Explain Pain
Nociception
There are no pain receptors. There ARE specialized receptors in your body called nociceptors, which detect potential threats to the body (in the form of temperature, pressure, chemicals, etc). These receptors project this information about potential threat to the brain’s center for sensory integration (the thalamus), where these signals are integrated with other information (related to threat: fear information, emotions, visual perception, etc.) to be projected to the cerebral cortex where they result in the subjective experience of pain.Stimulation of these nociceptors is NOT enough to cause pain. Why? Because the experience of pain is an integration of all that information. You must perceive a threat to experience pain. (If you don’t notice the cut, however traumatic, on your leg, it doesn’t hurt.)Likewise, pain can occur in the absence of the stimulation of these receptors. This is best demonstrated by the rubber hand illusion: we can stimulate feelings of pain by "injuring" pretend body parts which the brain temporarily believes, due to visual misinformation, is actually part of us. This occurs despite the absence of nociceptive input.
Chronic pain
Another important thing to consider is that chronic pain (e.g., low back pain, tendinopathies such as golfer’s elbow, climber’s elbow, achilles tendinopathy, patellar tendinopathy) is very poorly correlated with structural damage. There is chronic pain in the absence of structural damage, and there is structural damage in the absence of pain. It is well documented that a) extremely large percentages of asymptomatic people have herniations as well as b) many cases of tendon ruptures occur in the absence of pain.So why chronic pain in the absence of structural damage? It is suggested that it’s a hypersensitivity of the nervous system. It over-reacts to small stressors (let’s say, a small strain of a muscle, nothing serious, or just a twinge in the joint, again nothing serious) which should not cause pain, or even does so in the absence of these stressors. Possibly, this hypersensitivity arises from a previous and quite real structural injury, one which has resolved but which you continue to internalize a fear of.
Why would the brain do this?
Most people psychologically/cognitively associate various somatic experiences with structural damage. We have a tendency to assume we’ve hurt ourselves when we “feel” things in our body. We’ve come to the point where we panic over every physical anomaly, whether structural or sensory. Part of this is the result of an emphasis on medicalization of our experiences. We think in terms of structural damage. We think the strain in the low back is a “pulled” muscle, and we vividly (thanks to the medical industry) project an image of damage fibers and injured tissue. We create illustrations in our mind of the inflammatory response, of lactic acid burning through our tissues, and so on and so forth.These higher level perceptions are integrated as well into the experience of pain (people who don’t hold these thoughts experience less pain, for example). In many cases, higher level systems override lower level systems in cognition. Many of us have experienced this personally.Extrapolating to the experience of chronic back pain, you’d have to be crazy not to experience pain if you simultaneously felt strain in the low back while thinking you had damaged your back muscles. It would be anything but adaptive otherwise. Problems arise when we form false cognitive beliefs. We’ve used the higher-level system, which can override lower level systems.
Top-down / cognitive approaches
It turns out the most effective treatment for most of these chronic pains is actually a form of cognitive re-education, a "top-down approach" teaching the individual about the nature of pain. It’s more effective than bottom-up approaches: corrective exercises, drugs, surgery, even manual tissue work. Why? Because it removes the fear upon which your pain is contingent: a fear that you’ve damaged yourself.This isn’t to say we don't experience pain; of course we do, but a large part of that pain is the interpretation of non-damaging strains of the musculature, and projecting “injurious” narrative on it. "Oh, I feel something in my elbow, I must have done something to it”.So why do we do corrective exercises? I think the minor physical adaptations are only part of the equation. Good corrective exercises actually contribute to the top-down approach: teaching you that a range of motion is safe, to dissociate that movement from pain. This idea is supported by the observation that eccentric versions of painful exercises are probably one of the best treatments for tendinopathies.And what about soft tissue work? I think this kind of work reduces those intra-muscular stressors, the signals that are being sent to the brain. You haven’t actually reduced the hypersensitivity of the nervous system, but you’ve reduced the inputs which trigger it’s over-reaction.So soft tissue work is actually a bottom-up approach.
Application
The application of this knowledge doesn't imply that you should train through pain. Even if you spontaneously believe that there is no structural damage in your tissue, your nervous system does not. It still has the association of pain. These things are not under direct conscious control. This could do more harm than good, since that fear might (this hasn’t been shown empirically, but it seems rather likely) trigger local stress responses which degrade tissue quality. It has been shown, however, that continuing training while rehabbing an achilles tendinopathy did not impair recovery (compared to just rehab), so long as the pain did not exceed 5 on a 1-10 scale.Even in the case of a legitimate injury, this effect is going to be at play. It’s not some miscellaneous phenomenon, or some minor illusion. This effect is always at play.
Need further convincing?
Pain scientist Lorimer Moseley talks about "Why Things Hurt" (TED Talk)Exercise physiologist (and good friend) Anoop Balachandran on "What Should Fitness Professionals Understand About Pain and Injury" (Article)An article regarding "The Real Reason You Still Have Back Pain" (Article)