Exercise–induced hypoalgesia: Mechanisms and barriers

Abstract

Physical activity and exercise not only improve physical fitness, mental health, and quality of life but also play an important role in preventing and improving several chronic diseases, including chronic pain. Exercise–induced hypoalgesia (EIH) is a notable phenomenon underlying pain relief, which has been demonstrated in healthy adults, chronic pain patients, and animals. In this mini–review, we describe the possible roles of anti–inflammatory cytokines, serotonin, endogenous opioids, and myokines in developing the EIH effect. We consider three brain systems involved in producing EIH: the reward, the medial part of the basal amygdala–nucleus accumbens, and the ventral hippocampus–basolateral amygdala systems constituting the mesocorticolimbic system. Furthermore, we discuss how orexin neurons located in the lateral hypothalamus may assist in triggering this system. Notably, the EIH effect was not observed in mice that were subjected to ultrahigh–intensity treadmill running and exhibited anxiety, fear, and aversion behaviors, suggesting that negative emotions hinder EIH development. Thus, the effects of exercise are not only dependent on the intensity, duration, and frequency of exercise but also strongly influenced by emotions, which may be produced by or during the exercise. In conclusion, the present review supports the development of more effective pain relief strategies for both chronic pain patients and healthy people.

Negative emotions such as fear and anxiety generated by exercise are a powerful barrier to the EIH effect