Back Protector
Some motorcycle jackets are provided with built-in back protectors with varying levels of quality. Some jackets have a flimsy piece of foam padding stuffed in the back, designed mostly for the manufacturer to claim that their jacket includes a back protector. Others may include more robust forms of removable or non-removable padding, back protection or "armor". If your jacket doesn’t have one, you could purchase one as an accessory which is not very expensive.
Back protectors have been used by motorcycle racers for some time; they fit under a set of full leathers or other clothing and their job is to protect the rider's backbone, back and ribs and to distribute the forces generated in a crash over a wider surface area.
The ability of most original equipment back protectors to actually do anything to help the rider is arguable but something is better than nothing. Motorcycle racers know this, and they use all the protection they can stuff into their leathers, including a "turtleback" type back protector.
There are many types and styles of back protectors, such as mini protectors that act as a kidney belt and protect a few vertebrae; thin, light weight models designed for riders and the full coverage back protectors used by motorcycle racers. We have trained A&E staff at hospitals and Ambulance services and they say most of the fatal crashes are due to the extensive damage caused to vertebrae or neck which has nothing to do with your helmet.
I would recommend The BMW Motorrad Neck Brace System which significantly reduces the risk of injuries to the cervical vertebrae, yet at the same time is surprisingly light.
Prevention is better than cure.