Biomechanical parameters of the elbow stretch reflex in chronic hemiparetic stroke

Abstract

Introduction: we sought to determine the relative velocity sensitivity of stretch reflex threshold angle and reflex stiffness during stretches of the paretic elbow joint in individuals with chronic hemiparetic stroke, and to provide guidelines to streamline spasticity assessments. Methods: we applied ramp-and-hold elbow extension perturbations ranging from 15-150°/s over the full range of motion in 13 individuals with hemiparesis. After accounting for the effects of passive mechanical resistance, we modeled velocity-dependent reflex threshold angle and torque-angle slope to determine their correlation with overall resistance to movement. Results: Reflex stiffness exhibited substantially greater velocity sensitivity than threshold angle, accounting for ~74% (vs. ~15%) of the overall velocity-dependent increases in movement resistance. Discussion: Reflex stiffness is a sensitive descriptor of the overall velocity dependence of movement resistance in spasticity. Clinical spasticity assessments can be streamlined by using torque-angle slope, a measure of reflex stiffness, as their primary outcome measure, particularly at stretch velocities greater than 100°/s.

Impact of Voluntary Muscle Activation on Stretch Reflex Excitability in Individuals With Hemiparetic Stroke

“…A plethora of stretching approaches exist, which vary in angular range, velocity, repetitions, and frequency ( 22 ). The stretching protocol selected for this study was modeled after one protocol that demonstrated stretch reflex accommodation in the stroke population ( 15 ); this approach is commonly used in quantitative ramp stretching protocols ( 3 , 19 , 23 ). Using this protocol, participants completed a 2 h session on two separate days ( Figures 1B,C ).…”

“…The stretching sequence described above was repeated 20 times at an angular speed of 120°/s to evoke flexor and extensor stretch reflex activity, as determined with sEMG ( 3 , 15 , 24 ) ( Figure 1D ).…”

“…The torque data were filtered using a forward-backward low-pass filter with a 5 Hz cut-off frequency ( 3 , 12 , 25 , 30 , 31 ). Following, torque values at the angles of 135° and 88° were extracted during each stretch in extension and flexion, respectively, to quantify stretch reflex activity of the flexor and extensor muscles, respectively ( Figure 1E ).…”

Knee Muscle Stretch Reflex Responses After an Intrathecal Baclofen Bolus in Neurological Patients With Moderate-to-Severe Hypertonia

“…Alternatively, the angle at which SRR appears can be determined based on the increase in torque (12)(13)(14). Starsky et al (14) used an isokinetic dynamometer to stretch the elbow flexors of 16 chronic stroke participants at velocities up to 90 /s and, based on the joint stiffness (reflex torque/angle) curve, the onset of SRR was defined as the joint angle at which the stiffness first reached…”

“…The onset angle was found inversely correlated with the Ashworth score. McPherson et al (13) also used an isokinetic dynamometer to stretch the elbow flexors of 13 chronic stroke participants at 10 different angular velocities (6 to 150 /s) and defined reflex threshold as the elbow angle at which the torque exceeds 0.2 Nm above the pre-stretch resting torque. A significant negative correlation between the reflex threshold angle and stretching velocity was found in seven participants while one showed a significant positive correlation and five showed no significant correlations.…”