Whether it's for everyday activity or weight training, adequate curves are important in the spine as it increases its load bearing capacity. When the spine has greater or lesser curvatures than normal, it decreases the individuals ability to bear the loads placed on it as it places a greater force at a distance from the spine.
For example, in optimal condition, the curvature of the neck is designed to have the cranium sit directly on top the spine to reduce the amount of work (a function of force/weight, moment arm and gravity) necessary for the postural muscles to keep the head upright and the eyes looking directly ahead.
In order to better understand this we can think of how we change a tire on a car. In order to produce the greatest amount of force (torque) at the desired location (bolt on a wheel), we choose to use a longer moment arm (long socket wrench) as opposed to a shorter moment arm (Trying to unscrew the bolt with just the socket). This is because the greater the length of the lever, the more force is concentrated into the fulcrum (bolt). However, in the case of the neck, when it sits directly over top of the spine, as it is designed to, the moment arm is zero and the force of the head on the spine is equal to that of the weight of the head multiplied by gravity. When the neck moves forward into an anterior head carriage and is sitting at an angle, this creates a longer moment arm that increases the force on the joint in question. To understand the physics behind this you can try it out for yourself!
1. Take a weight and hold it directly at your side with a straight arm. If the weight is reasonable it should be really quite easy!
2. Now take the same weight and hold the forearm at a 90 degree angle with the upper part of your arm still tucked at your side. You will feel a slight increase in the effort required to hold this exact same weight.
3. Lastly, hold your arm straight out in front of you so that the arm is perpendicular with your body.
Feel the difference? This is because when the arm is completely straight, only gravity is acting on it. However, when the weight is moved away from the body you create something called a moment arm. This moment arm increases the force in addition to the gravity already acting on the weight.
Here we see how to angle of the neck creates that moment arm, thus increasing the amount of force (measured in weight) on the spine.
This particular lesion pattern that I am discussing here is something that has been coined "text neck", caused by individuals who spend extended periods of time on their phones looking down. This causes the neck to flex forward every time you look down, and the more time you spend looking downwards, the more your neck is going to like that new position as it adjusts, which also means that it can get a little bit stuck here and not want to come back into its full extension. Now, you would likely this that this can just be fixed by looking back up right? The problem with this is that the movement will come from the area of least resistance, which typically happens in a very important joint in the neck called the occipito-atlantal joint. This joint is responsible for 50% of all flexion and extension of the neck. That's quite a bit for such a small joint! When the lower cervical unit (neck) gets this way, the occipito-atlantal joint is forced into an extended position as the individual attempts to bring their head back into a position where the eyes are looking forward again. This causes the curvature of the neck to shift forwards and the base of the skull to extend.
Based on this new position, there can be many down chain effects called compensation patterns that will occur in response to this new position. One example of this is shift in the individuals center of gravity in order to support the now off center weight of the head. Therefore, what may have started as an isolated action, may end up causing a variety of structural problems elsewhere in the body!
The importance of the spinal curvature is not isolated to the neck, but also applies in the thoracic (upper-mid back), lumbar (lower back), and tailbone (sacrum and coccyx) regions. These problems can manifest in a variety of different symptoms including, but not limited to, headaches, shoulder pain, neck pain and upper back pain.
Osteopathic manual practitioners are trained to not only identify these shifts but are also able to assist in re-establishing the normal curvatures.
"The work of the Osteopath is to adjust the body from the abnormal to the normal; then the abnormal condition gives place to the normal and health is the result of the normal condition . . ."
—Osteopathy Research and Practice
This bio-mechanical concept not only applies to postures but also serves as a means of understanding how to effectively treat the body. When it comes to treatment we refer to the moment arm as a lever, which we use as a means of taking advantage of the ability to concentrate a force into a specific location. The longer the lever, the less energy is required from both you and your practitioner to make an efficient and effective change to the anatomy.