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Endurance training stats usually get compressed into two numbers: how much did you run, and how hard was it?
That is why we spend so much time debating mileage, the 80/20 rule, and whether an athlete’s training is polarized, pyramidal, or something in between. These summaries are useful. But they also flatten a workout into a single dimension.
A new study of elite Ethiopian distance runners shows what can disappear in that flattening.
On a standard easy/moderate/hard chart, this group’s training looked relatively familiar to most of us—lots of easy running, very little moderate running, and a modest amount of hard work (characteristic of the polarized training model). But when the researchers added where the athletes ran, what was underfoot, how the terrain changed, how long the session lasted, and who was running together, a much richer structure emerged.
So let’s take a look…
Reconstructing 97 days of elite training
The new paper followed 14 elite Ethiopian distance runners—six men and eight women—for 97 consecutive days between September and December 2025. Most specialized in the marathon or half marathon, with one 10K road runner.
Their watches produced 22,605 GPS segments containing pace, heart rate, altitude, location, and elapsed time. Field information identified eight training venues between 2,065 and 3,100 meters of altitude and across six different surfaces. That’s a LOT of data…
The analysis itself used an unusual human-AI workflow. AI systems searched the large dataset, helped develop the numerical analyses, and then independently tested the methods and claims. The investigators chose the questions, corrected the analyses, and supplied the final interpretation. So this framework came from domain experts recognizing what the data meant in the context of elite training and using AI to dissect it all.
The average athlete ran about 75 miles/119 kilometers per week across roughly eight and a half training sessions, but the runners ranged from 40 to 100 miles (64 to 161 kilometers) per week.
The week followed a recognizable hard-easy rhythm.
Tuesday, Thursday, and Saturday carried the most running—typically 13–14 miles (21–22 kilometers).
Monday, Wednesday, and Friday were lighter.
Sunday was a rest day in about 80% of athlete-weeks.
About 40% of training days included a second run (a “double”), usually a short, low-heart-rate recovery session in the afternoon after the main morning run.
The intensity distribution looked ordinary
The researchers classified training intensity several ways because neither pace nor heart rate offers a perfect answer in this setting.
Across the altitude-corrected pace methods, roughly:
75% to 93% of training time was easy
3% to 5% was moderate, and
4% to 23% was hard.
There was also a revealing pattern when the researchers removed the zones entirely and simply plotted training time by altitude-adjusted pace. The data formed two preferred pace regions: a clearly easy mode and a faster mode closer to marathon pace, with relatively little running in between. Eleven of the 14 athletes showed this same dip individually!
Place was part of the prescription
The researchers identified eight venues in which training was performed. Each one offered a particular combination of altitude, surface, and terrain, and the athletes used them for different purposes.
Long aerobic runs concentrated on gently rolling, mid-altitude gravel roads. Those roads accounted for about two-thirds of all long-run time.
High-altitude trails hosted slower, more variable running over routes that often changed from one session to the next.
The synthetic track hosted short, structured repetitions.
Easy recovery running was spread across several other venues, influenced partly by where individual athletes lived (we all can relate… my “preferred” route is right out my front door).
In other words, a track session offered precision and repeatability. A road offered a stable setting for sustained work. A trail offered variation—different climbs, descents, turns, and footing—even when the athlete’s effort remained controlled.
More than one third of all training time occurred as easy running on high-altitude soft trails, at roughly 71% of maximum heart rate and a pace near 9:00 per mile or 5:40 per kilometer. Taken out of context, that pace might look almost comically slow for a world-class distance runner. Put it back at high altitude, on soft and rolling terrain, and it makes sense.
The group did some of the individualizing
The social structure of the training mattered too.
About three-quarters of all sessions were completed in groups, usually with around nine athletes. Long runs and harder sessions were especially likely to be shared: 93% of long steady runs, 97% of long mixed sessions, and 80% of interval sessions were group runs.
But “group training” did not mean every runner received the same dose. In runs of 5 athletes or more, the group separated into two pace bands about 30 seconds per kilometer apart. Athletes with performances closer to the world record were (obviously) more likely to occupy the faster band.
The researchers describe this as a form of group-based individualization. Instead of every athlete receiving a different written pace target, the group appeared to sort itself by fitness while still completing the session together.
