A stiff back and neck after sleeping wrong?
By Jan Willem Elkhuizen
Many have experienced that the back or neck can be stiff and painful in the morning upon waking. But little is known about the cause. What exactly happens to the back and neck, and why do they sometimes become stiff and painful after sleeping?
The explanation will be given in this article. It is based on literature research, dissection research, and practical experiences. Part of this article corresponds with an earlier article by the same author about RSI and collagen. In that article, the question focused on what happens during static loading in work postures; in the article below, what happens during stressful sleeping postures.
This is a professional anatomical article intended for professionals and people who are truly interested in this subject. For the more casually interested reader, this goes too far and is not intended for them.
Collagen connective tissue in back and neck
Collagen connective tissue plays an important role in the back and neck. It is found, among other places, in intervertebral discs, ligaments, and joint capsules and plays an important role in transmitting forces. When a tensile force is applied to a collagen fiber, it becomes longer. The relationship between the applied force and the elongation of collagen is shown in figure 1.
Figure 1 The length-force diagram of collagen. On the horizontal axis the elongation (strain).
a = foot section, b = start of the sprain phase, c = total tear. (After Rozendal, 1968)
At the beginning of the foot section of this length-force diagram, the fibers are not yet really tight. This is the case at the start of the linear section. In this part of the curve, there is a linear relationship between force and elongation. At the end of the linear part, the sprain phase begins. In this phase, damage gradually increases until the tissue is completely torn. Normally, forces remain limited to the start of the linear part.
When collagen tissue is loaded and thus put under tension, it temporarily becomes somewhat longer, even after the load is removed. Through rest, the initial state is eventually restored. The elongation that occurs after the tensile force is removed is referred to as ‘set’ (Twomey 1982, see figure 2).
Figure 2 The increase in length after the tensile force is removed is called ‘set’. On the horizontal axis the elongation (strain) and on the vertical axis the stress (stress, force / mm2). (After Twomey, 1982)
Static loading and collagen
If the applied tensile force remains, the collagen connective tissue will gradually elongate further. This phenomenon is called creep (creep) (Rozendal, 1968, Twomey 1982). The connective tissue ‘creeps’ progressively.
The speed of stretching affects the degree to which the tissue elongates. The faster a movement occurs, the stiffer the connective tissue behaves. This is shown in figure 3.
Figure 3 Two stress-strain curves of a joint ligament where the load was applied at two constant speeds: 2% and 30% of the resting length per minute. More elongation occurs as the speed is lower. (After Rozendal et al., 1968)
This shows that at a low strain rate (speed of stretching), the length-force curve becomes less steep. At equal force, the slower the movement speed, the more the connective tissue is stretched. If the speed approaches 0 (there is little to no movement), the elongation is maximal. This is the case with static loading, such as in sleeping positions where the connective tissue is loaded.
Recovery process
As the connective tissue shows more creep, a longer recovery time is needed to return the tissue to its initial state. For short periods of loading, with sufficient rest time between loading phases, this will not cause any problems.
But with static loading, it is different. With static loading of collagen in an intervertebral disc for 20 minutes, recovery takes much longer than the loading time (McGill et al., 1992, see figure 4). The elasticity of collagen connective tissue temporarily decreases due to static loading.
Figure 4 Sustained loading applied to intervertebral discs in an end position. Due to continuous loading, creep occurs: the vertebral segments slowly bend further (from 0-20 min.). After 20 minutes, the load is removed and the tissue slowly recovers. (After Mc Gill & Brown, 1992)
The effects of sustained loading
The temporary lengthening and temporary reduction in elasticity of collagen connective tissue affects the functional properties. This applies both to connective tissue in ligaments and in intervertebral discs.
A. Connective tissue in ligaments
Ligaments guide movements in joints (Oonk, 1988), and ligament injury can change joint movements (Soudan et al., 1979, Oonk, 1988). Functional disorders can lead to stiffness, limitations, and pain complaints. Additionally, ligament injury sometimes leads to increased muscle tension, also called ‘bracing’ or ‘freezing’ (Doorenbosch et al., 1997). For example, with a torn cruciate ligament in a knee, both the knee flexors and extensors contract simultaneously. This somewhat compensates for the stability reduced by the torn knee ligament.
