Reliability of corticomotor excitability in leg and thigh musculature at 14 and 28 days.

Context: Alterations in corticomotor excitability are observed in a variety of patient populations, including the musculature surrounding the knee and ankle after joint injury. Active motor threshold (AMT) and motor-evoked-potential (MEP) amplitudes elicited through transcranial magnetic stimulation (TMS) are outcome measures used to assess corticomotor excitability and have been deemed reliable in upper-extremity musculature. However, there are few studies assessing the reliability of TMS measures in lower-extremity musculature. Objective: To determine the intersession reliability of AMT and MEP amplitudes over 14 and 28 d in the quadriceps and fibularis longus (FL). Design: Descriptive laboratory study. Setting: University laboratory Participants: 20 able-bodied volunteers (10 men, 10 women; 22.35 +/- 2.3 y, 1.71 +/- 0.11 m, 73.61 +/- 16.77 kg). Main Outcome Measures: AMT and MEP amplitudes were evaluated at 95%, 100%, 105%, 110%, 120%, 130%, and 140% of AMT in the dominant and nondominant quadriceps and FL. Interclass correlation coefficients (ICCs) were used to assess reliability for absolute agreement and internal consistency between baseline and 2 follow-up sessions at 14 and 28 d postbaseline. Each ICC was fit with the best-fit straight line or parabola to smooth out noise in the observations and best determine if a pattern existed in determining the most reliable MEP value. Results: All muscles yielded strong ICCs between baseline and both time points for AMT. MEPs in both the quadriceps and FL produced varying degrees of reliability, with the greatest reliability demonstrated on day 28 at 130% and 140% of AMT in the quadriceps and FL, respectively. The dominant FL muscle showed a significant pattern; as TMS intensity increased, MEP reliability increased. Conclusion: TMS can be used to reliably identify corticomotor alterations after therapeutic interventions, as well as monitor disease progression.