Sit-ups with a constant neck strain may be related to the following reasons. This condition is common in young, relatively thin female patients. This kind of patients in sit-ups, the upper limbs itself to provide the auxiliary force is not enough, at this time the patient in order to continue to lift the head, you need to make the neck muscles continue to force. 2, may be due to the exercise posture is not right. Many patients do sit-ups, due to the hands to cross behind the head, will involuntarily have flexion force on the neck, then the neck may involuntarily to resist this force. So on the one hand, the hand to pull up the head, on the other hand, the neck to try to tilt back. 3, there may be neck muscle spasm. This situation is often seen in patients with cervical spondylosis, or there is a long-term sitting and standing with the head down. At this time, the muscles of the neck itself have spasm, when doing sit-ups, you will feel the muscles of the neck are very stiff, and continuous force.