Employee was using a pry bar to dislodge broken plow tips in RMI. They felt the job was strenuous but was alright when they completed it. They had a prescheduled day off 10/28/24 and returned to work on 10/29/24. Their back was stiff and mentioned it to the Maint. Coordinator. By 10:00 AM their back had a spasm, and they could hardly walk.