Objective To evaluate the changes in knee cartilage before and after 3000­meter running using magnetic resonance T2 quantitative (T2mapping) imaging and to understand the mechanisms of knee cartilage injury and repair, providing imaging evidence for the prevention of sports training injuries. Methods A total of 20 volunteers (40 knees) were selected. Knee joint magnetic resonance imaging (MRI) examinations were conducted 12 hours before 3000­meter running, 6 hours after running, and 24 hours after running. T2 values and cartilage thickness were measured in the following cartilage regions: central medial femoral condyle (CMFC), central lateral femoral condyle (CLFC), anterior medial femoral condyle (AMFC), anterior lateral femoral condyle (ALFC), posterior medial femoral condyle (PMFC), posterior lateral femoral condyle (PLFC), medial tibial cartilage (MTC), and lateral tibial cartilage (LTC). T2 values were also measured in the anterior medial meniscus (AMM), posterior medial meniscus (PMM), anterior lateral meniscus (ALM), and posterior lateral meniscus (PLM). Independent t­tests were used to compare T2 values of the knee cartilage regions. One­way analysis of variance (ANOVA) was employed to compare T2 value differences in the meniscus regions across time points, with the Least Significant Difference (LSD) method used for post­hoc pairwise comparisons. Results Compared with 12 hours before running, , T2 values significantly decreased in the CLFC, CMFC, LTC, and MTC, and the differences were statistically significant (P<0.05). No significant differences were found in the T2 values of the AMFC or ALFC. T2 values increased in all knee cartilage regions at 24 hours after running compared to pre­running levels, but these increases were not statistically significant. There was no statistically significant difference in the cartilage T2 values among the knee joint regions at 6 hours after running compared with 12 hours before running. Compared with 12 hours before running, the T2 values of PMM and PLM decreased at 6 hours after running, and the differences were statistically significant(P<0.05). By 24 hours after running, the cartilage T2 values basically recovered, with no statistically significant differences observed compared to the 12­hour pre­running baseline. Conclusions Magnetic resonance T2 mapping imaging can accurately assess changes in T2 values of knee cartilage before and after running. T2 values in the load­bearing cartilage of the femur and tibia decrease at 6 hours following a 3000­meter running, and the T2 values of the posterior horns of the menisci decrease. These values largely return to pre­running levels by 24 hours after running.