| Objectives:1. To create an animal model that simulates exercise-induced acute biceps femoris strain, in order to provide basis for the further study on muscle structure, functions and pathology.2. To observe the mechanics and histology, so as to identify the features of structure, function and pathology after biceps femoris strain.3. To observe the effect of low-intensity electrical stimulation at different frequencies (20 Hz and 80 Hz) on the rebuilding of muscle structure.4. To observe the effect of low-intensity electrical stimulation at different frequencies (20 Hz and 80 Hz) on the gene regulatory of MyoD and Myogenin on proliferation, termination and new fibers rebuilding after acute biceps femoris strain, in order to find a new way for analysis the manchnism of muscular strain. Therefore, it will be helpful to choose better protocol of electrical therapy.Methods:Forty-five male SD rats were randomly divided into control group, D0 group, D3 group, D7 group, D7-20Hz group, D7-80Hz group, D14 group, D14-20Hz group and D14-80Hz group. All male SD rats except ones of control group were anesthetized. One limb was chosen at random to create a partial biceps femoris stretch injury.The biceps femoris was stimulated to tetany by activating the sciatic nerve via subcutaneous needle electrodes, which were placed over the sciatic nerve in the region of the ischial tuberosity. The limb was moved from knee flexion 700 to full knee extension at 9600?s-1 angular velocity and then returned to the starting position.After torque test and the observation of ultrasound, the biceps femoris was harvested for procedure of histology. After injury, no interventions were given to D0 group, D3 group, D7 group and D14 group. The electrical protocol was made in D7-20Hz group, D7-80Hz group, D14-20Hz group and D14-80Hz group. The biceps femoris was stimulated using a modified stimulator. Square wave stimuli at 20Hz\80Hz were applied twice a day for 30 minutes each time with a 4 hour interval. After experiment, we had an observation on torque, ultrasound diagnosis, HE staining, western-blotting and immuno-staining.Results:1. After injury, histology showed fiber necrosis, and hemorrhage. HE staining revealed structural disorder, edema, and increased gap between muscle fibers.The injuries of biceps were more severe than injury of Semitendinosus and Semimembrinosus. At 3 days post-injury, there was intense inflammatory cell proliferation. At 7 days, injured muscle fibers recovered but did not mature. Given electrical therapy in D7-20Hz group, the new fibers became more mature, neat formation and clear boundary.However, low-intensity 80Hz electrical stimulation show no significant effects. At 14 days, injured muscle fibers became mature and recovered.2. The images of Semitendinosus and Semimembrinosus are lack of any ultrasonic lesion. Injured Biceps correspond to lesions involving from 5 to 50% of the muscle volume or cross-sectional diameter, which belongs toⅡdegree injury. No significant difference between them(P>0.05).3. The isometric maximal knee torque of control group was 0.337±0.025Nm. The isometric maximal torque showed a significant drop by 73.05±5.37% of control muscle at day 0(P<0.05), 79.79±6.95% at Day 3 post-injury, 89.84±4.75% at Day 7 post-injury. At Day 14, the isometric maximal torque recovered to normal level.4. The isometric maximal knee torque of D7-20Hz group and D7-80Hz group respectively were 0.312±0.043Nm and 0.302±0.033Nm. Compared to the isometric maximal torque of D7 animal model group, no significant difference existed(P>0.05). The isometric maximal knee torque of D14-20Hz group and D14-80Hz group respectively were 0.335±0.028Nm and 0.334±0.060Nm. Compared to the isometric maximal knee torque of D7 animal model group, no significant difference existed(P>0.05).5. The optimal angle of control group was 130.000±3.540. It showed a significant right shift to 144.500±3.710 at day 0 post-injury. Compared to the optimal angle of control group,there was significant difference(P<0.05). At day 14 post-injury, it showed a significant left shift to 120.000±3.530 compared to the optimal angle of control group (P<0.05). After electrical stimulation, the optimal angle of D14-20Hz group and D14-80Hz group were 125.000±3.530 and 121.000±4.180. A significant difference existed between D14 group and D14-20Hz group(P<0.05).6. At 7 days post-injury,the protein expression of MyoD and Myogenin increased in D7group,D7-20Hz group and D7-80Hz group. Compared to control group, there was a significant difference (P<0.01). Between D7 group and D7-20Hz group, there was also significant difference(P<0.01).At 14 day after injury, the protein expression of MyoD decreased in D14 group and D14-80Hz group. Compared to control group, there was no significant difference (P>0.05). However, the protein expression of MyoD was still significant higher in D14-20Hz group compared to D14 animal model group (P<0.05). The protein expression of Myogenin was still higher in D14-20Hz. Compared to D14 group, there was a significant difference (P<0.05). Conclusions:1. The animal model, which was created in this experiment, simulated a sports injury well.2. The low intensity 20Hz electrical stimulation was useful for muscular rebuilding of the injured biceps femoris in morphological structure and function.3. The low intensity the 20Hz electrical stimulation could not increase the maximal isometric toque but was able to improve the torque-angle relationship in injured biceps femoris during 2 weeks post-injury.4. The low-intensity 20Hz electrical stimulation could improve the gene regulatory of MyoD and Myogenin as well as muscular rebuilding, which proved the low-intensity 20Hz electrical stimulation was helpful for the rapair of injured biceps femoris through the intervention on gene regulatory of MyoD and Myogenin.5. The low-intensity 80Hz electrical stimulation had no effects on the gene regulatory of MyoD and Myogenin as well as muscular rebuilding.
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