Reliability of transcranial magnetic stimulation measurements of maximum activation of the knee extensors in young adult males

Purpose: • Transcranial magnetic stimulation (TMS) provides an indication of changes occurring in the corticospinal pathway. This study aimed to determine the between-day (trials 1 week apart) and within-day (trials 1 h apart) reliability of TMS and peripheral nerve stimulation. Methods: • 22 male participants (age 23 ± 4 years; height 1.80 ± 0.07 m; body mass 75.1 ± 11.7 kg; body mass index 23.1 ± 2.5 kg.m−2) completed 2 familiarisation sessions and 3 experimental trials (trial 2 and 3 split by 1 h). The interpolated twitch technique was used to determine TMS-assessed voluntary activations (VA-TMS) superimposed on submaximal and maximal leg extension performed on a custom-built dynamometer. Reliability was assessed using equivalence tests, systematic error, 95% limits of agreement, intraclass correlation coefficient (ICC) and coefficient of variation (CV). Results: • VA-TMS was equivalent between-day (94.1 ± 4.4% versus 93.7 ± 4.9%, P < 0.01) and within-day (93.7 ± 4.9% versus 93.7 ± 4.8%, P < 0.01). Systematic error (95% limits of agreement) for VA-TMS was −0.5% (−5.1%, 4.2%) for between-day and − 0.0% (−5.3%, 5.4%) for within-day. ICC and CV values demonstrated high reliability between-day (ICC = 0.93, CV = 2.5%) and within-day (ICC = 0.92, CV = 2.9%). Conclusion: • Results indicate that TMS can reliably estimate the output of the motor cortex to the knee extensors, both between-day and within-day. The findings have been used to estimate sample sizes for this technique for future research.