Electrical impedance myography in healthy adults: Reliability, sex differences, and regional variations in the anterior thigh muscles

This study investigated the intra-day and inter-day reliability of electrical impedance myography (EIM) components and explored sex and regional differences in healthy adults' anterior thigh muscles. Using a multifrequency device, impedance values across various frequencies, alongside 50-kHz resistance (R), reactance (Xc), and phase angle (PhA) were assessed in both sexes and at whole anterior thigh, proximal and distal regions. Findings revealed excellent reliability (ICC > 0.90) and low standard error of measurement (<5.0 %) for impedance at all frequencies, 50-kHz R, Xc, and PhA regardless of sex or measurement region during both intraday and inter-day assessments. Moreover, differences were observed between women and men across most parameters, except for Xc, indicating the sensitivity of EIM in detecting established disparities in tissue composition between sexes. Notably, whole anterior thigh impedance at all frequencies and 50-kHz R, Xc, and PhA displayed dissimilarities compared to proximal or distal regions in both sexes. Additionally, women exhibited differences between proximal and distal regions in the 100-kHz impedance and 50-kHz impedance, R, Xc, and PhA highlighting possible variations in tissue composition along the muscle length compared to men. These findings underscore the relevance of electrode placement and emphasize sex-specific differences in EIM assessments within anterior thigh muscle regions.