Design of an experimental protocol to test voluntary reflex modulation in the wrist flexor

Abstract

Background: Determining how the reflex voluntarily modulates while performing activities of daily living (ADL), and understanding how this modulation might differ between healthy subjects and patients with motor disorders, can aid in developing a rehabilitative program to improve the functional performance of thewrist. The current study designs an ideal experimental protocol that would test reflex modulation as a response to perturbations during a goal-directed movement. Methods: A total of twelve participants participated in the five experiments (mean age 25.9 9 ± 3.6 years in the range 22 - 34, seven men and five women, all right-handed and with no history of neuromuscular impairment). The TU Delft Human Research Ethics Committee gave approval for the current study. The experimental protocol is separated into three pilot experiments, one main experiment and an addendum experiment after proven effectiveness of the protocol. The main experiment is conducted with ten subjects. The design process was iterative. The experiments were tested, designed and implemented on a wrist manipulator (PoPe). The transient perturbations are designed to be Ramp-and-Hold (R&H) perturbations of amplitude 0.08rad, 2rad/s with a 180ms hold, causinga stretch reflex response in the flexor carpi radialis (FCR). Results: The main experiment showed that the short-latency (M1) and long-latency (M2) areas in the FCR significantly differ with respect to the posture at which a perturbation is elicited. Upon showing the effectiveness, the experiment is further improved with the implementation of continuous pseudo-random binary signal (PRBS) perturbations to allow for continuous measuring of the stretch reflex, and thereby increasing protocol efficiency. Conclusions: The designed experimental protocol is, therefore, effective in observing reflex modulation during a goal-directed movement performed by the wrist.