A Comparison of the Effects of Continuous versus Discontinuous Movement Patterns on Parkinsonian Rigidity and Reflex Responses to Passive Stretch and Shortening

Abstract

Objective: Quantify the effect of a continuous compared to discontinuous movement trajectory on parkinsonian rigidity and reflex responses to passive stretch and shortening.

Methods: Eighteen participants with Parkinson's disease (PD) performed passive wrist flexion and extension movements through a 90° range of motion at 50 °/sec using continuous (CONT) and discontinuous (DISC) movement trajectories. Participants were tested in both the OFF-MED and ON-MED states. Rigidity was quantified by rigidity work score and slopes of the moment-angle plots during both flexion and extension. Reflex response was quantified by mean EMG amplitudes of forearm musculature.

Results: No differences were observed between CONT and DISC for rigidity (p = 0.18) or moment-angle plot slopes (Flexion: p = 0.97; Extension: p = 0.89). However, medication was associated with reductions in rigidity (p = 0.02) and increases in moment-angle plot slopes (Flexion: p = 0.03; Extension: p = 0.02). The CONT compared to DISC trajectory was associated with greater EMG amplitudes in the shortened muscles (p = 0.04) and smaller EMG ratios (p < 0.05) during flexion, and greater EMG amplitudes in the lengthened muscles (p = 0.02) during extension. Dopaminergic medication reduced EMG amplitudes in stretched muscles during extension (p < 0.05).

Conclusions: The nature of the movement trajectory (continuous vs. discontinuous) used during clinical assessment does not alter the presentation of rigidity in PD. Rigidity is reduced with the administration of dopaminergic medication, independent of movement trajectory.

Significance: These data suggest that the presentation of rigidity used in the determination of diagnosis, treatment and prognosis in PD will not be affected by the continuous nature of the movement trajectory used during clinical assessment.

Keywords: Dopaminergic medication; EMG; Kinetics; Parkinson’s disease; Rigidity.

Figure 1

A sample moment-angle plot from a representative subject with Parkinson’s disease in the OFF-MED state during the passive wrist flexion and extension movements through the 90° range of motion at 50 °/sec.

Figure 2

A representative sample of joint position (dotted) and joint torque (solid) signals recorded from one subject during an imposed flexion and extension movements at 50°/s. Rigidity work scores were calculated for the periods of flexion and extension while the inertial components of torque, denoted by brackets, were omitted from the analysis.

Figure 3

Representative joint position and EMG tracings of the wrist flexors and extensors from a subject with Parkinson’s disease during the wrist extension movement at 50°/s with 60° range of motion. In the OFF-MED condition (A), a shortening reaction was observed in the extensors while a stretch reflex was recorded in the wrist flexors. Dopaminergic medication greatly diminished the amplitude of these phenomena in the ON-MED condition (B). The onset of movement is indicated by the vertical line. Top panel: joint position (°); middle panel: average EMG of wrist flexor muscles; lower panel: averaged EMG of wrist extensor muscles.