Reaching to multiple targets when standing: the spatial organization of feedforward postural adjustments

Area of Science:

• Biomechanics
• Neuroscience
• Human Movement Science

Background:

• Postural adjustments are crucial for maintaining stability during voluntary movements.
• Understanding the spatial organization of these adjustments informs our knowledge of motor control.

Purpose of the Study:

• To investigate directional tuning in postural muscle activity before and during arm reaching.
• To determine if a horizontal force constraint strategy is employed during these movements.

Main Methods:

• Eight subjects performed self-paced arm reaches to 13 targets.
• Electromyographic activity of lower limb muscles was recorded.
• Horizontal ground reaction forces were analyzed during pre- and active-postural adjustment (pPA and aPA) periods.

Main Results:

• Clear directional tuning of postural muscles was observed in both pPA and aPA periods.
• A horizontal force constraint strategy was evident in the pPA period but not the aPA period.
• Ground reaction forces were more dispersed during the aPA phase.

Conclusions:

• Feedforward postural adjustments utilize tuned muscle synergies to constrain forces and control center of mass (CoM) movement within the base of support.
• The shift in strategy during the aPA period reflects the need to control final limb and body position.
• Endpoint limb force in postural tasks relies on functional muscle synergies for CoM displacement and deceleration.