Objective: To determine the impact of skin-subcutaneous fat layer thickness on electrical impedance myography (EIM) measurements.
Methods: Linear 50 kHz EIM was performed on quadriceps of 62 healthy subjects (mean age 52.2+/-20.6 years) with a wide variety of skin-subcutaneous fat layer (SFL) thicknesses, as measured by ultrasound. Correlations were sought between the main EIM outcome parameter phase (theta) and SFL thickness. A multiple regression analysis was also performed for theta with SFL thickness and age as independent variables.
Results: Mean skin-fat thickness was significantly different (p<0.01) between men (0.76+/-0.23 cm) and women (1.43+/-0.51 cm). Neither linear nor quadratic fits produced significant correlations between theta and SFL thickness. A significant but weak positive correlation (r(2)=0.14, p<0.05) was seen between age and SFL thickness in women, but not in men. A strong negative correlation between age and theta was observed for both men (r(2)=0.48, p<0.01) and women (r(2)=0.68, p<0.01). In multiple regression analysis, age but not SFL thickness was found to have a significant association with theta.
Conclusions: SFL thickness does not contribute substantially to the phase measured by linear-EIM.
Significance: EIM data can be interpreted confidently in individuals with varying SFL thickness.