Deep-Tissue Hydration Assessment Strategies: A Comparison of the RF-Based Solutions

Accurate assessment of muscle hydration is essential in clinical practice, athletic performance, and rehabilitation, as changes in intramuscular water content directly affect physiological function and performance. Bioelectrical Impedance Analysis (BIA) is widely used for hydration evaluation, but its capability to characterize deep muscle hydration is limited by poor spatial selectivity and strong sensitivity to superficial tissues. Microwavebased electromagnetic (EM) sensing has recently emerged as a promising alternative, exploiting the correlation between tissue dielectric properties and water content to enable localized interrogation. However, the multilayer structure of biological tissues complicates spectral interpretation, as superficial layers significantly influence the measured response. This paper overviews current non-invasive hydration assessment approaches, highlighting the limitations of conventional and predictive BIA techniques and the potential of microwave-based sensing combined with multivariate predictive modeling to achieve accurate and localized intramuscular hydration monitoring.