Effect Of Treadmill Exercise On Rat's Achilles Tendon And Its Mechanism

Objective:Tendon is important in musculoskeletal system which is the second mechanism of muscle contraction.Many researchers concerned on the metabolism of muscle and bone,little is on the tendon.In this experiment,we investigate the effect and mechanism of Achilles tendon adaptation to exercise through the Achilles tendon's response to a bout of treadmill exercise and the adaptation to 12 weeks treadmill exercise by biomechanics,histology,biochemistry and molecular biology techniques.Methods:The experiment adopted two kinds of exercise model.â‘ A bout of treadmill exercise group:95 male rats were selected randomly as control group,0h,12h, 24h and 72h group running on the treadmill.â‘¡Long-term treadmill exercise group:40 male rats were used in this model,including 16 rats selected as control and 24 rats as long-term exercise group running for 12 weeks running on the treadmill randomly. Parameters and methods of measure:â‘ The structure of fiber,fibril and the activity of tenocytes were observed with optics microscope and electronic microscope.â‘¡The biomechanics of Achilles tendon was measured by material testing machine (Instron3365).â‘¢The concentrations of Pâ… NP,Pâ…¢NP,IGF-â… of Achilles tendon and IGF-â… in serum were measured by ELISA methods.â‘£The expression of procollagenⅠα₁,procollagenⅢα₁,IGF-â… ,MMP-1 and TIMP-1 in mRNA level were analyzed by real-time quantitative PCR technique.Results:(1) The effects of a bout of treadmill exercise on the rat's Achilles tendon:â‘ The stiffness,the ultimate load,the energy absorbed and the strain under the ultimate load and the hysteresis didn't change markedly after running on the treadmill.The disarrangement of fiber and the augment of longitudinal spaces fibril were observed. Tenocytes became active.â‘¡The concentrations of PINP in Achilles tendon decreased significantly immediately and 12h after running(p＜0.05) while it rose at 72h(p＜0.01 ). The expression of procollagenⅠα₁ in mRNA level decreased signiciantly at 24h (p＜0.05).â‘¢Immediately after running the contents of Pâ…¢NP decreased(p＜0.01) while at 12h and 24h it didn't change any more.At 72h it rose significantly(p＜0.01). The procollagenⅢα₁ mRNA expression was upregulated at 12h(p＜0.05),peaked at 24h(p＜0.01),and still remained at higher level at 72h(p＜0.05).â‘£Neither the concentrations of IGF-â… of the Achilles tendon and in serum nor the level of mRNA had any change after running.⑤The transcription of MMP-1 was upregulated at 12h (p＜0.05),downregulated at 24h(p＜0.05),and return to baseline at 72h.â‘¥The level of TIMP-1 was upregulated signicificantly at 24h(p＜0.01) after exercise and reverted to basal level at 72h.(2) The effects of long-term treadmill exercise on the rat's Achilles tendon:â‘ The stiffness,the ultimate load and the energy absorbed under the ultimate load increased significantly(p＜0.05 or p＜0.01) while the strain of ultimate load and the hysteresis remained unchanged.â‘¡The arrangement of fiber and the fibril became more regular. More tenocytes metabolism was high.â‘¢The mass of tendon and the total collagen didn't change.â‘£The concentrations of PINP and the expression of procollagenⅠα₁ in mRNA level increased(p＜0.01).â‘¥The concentrations of IGF-â… of Achilles tendon and in serum increased(p＜0.01),and the transcription of IGF-â… was also upregulated (p＜0.01).⑦After long-term exercise the expression of MMP-1 and TIMP-1 in mRNA level both upregulated(p＜0.05),and the range of the former was higher than the latter.Conclusion:(1) The microstructure of Achilles tendon has transient change to unaccustomed load and has adaptation after long-term exercise.(2) The Achilles tendon has functional adaptation related to biomechanics after long-term treadmill exercise which can decrease the incidence of injury.(3)Running can upregulate the anabolism of collagen.Accelerating the process of fibril assembly and the synthesis of collagenâ…¢which can self-assemble quickly are an important requirement for adapting to the immediate change of mechanics condition while increasing the synthesis of collagenâ… , which can improve the strength of tendon,is the chief adaptation to long-term exercise. (4) After long-term treadmill exercise IGF-â… in the serum and local of tendon cooperates on mediating the metabolism of tendon.(5) MMPs and TIMPs play important role in extracellular matrix adaptation to exercise in tendon.The ability of degradation may affect the tendon adaptation to exercise.