Because it causes what physiotherapist term as “mechanical pain”. In simple terms sitting, especially if sat in a prolonged or unsupported posture greatly increases the stretch and loading of the soft tissues of the neck (the discs and ligaments). This sustained stretch can eventually lead to pain.
• For example – if you bend your finger back and hold it, on stretch, eventually it will hurt!
• Letting go of the finger will ease the pain.
• Sitting has the same effect and regularly taking a break by standing up or moving the head will help it stop!