Target size modifies anticipatory postural adjustments and subsequent elementary arm pointing

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Anticipatory postural adjustments (APAs) are crucial for maintaining balance during voluntary movements.
• The influence of target precision on APAs during arm pointing from an upright posture remains incompletely understood.

Purpose of the Study:

• To investigate how varying target sizes, demanding low precision, affect APAs and arm movements in an upright posture.
• To explore the cognitive and biomechanical underpinnings of motor strategy selection during pointing tasks.

Main Methods:

• Six subjects performed unguided arm-pointing movements towards targets of 2, 4, and 8 cm diameter (D2, D4, D8).
• Electromyographic activity of the anterior deltoid and biceps femoris was recorded.
• Arm kinematics were analyzed to assess movement characteristics and APA durations.

Main Results:

• Longer APA durations were observed for the medium target (D4) compared to smaller (D2) and larger (D8) targets.
• The ratio of acceleration duration to total movement duration was lower for D4.
• Movement precision remained consistent across all target sizes, despite differences in APAs.

Conclusions:

• A medium target size (D4) appears to optimize motor strategy for balancing accuracy and velocity requirements.
• APAs not only serve to stabilize posture but also reflect cognitive representations of task precision.
• These findings highlight the integration of environmental and action-related representations in motor planning.