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Abstract

The regularity of human motor patterns has been linked to age and disease states [1]. For example, the structural variations that are found in a rhythmical finger force task are less regular in the aged and individuals with Parkinson’s disease (PD) [1]. These observed changes represent an inability of the nervous system to integrate the motor-sensory information for the maintenance of a regular motor pattern [1,2]. Currently, it is unknown if the changes in regularity of the structural variations persist while performing a rhythmical motor task with the lower extremity, and if the frequency of the rhythmical pattern influences the regularity. Further exploration of the neuromechanical mechanisms that affect the regularity of the structural variations present in the motor output may lead to development of new biomedical tools that can be used for the assessment and management of movement disorders.

The aim of this study was to identify neuromechanical factors associated with changes in kinematic regularity of the structural variations present in a simple rhythmic leg swing task.

A leg swing task was used to explore the neuromechanical factors that govern the regularity of the structural variations present in the motor output. Young (n=9, Age=19.9+1.3 yrs.), aged (n=9; Age= 74.7+6.1 yrs.) and individuals with PD (n=9, Age=73.4+6.6) participated in the study. PD individuals had a Hoehn-Yahr score between 2 and 3, and performed the experiment while “on” levodopa therapy. Participants swung their leg at their preferred pendular frequency, and frequencies that were 20% faster and slower. Metronome was used to help the participants maintain the prescribed frequency. Participants swung their leg for two minutes at each frequency. Approximate Entropy was used to measure the regularity of the structural variations present in the leg swing kinematic data collected by electronic goniometer (100 Hz) [1,3]. Repeated measures design with a 0.05 alpha level was used for statistical analyses of the data.

The main effects for frequency were significantly different (p<0.001), and less regular structural variations were associated with faster frequencies. The group main effects were significantly different (p<0.05). The regularity of the structural variations present in the leg swing kinematics of the aged group were not significantly different than the young at all frequencies (p>0.05). The regularity of the structural variations present in the PD group’s leg swing kinematics were significantly different than the aged and young at all frequencies (p<0.05).

Our results indicate that the regularity of the structural variations present in a leg swinging task are influenced by the frequency of the movement pattern. However, the regularity of these variations are not influenced by age. This indicates that changes in the regularity of the structural variations are not consistent for the upper and lower extremities in the aged. PD resulted in less regular structural variations at all movement frequencies. This suggests that the basal ganglia plays a large role in the control of the regularity of the structural variations present in a rhythmical task. Our results present a foundation for future research on development of new biomedical tools for the assessment and management of PD.

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