Compound workouts combine exercise types to load the muscle group in a concentric and eccentric fashion, creating both a metabolic load (as the muscles increase their energy demand over time) and a cardiovascular one (with demand for oxygen rising and the need for metabolites to be removed increasing). Epic Arms works your arms (as expected) but also your core, abs and lower back as your body braces against the weights each time you curl and your torso twists every time you throw punches.