Exercise prevents development of autonomic dysregulation and hyperalgesia in a mouse model of chronic muscle pain

Abstract

Chronic musculoskeletal pain (CMP) conditions, like fibromyalgia, are associated with widespread pain and alterations in autonomic function. Regular physical activity prevents development of CMP and can reduce autonomic dysfunction. We tested if there were alterations in autonomic function in sedentary mice with CMP, and if exercise reduced the autonomic dysfunction and pain induced by CMP. CMP was induced by two intramuscular injections of pH 5 in combination with a single fatiguing exercise task. A running wheel was placed into cages so that the mouse had free access for either 5 days or 8 weeks (exercise groups) and these animals were compared to sedentary mice without running wheels. Autonomic function and nociceptive withdrawal thresholds of the paw and muscle were assessed before and after induction of CMP in exercised and sedentary mice. In sedentary mice, we show decreased baroreflex sensitivity, increased blood pressure variability, decreased heart rate variability and decreased withdrawal thresholds of the paw and muscle 24h after induction of CMP. There were no sex differences after induction of the CMP in any outcome measure. We further show that both 5 days and 8 weeks of physical activity prevent the development of autonomic dysfunction and decreases in withdrawal threshold induced by CMP. Thus, this study uniquely shows development of autonomic dysfunction in animals with chronic muscle hyperalgesia that can be prevented with as little as 5 days of physical activity, and suggest that physical activity may prevent the development of pain and autonomic dysfunction in people with CMP.

Modest Amounts of Voluntary Exercise Reduce Pain- and Stress-Related Outcomes in a Rat Model of Persistent Hind Limb Inflammation

“…While physical activity is effective in preventing or delaying the onset of persistent pain in animal models [10; 77; 99; 107] and is associated with lower risk of chronic pain in humans [118; 124], outcomes of therapeutic exercise (i.e. exercise initiated after injury) in human chronic pain populations are mixed, mainly due to differences in type of pain, type of exercise and exercise intensity [40; 55; 67; 72; 95].…”

Neurobiology of fibromyalgia and chronic widespread pain

“…Further animals show increases in the anxiety index on the elevated plus maze suggesting animals show a co-morbid anxiety (Green et al, 2011b). On the other hand, induction of chronic widespread pain in animals can alter autonomic function with decreased baroreflex sensitivity, increased blood pressure variability and decreased heart rate variability (Oliveira et al, 2012, Sabharwal et al, 2015). Together these symptoms of widespread hyperalgesia (paw, viscera, jaw), and anxiety mimic clinical symptoms and co-morbidities in fibromyalgia who have widespread pain, and a higher incidence of irritable bowel syndrome, temporomandibular disorder, autonomic dysfunction, and anxiety.…”

Effects of regular physical activity on pain, anxiety, and depression in patients with treatment-resistant arterial hypertension

“…the type, length, and intensity of physical effort influence the nature of posteffort hypoalgesia. works on chronic musculoskeletal pain point to the beneficial effect of physical activity and its preventative function, as well as to the improvement of the autonomic system activity [26].…”