Thursday night was warm and clear in Yokohama. A cloudless, gradually darkening sky stretched over the 400-meter track at the Yamato Sports Center — seemingly boundless in its ability to absorb the shouts and laughter coming from the 20 boisterous young members of the Yokohama Athlete Club, who had gathered for their weekly training session.

"Good evening everyone," called out Shushi Kuge, the clean-cut 55-year-old club director. "As you all know, we have a competition coming up on Monday, and so today the key focus is to train carefully, avoid injuries. Should we do an 800? Let's do an 800-meter run, then we'll break up into groups to focus on particular events — relay, long-jump, sprint, hurdles, as always."

By now the children had assembled in a line in front of Kuge. Aged from 9 to 12, they were a mixed group, with the youngest just two-thirds the height of the oldest, but they were recognizable instantly for their green-colored club T-shirts.