Painful puzzles: the potent power of exercise

The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”⁽¹⁾. Pain problems are complex, multidimensional developmental processes influenced by various psychosocial factors⁽²⁾. Furthermore, it affects physical activity through fear-avoidance, guarding, and deconditioning^(2,3). Athletes can experience acute and chronic pain, both of which can affect their quality of life. In musculoskeletal injuries, pain may limit the athletes’ willingness to participate in exercise. Yet, exercise is an effective treatment strategy for reducing pain and improving function. Therefore, clinicians need to understand how to effectively use exercise as a form of treatment and how it affects the pain response, particularly regarding pain-related fear and fear-avoidance models.

Sensitization mechanisms

Central sensitization is an increased responsiveness of nociceptive neurons in the central nervous system (CNS) to normal input⁽³⁾. Changes in the function and properties of the neurons in the CNS increase the pain response relative to the intensity and presence of noxious peripheral stimuli⁽³⁾.

The four main characteristics of central sensitization are hyperalgesia, allodynia, temporal summation of pain (TSP), and diffuse noxious inhibitory controls (DNIC)⁽³⁾. Hyperalgesia is an increased pain response to normally painful stimuli due to central or peripheral sensitization⁽³⁾. Allodynia is the exact opposite, as it is a pain response to a stimulus that is not usually painful⁽³⁾. Next, TSP is the progressive increase in pain perception in response to repeated stimuli of the same intensity⁽³⁾. To assess temporal summation, clinicians can use various stimuli, including cold, heat, electrical, and pressure⁽³⁾.

Diffuse noxious inhibitory controls (DNIC) are endogenous descending pain modulation mechanisms⁽³⁾. The two main mechanisms are the activation of descending nociceptive inhibitory mechanisms and the release of endogenous opioids⁽³⁾. Clinicians can assess DNIC using the conditioned pain modulation (CPM) response, as it challenges inhibitory descending pain responses during exposure to a painful stimulus⁽³⁾. Conditioned pain modulation is also known as ‘pain inhibits pain’ ⁽³⁾.

Pain-related fear and fear-avoidance

When an individual has a heightened psychophysiological reaction to a situation they perceive to be dangerous, they experience pain-related fear⁽²⁾. This fear amplifies the pain experience⁽³⁾. For example, as pain persists, such as in chronic pain, individuals begin to avoid activities that are perceived to increase the pain or cause reinjury⁽²⁾. Fears also originate from a traumatic experience, and in chronic pain, this mechanism of injury is the most significant in creating fear-avoidance beliefs⁽²⁾. Individuals who experience a traumatic onset of pain also report higher Tampa Scale for Kinesiophobia scores than those with a gradual onset⁽²⁾.

There are three proposed mechanisms by which pain-related fear influences central sensitization. Firstly, increased nociception transmission via the spinal gate, the modulation of the descending pathways, and finally, temporal summation⁽³⁾.

The fear-avoidance model proposes two opposing behavioral responses: avoidance and confrontation (see figure 1)⁽²⁾. The opposing behavioral responses are in a continuous cycle that influences each other. When an individual sustains an injury, they will likely have a painful experience. At this moment, they either go down the path of confrontation or avoidance. If they experience low fear, they can confront their painful experience and head down the recovery path. However, if they have a negative pain experience (emotional, sensory, or psychological), they will experience pain-related fear causing immediate avoidance and escape behaviors with activities they perceive as threatening⁽²⁾. This leads to functional disability due to disuse. Avoidance occurs because pain is anticipated based on the individual’s beliefs and expectations rather than a response to pain⁽²⁾. Avoiding activities and being physically inactive has a detrimental impact on the cardiovascular and musculoskeletal systems, worsening the pain experience⁽²⁾. This may lead to hypervigilance that occurs, which makes it more difficult for them to move their attention away from the pain-related threat⁽²⁾. When individuals are exposed to situations seen as being dangerous, they will have increased psychophysiological reactivity, and so the cycle continues⁽²⁾.