Objective:To explore MRI T 2-mapping and blood oxygenation level dependent (BOLD) to evaluate the functional changes of paraspinal muscle in rats with discogenic low back pain (DLBP) after swimming. Methods:Totally 54 female 1-month-old SD rats were selected, which were divided into 3 groups by random number table method, sham operation (Sham) group, DLBP non-swimming group and DLBP swimming group, with 18 rats in each group. Under the guidance of X-ray fluoroscopy, the L4/5 and L5/6 intervertebral discs of the rats in the DLBP non-swimming group and DLBP swimming group were punctured by the posterior approach, and establishment of DLBP rat model by destroying nucleus pulposus, and only paraspinal muscles at the same level were punctured in the Sham group. After modeling, the DLBP swimming group received swimming exercise intervention for 5 consecutive days (30 min/d), while the DLBP non-swimming group and Sham group did not receive any rehabilitation exercise intervention. Each group was divided into 3 time point subgroups on average, the T 2-mapping and BOLD sequences were scanned at 30, 90 and 180 days after modeling to obtain the T 2 value, R 2* value of the paraspinal muscles, and the paraspinal muscles at the modeling level were taken for immunofluorescence staining, and the fluorescence intensity of myosin heavy chain (MYH)1 (type Ⅱ muscle fiber) and MYH7 (type I muscle fiber) was analyzed. One-way analysis of variance was used for comparison among the 3 groups, and the Bonferroni method was used for multiple comparisons, and Pearson correlation coefficient was used to evaluate the correlation between quantitative MRI parameters T 2 value, R 2* value and MYH1, MYH7 immunofluorescence intensity of rat paraspinal muscles at 180 days after modeling. Results:At 30 days after modeling, there was no significant difference in T 2 value and R 2* value among the 3 groups (all P>0.05). At 90 days after modeling, the T 2 value of the DLBP swimming group was higher than that of the DLBP non-swimming group, and the T 2 value of the DLBP non-swimming group was lower than that of the Sham group (all P<0.05), and there was no significant difference in the R 2* value among the 3 groups ( P>0.05). At 180 days after modeling, the T 2 value of the DLBP swimming group was higher than that of the DLBP non-swimming group, and the R 2* value was lower than that of the DLBP non-swimming group; the T 2 value of the DLBP non-swimming group was lower than that of the Sham group, and the R 2* value was higher than that of the Sham group (all P<0.05). At 30 and 90 days after modeling, there was no significant difference in the expressions of MYH1 and MYH7 among the 3 groups (all P>0.05). At 180 days after modeling, the expression of MYH1 decreased and the expression of MYH7 increased in the DLBP swimming group compared with the DLBP non-swimming group; the expression of MYH1 increased and the expression of MYH7 decreased in the DLBP non-swimming group compared with the Sham group (all P<0.05). At 180 days after modeling, the T 2 value had a moderate negative correlation with the fluorescence intensity of MYH1 ( r=-0.511, P=0.043), and a moderate positive correlation with the fluorescence intensity of MYH7 ( r=0.564, P=0.023); R 2* value was moderate positive correlated with the fluorescence intensity of MYH1 ( r=0.625, P=0.010), and moderate negative correlated with the fluorescence intensity of MYH7 ( r=-0.653, P=0.006). Conclusions:Swimming exercise can improve the reduction of water content and perfusion in the paraspinal muscles of DLBP rats, and reduce the transformation of muscle fibers from type Ⅰ to type Ⅱ, the changes of T 2 and R 2* value can reflect the transformation of paraspinal muscle fiber types to a certain extent.