They analysed the blood and urine of a small group of participants in the 2015 Hartford Marathon before and after the 26.2-mile event. In particular they examined a variety of markers of kidney injury, including serum creatinine levels, kidney cells on microscopy, and proteins in urine.

The researchers found that 82% of the runners that were studied showed Stage 1 Acute Kidney Injury (AKI) soon after the race. AKI is a condition in which the kidneys fail to filter waste from the blood.