Abstract: A biofeedback exercise stimulation apparatus for sensing the state of the abdominal muscles and providing feedback signals to a user when the user relaxes the contraction of their abdominal muscles. The housing of the apparatus is configured to be readily inserted inside a waistband of the user and is self-retaining when positioned behind the waistband. The apparatus has a back side for positioning against the user and a front side with the self-retaining configuration. A sensor mechanism is positioned in proximity to the self-retaining configuration that detects the increased pressure between the user and the waistband when the user relaxes their abdominal muscles. The sensor mechanism is connected with a signal mechanism for the sending of a feedback signal, such as a light, sound, vibration, or electrical signal to the user that the abdominal muscles have been relaxed.