A durable and impact-resistant exercise apparatus that is portable, modular, stackable, and weight-adjustable to allow a user to perform a variety of isolated lower body, core, and upper body resistance training exercises as well as full-body strength training exercises to improve a fitness of the user. The exercise apparatus is configured both as a platform for supporting the user during a first plurality of exercises as well as a weighted body for being lifted or moved by the user during a second plurality of exercises.