Background Although important, scarcely has been studied the viscoelastic behavior of ankle's lateral side.

Objective The aim of the present study was to assess the change in the viscoelastic behavior of this region during cyclic inversions.

Design A quazi-experimental, repeated measures design.

Setting Laboratory research.

Participants 18 amateur healthy males.

Interventions The participants underwent 40 cyclic inversions passively by Biodex dynamometer at 5^os⁻¹ through 80% of the maximum inversion range of motion.

Main outcome measurements Passive work (area under passive torque-angle curve) and simultaneous electrical activity of proneus longus in consecutive repetitions were calculated. The average of five consecutive repetitions was allocated in one class. Two separate one-way analyses of variances with repeated measures and Bonferroni adjustments were conducted to compare the changes in the passive work as well as normalized electromyography from the first to the eighth class.

Results The means of the passive work for consecutive classes decreased significantly until the fifth class (P<.01), but there were no significant differences consecutively between the means of the fifth class forward (P>.05). The means of the normalized electromyography, although increased, didn't show any significant differences between consecutive repetitions (P>.05).

Conclusions Passive work showed decreasing trend due to probable thixotropy but stopped after about 395 seconds and leveled out.The decline of the viscoelastic response due to cyclic inversion, accompanying with low level activity of peroneus longus, may leave unprotected the tissues; expose them to injury in prolonged consecutive movements e.g. in prolonged sports competitions and exercises.