Maybe it's because they've learned to live life that bit faster, maybe it's because they're doing it for someone they love; in the Olympic cycling time trial, being a mother is no obstacle to getting on the podium.
The American winner, Kristin Armstrong, retired from competitive cycling in 2009 to have a baby.
Few people doubted that she would get back on her bike, though some might have doubted she would get back to exactly where she left off, winning her second straight Olympic time trial gold overnight (NZ time) at age 38.
And Russia's Olga Zabelinskaya, whose bronze was her second after Sunday's road race, has two small boys at home of barely school age. Zabelinskava's ride pushed New Zealand's Linda Villumsen into fourth place.
How do they manage it?
"My son has given me balance," Armstrong said. "I can stop thinking about cycling."
She says she has had to get tougher, fitting training around her son's needs instead of her own.
But there are downsides too, and they go beyond the demands of combining hard road miles with childcare.
"Today's corners were a bit grandma-like," she told a news conference. "I was a bit hesitant on the corners, just making sure I stayed upright ...
"When I first got back on my bike six weeks after having Lucas, I would look back and think I was going to be hit by a car. Every mum I spoke to said this was normal. I had a lot more fear in racing."
Zabelinskaya, at age 32 one of no fewer than 11 over-30s in a field of two dozen elite time triallers, knows that fear from the other side.
Compared to male cyclists, she told the newspaper "Sovietsky Sport", "our psychology is different. We think about our families more, and miss our children".
Her older son Bogdan broke his collarbone riding his bicycle before he started school. Her younger son Vitaly has been playing bike races with older children since he was two.
What is certain is that they won't be playing with her new medals.
"They did do that once, they were pretty rough with them and messing around, and I had to say to them: 'Boys, those took a lot of hard work to get.'
"Now they understand that medals aren't something that you play around with. They see me training, and being tired, and they know what it's all about. They don't play with them any more."
If that sounds tough, the boys aren't put off; they both already want to be cyclists like their mother.
But then, as the daughter of an Olympic gold-medal-winning cyclist who wanted to follow in his footsteps for as long as she can remember - even though she did not meet her father until she was an adult - it's something that Zabelinskaya sees no need to prevent. (Editing by Patrick Johnston)