The relationship between the flexion synergy and stretch reflexes in individuals with chronic hemiparetic stroke

Abstract

This study utilized a novel robotic device, the ACT-4D, to investigate the relationship between the flexion synergy and stretch reflexes in individuals with chronic hemiparetic stroke. Because the flexion synergy influences the amount of elbow flexor muscle activation present in the paretic limb during tasks requiring shoulder abduction loading, it was hypothesized that stretch reflexes may be modulated by expression of this abnormal muscle coactivation pattern. To test this hypothesis, the ACT-4D was used to enable 10 individuals with chronic hemiparetic stroke to generate varying amounts of shoulder abduction torque while concurrently receiving elbow extension position perturbations. It was found that increased expression of the flexion synergy led to greater reflex amplitudes as well as lower reflex velocity thresholds. The physiological basis of the flexion synergy is briefly discussed, as are the implications of the flexion synergy and stretch reflexes for purposeful movement.

LIMPACT:A Hydraulically Powered Self-Aligning Upper Limb Exoskeleton

“…Based on the experimental results, the LIMPACT seems suitable for diagnostic measurements as for instance done by McPhersen et al, [4]. Here, the relationship between the flexion synergy and stretch reflexes in chronic hemiparetic stroke patients is determined.…”

“…The isometric and top view of the hydraulic motor as well as a horizontal (A) and vertical (B) section view. The hydraulic motor is build up with a cylinder (1) which contains two chambers (2) created by the vane (3) and the window seals (4). Oil pressure in the chambers can be regulated by an oil flow through the in-and outlet ports (5).…”

“…The intrinsic joint dynamics can then be subtracted from a combined dynamic response to reveal the dynamics of the reflex pathway [2]. This requires application of a position [2], [3], velocity [4] or torque [5] perturbation and measurement of the resulting torque or position dynamic response. The required perturbations should have speeds of 5 rad/s and up [4] or a minimum (force) frequency content of 20 Hz [5], [6].…”

The ACT-4D: A novel rehabilitation robot for the quantification of upper limb motor impairments following brain injury

“…It has a limited range of movement of the shoulder and elbow, which is further limited when a damper is needed to enhance the positional stiffness of the HapticMaster. The ACT-4D has been successfully used for the first elbow impairment quantifications despite these limitations [33].…”

Biomechanical parameters of the elbow stretch reflex in chronic hemiparetic stroke

“…Building on recent work (Condliffe et al 2005; McPherson et al 2011; McPherson et al 2017), we chose to use larger displacement stretches (~90 degrees) than are traditionally used with ramp-and-hold (Powers et al 1989; Powers et al 1988; Thilmann et al 1991), pseudo-random binary (Ludvig et al 2011; Mirbagheri et al 2012), or multi-sine perturbations (Forbes et al 2011; Ludvig et al 2011; Mirbagheri et al 2012). The choice of large displacement ramp-and-hold stretches facilitates clinical translation because it most closely mirrors current clinical examinations in terms of the stretch profile (e.g., Ashworth, Tardieu), it does not require reprogramming of commercially available mechatronic devices, it does not require use of advanced system identification techniques or applied mathematics to compute reflex-related parameters (as do pseudo-random binary and multisine perturbations), and it ensures a sufficient angular range over which to exceed the threshold angle and estimate reflex stiffness.…”