A crossover study put 15 average-trained men through an exhaustive treadmill run and then measured what showed up in blood and urine. Plasma cell-free DNA rose roughly 25-fold within minutes, while the same marker in urine barely moved.
Treadmill Run testing to the point of exhaustion raised urinary albumin and creatinine in 15 average-trained men while leaving urinary cell-free DNA unchanged, according to a crossover study published on 03 November 2026 in Scientific Reports. Plasma cell-free DNA, by contrast, increased about 25-fold immediately after the treadmill run.
The work comes from a group led by corresponding author Dariusz Nowak, with first author Emilia Stec-Martyna and colleagues including Jacek Szymanski, Piotr Falkowski, Tomasz Konecki, Karolina Kopacz and Agata Sarniak. Most of the authors are based in departments of the Medical University of Lodz in Poland, with additional affiliations at Medical Centre OLMED in Lodz and Warsaw Medical Academy.
The paper was received on 26 April 2026 and accepted on 29 October 2026. Its stated purpose was narrow and methodological: to find out whether urine is a meaningful route by which the body clears the cell-free DNA that hard exercise releases into the bloodstream.
Participants were 15 average trained men without urogenital pathology, with a mean VO2max of 45.5 ± 6.25 ml/kg per minute. Each man completed both arms of a comparative, crossover protocol: an exhaustive treadmill run at a speed corresponding to 70 percent of VO2max, and a separate one-hour rest session used as the comparison condition.
At a Glance
- Published 03 November 2026 in Scientific Reports; received 26 April 2026 and accepted 29 October 2026.
- 15 average trained men without urogenital pathology, mean VO2max 45.5 ± 6.25 ml/kg per minute.
- Comparative crossover design: an exhaustive treadmill run at a speed corresponding to 70 percent of VO2max, versus a 1.0 hour rest session.
- Run distance averaged 11.2 ± 4.7 km and run time averaged 67 ± 19 minutes.
- Plasma cell-free DNA rose about 25-fold just after the treadmill run and returned to baseline after 4 hours.
- Urinary albumin and creatinine increased after exercise, while no significant changes in urinary cell-free DNA were recorded.
- Main caveat: this is a 15-man physiology study in one sex at one intensity, and the published abstract carries no separate limitations section.
How the Treadmill Run Was Set Up
The protocol is unusual in a useful way. Rather than a fixed-distance time trial, the men ran at a speed pegged to 70 percent of their own VO2max and kept going until they could not continue. That produced a long effort rather than a short maximal one: 11.2 ± 4.7 km covered in 67 ± 19 minutes.
The spread in those averages is as informative as the averages themselves. A standard deviation of 4.7 km on an 11.2 km mean means some men ran well under 7 km and others past 15 km, so the treadmill run was equated by relative intensity and exhaustion rather than by workload.
Each participant also completed a one-hour rest session, which gives the design its internal comparison. Because the same men supplied both conditions, differences in baseline kidney function or hydration habits between individuals cannot explain the exercise effect.
A 25-Fold Blood Signal That Faded Within Four Hours
Plasma cell-free DNA was the loudest result. It climbed roughly 25-fold just after the treadmill run, then returned to baseline after four hours. Cell-free DNA is genetic material circulating outside cells, and a sharp rise in it after a hard treadmill run has been reported in earlier work from this field.
The speed of the return is the part worth noting. Whatever released the DNA during the treadmill run, the body had cleared the surplus from circulation inside a single afternoon.
The approximate rise in plasma cell-free DNA measured immediately after the exhaustive treadmill run, a surge that had returned to baseline four hours later.
What Changed in the Urine, and What Did Not
Two routine urine markers moved. Urinary albumin and urinary creatinine both increased after the treadmill run, relative to the rest condition. Cell-free DNA in urine did not: the authors report no significant changes in urinary cell-free DNA across the protocol.
Because albumin and creatinine went up after the treadmill run while cell-free DNA held steady, the ratios between them fell. The abstract reports that urinary cell-free DNA to creatinine ratios were 4.8 ± 8.4 and 3.7 ± 5.7 ng/mg, and cell-free DNA to albumin ratios were 614.0 ± 586 and 324.7 ± 494.8 ng/mg, describing these ratios as decreased after exercise, at P below 0.05.
Those large standard deviations relative to the means deserve a flag. With 15 participants and variability that wide, the ratio comparisons are fragile even where the P value clears the conventional threshold.
Why the Authors Were Measuring This at All
The question is a laboratory one before it is a training one. Cell-free DNA in blood is used as a marker in several areas of clinical research, and researchers have asked whether urine could serve as a simpler, non-invasive sample for the same purpose.
This study answers that question in the negative for exercise-released DNA. The authors conclude that urinary cell-free DNA excretion is not a significant elimination route for the cell-free DNA that exercise releases, which means a urine sample will not reflect the blood surge an exhaustive treadmill run produces.
They draw a practical inference from it as well, suggesting that it is not necessary to limit physical activity in urine donors who are providing samples for cell-free DNA analyses. For a methods paper, that is the usable conclusion.
The Albumin Finding Is Familiar Territory
Of the two markers that rose, urinary albumin is the one with the longer research history. Transient increases in urinary protein after strenuous exertion have been described for many years, and the finding in this treadmill run is consistent with that pattern rather than a departure from it.
This paper does not test a mechanism for what the treadmill run did, and it should not be read as reporting kidney injury. It reports concentrations in urine collected around a single bout of exercise in men screened to be free of urogenital pathology.
The creatinine rise matters mostly as a technical detail. Urinary creatinine is widely used to normalize other urine measurements, so a bout of exercise that shifts creatinine shifts every ratio built on it.
What a 15-Man Study Changes for Runners
Very little in training terms, and that is the honest answer. Nothing here suggests a hard endurance session is harmful, and nothing here supports altering how anyone trains. The practical value sits with anyone handling urine samples or interpreting them.
There is one everyday implication worth knowing. Because a long, hard effort can transiently raise urinary albumin and creatinine, recent strenuous exercise is relevant context for a clinician reading a urine test, and mentioning a hard session the day before is reasonable, general practice.
Readers interested in how exercise reshapes circulating markers can see the pattern in other FLM coverage: a short effort was enough to move the blood proteome in our report on three minutes of sprinting and blood proteins, and a larger survey appears in the 3,000-protein human study. Endurance-specific physiology shows up in spirometry work on marathon runners and in a study of endocannabinoids after marathon and ultramarathon racing.
Three cautions carry over from the design, none of them individualized advice:
- Findings from 15 trained men at one intensity are a starting point, not a general rule.
- A marker that rises after exercise is not the same thing as a marker that signals damage.
- Anyone with a known kidney condition should take questions about exercise and urine testing to their own clinician.
The Fitness Living Takeaway
An exhaustive treadmill run at 70 percent of VO2max raised urinary albumin and creatinine in 15 average-trained men, while plasma cell-free DNA rose about 25-fold and urinary cell-free DNA did not change significantly.
The authors read that mismatch as evidence that urine is not a significant elimination route for exercise-released cell-free DNA, and they suggest urine donors need not restrict physical activity before giving samples. With 15 participants, one sex and one exercise condition, this is a methodological result for laboratories rather than a training finding for runners.
Research & Sources
- Scientific Reports: Exhaustive treadmill run increases urinary excretion of albumin and creatinine but not cell-free DNA in average trained healthy men
- Study DOI
- Images: eran design / Unsplash; Hannah Coleman / Unsplash
This article summarizes peer-reviewed research for general information and is not individualized medical or exercise advice.
