Axially evoked postural reflexes: influence of task.

Area of Science:

• Biomechanics
• Neuroscience
• Human Motor Control

Background:

• Postural reflexes are crucial for maintaining balance.
• Understanding how external stimuli evoke these reflexes is key to understanding postural control.

Purpose of the Study:

• To investigate the characteristics of short latency (SL) postural reflexes in healthy subjects.
• To determine the influence of trunk orientation and postural tasks on these reflexes.
• To explore the sensory pathways involved in evoked postural responses.

Main Methods:

• Healthy subjects (n=17) were subjected to axial accelerations and tap stimuli at C7 and the manubrium sterni.
• Short latency (SL) responses were recorded from soleus, hamstrings, and tibialis anterior muscles.
• Experiments were conducted under various postural conditions, including standing and leaning, with and without cutaneous anesthesia.

Main Results:

• SL responses varied significantly between muscles (soleus, hamstrings) depending on the postural condition (standing vs. kneeling).
• Concordant head and trunk accelerations yielded larger SL responses than discordant ones.
• Postural reflexes were significantly enhanced under conditions threatening stability, with specific responses to C7 and sternal stimulation during anterior and posterior leans, respectively.

Conclusions:

• Evoked postural reflexes are significantly modulated by postural tasks and trunk orientation.
• These reflexes appear independent of cutaneous receptors, vestibular, and ankle proprioceptors.
• The findings support a role for these reflexes in dynamic postural stabilization.