Effect of increased excursion of the ankle on the severity of acute eccentric contraction-induced strain injury in the gastrocnemius - An in vivo rat study

Background: Although muscle strain injury models are frequently employed, highly invasive procedures, including surgical intervention, are typically used to produce these models. In this study, a minimally invasive model of acute strain injury was produced with a single eccentric contraction. Hypothesis: The authors tested whether the severity of strain injury in the in vivo gastrocnemius depends on the excursion of the ankle. Study Design: Controlled laboratory study. Methods: Animals were randomly assigned to 2 groups: a small range of motion group (90degrees-105degrees, n = 10) and a large range of motion group (90degrees-125degrees, n = 10). Tetanically activated gastrocnemius muscles with percutaneous electrical stimulation were simultaneously elongated by forced dorsiflexion of the ankle joint. Results: Isometric tetanic force of the large range of motion group was significantly lower than the pretreatment control 1, 2, and 3 days after treatment. Such reduction was not observed in the small range of motion group. Apparent pathologic damage was observed in the large range of motion group throughout the study period of 10 days. Conclusions: A larger range of motion causes more damage in eccentric contraction by using the in vivo model. Clinical Relevance: This in vivo model is useful to elucidate mechanisms of prevention and recovery of strain injury.