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Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings
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Published on: July 26, 2022

Arm movement control in gravity.

Dinant A Kistemaker1, Rick Staa1, Martijn van der Sar1

  • 1Vrije Universiteit Amsterdam, The Netherlands.

Journal of Neurophysiology
|July 13, 2026
PubMed
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Gravity does not affect goal-directed arm movements. Researchers found movement direction, not body orientation relative to gravity, influences arm movement kinematics. Kinematic models accurately predict movement.

Keywords:
arm movement asymmetriesgoal directed arm movementsoptimal control

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Area of Science:

  • Biomechanics
  • Human motor control
  • Robotics

Background:

  • Goal-directed arm movements are crucial for daily activities.
  • Understanding the influence of external forces like gravity on motor control is essential for developing advanced robotic systems and rehabilitation strategies.

Purpose of the Study:

  • To investigate the influence of gravity on goal-directed planar arm movements.
  • To determine if body orientation relative to gravity affects movement kinematics.
  • To identify the most accurate cost functions for predicting arm movement trajectories using an optimal control model.

Main Methods:

  • Participants performed point-to-point arm movements in a reclinable chair at various angles (0° to 90°) relative to gravity.
  • Movement kinematics (curvature and time-to-peak-velocity) were recorded under strict temporal and spatial constraints.
  • An optimal control musculoskeletal model was used to predict movement trajectories based on different cost functions.

Main Results:

  • Movement direction (inward vs. outward) significantly affected movement curvature and time-to-peak-velocity.
  • No significant effect of gravity or body orientation was observed on these kinematic parameters.
  • Jerk-based (kinematic) cost functions accurately predicted experimental movement kinematics, unlike models incorporating muscle activation or force.

Conclusions:

  • Gravity does not influence the kinematics of goal-directed arm movements.
  • Observed differences in movement characteristics are primarily due to movement direction.
  • Kinematic cost functions provide a more accurate representation of observed arm movement patterns than those based on muscle effort.