In layman's terms, spine is the stiffness of the arrow shaft. The term 5575 can be misleading because other factors affect the required spine or stiffness in any given bow set-up. Inlcuding draw length, arrow length, accessory (including point) weight, cam type etc. It is better to be a little on the stiff side of the spine scale than weak. I suspect you're set-up is on the weak side of spine and the tuning procedures in the Easton Tuning Guide will confirm.