Impaired coordination between grip force and load force in amyotrophic lateral sclerosis: a case-control study

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• Grasped object manipulation requires predictive grip force adjustments to inertial load changes.
• Accurate motion planning relies on an internal model of limb dynamics and object properties.

Purpose of the Study:

• To investigate grip force control during arm movements in a patient with amyotrophic lateral sclerosis (ALS).
• To compare motor control strategies between an ALS patient and healthy controls.

Main Methods:

• Participants performed discrete vertical arm movements holding an instrumented object.
• Grip force and load force were measured during stationary holds and movements.
• Comparison of grip force adjustments between the ALS patient and three healthy controls.

Main Results:

• The ALS patient exhibited a higher grip-to-load force ratio and greater grip force during stationary holds.
• Control subjects decreased grip force during downward movements, anticipating load reduction.
• The ALS patient increased grip force during both upward and downward movements, regardless of load changes.

Conclusions:

• Amyotrophic lateral sclerosis impairs economical grip force adjustment relative to loading requirements.
• ALS may specifically affect the temporal grip force profile adjustment to movement-induced loads.
• ALS patients demonstrate an undifferentiated grip force increase upon object acceleration, potentially overriding internal forward models.