Mechanism of exercise-induced analgesia: what we can learn from physically active animals

PAIN Reports®, 2020 · DOI: http://dx.doi.org/10.1097/PR9.0000000000000850 · Published: September 23, 2020

Simple Explanation

Physical activity is a key treatment for chronic pain, and research is starting to uncover how exercise reduces pain. Studies using animal models show exercise changes the brain, spinal cord, immune system, and injury site, helping to prevent and lessen pain. Different types of exercise, like running, swimming, and resistance training, can have beneficial effects. This review explores how exercise-induced pain relief works, focusing on the central and peripheral mechanisms involved. Understanding how exercise relieves pain can help us prescribe it more effectively for chronic pain and potentially develop new drug targets.

Study Duration

Not specified

Participants

Animal models

Evidence Level

Review

Key Findings

1
Exercise-induced analgesia is mediated by endogenous opioid activity, as studies show that naloxone, an opioid receptor antagonist, blocks the analgesic effects of exercise.
2
Exercise produces analgesic effects through modulation of the serotonergic system, with increased levels of serotonin (5-HT) found in the brainstem and spinal cord after exercise.
3
Activation of the endocannabinoid system contributes to the analgesic effects of exercise, with increased circulating levels of endocannabinoids after exercise, which contributes to the feeling of “runner’s high”.

Research Summary

This review explores the mechanisms of exercise-induced analgesia in animal models, focusing on both pain prevention and alleviation. It addresses questions about the appropriate prescription of exercise type, duration, intensity, and volume for chronic pain populations. The review discusses central mechanisms such as the involvement of endogenous opioids, the serotonergic system, endocannabinoids, NDMA receptor alterations, and the noradrenergic system. Peripheral and neuroimmune changes that occur to produce exercise-induced analgesia are also covered. The clinical implications of this research for improving exercise prescription guidelines for humans are discussed, including the importance of duration and intensity of exercise to maximize pain relief while limiting negative side effects.

Practical Implications

Personalized Exercise Prescription

Tailoring exercise programs to individual patient preferences, therapist training, available equipment, cost, and safety may improve adherence and outcomes.

Dosage Considerations

Carefully dosing exercise intensity and duration to maximize pain relief while minimizing negative side effects, such as exercise-induced symptom flares, is crucial.

Adjunctive Therapies

Combining exercise with other treatments like TENS or psychological interventions can help manage activity-induced pain and improve adherence.

Study Limitations

1
Majority of research conducted on aerobic-based exercise (running and swimming) as opposed to strength training.
2
Nearly all exercise-induced analgesia research has been conducted in populations using only male animals.
3
The neurological and immune response to exercise may differ in pain-free animals compared to animals after injury.

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