Due to prolonged periods of riding in a car and/or inactivity (starting to skip the gym) you begin to lose your flexibility. Then one day you are quickly placed into a dynamic situation, and your chances of injury greatly increase. A cold rainy night on patrol only further increases chances of a muscle injury.
How can you prevent this? A martial arts pal of mine recommends taking frequent stretch breaks. No, I did not say coffee breaks, snack breaks, or smoke breaks; I said stretch breaks.
Begin a routine with a regular stretch break worked into your shift. When you have to get out of the car to check a building; perform some park, walk, and talk time with the citizens; or even to go in and out of the station, take some time to stretch. Focus on the legs (especially hamstrings), a few torso rotations, lower back, and then shoulders. Only a couple of minutes are needed, and then continue to do this a few times during the shift.
I would even make this a daily ritual. Start stretching on a day off, before and after workouts, and it soon becomes a part of the daily routine. Stretching will not prevent all injuries, but will greatly decrease pulls and strains. It will improve your flexibility and make your range of motion better.
Avoid inactivity and do not become a patrol troll. Today's radio cars have wonderful climate controls and creature comforts that are apt to keep you sedentary. Checking a building or park could provide a fitness walk. Get out and move around.