Phasic stretch reflex of the abdominal muscles

Area of Science:

• Neuroscience
• Physiology
• Biomechanics

Background:

• The abdominal stretch reflex (ASR) is a spinal reflex crucial for posture and respiration.
• Understanding how motoneurons integrate respiratory and nonrespiratory signals is essential for elucidating ASR control.

Purpose of the Study:

• To investigate the influence of respiratory phase, lung volume, and trunk posture on the abdominal stretch reflex (ASR).
• To explore how voluntary abdominal muscle contractions modulate ASR amplitude and timing.

Main Methods:

• Surface electromyography (EMG) of external and internal oblique muscles was recorded in standing subjects.
• The ASR was evoked by abdominal taps, with variations in tap force, trunk rotation, and respiratory maneuvers (breath-holding, rebreathing).

Main Results:

• ASR amplitude varied with tap force and was modulated by trunk rotation and voluntary abdominal muscle contraction.
• Reflex amplitude was inversely proportional to static lung volume and showed a distinct pattern during the respiratory cycle, peaking near end-expiration.
• Respiration phase influenced ASR, with changes observed during quiet breathing, breath-holding, and rebreathing.

Conclusions:

• The abdominal stretch reflex is under significant neural control from muscle spindles, lung proprioceptors, and chemoreceptors.
• Respiratory phase and lung volume dynamically regulate ASR, highlighting the interplay between respiratory and postural control systems.
• Further research is needed to precisely determine the contribution of each input source to ASR modulation.