring his guests? When we returned to his training camp, another possibility emerged. This was a recovery run, and Kipchoge really does take his recovery runs that slowly. The data the Nike science team analyzed from his GPS watch shows that the kind of run he had done with us was exactly the kind of run he would have done anyway.

The thought remained with me. The previous day, at a dusty athletics track, I’d watched Kipchoge and his training group run 12 repetitions of 1,200 meters at roughly world-record pace for the marathon. (Kipchoge later told me it was “an 80 percent session”—hard but not crazy.) The day after our jog in Kaptagat, I’d watch the same group scorch 40 kilometers—or 25 miles, nearly a whole marathon—in 2 hours, 17 minutes. That, too, was real work. But on the Wednesday in between two intense days, Kipchoge had ambled his way to 20 easy kilometers, jogging in the morning and evening. Meanwhile, at his camp—a simple plot next to fields with cows, containing two tin-roofed bungalows, with no running water and long-drop toilets—he and his friends had spent their non-running time performing chores, listening to the radio, sleeping, and drinking gallons of sweet, milky tea.

I knew Kipchoge was fast. I didn’t understand how slow he could be. This, I thought, might be a moment to learn something.

The runners rinsing off the dust kicked up from their training session. Cait Oppermann for WIRED

Stress vs. Rest

A few weeks earlier, I had been training at Paddington Recreation Ground, in London, just starting on a set of mile repetitions, when I felt a little pop in my left calf. I ground to a halt. The injury was frustrating, to say the least. I’d been training hard and had been making progress. My times were coming down, my fitness was improving, I felt light. And now—out of nowhere—a setback.

But then I thought: Cowboy up. The leg didn’t feel so bad. I rested for a couple of days, then tried out the calf on a short jog. After two days of decent training—a glorious “progression run,” each kilometer faster than the last, with my friend Pete the Trumpet, plus a great track session—I felt that little pop again and once more stopped dead. I was about 3 miles from home, with no money in my pocket. It was freezing cold. The walk back seemed to take forever.

The Nike team begged me to rest properly. I saw a physiotherapist named Matt Fox, who has worked at Manchester City and Bolton Wanderers football clubs and has seen more than his share of injured calf muscles. He thought the strain was most likely a grade 1 tear of my soleus. He also counseled inactivity. “You can either rest properly now, or you can turn a one-week injury into a six-week injury,” he said. Foxes are smart, I knew.

During my eight days off, I rethought other aspects of my training. Perhaps I’d injured myself because I was working too hard. In addition to five or six runs, many of which were intense, I was also training at CrossFit twice a week—throwing weights around, jumping on boxes, and so on. The CrossFit had been excellent for me but, with the running, I was exhausted. Eventually, something was going to give. Eventually, it did.

The author recovering from the early morning run. Cait Oppermann for WIRED

The data that the scientists had collected on me also altered my thinking. Nike has recently contracted a garrulous Chicago physician named Phil Skiba, who has trained many elite endurance athletes, to work on Breaking2. Skiba has developed algorithms that accurately measure and predict training loads. He is particularly interested by fatigue, and the balance between what he calls the “positive and negative effects of training.” In particular, Skiba uses athletes’ training data to predict when, before a race, they should begin their taper—that is, to progressively decrease their volume of training so that they arrive on race day fresh and fast.

Every athlete has a different taper point. Some people need only a few days. Some people need weeks. The variations are explained both by differences in workload and by our physiological differences. Some athletes simply recover quicker from hard training than others, in ways that geneticists and physiologists are still trying to fully understand. Skiba’s data, however, is precise. He and the Breaking2 crew believe that Kipchoge’s taper may have started a day or two late before his previous marathons and that he would have benefitted from around a week of rest rather than his normal five days.

Kipchoge, center, and other runners from the camp on their way to a training session. Cait Oppermann for WIRED

Whether it’s worth shifting Kipchoge from his normal patterns for this one race is a concern among the Breaking2 team, especially because routine is psychologically important to athletes. But their analysis shows how a data-augmented approach might yield benefits even for the greatest runners. (As for Lelisa Desisa, another of the three elite runners contesting Breaking2, the Nike scientists believe his taper may be a few days too long.) In my case, based on how I’ve reacted to my training load so far, they believe I should taper for 21 days. 21 days! Clearly, I am more in need of rest than the average lummox.

Slowly by Slowly

Back to Kenya. Watching Kipchoge’s group at work, I saw that they never did two intense days back to back; they were always committed to developing their fitness, in the Kenyan parlance, “slowly by slowly.” Patrick Sang, Kipchoge’s coach and a formidable presence in the athlete’s life, explained to me the basis of this philosophy as he stood at the side of the track with a stopwatch in his hand and his red-and-black hoodie fastened tightly around his head. Our conversation had begun when I asked Sang why Kipchoge’s group were doing a 12 x 1,200-meter session on that day.

Sang said this session was to build “speed-endurance”—the ability to maintain a high speed for a long time. But if you thought about only one workout, you missed the point. The idea of a training program, Sang told me, was to improve every aspect of a runner. The approach was holistic. If you scheduled a speed-endurance session for a Tuesday, you needed to make sure that the following day would be light, so that the guys had time to recover before the Thursday long run. Friday would again be light, before a different kind of speed workout on Saturday. Sunday was a day of rest. A good day of training was worth little on its own, but a good month was worth plenty. Slowly by slowly, the athlete’s shape came. “Every session is a building block,” Sang said.

Patrick Sang, Kipchoge’s longtime coach and a proponent of the “slowly by slowly” training philosophy. Cait Oppermann for WIRED

Valentijn Trouw, Kipchoge’s Dutch manager, told me something else interesting: He thought Kipchoge never killed himself in training. The only day on which he would drain every resource he possessed was on race day. “Never 100 percent in any session,” Trouw said. “That’s the philosophy.” This approach made sense to Skiba. “The time to open up a can of whup-ass is on race day,” he told me. “Otherwise, you risk leaving your best performance in training, where nobody sees it.”

“Slowly by slowly” is not a mantra that lends itself to hard-charging Western approaches to fitness. How often do we hear that only hard work brings rewards—that the more you put in, the more you get out? Also, many average Western athletes, like me, do so much of their training at a consistent pace. There’s not enough variation or rest in their schedules. The Kenyans, particularly those in Sang’s group, are more sophisticated in their approach. I’ve never seen more-committed athletes, in any sport, anywhere in the world. But they also know it would be crazy to grind themselves into the dust.

On my last day in Kenya, I was talking to Geoffrey Kamworor, a runner with a wide gap-toothed smile and an easy manner that masks a profound belief in his own talents. As a runner, everything about him is purposeful. In training, he leans into bends with his shoulder, kicking up dust behind him, like a young bull on the charge. In competitions, he is fearless. Now in his mid-twenties, he is the reigning world half-marathon champion and the world cross-country champion. He also won a silver medal in the 10,000 meters at the 2015 World Championships in Beijing.

Kipchoge and his team enjoy a post-training tea. Cait Oppermann for WIRED

When I asked him what tips he could give to a mzungu attempting to break 90 minutes for the half-marathon, his first thought was to get a good pacemaker. He offered his services. “If you want 4:20 [minutes per kilometer], that’s no problem, I will bring a newspaper,” he said, a bright smile on his face. “If you want 2:50 [minutes per kilometer; 2-hour-marathon pace] that’s also no problem.”

He then became more serious and gave me some real advice.

“Work hard,” he said. “But not every day.”

I wrote that one down.