hang cleans are the last half of the power clean motion. to refresh - the power clean starts with the barbell on the ground, you basically deadlift the weight until the bar's over the knees, when you accelerate with a pull of the bar as high as you can, then drop under the weight and "catch" it on your chest. you end up looking like you're doing a front squat. the hang clean starts with the bar already just above the knees - so the emphasis is on the "pull" (explosive) half of the clean. it will necessitate a drop in weight, but will improve your explosiveness to no end. not exactly the bodybuilding exercise of the century, however. best suited to sports specificity.