A door-mounted exercise apparatus, comprising: a) a first strap, operable to removeably circumnavigate a door along its width even when the door is closed, said first strap comprising: (i) a first fastener operable to adjustably tighten the first strap circumferentially around the door's width, such that a user's feet can be inserted between the first strap and the door to securely adhere the feet up against a front or back surface of the door along the door's width, and; b) a second strap affixed to the first strap along a length of the first strap, and; c) a third strap, affixed at the two ends of its length along a width of the first strap, such that the second strap is operable to loop in between the first strap and the third strap, such that each of the user's feet fits between the second strap and the first strap on either side of the third strap, and such that the balls of the user's feet touch the first strap instead of the door's surface; Whereby the door-mounted exercise apparatus enables the user to perform sit-ups with their feet secured.