To provide devices and methods to reduce the occurrence of pressure ulcers for patients lying on respective support surfaces, such as hospital bed mattresses, for extended periods of time.

A control system 16 includes: at least one inflatable bladder; a cover including a portion above the at least one inflatable bladder; a plurality of sensors 56 that generate data signals indicative of a characteristic of the at least one inflatable bladder and a person's tissue contacting the cover; a processor operatively which is coupled to the plurality of sensors 56, and configured to execute operating logic to determine a surface performance index as a function of the data signals; and a fluid supply 14 which is coupled to the at least one inflatable bladder, and whose operation is controlled by the processor as a function of the surface performance index.