Influence of exercise on the pain modulation system

Abstract

Exercise therapy is recommended in the management of patients with chronic pain. However, there is little evidence supporting a relationship between changes in pain or physical disability and changes in physical performance by exercise therapy. Thus, exercise is thought to be involved it directly in the improvement of pain. Exercise has been shown to reduce the peripheral pain sensitivity in healthy subject. This effect, known as exercise–induced hypoalgesia (EIH), may be induced by the activation of central pain modulation systems. However, the effects of acute exercise in chronic pain conditions are heterogeneous and adverse. In patients with chronic pain, for example, exercise seems to decrease pain threshold. Notably, acute exercise followed by physical fatigue induces hyperalgesia. Therefore, regular exercise, rather than acute exercise, is recommended, in the management of patient with chronic pain.

Physical inactivity is a perpetuating factor which can cause pain to become chronic. We investigated the relationship between intensity of physical activity in daily life and the function of central pain inhibitory systems. Our results suggested that the function of central pain inhibitory systems may decrease with a low amount of physical activity in women; therefore, maintaining physical activity may be more important for women than for men in preventing chronic pain.

The effects and mechanisms of pain inhibition through regular exercise have been suggested using the animal model of pain. According to one of these suggested mechanisms, regular exercise increases the release of met–enkephalin in the rostral ventromedial medulla (RVM) and uses opioid receptors centrally to mediate analgesia. We investigated the influences on central pain inhibitory systems by regular exercise in subjects with chronic pain. While regular exercise for 2 weeks carried out three times a week improved the central pain modulation systems, it was ineffective if only done twice a week. However, an effect was seen if twice–weekly exercise continued for 3 weeks. Therefore, we conclude that increasing physical activity in daily life by regular exercise may be important in prevention and management of chronic pain.