Yes, a chest strap on the backpack can definitely help to relieve the back and prevent back pain. By attaching the chest strap, the weight of the pack is evenly distributed over the shoulders and chest area, reducing pressure on the lower back. In addition, the chest strap ensures that the backpack fits snugly against the body and does not slip back and forth, which also means relief for the back.
A chest strap is therefore highly recommended, especially for longer hikes or trekking tours. It can help ensure that you can travel longer without pain and thus enjoy the tour even more. However, you should make sure that the chest strap is not too tight so as not to have any restrictions on breathing.