A new study raises the question whether there is a biological limit to human endurance that begins long before adulthood, perhaps starting at birth.
Researchers are investigating whether birth weight, a known risk factor for disease later in life, may also influence the body’s response to extreme endurance exercise. Research published in Frontiers of ecology and evolutionFor the first time, a group led by biological anthropologist Alison Murray from the University of Victoria has investigated the potential link between birth weight and kidney stress in ultramarathoners.
Humans are often described as having an innate capacity for endurance, a trait thought to have evolved during hunter-gatherer times when long-distance travel was essential for survival. But our new research suggests that extreme endurance events can push some internal systems closer to their limits than previously understood. ”
Alison Murray, biological anthropologist, University of Victoria
Kidney health in particular has emerged as an important factor in endurance sports, researchers say. Events such as ultramarathons (races longer than 42.2 miles and often held in high temperatures) can put a huge strain on the kidney’s filtration system, leading to cell damage.
Dr. Murray’s research focuses on whether an individual’s birth weight influences how the kidneys respond to this stress. Birth weight is already recognized as an independent risk factor for later health outcomes, and research suggests that birth weight may also be associated with kidney resilience under extreme physical conditions.
Participants in this study underwent blood tests before and after an ultramarathon race to measure biomarkers related to kidney function and potential damage.
In Murray’s group of ultrarunners, the optimal birth weight to minimize kidney damage was about 8 pounds. Those at the lower or upper end of the birth weight range may be at increased risk of kidney stress and damage during extreme endurance events.
“Our research raises the question of whether there is such a thing as ‘excessive’ exercise, and how early biological factors shape the body’s response to extreme physical demands,” added Professor Murray.
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Reference magazines:
Murray, A.A. Others. (2026) Birth weight shapes subsequent long-term endurance activity kidney damage. Frontiers of ecology and evolution. DOI: 10.3389/fevo.2026.1800460. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2026.1800460/full
