Chronic pain is enormously different from acute pain. It is not just a symptom of an underlying problem - it is the problem. It often does not respond to treatments used for acute pain. In fact, acute pain treatments can sometimes make it worse. For instance, when we injure ourselves, rest is important; it allows us the body time to heal. If we have chronic pain, however, this approach won’t work; we can’t waste our entire lives resting. Excessive rest brings about harmful physiological and psychological changes such as neuromuscular weakness, an elevated heart rate, harmful elevations in fats, cardiovascular deconditioning, and muscular contractions.
Behaviors perfectly appropriate in the case of acute pain (such as resting) now becomes a part of the problem. The guarding and bracing that are protective mechanisms with acute pain may lead to additional muscular pain if the muscles are now unable to relax and become tighter or contracted. The body is supremely economical; muscles become tighter when they are not regularly stretched to the full length. If we fail to routinely stretch a muscle, it will eventually shorten. Normally, we strengthen muscles by lifting something or bearing the weight that the muscles support, or by applying a force that muscles must resist. If we do these things less frequently, our muscles, which are not challenged as much, will get weaker. For instance, if we lie in bed all day and do not use our muscles, in twenty-four hours we will lose 1-3 percent of our muscle strength. In one week we can lose 7-21 percent of our strength, and in three to five weeks, half of our original strength will be gone.
This applies to our heart as well - which, after all, is a muscle. Inactivity will reduce the physical challenges of our hearts and eventually lead to weakness. Restoring the heart rate is one indicator of health. An athletic person will have a lower than average heart rate. But with inactivity, which may be brought about from fear of pain, the body becomes less efficient, less able to deal with the physical stress of life, and our resting heart rate gets faster and faster. For every two days of bed rest, our resting heart rate increases by one beat per minute. In fact, it has been shown that after three weeks of immobility there is a 25 percent decrease in cardiovascular performance.
Excessive inactivity often leads to tightness on the muscles. This tightness alters the posture and spinal alignment, increasing the concavity (the inward curve) of the lower back, which can lead to the development or worsening of lower back pain. Under such conditions, just trying to stretch the muscles back to their original length can result in pain.
Finally, we can become so inactive that we begin to breathe with more shallow breaths. At some point, it may become uncomfortable to take a deep breath because we are so used to not doing it. This is a serious problem. It is necessary to breathe deeply to exercise aerobically, and aerobic exercise is a basic prerequisite to regaining our lost endurance.