A Novel Stimulation Paradigm to Limit the Habituation of the Nociceptive Withdrawal Reflex

In gait rehabilitation, combining gait therapy with functional electrical stimulation based on the nociceptive withdrawal reflex (NWR) improves walking velocity and gait symmetry of hemiparetic patients. However, habituation of the NWR can affect the efficacy of training. The current study aimed at identifying the stimulation parameters that would limit, in healthy participants, the habituation of the NWR. The NWR was elicited at every heel-off while the participants walked on a treadmill. Three stimulation paradigms were tested: deterministic paradigm (fixed parameters), stochastic pulse duration paradigm (varying the pulse duration of the stimuli), and stochastic frequency paradigm (varying the frequency of the stimuli). The charge delivered for the three paradigms was identical. The reflex response was quantified by the EMG activity of the tibialis anterior (TA) muscle and as ankle and hip joints angle changes. The ankle dorsiflexion and TA EMG responses were not significantly reduced with the stochastic pulse duration paradigm, in contrast to the two other paradigms. Hence, using a stochastic pulse duration stimulation paradigm seemed to be effective in limiting the habituation of the NWR in heathy individuals. This might be highly relevant for effective gait rehabilitation.