Typical: fibres packed tight, a thin film of fluid between them. Most of the arm's water is inside the fibres.

Change the fibres or the fluid · then the frequency
Muscle fibre (water inside: ICW)Fluid between fibres (ECW)Current, flowing toward youMost of the body's water sits inside cells, and much of that inside muscle fibres. The rest bathes the cells and fills the blood. InBody's current runs along the arm (toward you in this slice, ⊙). At low frequency, cell membranes block it, so it flows only through the fluid between the fibres; that reading gives extracellular water (ECW). At higher frequencies some current crosses the membranes, adding the water inside (ICW) to give total body water (TBW).ECW/TBW is the share outside. It rises if fibres shrink (0.399 here) or if fluid collects between them (0.413), so a high number says the balance has shifted, not why. Bigger fibres nudge it down (0.369).A teaching model: skeletal muscle is taken to hold about half the body's water, and only the muscle changes in each scene; values are typical, not a measurement of anyone. Bands follow InBody's result sheet: under 0.390 normal, 0.390–0.400 slightly over, above 0.400 over. Fibres drawn far larger than life (a fibre is about the width of a hair).