| 1.Objective:Overuse injury of skeletal muscle is a common chronic skeletal muscle system injury caused by work or exercise,which seriously hinders the daily life of patients or athletes’ training and competition.Therefore,it is of great significance to explore its mechanism for the prevention and treatment of skeletal muscle overuse injury.In this study,an animal model of skeletal muscle overuse injury induced by excessive centrifugal training was established to monitor the morphological and structural changes of cells and extracellular matrix in different phases,aiming to explore the process and mechanism of skeletal muscle overuse injury.2.Methods:72 healthy male Wistar rats aged 6-8 weeks were randomly divided into three groups: the control group(C,n=24),the continuous exercise group(E,n=24)and the intermittent exercise group(I,n=24).After one week of adaptive training,the rats were formally centrifuged for four weeks(Week 1:-16°,16m/min,60min;Week 2:-16°,20m/min,60min;Week 3 and 4:-16°,20m/min,90min),the continuous exercise group trained continuously every week,5 times a week;The intermittent exercise group trained three times every other day of the week.After 36 h of every week’ s last training,anatomy of the rats in the ipsilateral femoral muscle,used in the immunohistochemical testing,observed the different phase Ⅰ,Ⅲ and Ⅳ type collagen fiber concentration change,and the variation characteristics of shape and structure of cells and extracellular matrix.At the end of the fourth week,after 36 hours of training,the femoris medius muscle of the ipsilateral rats was taken and divided into two segments.One segment was tested by transmission electron microscopy to observe the ultrastructural changes of the skeletal muscle.The other section was used for scanning electron microscopy to observe the structural changes of collagen fibers in skeletal muscle.3.Results:3.1 Morphology and structure of skeletal muscle fibers:(1)Compared with group C,the mean cross-sectional area of muscle fibers increased in group E from 1 to 4 weeks.The mean cross-sectional area of muscle fibers in the 2E group was the largest,and the 1E group was the smallest.(2)The mean cross sectional area of muscle fibers from 1 to 4 weeks in group I was greater than that in group C.When compared within groups,the mean cross-sectional area of muscle fibers in group 4I was the largest,and that in group 2I was the smallest.(3)Comparison between group E and group I showed that the cross-sectional area distribution of muscle fibers in group 4E and 4I was similar.3.2 Type Ⅳ collagen concentration and basement membrane thickness:(1)Group E at different phase,the Ⅳ type collagen fiber concentrations were significantly higher than that of group C(P< 0.001).2E is the lowest and 3E is the highest,comparing with the other three groups to have very significant differences(P < 0.001);Basement membrane thickness in group E decreased at week 2 and 3,and it was less than that in group C,and increased at week 4,with no statistical significance for each time phase in the group.(2)Group I typeⅣ collagen fiber concentration during the first three weeks,4I increased.Group 1I,2I,4I is significantly higher than C group(P< 0.001).In the group,3I is the lowest,and comparing with other groups 3I were very significant differences(P < 0.001);Compared with group C,the basement membrane thickness of group I was significantly increased at 3I(P < 0.01)and 4I(P < 0.05),and the maximum of 3I comparing with 1I were significantly changed(P < 0.001).(3)Type Ⅳ collagen concentration between group comparison,2E was significantly lower than 2I(P < 0.01),3E was significantly higher than 3I(P < 0.001),4E and 4I had no statistical significance;Compared with the basal membrane thickness groups,2E and 3E were less than 2I(P < 0.05)and 3I(P < 0.001),respectively.There was no statistical significance between 4E and 4I.3.3 Type Ⅲ collagen concentration and thickness of endomysium:(1)In group E,type Ⅲcollagen concentration in 1E,3E,and 4E were significantly greater than C group(P < 0.001),2E was significantly lower than group C(P < 0.05).In the group 2E was the lowest and comparing with the other three groups were very significant differences(P < 0.001),3E was the highest and significantly changed with 1E(P < 0.01)and 2E(P < 0.001),respectively.At the 1st,2nd and 4th week,the endomysium thickness of group E was significantly higher than that of group C(P <0.001),and group 3E was significantly different with group C(P < 0.05).When comparing within groups,3E was the lowest,which was significantly different with group 1E(P < 0.01)and group 4E(P < 0.001).(2)In group I,Ⅲ type collagen concentration in 1I and 4I significantly greater than group C(P < 0.001),collagen type group within the first three weeks Ⅲconcentration drops every week,the lowest 3I,significantly lower than 1 I(P < 0.001),2(I)(P <0.05),4(I)(P < 0.001);Type Ⅲ concentration drops every week at the first three weeks.The lowest 3I,significantly lower than 1I(P < 0.001),2I(P < 0.05),4I(P < 0.001);Compared with group C,the endomysial thickness of 1I(P < 0.01),2I(P < 0.01),3I(P < 0.001)and 4I(P < 0.05)was significantly increased,but there was no significant difference within groups.(3)Type Ⅲcollagen concentration between group comparison,2E is significantly lower than 2I(P < 0.01),3E is significantly higher than 3I(P < 0.001),4E and 4I have no statistical significance;Intergroup comparisons of endomysial thickness showed that 4E was significantly greater than 4I(P < 0.001).3.4 Type Ⅰ collagen concentration and perimysium thickness:(1)In group E,collagen type Ⅰconcentrations in 1E-4E were higher than in group C,among them 1E,3E,4E has the extremely significant difference(P < 0.001).Group 2E lowest has the extremely significant difference with the other three groups(P < 0.001);Compared with group C,the perimysium thickness of 1E(P <0.01),2E(P < 0.05),3E(P < 0.001)and 4E(P < 0.001)were significantly increased,and 4E had the highest thickness,which was significantly different from that of 1E(P < 0.001),2E(P <0.001)and 3E(P < 0.05).(2)In group I,type Ⅰ collagen concentrations in 1I-4I compared with C group were increased,1I and 2I compared with group C had extremely significant difference(P <0.001).There was no significant difference within the group.The thickness of perimysium in group I was increased compared with that in group C,and there were significant differences in 1I(P <0.001),2I(P < 0.01)and 4I(P < 0.05)compared with that in group C,but no significant differences were found within the groups.(3)Type Ⅰ collagen concentration between group comparison,2E and 2I have a very significant difference(P < 0.01).3E,4E and 3I,4I were very significant differences(P < 0.001),respectively;There was a significant difference between 3E and 3I(P <0.01),and there was a significant difference between 4E and 4I in perimysium thickness(P <0.001).4.Conclusion:4.1 In group E,the continuous remodeling of the extracellular matrix is used to maintain the cell morphology,but the remodeling of the extracellular matrix cannot match the changes of cell morphology,resulting in excessive increase in the concentration of Ⅰ type collagen fibers and the thickness of perimysium.Symptoms of overuse injury occur.4.2 In group I,intermittent centrifugal training caused continuous remodeling of extracellular matrix structure,which was used to maintain the cell morphology.The remodeling of extracellular matrix could match the changes in cell morphology,and did not cause excessive increase in the concentration of Ⅰ type collagen fibers and the thickness of perimysium,resulting in benign adaptation. |
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