abdominizer
/abˈdɒmɪnʌɪzə/ /əbˈdɒmɪnʌɪzə/(also abdominiser)
noun
A piece of exercise apparatus on which the user lies supine and rocks backwards and forwards, flexing the abdominal muscles. Later also more generally: any of various different types of apparatus designed to exercise the abdominal muscles.
Origin
1980s; earliest use found in The Washington Post. From abdomin- + -izer.