External biomechanical constraints impair maximal voluntary grip force stability post-stroke

Area of Science:

• Biomechanics
• Motor Control
• Rehabilitation Science

Background:

• Grip strength is a key indicator of motor function, particularly relevant for individuals with hemiparesis post-stroke.
• Variations in distal arm and hand biomechanical configurations across studies complicate grip force measurements.
• The precise influence of these biomechanical factors on grip force magnitude and stability remains unclear.

Purpose of the Study:

• To investigate how distal arm and hand biomechanical configurations affect maximal voluntary grip force.
• To determine the impact of external constraints on grip force magnitude and trial-to-trial variability.
• To clarify the relationship between biomechanical setup and grip performance in healthy and post-stroke populations.

Main Methods:

• Studied three groups: healthy young, healthy older, and individuals post-stroke (n=20 each).
• Measured maximal voluntary grip force under four conditions: self-determined, standard, fixed arm-rest, and fixed gripper.
• Utilized an instrumented grip dynamometer, testing both dominant/non-dominant and paretic/non-paretic hands.

Main Results:

• Maximal grip force was highest with the most constrained limb (Condition 4) and lowest with the least constrained (Condition 1).
• The coefficient of variation was greater in the paretic hand compared to healthy individuals, especially under higher constraint conditions.
• Increased external biomechanical constraints led to greater grip force variability in the paretic hand.

Conclusions:

• External biomechanical constraints significantly influence maximal voluntary grip force magnitude and variability.
• Fewer biomechanical constraints promote more stable grip performance, particularly crucial for post-stroke individuals.
• Findings inform the design of more effective rehabilitation interventions and assistive devices for upper-extremity motor impairments.