Among these non-pharmacologic interventions, therapeutic exercise is the most studied and supported in the literature (Zhang et al., 2007; Fransen et al., 2009a; Fransen et al., 2009b). Exercise is an effective treatment for various chronic musculoskeletal pain disorders, including chronic low back pain (van Middelkoop et al., 2010), chronic whiplash associated disorders (Stewart et al., 2007; Teasell et al., 2010), osteoarthritis (Jansen et al., 2011).
Somatosensory neurons are physiologically activated by strong muscle contractions induced by protracted exercise. Exercise produces rhythmic discharges in nerve fibers, and cause the release of endogenous opioids and OXT essential to the induction of functional changes in different organ systems.
The exercise-induced analgesia is presumably due to the release of endogenous opioids from the PAG (Koltyn et al., 1998; Koltyn, 2000) and OXT from the hypothalamus.