A portable, fully adjustable punching bag exercise system is disclosed whereby a punching bag structure is releasably mounted to the waist of a user and is fully adjustable to any height or distance in front of the user for use in physical training. The punching bag is supported in any orientation via attachment to a spring means which is adjustable in order to control the speed or action of the bag to suit users of varying skill levels. A preferred embodiment also has an optional rebounding means that is fully adjustable for the further control of the effective speed or action of the bag by adjusting the maximum angular deviation of the bag relative to its support mechanism at which the bag is caused to bound back toward the user. Alternative embodiments include resistance straps which elastically couple the belt assembly to the user's hands in order to provide resistance to the punching motion for enhanced physical training and a multi-bag design which provides for enhanced dexterity training.