Anticipatory postural adjustments in stance and grip

Area of Science:

• Motor control
• Human movement science
• Biomechanics

Background:

• Reactive forces during object manipulation can destabilize hand-object interaction and body posture.
• Prior research shows grip force increases stabilize objects and early postural adjustments minimize body perturbations.
• The interplay between grip force and postural control during anticipatory actions requires further investigation.

Purpose of the Study:

• To investigate the concurrent development of grip force and postural adjustments in anticipation of dynamic and static loads.
• To examine the temporal relationship between grip force, postural adjustments, and load force onset.

Main Methods:

• Subjects performed precision grasps while pulling or pushing dynamic or fixed loads horizontally.
• Ground reaction torques were measured using a force plate.
• Grip (normal) and load (tangential) forces were measured using force transducers in a manipulandum.

Main Results:

• Increases in grip force and ground reaction torque consistently preceded load force onset across all conditions.
• The rates of change for grip force and ground reaction torque were correlated, even when accounting for load force rate.
• Grip force and ground reaction torque rates at load force onset were also correlated.

Conclusions:

• Motor planning processes anticipate the dynamic consequences of voluntary actions.
• Coordinated anticipatory grip force and postural adjustments are essential for maintaining stability during object manipulation.
• These findings highlight the predictive nature of motor control in human movement.