Agreement Between Investigators Using Paired-Pulse Transcranial Magnetic Stimulation to Assess Quadriceps Intracortical Excitability.

CONTEXT

Transcranial magnetic stimulation (TMS) may provide important information regarding the corticospinal mechanisms that may contribute to the neuromuscular activation impairments. Paired-pulse TMS testing is a reliable method for measuring intracortical facilitation and inhibition; however, little evidence exists regarding agreement of these measures in the quadriceps.

OBJECTIVE

To determine the between-session and inter-rater agreement of intracortical excitability (short and long interval intracortical inhibition [SICI; LICI] and intracortical facilitation [ICF]) in the dominant limb quadriceps.

DESIGN

Reliability study.

SETTING

Research laboratory.

PARTICIPANTS

Thirteen healthy volunteers (n=6 female; age: 24.7±2.1 years; height: 1.7±0.1m; mass: 77.1±17.4kg).

INTERVENTION

Participants completed 2 TMS sessions separated by 1 week.

MAIN OUTCOME MEASURES

Two investigators measured quadriceps SICI, LICI, and ICF at rest and actively (5% of maximal voluntary isometric contraction). All participants were seated in a dynamometer with the knee flexed to 90°. Intracortical excitability paradigm and investigator order were randomized. Bland-Altman analyses were used to establish agreement.

RESULTS

Agreement was stronger between sessions within a single investigator than between investigators and for active compared to resting measures. Agreement was strongest for resting SICI and active ICF and LICI between sessions for each investigator.

CONCLUSIONS

Quadriceps intracortical excitability may be measured longitudinally by a single investigator, though active muscle contraction should be elicited during testing.