This phenomenon has been reported by various authors (Sinkjaer et al., 1991, O’Connor, 1993) and convincingly demonstrated (Doorenbosch, 1996). The enormous muscle tension in an acute stiff neck, for example after a whiplash, can also be seen as a form of protection through bracing. An acute stiff back after injury to the intervertebral disc is another example.
The above examples concern acute reactions after a trauma. But even without trauma and without damage, statically loaded connective tissue can cause complaints. An example:
You are sitting on the couch with your feet on a footstool. The knees are fully extended and hang relaxed slightly bent. The ligaments are under tension, limiting further extension of the knee. After some time, the knees become sensitive, and when you stand up, they are initially stiff and a bit painful. You feel you need to move carefully; it seems you don’t have 100% control over your knees for a moment. Fortunately, after a few cautious movements, it gets better, and shortly after, there is no problem.
In the above example, the collagen support tissue (capsule and ligaments) stretches somewhat and creep occurs. This promptly results in stiffer movement. Creep due to static load can, like permanent damage to connective tissue, affect joints. The difference lies in the degree and duration of this effect.
If the connective tissue in ligaments is under tension daily due to poor posture, sometimes for years, the complaints can become more chronic. Examples include blockages in the cervical spine caused by neck-straining sleeping positions (Ankerman et al., 1990) and forward flexion headaches from stretching the ligaments high in the neck. The latter can occur, for example, in people who read and write a lot with their neck bent (Jull, 1989, Gutmann & Wörz, 1988).
Ligaments play an important role in guiding movements in joints. How this works is explained in videos C0-2 and C1-2 on this site.
B. Connective tissue in intervertebral discs
Various functions are attributed to the intervertebral disc, such as shock absorption and movement control. Creep can also occur in the connective tissue of the intervertebral disc. Humans are about 2 cm taller in the morning than in the evening (Keller, 1987, Kaigle, 1992). The circular fibers in the intervertebral disc stretch somewhat during the day and the height of the disc decreases. It is also known that people sometimes get out of the car stiff after a long drive (vacation): this is static prolonged load on the intervertebral discs. Elasticity is reduced and one must move carefully at first to avoid "throwing out the back." In such a situation, one is more susceptible to damage.
Hernia
The connective tissue of an intervertebral disc can be damaged. A partial tear often leads to chronic or periodically recurring back complaints and can cause pain and stiffness in the back. If the tear is complete (from the core to the outside), it is called a hernia. It is beyond the scope of this article to discuss this in detail. An article on this topic is in preparation and will be posted on this site in due course.
Sleeping position
It is a natural process that stressed parts recover during sleep. It is no coincidence that people are about 2 cm taller in the morning than the evening before. The condition for recovery is that a sleeping position is chosen in which no new tension arises in the connective tissue, especially if this occurs for a long time.
For example, when lying on the stomach, the neck is twisted and the connective tissue in the capsules and ligaments of the cervical spine is stressed, while it should actually relax. In the ¾ position, there is also stress on collagen tissue: between the shoulder blades, in the neck, and often also in the lower back.
Elsewhere on the Ligwijzer.nl site, it is discussed which positions are stressful and which are not or less so.
Conclusion
If constant tensile load is applied to collagen fibers, they gradually stretch and become less elastic. This is a temporary and physiological process (creep) that is reversed by sufficient rest. Creep affects the properties of these fibers and thus their function.
The changes in connective tissue under load are greatest during prolonged static load. Such a situation often occurs during sleep. In all sleeping positions where the connective tissue in the intervertebral discs and ligaments is under tension, this can have consequences.
This can lead to stiffness in the affected parts of the back or neck. If this situation occurs frequently, it can eventually lead to dysfunction and pain. Treatments by doctors and therapists can temporarily improve the symptoms, but as long as the underlying cause is not addressed, the symptoms will sooner or later return.
For sustainable improvement, a 24-hour approach is actually needed, involving all postures and activities that strain the collagen system. Besides sleeping posture, this especially applies to work postures and hobbies.
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