Marathon running transiently increases medial meniscus extrusion by 38%, remaining significantly elevated through Day 3 but returning to baseline by approximately Day 4.
Key Findings
Results
Marathon running caused a significant acute increase in medial meniscus extrusion (MME) immediately post-race.
Mean baseline MME was 1.14 mm (95% CI 1.06–1.22) and increased to 1.57 mm (95% CI 1.49–1.66) immediately post-race.
This represented a 38% increase, with a mean ΔMME of 0.44 mm (95% CI 0.41–0.47; p < 0.001).
Study included 100 recreational runners (200 knees; mean age 47.2 years; 77 men, 23 women) from five marathons.
Meniscus extrusion was measured as the distance from the medial tibial plateau to the outer meniscal edge using weight-bearing, fully extended-knee portable ultrasonography.
Results
MME remained significantly elevated through post-race Day 3 but returned to baseline levels from Day 4 onward.
MME was significantly elevated through Day 3 (p < 0.01).
MME returned to pre-race levels from Day 4 onward (p > 0.05).
90 runners (180 knees) were reassessed on post-race Days 1 through 5.
Recovery time course was characterized using linear mixed-effects models.
Results
Higher normalized knee adduction moment (KAM) impulse was independently associated with a greater acute increase in MME.
In multivariable analysis, normalized KAM impulse was independently associated with greater acute MME increase (β = 0.24, 95% CI 0.10–0.37).
KAM impulse was measured as walking knee adduction moment impulse from a tibia-mounted inertial measurement unit, normalized to body mass and height.
KAM impulse reflects medial-to-lateral load distribution across the knee.
Results
Higher BMI was independently associated with a greater acute increase in MME following marathon running.
BMI was independently associated with greater acute MME increase in multivariable analysis (β = 0.22, 95% CI 0.09–0.36).
This association was identified alongside KAM impulse and monthly running distance as significant independent predictors.
Results
Higher monthly running distance was independently associated with a greater acute increase in MME.
Monthly running distance was independently associated with greater acute MME increase (β = 0.18, 95% CI 0.04–0.31).
This finding was counterintuitive in that higher training volume was associated with greater, not lesser, extrusion response.
Results
Age showed a borderline association with greater acute MME increase that did not reach statistical significance.
Age showed a borderline association with acute MME increase (β = 0.15, 95% CI −0.00 to 0.31).
The confidence interval crossed zero, indicating the association was not statistically significant at conventional thresholds.
Mean participant age was 47.2 years.
Methods
The study used portable ultrasonography in a weight-bearing, fully extended-knee position to measure meniscus extrusion in a field setting.
Assessments were conducted at baseline and immediately post-race across five different marathons.
This methodology allowed practical, on-site measurement of meniscal extrusion in recreational runners.
100 runners were assessed at baseline and immediately post-race; 90 runners completed follow-up assessments on Days 1–5.
What This Means
This research suggests that running a full marathon causes the medial meniscus — a cushioning cartilage structure in the knee — to temporarily shift outward from its normal position. Immediately after a race, this 'extrusion' increased by about 38% on average (from 1.14 mm to 1.57 mm). This is a meaningful structural change, though the researchers note it was temporary: meniscal extrusion remained elevated for the first three days after the race but had returned to pre-race levels by around Day 4. The study followed 100 recreational runners with an average age of 47 years across five different marathons, measuring meniscal position using portable ultrasound at the race venue and during follow-up visits.
The study also identified factors linked to larger meniscal shifts after the race. Runners with higher body weight relative to height (BMI), those who put more load on the inner side of the knee while walking (higher knee adduction moment), and those who trained more miles per month all tended to show greater meniscal extrusion after the race. Older age showed a trend in the same direction but did not reach statistical significance. Interestingly, running more miles per month was associated with a greater response, not a smaller one, which may reflect cumulative loading effects.
This research matters because it provides the first data on how long the meniscus takes to recover after a marathon, which is relevant for decisions about when runners can safely return to training. The authors caution that it is not yet clear whether this temporary change has any clinical consequences or whether a specific rest period is necessary, and they call for further study to answer those questions.
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Dobashi S, Iwasaki K, Tanaka S, Hishimura R, Matsuoka M, Ebata T, et al.. (2026). Marathon Running Transiently Causes Medial Meniscus Extrusion: Recovery Time Course and Factors Associated With Extrusion.. Scandinavian journal of medicine & science in sports. https://doi.org/10.1111/sms.70366