The first part of this blog discussed how traditional thinking often attributes improvements to pain to changes tissues structure and function. This historical model of clinical reasoning fails to consider the full biopsychosocial spectrum of factors. This model is frequently attributed to the dualistic philosophy of René Descartes (1596 – 1650) . Referred to as ‘mind-body dualism’, it was a philosophical viewpoint that separated the mind and body into two separate distinctions. The body was suggested as working like a machine, whereas the brain was considered the soul, not confirming to laws of natural science. It initiated a paradigm of medical practice through which the body was considered a machine that had ‘broken down’; Descartes describes pain as functioning “to indicate to the soul the bodily damage suffered” . However, this orientation of medical practice neglects to consider important psychosocial factors in health and illness .
Over the last half-century, knowledge surrounding pain and pain mechanisms has expanded beyond this reductionist understanding. Historically, Melzack and Wall’s (1965) gate-control model proposed that pain signals could be modulated in the spinal cord and brain, creating a feedback system . The biopsychosocial model of pain developed further in the 1980s, partly in response to Melzack and Wall’s seminal paper, but also in response to poor treatment outcomes in patients with chronic musculoskeletal conditions , and due to innovative non-harmful noxious stimuli in vivo experiments, that cast doubt about the validity of the biomedical model of pain . These experiments recorded activity in nociceptors, while simultaneously monitoring pain levels during experimentally induced pain. They demonstrated that pain did not correlate with tissue damage, and that relationships between pain and nociception was variable.
It is now understood that while nociceptors provide a physiological sensory input, pain emerges in the person as a result of a scrutiny process and we experience it in an area of the body deemed under threat , and that the severity of the pain response is not always associated with the intensity of the stimulus, but other factors including pain history and memory and psychological factors. There are now several modern models in relation to pain perception and nociception, including the mature organism model , the pain and movement reasoning model , and predictive processing . However, the most widely accepted is the neuromatrix model, proposed by Melzack in 2001 [8,9].
The neuromatrix model of pain proposes pain is perceived and experienced when tissue is considered to be under threat. Many inputs into the central nervous system will affect the perception of threat, with each one further influencing other inputs. This includes: nociception from the musculoskeletal system; psychosocial factors like memories, anxiety, beliefs; and affective factors such as pain behaviour. A pain experience may be triggered by sensory input from nociceptors alone, or independently from them from other inputs .
The fear-avoidance model of pain has been identified in patients , and in clinicians [11–13]. This model asserts that cognition and emotion underpin fear of pain and potential ‘tissue damage’, leading to ‘safety-seeking’ behaviours and hypervigilance; which paradoxically maintain or exacerbate the pain and disability . When researched qualitatively, within shoulder pain populations, clinicians have confessed to fear of tissue damage with pain during exercise . And, despite a lack of empirical evidence to support this view , it has been further suggested that pain with exercise could also result in increased stress responses within the brain, with subsequent increases in overall pain sensitivity .
The iatrogenic effect of healthcare, where actions of the healthcare professional negatively affect the patient, is an emerging field of research; with low back pain, knee and shoulder pain populations demonstrating this phenomenon [18–21]. My work on patellofemoral pain has shown an iatrogenic effect of reduced physical activity and exercise levels as a result of pain and activity avoidance advice from clinicians. In contrast, if pain is perceived as non-threatening by patients and clinicians, it can help patients maintain physical activity levels, which may have a positive influence on recovery [22,23].
Pain and exercise is an important factor. Advice is often given by healthcare practitioners on how to manage exacerbations of musculoskeletal pain during physical activity or exercise. This is significant when we consider that, for example, 50% of dropouts from exercise interventions for type 2 diabetes is attributable to musculoskeletal pain . Physical inactivity is one of the 10 leading risk factors for death worldwide , and an estimated $117 billion a year in healthcare costs in the US are attributable to physical inactivity . Healthcare practitioners should have the skills to encourage people, through education on interventions, with persistent musculoskeletal pain to remain as physically active as possible. This education should involve discussing that there is no evidence pain during exercise exacerbates musculoskeletal symptoms in the long-term, and there may be a short-term benefit.
This two-part blog has challenged the idea that therapeutic exercises for chronic musculoskeletal pain should be pain-free. In the current practice surveys that have examined this aspect of exercise prescription, pain-free exercise is the most common form of therapeutic exercise prescribed [12,13], and should be open to scrutiny. Traditional pain models that describe tissue pathology and biomechanics as a source of nocioceptive input, with associated pain equating to ‘harm’, have been insufficient in the management of long-term musculoskeletal pain .It seems plausible to suggest that such approaches might exacerbate fear-avoidance behaviours to the detriment of patients’ recovery and overall level of physical activity participation . In conclusion, pain may not need to be avoided during therapeutic exercises and may have some additional benefits, for example, the associated health benefits from improvements in physical activity levels [20,22,23].