Unloading reaction to electrical stimulation at neutral and supinated ankle positions

An unloading reaction has been characterized as a modified flexor reflex (FR), in which the standing subjects decrease the load on the stimulated foot and increase the load on the contralateral side, but, without withdrawal of the stimulated foot. Different behavioral circumstances have been shown to modulate this reflex. It is not known whether unloading reactions can be modulated with a loaded supinated ankle position, which, in excess, may result in an ankle sprain injury. Since ankle sprain depends on the load applied to a supinated foot, our premise is that unloading reactions may protect the ankle from a sprain injury. Therefore, this study investigated how the unloading reactions were modulated during a loaded supinated ankle condition. We delivered non-nociceptive and nociceptive electrical stimulations on the lateral aspect of the ankle in standing subjects with the foot in neutral and in a supinated position. The magnitude and latencies of reflex responses were registered using kinetic and kinematic analyses and subsequently compared among the conditions. The analysis demonstrated greater reactions for the supinated ankle condition. The individuals also moved their whole body downwards and shifted the body weight to the non-stimulated foot. Therefore, this study suggested that a modified type of the classic flexion reflex, i.e., unloading reaction, may be used as a strategy to unload a supinated ankle and potentially minimize the risk of ankle sprain injuries.