voluntary guarding is when the patient tenses up the abdomen in response to your palpation. involuntary guarding is a patient with a rock hard rigid abdomen (not from doing crunches) whether or not you press.
voluntary guarding may or may not be significant - tenderness? ticklish patient?
involuntary guarding equates to peritonitis, that is, peritoneal irritation from underlying inflammation that results in the abdominal muscles tensed up. it usually signifies a surgical emergency.
