i get a stiff neck from tennis. my cure was working with weights at the gym. not sure what particular exercise helped, but I do bench press, squat, shoulder press, lat pull downs, curls, triceps , leg extensions, hamstrings, calfs, and ab work. I think doing exercise that’s different from tennis is what helped my neck—Works different muscles than the same muscles you use over and over again in tennis.unfortunately, haven't been to the gym since march 2020, and my neck is sore again.