Study suggests birth weight affects kidney resilience in ultramarathon athletes

April 30, 2026

A new study is raising questions about whether human endurance has biological limits shaped long before adulthood-possibly beginning at birth.

Researchers are examining whether birth weight, a known risk factor for disease later in life, may also influence how the body responds to extreme endurance exercise. The study published in Frontiers in Ecology and Evolution, led by University of Victoria biological anthropologist Alison Murray, is the first to investigate a potential link between birth weight and kidney stress in ultramarathon athletes.

Kidney health, in particular, is emerging as a critical factor in endurance sports, according to researchers. Events such as ultramarathons-races exceeding 26.2 miles and often held in high temperatures-place significant strain on the kidneys’ filtration system and may lead to cellular damage.

Murray’s study focuses on whether an individual’s birth weight plays a role in how the kidneys respond to this stress. Birth weight is already recognized as an independent risk factor for health outcomes later in life, and the research suggests it may also be linked to kidney resilience under extreme physical conditions.

Participants in the study underwent blood testing before and after ultramarathon races to measure biomarkers associated with kidney function and potential damage.

In Murray’s group of ultrarunners, the optimal birth weight for minimal kidney damage was approximately eight pounds. Individuals at either the lower or higher end of the birth weight range may face a greater risk of kidney stress or damage during extreme endurance events. Medical.net