Abstract: BACKGROUND:  Patella tendon degenerative disease is a common sport injury, which mainly results from long-term jumping and running exercises. Cold water immersion is a common method to deal with post-exercise inflammation, which can slow down the local blood flow and reduce the local metabolic reaction, thereby reducing the inflammation.
OBJECTIVE: To investigate the effect of cold water immersion on inflammation and remodeling of the patellar tendon after one-off high-intensity jumping. 
METHODS: Thirty adult female rabbits, weighing 3.0 kg, were randomly assigned into a quiet control group (n=6) and an exercise group (n=24). In the exercise group, 24 left legs were considered as the exercise and cold water immersion (PE+CWI) group, and 24 right legs were considered as the exercise (PE) group. Six rabbits from the experimental group were selected at each observation times, including 0, 6, 24, and 48 hours after cold water immersion. All rabbits were subjected to one-off 150 times jumping: 80-120 N per jumping, with an interval of 2 minutes after 10 times jumping, and with an interval of 10 minutes after 50 times jumping. Immediately after jumping, the legs were immersed in the cold water (4 oC) for 15 minutes. Tendons and rectus femoris were taken at 0, 6, 24, and 48 hours after cold water immersion. Relative quantitative PCR was used to determine the mRNA expression of interleukin 1β, tumor necrosis factor α, cyclooxygenase 2, and matrix metalloproteinase 1 in tendon tissue. Immunohistochemical staining was used to determine the type I/III collagen and transforming growth factor β proteins in the tendon. Hematoxylin-eosin staining was used to observe the changes of collagen fibers in the tendon. 
RESULTS AND CONCLUSION: The mRNA level of interleukin 1β significantly increased at 0-24 hours, but there was no difference between the PE+CWI and PE groups. The mRNA level of tumor necrosis factor-α showed a significant increase, and was significantly higher in the PE group than the PE+CWI group at 0 hour    (P < 0.05). The mRNA level of cyclooxygenase 2 showed a significant increase at 0-24 hours, and was significantly higher in the PE group than the PE+CWI group at 0-6 hours (P < 0.05). The mRNA level of matrix metalloproteinase 1 showed a significant increase, and was significantly higher in the PE group than the PE+CWI group at 0 hour (P < 0.05). The expressions of type I/III collagen and transforming growth factor β were significantly increased at 6-24 hours, and there was no significant difference between the PE group and PE+CWI group. Results from hematoxylin-eosin staining revealed the arrangement of collagen fibers in the tendon disordered at 0-24 hours after exercises, and basically returned to the pre-exercise state at 48 hours after exercises. There was no significant difference in tissue morphology between PE group and PE+CWI group. To conclude, cold water immersion can inhibit early inflammation after exercise, but cannot impact the remodeling of the tendon.

Key words: high-intensity jumping, tendon, inflammatory factor, cold water immersion, experimental animal