The sisters say they understand. As girls, they experienced anxiety when separated at school. Now they live apart. They will turn 31 in October and will be forever close, but they are also adults living their own lives.

Liina spends much of her time with her boyfriend in Tallinn, the Estonian capital. Leila is engaged to be married. Leila and Lily are artists and have begun to sell their work, flowers and landscapes and portraits. And also swans, the English translation of their family name, which appear on coffee mugs and on their windproof running jackets.

“If you are alone, you have to make yourself keep an eye on your body and your rhythm,” said Liina Luik, who has swans tattooed on her forearm. “If you are together, maybe the stronger one does a little weaker than she should in a workout. Or the weaker sister overtrains.”

Lemberg is also sensitive to another aspect of coaching triplets. He speaks to them collectively, and individually, but he has a rule of not speaking privately about one sister’s training or health or personal life to another sister.

“If he speaks about me, it shouldn’t be to the others,” Liina Luik said. “We don’t like that.”

Olympic Race Strategy

In Rio, the sisters are tempted to pace one another, or to draft off one another if the day is windy, to experience the highlight of their careers in unison, identical triplets with identical results. But it is impossible to predict how a marathon will unfold. To achieve their best results, they know they may have to run apart, not together.