Papers of the Week

Resistance training-based exercise is commonly prescribed in the clinic for the treatment of chronic pain. Mechanisms of aerobic exercise for analgesia are frequently studied, while little is known regarding resistance training mechanisms. We developed a resistance training model in mice and hypothesized resistance training would protect against development of muscle pain, mediated through the activation of androgen receptors. Activity induced muscle hyperalgesia was produced by two injections of pH 5.0 stimuli with fatiguing muscle contractions. Resistance training was performed by having mice climb a ladder with attached weights, 3x per week. Resistance training acutely increased blood lactate and prolonged training increased strength measured via forepaw grip strength and 1 repetition maximum, validating the exercise program as a resistance training model. Eight weeks of resistance training prior to induction of the pain model blocked the development of muscle hyperalgesia in both sexes. Resistance training initiated after induction of the pain model reversed muscle hyperalgesia in males only. A single resistance training bout acutely increased testosterone in male but not female mice. Administration of the androgen receptor antagonist flutamide (200mg pellets) throughout the eight-week training program blocked the exercise induced protection against muscle pain in both sexes. However, single administration of flutamide (1, 3, 10mg/kg) in resistance trained animals had no effect on existing exercise induced protection against muscle pain. Therefore, resistance training acutely increases lactate and testosterone and strength overtime. Eight weeks of resistance training prevents development of hyperalgesia through activation of androgen receptors in an animal model of muscle pain.