PURPOSE: Foot orthoses are a standard option to treat overuse injury. Biomechanical data providing mechanisms of foot orthoses' effectiveness are sparse. Stability of the ankle joint complex might be a key factor. The purpose was therefore to analyze neuromuscular activity of the musculus peroneus longus in runners with overuse injury symptoms treated with foot orthoses. METHODS: A total of 99 male and female runners with overuse injury symptoms randomized in a control group (CO) and an orthoses group (OR) were analyzed on a treadmill at 3.3 m/s before and after an 8-wk foot orthoses intervention. Muscular activity of the musculus peroneus longus was measured and quantified in the time domain (initial onset of activation (Tini), time of maximal activity (Tmax), total time of activation (Ttot)) and amplitude domain (amplitude in preactivation (Apre), weight acceptance (Awa), push-off (Apo)). RESULTS: Peroneal activity in the time domain did not differ initially between CO and OR, and no effect was observed after therapy (Tini CO -0.88 +/- 0.09, OR -0.88 +/- 0.08; Tmax CO 0.14 +/- 0.06, OR 0.15 +/- 0.06; Ttot CO 0.40 +/- 0.09, OR 0.41 +/- 0.09; p > 0.05). In preactivation (Apre), muscle activity was higher in OR after intervention (CO 0.97 +/- 0.32, 95% confidence interval 0.90 to 1.05; OR 1.18 +/- 0.43, 95% confidence interval 1.08 to 1.28; p = 0.003). There was no group or intervention effect during stance (Awa CO 2.33 +/- 0.66, OR 2.33 +/- 0.74; Apo CO 0.80 +/- 0.41, OR 0.88 +/- 0.40; p > 0.05). CONCLUSIONS: Enhanced muscle activation of the musculus peroneus longus in preactivation suggests an altered preprogrammed activity, which might lead to better ankle stability providing a possible mode of action for foot orthoses therapy.

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