This is an involuntary response to prevent pain caused by pressure on your abdomen. Another term for this protective mechanism is guarding. This symptom isn't the same as intentionally flexing your abdominal muscles or the rigidity associated with severe gas. Guarding is an involuntary response of the muscles.

What causes abdominal muscle guarding?

Abdominal guarding is detected when the abdomen is pressed and is an indication that inflammation of the inner abdominal (peritoneal) surface may be present due, for example, to appendicitis or diverticulitis.

What causes guarding in appendicitis?

Guarding of the abdomen

Voluntary guarding is a conscious contraction of the abdominal wall in anticipation of an exam that will cause pain. Involuntary guarding is a reflex contraction or spasm of the abdominal muscles on palpation due to localized peritoneal inflammation.