The effect of subcutaneous fat on electrical impedance myography when using a handheld electrode array: the case for measuring reactance.

OBJECTIVE: Recent developments in electrical impedance myography (EIM) have led to the use of handheld electrode arrays (HEAs) for data acquisition. Although preferable for several reasons, this approach tends to be more affected by subcutaneous fat (SF) than the original approach in which the impedance-measuring electrodes are widely spaced. In this study, we seek to identify the EIM parameter least impacted by subcutaneous fat (SF) when using an HEA.

METHODS: 18 normal subjects underwent 50 kHz EIM and ultrasound of the medial gastrocnemius muscles on the dominant side. Coefficients of determination (R(2) values) were calculated for each of the three major EIM variables (reactance, resistance, and phase) and SF thickness.

RESULTS: For both resistance and phase, a strong relationship to SF thickness was observed (R(2) = 0.64 and R(2) = 0.70, respectively, p < 0.001 for both). In contrast, for reactance, the relationship was non-significant, with R(2) = 0.07, p = 0.30.

CONCLUSIONS: Unlike resistance and phase, both of which are highly impacted by SF thickness, the reactance shows no significant relationship.

SIGNIFICANCE: Future clinical studies employing HEA's to perform EIM should evaluate alterations in reactance in addition to those in resistance and phase.