A patient would contract surface muscles as areaction called muscle guarding when experiencing discomfortand pain during physical palpation. This reaction carries impor-tant information about an affected location. Training physiciansto regulate palpation forces to elicit just enough muscle tensionis a challenge using real patients. Tunable stiffness mechanismsenabled by soft robotics can be effectively integrated intomedical simulator designs for effective clinical education. Inthis paper, we propose a controllable stiffness muscle layer tosimulate guarding for abdominal palpation training. Designswith soft, fine, and rigid granular jamming, stretchable andnon-stretchable layer jamming mechanisms were tested andevaluated as methods to create controllable stiffness muscle.User studies have been carried out on10naive participants todifferentiate the tense and relaxed abdomen with the proposedjamming mechanisms. Muscle samples made of ground coffee(fine granular jamming) and latex layers (stretchable layerjamming) show good usability in simulating abdomen withdifferent stiffness with at least 75% of the user data exhibitsmore than70%of decision accuracy for both tested palpationgestures (single finger and multiple fingers) after short pre-training.