Temporal structure of variability decreases in upper extremity movements post stroke

Abstract

Background The objective of this study was to determine movement variability in the more-affected upper-extremity in chronic stroke survivors. We investigated two hypotheses: (1) individuals with stroke will have increased amount of variability and altered structure of variability in upper-extremity joint movement patterns as compared to age-matched controls; and (2) the degree of motor impairment and joint kinematics will be correlated with the temporal structure of variability. Methods Sixteen participants with chronic stroke and nine age-matched controls performed three trials of functional reach-to-grasp. The amount of variability was quantified by computing the standard deviation of shoulder, elbow, wrist and index finger flexion/extension joint angles. The temporal structure of variability was determined by calculating approximate entropy in shoulder, elbow, wrist and index finger flexion/extension joint angles. Findings Individuals with stroke demonstrated greater standard deviations and significantly reduced approximate entropy values as compared to controls. Furthermore, motor impairments and kinematics demonstrated moderate to strong correlations with temporal structure of variability. Interpretation Changes in the temporal structure of variability in upper-extremity joint angles suggest that movement patterns used by stroke survivors are less adaptable. This knowledge may yield additional insights into the impaired motor system and suggest better interventions that can enhance upper-extremity movement adaptability.

Speed and Rhythm Affect Temporal Structure of Variability in Reaching Poststroke: A Pilot Study

“…Therefore, to minimize participant burden all subsequent participants performed only four trials in each condition, with the first serving as a practice trial. Additionally, we have validated this approach with similar number of trials in previous studies (Sethi, Davis, McGuirk, Patterson, & Richards, 2013; Sethi, Patterson, et al, 2013). …”

“…To retain the inherent temporal structure of variability in the data, kinematic trajectories were not filtered (Rapp, Albano, Schmah, & Farwell, 1993). The use of unfiltered data when evaluating the temporal structure of variability is a standard approach to evaluate how movement variability changes over time and has been used in multiple studies (Kyvelidou, Harbourne, Shostrom, & Stergiou, 2010; Sethi, Patterson, et al, 2013; Stergiou, Moraiti, Giakas, Ristanis, & Georgoulis, 2004). The kinematic data described here resulted in four time series, one for each joint (shoulder, elbow, wrist, and index finger PIP).…”

“…These small patterns might not be repeated in a single cycle of reach-to-point movement. in previous studies, we have successfully used this approach to analyze ApEn in reach-to-grasp movements with the same number of trials in healthy controls and participants with stroke (Sethi, Patterson, et al, 2013). For the RHYTHM condition, the time series for each joint angle was analyzed from the start of the reach through the entire length of the time series of the continuous three trials.…”

“…For instance, shoulder flexion is often accompanied by shoulder abduction, and elbow and wrist flexion (Bobath, 1990). These atypical reaching patterns reveal significantly reduced temporal structure of variability across UE joints, suggesting limited adaptability of reaching patterns, and thus are termed rigid (Lodha, Naik, Coombes, & Cauraugh, 2010; Sethi, Patterson, et al, 2013). The optimal variability model could thus explain reduced adaptability observed in these atypical UE movements in individuals with moderate motor impairments poststroke.…”

Effect of intense functional task training upon temporal structure of variability of upper extremity post stroke

“…Further, individuals with stroke might also not be able to adapt their grasps depending upon object size and shape. In fact, in a previous study we demonstrated that individuals post stroke exhibit significantly less ApEn across UE joints as compared to healthy adults 8 . These findings suggest that stroke alters the temporal structure of variability in UE movement, which might limit movement adaptability.…”