Serious spinal injuries are usually caused by axial forces due to blows to the head, or bending and twisting forces on the back caused by blows to the shoulders, hips or other parts of the body. In the Cambridge standard for motorcyclists clothing, Roderick Woods asserts that the majority of spinal injuries are caused by blows to the hips and shoulders. In the rare circumstance that a motorcyclist received a direct blow to the back the damage would be unmitigated by armour. The concept of a "back protector" is therefore not endorsed by Woods. Although back protectors are defined in the standard, cannot protect against axial forces they are required to protect the scapula and there is now a considerable anecdotal evidence that wearing a certified back protector can significantly reduce trauma in a major accident as they reduce the effect of impacts on the ribs and lessen the blows to the internal organs too