UC Riverside’s 30-Year Study Finds No Cost for ‘Super-Athlete’ Mice

For more than three decades, scientists at the University of California, Riverside have bred mice for extraordinary athletic ability, expecting the animals to eventually pay a biological price. Instead, a new study finds no such trade-off — challenging a long-standing idea in evolutionary biology.

The project began in 1993 and involved 100 pairs of mice: ordinary “control” mice and “high runner” mice selectively bred over generations for exceptional activity. Given exercise wheels, the high runner mice can cover up to three times the daily distance of unaltered mice. Researchers tracked each mouse’s lifespan and how many offspring its breeding pair produced.

“We did expect to find a reproductive cost for this athletic behavior,” said Theodore Garland, a distinguished professor of evolution, ecology and organismal biology who led the study with doctoral student Natalie Whitehead. Instead, the high runner and control lines produced the same average number of litters. “We also thought the runners wouldn’t live as long, but they did,” Garland said. The findings appear in a new paper in the journal Behavior Genetics, published August 12, 2026, and funded by the National Science Foundation.

During the breeding phase the mice lived under standard laboratory conditions with unlimited food and water; the high runner mice were not given running wheels, though earlier research found them more active than control mice even without wheels. Garland said one possibility is that, with food always available, the mice could eat enough extra energy to sustain high activity without sacrificing reproduction or survival. He cautioned the results should not be read as evidence about human athletes: “These are mice. They aren’t humans,” he said, noting human exercise is shaped by genetics, culture and environment that are hard to disentangle.

The researchers also found no link between the lifespans of male and female mice in a breeding pair — a hypothesis that grief or loneliness after a mate’s death might shorten life was not supported.