Reproducibility of bioimpedance spectroscopy parameters to evaluate skeletal muscle properties

Bioimpedance spectroscopy (BIS) can be used to evaluate skeletal muscle hydration and integrity in healthy and injured skeletal muscle, thanks to resistance and reactance variations. However, skeletal muscle measurements reproducibility and the effect of length changes have not been evaluated. The aim of this study was to assess the reproducibility and the effect of knee angle on BIS measurements in the knee extensor. Healthy males participated in two experimental sessions, whole-body BIS measurements at rest, isometric maximal voluntary torque (T_max), and BIS assessments at five knee angles (20°, 40°, 60°, 80° and 100° - full extension: 0°) at rest and during T_max. Reproducibility was evaluated with intra-class correlation coefficient (ICC) and coefficient of variation (CV). Whole-body BIS displayed moderate to very good reproducibility at rest (ICC: 0.56-0.82; CV: 3.8-15.4 %). Knee extensors BIS parameters showed a good reproducibility at rest (ICC: 0.53-0.94 and CV: 2.8-8.0 %) and were affected by muscle length, with an increase in intracellular resistance, membrane capacitance and a decrease in characteristic frequency at long muscle lengths (p < 0.05). Whole-body and local BIS parameters showed reproducibility values suitable for daily practice. These parameters are modified by knee angle suggesting a dependency to structural changes of the skeletal muscle.