Yang, G., Im, H. J., & Wang, J. H.(October 12, 2005). Repetitive mechanical stretching modulates IL-1beta induced COX-2, MMP-1 expression, and PGE(2) production in human patellar tendon fibroblasts. Gene, October 12, 2005.

Mechanical loading is known to be essential in maintaining tendon homeostasis, however, repetitive mechanical loading has also been implicated in the development of tendon overuse injuries. This study determined whether cyclic mechanical stretching regulates inflammatory responses induced by interleukin-1beta (IL-1beta) treatment in human patellar tendon fibroblasts (HPTFs). HPTFs were grown in vivo. Cyclic uniaxial stretching was then applied with a 4% or 8% stretch at a stretching frequency of 0.5 Hz for a duration of 4 h in the presence or absence of 10 pM IL-1beta treatment. Non-stretched cells in the presence or absence of IL-1beta were used for controls.

Results suggested that repetitive, small-magnitude stretching is anti-inflammatory, whereas large-magnitude stretching is pro-inflammatory.

Implication. Hard stretching routines are likely to cause at least an inflammatory response in the exercised tissues. The interpretation of this finding will be difficult for those who advocate that stretching is injury preventing.

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