Perturbed upper limb movements cause short-latency postural responses in trunk muscles

Area of Science:

• Biomechanics
• Human Movement Science
• Neuroscience

Background:

• Perturbations to a moving limb transmit forces to the trunk.
• Understanding trunk muscle responses to unexpected limb loading is crucial for motor control.
• Previous research has not fully elucidated the timing and origin of these postural adjustments.

Purpose of the Study:

• To investigate the postural response of trunk muscles to unexpected upper limb loading during rapid shoulder flexion.
• To determine the latency and characteristics of trunk muscle activation following limb perturbation.
• To explore the potential afferent pathways involved in initiating these responses.

Main Methods:

• Subjects performed bilateral shoulder flexion in response to a stimulus.
• An unexpected load was applied to the upper limbs during the initial phase of movement in a subset of trials.
• Measurements included trunk muscle electromyography, intra-abdominal pressure, and upper limb/trunk kinematics.

Main Results:

• A short-latency response (approx. 50 ms) was observed in the erector spinae and transversus abdominis muscles.
• This activation coincided with the onset of trunk perturbation caused by the early limb loading.
• The findings suggest a rapid, complex postural response mediated by afferent input.

Conclusions:

• The trunk muscles initiate a complex postural response to unexpected limb loading with short latency.
• This response is likely mediated by afferent sensory information, potentially originating from the upper limb.
• The findings contribute to understanding the neural control of posture and movement.