Within-day test-retest reliability of transcranial magnetic stimulation measurements of corticomotor excitability for gastrocnemius and tibialis anterior muscles

Background: Manual therapy interventions targeting the talocrural joint can improve gait and balance functions in individuals following ankle sprains. Less is known about the underlying mechanisms of functional improvements after manual therapy. One hypothesis involves change in corticomotor excitability (CE) following manual therapy procedures. Transcranial magnetic stimulation (TMS) is a brain imaging method that could provide important information regarding potential changes in CE associated with manual therapy techniques applied to the talocrural joint. However, within-day reliability of TMS to measure CE must first be established in order to measure CE changes associated with manual therapy procedures. Objective: To determine the within-day test-retest reliability of TMS CE measures for gastrocnemius (GAS) and tibialis anterior (TA) for use in test-retest designs assessing corticomotor excitability in manual therapy and exercise studies. Method: TMS measures, including motor evoked potential (MEP) amplitude and cortical silent period (CSP), were completed twice on the same day under resting and active conditions in n = 6 nondisabled participants. The absolute reliability (coefficient of variation), relative reliability (intraclass correlation coefficient), standard error of measures, and minimal detectable change outside the 95% confidence interval were calculated for both GAS and TA muscles in each experimental condition. Results: There were no statistically significant differences between the first and second TMS measurements. TMS measurements for GAS and TA demonstrated good absolute and relative test-retest reliability under the active condition, but not the resting condition. Discussion: TMS under the active condition can be reliably used to assess CE even in postural muscles with a small cortical representation area, such as GAS