The Step Response in Isometric Grip Force Tracking: A Model to Characterize Aging- and Stroke-Induced Changes

Area of Science:

• Neuroscience
• Biomechanics
• Rehabilitation Science

Background:

• Aging and stroke significantly alter motor control, particularly grip function.
• Understanding the mechanisms of grip control is crucial for rehabilitation.
• Quantitative models are needed to assess motor deficits accurately.

Purpose of the Study:

• To develop a model representing dynamic motor behavior for investigating aging and stroke effects.
• To quantitatively explore the underlying mechanisms of grip control.
• To assess the model's potential for evaluating motor disabilities.

Main Methods:

• Grip force tracking tasks were performed by stroke patients, age-matched healthy controls, and young adults.
• Participants exerted 25%, 50%, and 75% of their maximum voluntary contractions (MVC).
• Sensorimotor control was modeled using the step response of a second-order system.

Main Results:

• Aging did not significantly affect the model parameters, but stroke did.
• Target force level influenced damping ratio and natural frequency in young adults and damping ratio in stroke patients.
• Wolf motor function test scores correlated with damping ratio, natural frequency, and settling time at 25% MVC.

Conclusions:

• The developed model effectively describes stroke-induced oscillations and slow responses in dynamic grip control.
• The model shows potential as a quantitative tool for evaluating motor disabilities in clinical settings.
• The findings highlight significant differences in sensorimotor control between stroke survivors and healthy individuals.