TRX is a simple training device, which is basically a nylon parachute cord that you attach to a bar, doorjamb or tree limb. It provides instability in a range of motions that overload the core muscles.
Swiss balls are reminiscent of large beach balls that are used to provide instability during workout.
Core muscle stability is essential for back health and spinal stabilization during exercise. American researchers discovered that doing planks with the TRX device or Swiss balls provided greater loads to the core muscles than traditional stable planks. Loading was measured with electromyography, which measures the electrical activation of muscles. TRX and Swiss balls are practical ways of improving spinal stability and core fitness.