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BACKGROUND: Overuse tendinopalhy is a common disease with no ideal treatment because the pathnogensis of tendinopathy is still unclear. OBJECTIVE: To explore the effects of enzymes effecting collagen synthesis on the metabolism of collagen I and collagen Ill during load accumulation in a model of patella-patellar tendon junction rweruse injury. METHODS: Thirty-two adult female New Zealand wihite rabbits were randomly divided into a jumping group (n=16) and a control group (n=16). In the jump group, rabbits were subjected to jump training for 2, 4, 6, and 8 weeks, 150 jumps per day, 5 days per week. No intervention was performed in the control group. Bilateral patella-patellar tendon junction samples were taken at 24 hours after 2-, 4-, 6-, and 8- week training. The time-series changes of matrix metalloproteinase 1 (MMP1), tissue inhibitor of metelloproteinase 1 (T IMP1), collagen I, and collagen Ill ware measured by immunohistochemistry. The study was performed with an ethic approval from the Animal Ethical Committee of Be jing Sport University, China (approval No. BSU2015022). RESULTS AND CONCLUSION: Compared with the control group, the MMP1 activity was significantly lower within the first 6 weeks of training, TIMP1 activity was significantly higher at 4-8 weeks of training, and TIMP1/MMP1 was significantly higher at 4-8 weeks of training. Compared with the control group, the expression of collagen I was significantly increased in the first 6 weeks of training, but the expression of collagen Ill was significantly lowered after 8 weeks of training. TIMP1 activity was significantly positively correlated with collagen I expression, and MMP1 activity was significantly negatively correlated with collagen I expression. To conclude, the patella-patellar tendon junction, during jumping load accumulation, mainly responded to load stimulation by increasing collagen I expression. In the first 2 weeks of load accumulation, the expression of collagen I was mainly increased by inhibiting MMP1 activity; in the period of 4 to 6 weeks of load accumulation, the expression of collagen I was mainly increased by increasing the activity of TIMP1 and inhibiting the activity of MMP1; and after 8 weeks of load accumulation, TIMP1 could promote collagen synthesis but with inability to antagonize the degradation of collagen I and Ill by MMP1 . Then the expression of collagen I decreased from the peak level after 6 weeks of training to the control group level, and the level of collagen Ill decreased to be less than the level of the control group. [ABSTRACT FROM AUTHOR]

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BACKGROUND: Patella-patellar tendon junction (PPTJ) injuries are a common disease in athletes and vulnerable to re-injury. Post-injury training is a double-edged sword. OBJECTIVE: To examine the effect of post-injury resting days on the quality of healing in PPTJ in view of histomorphology, expression levels of growth factor and collagen, and muscle tension. METHODS: Forty New Zealand white rabbits were randomly divided into control, and five post-injury training groups representing different time to restart training after acute injury: the rabbits restarted training at 24 (PIT24), 48 (PIT48), 72 (PIT72), 96 (PIT96) and 120 (PIT120) hours, respectively. All post-injury training groups received acupuncture at the PPTJ and then underwent 4-week low-intensity training. Afterwards, all rabbits were killed to take specimens for hematoxylin-eosin, safranin O and immuohistochemical staining. The muscle tension and hardness were detected using Myoton-3. The thickness of fibrous cartilage zones, cell density, as well as the expression levels of vascular endothelial growth factor and collagen were measured on Metamorph software. RESULTS AND CONCLUSION: Compared with the control group, in the PIT groups, the collagens arranged in disorder, and decreased cell density, increased mucopolysaccharide and “rising tide” phenomenon appeared. The fibrocartilage in the PIT24 and PIT120 groups was significantly thicker than that in the control group (P < 0.05). The ratio of collagen type I/III was significantly decreased in the PIT24 and PIT48 groups compared with the control group (P < 0.05), and the highest in the PIT72 group. The expression level of vascular endothelial growth factor in the PIT48, PIT72 and PIT96 groups was significantly higher than that in the control group (P < 0.05). The muscle tension was negatively correlated with the collagen ratio (r=-0.538; P < 0.01) and chondrocyte density (r=-0.570; P < 0.01), while muscle hardness was positively correlated with the expression level of vascular endothelial growth factor (r=0.613; P < 0.01). Our results suggest that different resting time makes significant differences in the PPTJ healing and the 72-hour resting is the best choice. Moreover, muscular properties are related to the cell density, collagen synthesis and growth factor expression, which can be used as a non-invasive indicator to guide post-injury training and prevent recurrence. [ABSTRACT FROM AUTHOR]