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Anticipatory postural adjustments during load catching by standing subjects
1Department of Kinesiology, Rec. Hall-267, Pennsylvania State University, University Park, PA 16802, USA.
Summary
Anticipatory postural adjustments (APAs) are generated in arm and leg muscles when catching a load, regardless of who releases it. Kinetic energy, not momentum, better predicts APA magnitude when the experimenter releases the load.
Area of Science:
- Biomechanics
- Motor Control
- Human Physiology
Background:
- Anticipatory postural adjustments (APAs) are crucial for stabilizing the body before a voluntary or involuntary perturbation.
- Understanding APA generation is key to comprehending motor control strategies during dynamic tasks like load catching.
Purpose of the Study:
- To investigate differences in APA generation in arm and trunk/leg muscles when catching a load released by oneself versus an experimenter.
- To examine the influence of load's mechanical characteristics (mass, momentum, kinetic energy) on APA generation during load catching.
Main Methods:
- Subjects caught loads released by themselves or an experimenter from varying heights.
- Load mass and release height were manipulated, keeping either mass or momentum constant at impact.
- APAs were quantified using integral electromyographic (iEMG) indices.
Main Results:
- APAs were observed in leg, trunk, and arm muscles for both self- and experimenter-released load catches.
- Kinetic energy correlated more strongly with APA magnitude than momentum, but only in experimenter-release trials.
Conclusions:
- The body can generate APAs in anticipation of a load catch without explicit voluntary action.
- The differential importance of kinetic energy versus momentum in predicting APA magnitude reflects varying information sources used when preparing for self- versus experimenter-released perturbations.