This is what brings the vast majority of people in to chiropractors to begin with. Sometimes it's easy to identify the cause, but most of the time it's because of something which had been done "a million other times before" but this time it caused this episode of pain. Or, just as often, people have no idea what the cause is and it just came up out of the blue. To answer the question of "Why?" we have to look into this just a little deeper.
First, the science. In any given area, muscles and bones which all work together to allow you to move and be functional. The nerves, which carry the brain's directions to the body and relay information back to the brain, travel closely in all of these areas as well. When we overuse our body in any way we get muscle tissue trauma or fatigue. Since our muscular system, the mover of our body, is supposed to work in sync and contract and relax in just the right time, when there is trauma or fatigue, it won't perform the way it's supposed to. This leads to a number of possibilities: 1) damage to the actual muscle or an associated muscle group (strain), 2) damage to the muscle-bone junction, and 3) stress to the joint (where two bones meet, allowing for motion) which creates dysfunction (in the spine, this is "subluxation", elsewhere this is "joint dysfunction").
For the first two, the pain felt is fairly straight-forward: it hurts pretty much right where the problem is. There is inflammation and the pain-sensing nerves are highly active, sending the message of pain back to the brain. Many times, entire muscle groups are tight and if the problem has been ignored long enough there are areas of balled-up muscles called "trigger points" present. The way this is treated is through myofascial work:
**Massage Therapy: In-depth treatment to the muscle with the goal of lengthening the tight muscle and restoring tissue alignment
**Myofascial Disruption Technique: Very specific technique performed by Dr. Miller with the goal of restoring proper muscle function through 1 of 4 means depending on the type of problem it is: 1) "pushing back" the trigger point, 2) lengthening a shortened band of muscle, 3) restoring the integrity of the muscle-bone junction, and 4) "ironing" out the outer layers of the muscle through very comfortable tissue stretching.
The third possibility, stress to the joint, is a bit different. Sometimes it's straight-forward, and sometimes pain is felt in a different location. With regards to the spine, stress to the joint is termed "subluxation". Spinal subluxation, or vertebral subluxation, is a stress response that causes muscles to go into spasm, spinal bones to lock up, there is an inflammatory response to some degree and the adjacent nerves are choked or chafed. This interferes with the control and regulation of the body. Sometimes the pain will travel down the nerve and you will feel pain "travel" somewhere else. Other times it will be a dysfunction of an internal organ (irritable bowel, heartburn, etc.). The way to treat this is by adjusting the involved spinal joint, inducing function again. Dr. Miller tailors an approach to each individual to create the most comfortable experience possible.