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

The Interpolated Twitch Technique with electrical nerve stimulation (ENS) is the considered gold-standard to assess voluntary activation (VA) but causes discomfort. Magnetic nerve stimulation (MNS) offers a painless alternative, though its validity and reliability remain underexplored. This study validates MNS to ENS and evaluates inter-session reliability in 16 healthy young adults (11 females). Data on resting single twitches (RS), superimposed doublets (ST) during maximal voluntary contractions, and resting double twitches (RT) were assessed using both MNS and ENS, alongside discomfort ratings (VAS). Intraclass correlation (ICC), coefficient of variation (CV) and mean absolute percentage error (MAPE) were used to quantify agreement between stimulations and/or inter-session reliability. Strong agreement between MNS and ENS was found for RS, RT, and VA (ICC = 0.77-0.88), with MAPE values of 4.4 % (VA) and 9.5 % (RT). Discomfort was lower for MNS (VAS = 1.0 ± 0.9) than ENS (VAS = 1.9 ± 1.1). Intersession-reliability for MNS was good (ICC = 0.78-0.95) with low CV for VA (4.9 %) but high for RS, RT and ST (61.7 %, 28.9 %, 82.0 %). Based on these results, MNS provides a valid, reliable, and painless alternative to ENS for assessing VA in knee extensor muscles. However, individual evoked twitches varied across methods and sessions, warranting caution when interpreting absolute values.