Gregg Eschelmuller’s MSc Thesis Defence

Title: The effects of periodic vs aperiodic muscle tendon vibration input on stretch reflex circuitry: The role of intent to respond to a perturbation

Thesis Supervisor: Dr. J Timothy Inglis
Committee Members: Dr. Romeo Chua, Dr. Mark Carpenter
Chair: Dr. Bill Sheel

Abstract: When a muscle is mechanically stretched, a stereotypical EMG response known as the stretch response occurs. The stretch response can be subdivided into a short and long latency response. The short latency response is analogous to the tendon tap reflex, while the long latency response involves both spinal cord circuits and transcortical pathways. The short latency response is typically only modulated by peripheral factors such as the size of the perturbation. The long latency response, in addition to being modulated by peripheral factors, can also be modulated based on the participants motor task. For example, if a participant is asked to respond to the stretch as fast as possible, the amplitude of the long latency response increases which would help the participant complete the task.

If you apply mechanical vibration to a muscle tendon, it can also result in activation of the sensory receptors involved in the stretch response. This activation can cause a multitude of effects within the central nervous system, however one main effect that is of particular interest in this thesis is it causes a suppression of the stretch response. However, a few key features remain unknown as followed; how the vibration frequency characteristics and how a participant’s intent to respond to the perturbation effect this suppression. Therefore, the purpose of the current thesis was to investigate if the same effects are present when a periodic vs an aperiodic vibration was used, and whether asking a person to respond the perturbation as fast as possible could modulate this suppression.

The key findings from this thesis were that the suppression did not depend on the vibration characteristics, as both periodic and aperiodic vibration resulted in similar amounts of suppression. Additionally, it was found that a participant’s intent to respond did not modulate the amount of suppression seen. The findings from this thesis provide a more detailed understanding of the stretch response circuitry and the response to tendon vibration.