A sample of 55 athletes who sprained their ankle in the past month volunteered for treatment. The researchers are looking for data on the level of tear of the ankle. They conducted X-rays on the ankle before and after the treatment. After the first X-ray, they started specific physical training drills to determine if they helped with the level of tear. They will then take another X-ray after a week of physical training to compare the data. What is the response variable