Characteristics of Paraspinal Muscle Spindle Response to Mechanically Assisted Spinal Manipulation: A Preliminary...

Area of Science:

• Neuroscience
• Biomechanical Engineering
• Spinal Cord Research

Background:

• Muscle spindles are sensory receptors crucial for proprioception and motor control.
• Mechanically assisted manipulation (MAM) devices are increasingly used in clinical settings.
• Understanding the neural response to MAM is essential for optimizing therapeutic applications.

Purpose of the Study:

• To investigate the muscle spindle afferent response characteristics to two clinical MAM devices.
• To quantify the duration of altered muscle spindle activity following MAM thrusts.

Main Methods:

• Isolated L6 muscle spindle afferents in 6 cats with receptive fields in paraspinal muscles.
• Recorded neural activity during L7 MAM thrusts using Activator V and Pulstar devices at low force settings.
• Measured time to first action potential, changes in mean frequency (MF) and mean instantaneous frequency (MIF), and return to 95% baseline activity post-MAM.

Main Results:

• A significant percentage of muscle spindle afferents required over 6 seconds to return to baseline MF values post-MAM (44-80% for Pulstar, 11-63% for Activator V).
• Most spindle responses (66-100%) returned to baseline MIF within 6 seconds.
• Significant differences in return-to-baseline times for MF and MIF were observed between Pulstar device settings (22 N vs. 44 N).

Conclusions:

• Short-duration MAM thrusts can decrease muscle spindle discharge, with a majority of afferents showing prolonged recovery of MF activity (>6 seconds).
• The observed prolonged recovery of muscle spindle activity warrants further investigation into its physiological consequences and clinical relevance.
• Device-specific force settings may influence the duration of muscle spindle response alterations.