Inter-session Reliability of Magnetic Nerve Stimulation and Within-Session comparison to Electrical Nerve Stimulation in Evaluating Neuromuscular Function of Knee Extensor Muscles

Introduction Quantifying neural activation is crucial for evaluating rehabilitation progress and adaptations following resistance training. A commonly used method for assessing voluntary activation (VA) is the Interpolated Twitch Technique with electrical nerve stimulation (ENS). However, this method is often associated with discomfort, limiting its applicability in sensitive populations such as children or patients (Shield & Zhou, 2004). Magnetic nerve stimulation (MNS) offers a painless and promising alternative, but its validity and reliability remain insufficiently established (Verges et al., 2009). This study aims to address this gap by comparing ENS and MNS and assessing the reliability of MNS across sessions. Methods This study compares ENS to MNS (validity) and evaluates inter-session reliability in sixteen healthy young adults (11 females, 5 males). Data on resting single twitches (RS), 3-5 superimposed twitches (ST) during maximal voluntary contractions of knee extensors, and resting doublet twitches (RD) were assessed using both MNS and ENS. Discomfort was assessed using the visual analogue scale (VAS). Intraclass correlation (ICC), Coefficient of variation (CV) and mean absolute percentage error (MAPE) were used to assess measurement precision. Results There was strong agreement between MNS and ENS for RS, RD and VA (ICC=0.77-0.88). Accuracy was confirmed, with MAPE values of 4.4% for VA and 9.5% for RD. The inter-session reliability of MNS was good across all parameters (ICC = 0.78–0.95) with low CV for VA (4.9%) but high CV for RS, RD and ST (61.7%, 28.9%, 82%). Discomfort ratings were significantly lower for MNS (VAS = 1.0 ± 0.9) compared to ENS (VAS = 1.8 ± 1.2). Discussion/Conclusion This study demonstrates that MNS is a valid, reliable, and minimally discomforting alternative to ENS for assessing VA in knee extensor muscles. The use of a positioning arm in our methodology likely enhanced precision within sessions. However, individual twitch measurements varied between methods and sessions, warranting caution when interpreting absolute values. Given its minimal discomfort, MNS is especially suited for studying neuromuscular adaptations in vulnerable populations and should be widely adopted. References Shield, A., & Zhou, S. (2004). Assessing voluntary muscle activation with the twitch interpolation technique. Sports Medicine, 34(4), 253–267. https://doi.org/10.2165/00007256-200434040-00005 Verges, S., Maffiuletti, N. A., Kerherve, H., Decorte, N., Wuyam, B., & Millet, G. Y. (2009). Comparison of electrical and magnetic stimulations to assess quadriceps muscle function. Journal of Applied Physiology, 106(2), 701–710. https://doi.org/10.1152/japplphysiol.01051.2007