Objective To investigate the value of blood oxygenation level dependent(BOLD)fMRI in assessing the functional changes of the lumbar dorsal extensor muscles before and after exercise in healthy young people.Methods The changes of the R2*value of lumbar dorsal extensor group in 30 healthy young volunteers(15 males and 15 females)before and after exercise was prospectively studied.BOLD-fMRI scans were performed on healthy young volunteers before and after exercise, the exercise mode was to perform the upper body flexion and extension movement with a simple Rome stool.The scanned images were processed and analyzed, the cross-sectional area and R2* value of the lumbar dorsal extensor muscles (including the multifidus,the longissimus and the iliocostalis)were measured at the upper margin of the L3 and L4 vertebral body before and after exercise.The paired t test was used to compare CSA and R2*values of muscles before and after loading. The CSA and R2* value of different muscles in different sides were compared by independent sample t test. Pearson correlation analysis was used to analyze the relevance between CSA and R2* in muscle before and after exercise. Results After exercise, the R2* values of multifidus,longissimus and iliocostalis at the upper margin of the L4 vertebral body were[(39.2±8.6),(38.9± 7.7),(41.6±7.8)]Hz,significantly lower than before exercise[(46.1±6.9),(45.3±6.2),(46.0±6.7)]Hz(P<0.01);the changes of R2*values of the muscles between the left and right sides before and after the movements were not statistically significant(P>0.05).The R2*values of longissimus and iliocostalis at the upper margin of the L3 vertebral body were[(44.2±9.1),(46.6±9.3)]Hz,significantly lower than before exercise[(48.6±7.2),(49.7± 6.8)]Hz (P<0.01), but the R2* values of multifidus after loading was (43.9 ± 9.0)Hz, there was no statistical difference compared with before exercise (46.8 ± 6.6)Hz (P>0.05);there was a significant difference in the changes of R2*value before and after the movement between the left and right side of iliocostalis(P<0.05).A significant negative correlation between CSA and R2*value was found in the iliocostalis on the right side at the upper margin of L3 vertebral body and in the multifidus on the left side at the upper margin of L4 vertebral body,and the correlation coefficients were (-0.697,-0.616).Conclusion BOLD-fMRI can be a new way to assess the functional changes of the lumbar dorsal extensor group before and after exercise.