BERLIN — Eliud Kipchoge, the most decorated marathoner on the planet, is a man of immense self-discipline. He rolls out of bed at 5 a.m. for his morning runs. He splits his time between his home in Eldoret, Kenya, where he lives with his wife and three children, and a training camp up in the hills, 8,000 feet above sea level, where he shares chores with teammates.

Kipchoge is the distance running version of Usain Bolt. He is a wealthy man, but he still scrubs the toilet.

Since he began to take the sport seriously, he has recorded every workout in a notebook. He has 15 notebooks now, one for every year he has spent on the world stage. The thousands of miles contained within have propelled him to the pinnacle of his profession, a runner driven to trim seconds from performances that already stretch comprehension.

But perhaps what is most unusual about Kipchoge, 33, and his diet of monastic extremes is the one thing he does not do: overextend himself in training. He estimates that he seldom pushes himself past 80 percent — 90 percent, tops — of his maximum effort when he circles the track for interval sessions, or when he embarks on 25-mile jogs.