A size-adjustable hamstring device of unitary construction provides for easily, effectively, and efficiently exercising (stretching) the hamstrings. The device consists of a frame of unitary and is used in a prone position avoiding back strain. The device supplies means for supporting the user's foot and means for assuring that the user's leg is maintained in a straight position. Means for holding allows for ease in grasping the device so that the user is able to pull or push the device as desired. The means for supporting a foot, maintaining the leg in a straight position, and for holding may all be padded for increased ease of use and comfort. The frame is made of any readily available, strong, lightweight material, such as plastic or aluminum and it is contemplated that the device be made using a molding process to reduce the cost of manufacturing.