I took the philadelphia police test, and wanted to know do you take the physical fitness test before the academy or during the philadelphia police academy? Also what would they do if you are underweight?
Any agency that will potentially hire you will mandate you pass a physical agility test. They will also send you in for a comprehensive physical exam. Reason? Because for you to be covered by the local pension plan, you can not have any existing pre-employment defect that would prevent you from preforming your duties and put them in a position of liability.
As for underweight. You need to carb up as much as possible. Lots of fruits, pasta, rice and moderate exercise.
Maybe also see your doctor and express your concerns about your weight and see if they can recommend diet supplements that are safe and effective for your needs.