Computational studies of deep pressure sores (DPS) in skeletal muscles require information on viscoelastic constitutive behavior of muscles, particularly when muscles are loaded transversally as during bone-muscle interaction in sitting and lying immobilized patients. In this study, we measured transient shear moduli of fresh porcine muscles in vitro using the indentation method. We employed a custom-made pneumatic device that allowed rapid indentations. We tested 8 gluteus muscles, harvested from 5 adult pigs. Each muscle was indented transversally (perpendicularly to the direction of fibers) at 3 different sites, 7 times per site, to obtain nonpreconditioned (NPC) and preconditioned (PC) data. Short-term and long-term shear moduli were obtained directly from experiments. We further fitted measured data to a biexponential equation , which provided good fit, visually and in terms of the correlation coefficients. Typically, plateau of the stress relaxation curves (defined as 10% difference from final ) was evident after indentation. Short-term shear moduli (mean NPC: , PC: ) were greater than long-term moduli (NPC: , PC: ) by about an order of magnitude. Statistical analysis of parameters showed that only was affected by preconditioning, while , , , , , and properties were unaffected. Since DPS develop over time scales of minutes to hours, but most stress relaxation occurs within , the most relevant property for computational modeling is (mean ), which is, conveniently, unaffected by preconditioning.