Comparison of the mechanical response of muscle and adipose tissue under indentation loading between younger and older individuals in the context of pressure ulcer prevention.

RATIONAL AND HYPOTHESIS: This study investigates age-related differences in the mechanical response of muscle and adipose tissue under indentation loading to identify potential biomechanical markers for pressure ulcer (PU) risk. The assumption underlying this work is that variations in tissue stiffness may correlate with PU susceptibility, especially in older individuals. Our working hypothesis posits that older, at-risk individuals will exhibit altered tissue properties, reflected in the force-displacement and strain responses to mechanical loading. METHODS: Twenty-four participants were divided into three groups: younger asymptomatic, older asymptomatic, and older hospitalized individuals. Using a custom force sensor-ultrasound setup, force-displacement and force-strain responses from the anterior thigh were collected, and Ogden hyper-elastic constitutive parameters were derived through inverse optimization. This bedside-measured dataset allowed for the assessment of tissue behavior relevant to PU prevention, with a focus on clinical applicability. RESULTS: Results indicate age-associated stiffening in muscle tissue, with older participants displaying quicker stiffening and reduced initial stiffness compared to younger participants. Adipose tissue measurements, however, were more sensitive to noise, limiting their reliability. Despite observed differences, statistical significance was not achieved, likely due to the limited sample size and the predefined grouping of participants based on recruitment criteria. Future work will increase sample size, conduct retrospective participant analysis, and explore alternative constitutive laws to better understand tissue behavior and its relation to pressure ulcer risk.