In some examples, an apparatus comprises a platform having an upper surface to contact a plantar surface of a human foot positioned on the platform, a first pressure sensor to sense a pressure applied to the upper surface by a heel of the human foot, and a first probe extending through an opening in the platform and movable vertically upward through the opening to probe an adipose layer on a bottom of the heel. The apparatus also comprises a first actuator to displace the first probe upwardly against the adipose layer with a predetermined force, and a linear displacement sensor to sense a vertical displacement of the first probe.