Whether or not you can run with a bad cervical spine depends on the specific situation. If it is a simple cervical strain, such as cervical muscle strain caused by prolonged head-down work or prolonged computer reading, or cervical pain and restricted activity, not accompanied by neurological symptoms of the upper or lower limbs, that is, the hands and feet are normal, no numbness or pain, then running is perfectly fine at this time and will not have much effect. If it is spinal cervical spondylosis, or the cervical spine is unstable, or even subluxation, then it is not recommended to exercise vigorously at this time, including of course not running. Because of the vibration and back and forth swing of the neck when running, it is likely to aggravate the instability of the cervical spine, or lead to increased damage to the cervical spinal cord, which may lead to tetraplegia, urinary and fecal incontinence, or even life-threatening in serious cases.