Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Anita, Christie D.

Abstract

The Hoffmann reflex (H-reflex), when elicited in the soleus in healthy males and females, demonstrates sex-specific differences in the neuromodulation of spinal synaptic transmission. This study investigated the sex-related differences in H-reflex excitability and inhibition. Thirty healthy young individuals, 15M (24±2yrs) and 15F (23±3yrs) participated in the study. Surface electrodes were used to elicit and record the H-reflex. Excitability was assessed by stimulating the tibial nerve, beginning at a low-intensity voltage and increasing incrementally until the maximal amplitude of the muscle response was reached. Reciprocal inhibition (RI) was assessed with a conditioning - test stimuli protocol. No significant sex-related differences in excitability were identified; however, males exhibited significantly greater RI than females. This study will add to the growing body of knowledge surrounding differences in the modulation of spinal motor control between sexes and will contribute to the significant gap in neurophysiology research involving females.

Summary for Lay Audience

The physiological system has been well-defined in scientific literature involving male participants; however, research on females is sparse. This gap in the literature is vitally in need of research as findings from male participants should not be used to explain female neurophysiology. The nervous system's signaling pathway that makes up the spinal reflex loop can be manipulated with the electrical stimulation of a peripheral nerve. The response provides information about how efficiently the signal travels through the spinal cord and to the muscle. Studies on male and female differences in this pathway's activation and resistance to activation, known as excitability and inhibition, respectively, are limited and poorly understood in scientific literature. Therefore, this study aimed to investigate the sex-related differences in spinal reflex excitability and inhibition. We recruited thirty (15F) healthy young adults. Participants visited the lab for a single day of testing. Electrical stimulation of a nerve behind the knee evoked a reaction at the spinal level, and the response was recorded with surface electrodes over the calf muscle. The results showed that males and females do not differ in spinal excitability; however, males had greater spinal inhibition. The findings will help fill the gap in understanding sex-related physiological differences while directing future research on movement control tasks.

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