If you are one of those cycling really much in your spare time, then you have definitely considered whether it is a good idea to use different protection. You have already guaranteed a bicycle helmet, but buying a back shield can be a good investment. The forest is more bumpy, so the likelihood of you crashing and landing on a branch or rock is very high in many off-road bike types. With a back shield you get a very important part of your body which can often be damaged by a crash.
There are many different backpacks for cycling on the market today, and you can read much more about some of the best in testing and most popular on the market below. In general, you should consider safety level, comfort and price when looking for a back shield for cycling.