Exercise is an effective and recommended treatment for chronic pain conditions. In
the rehabilitation setting, both aerobic and resistance training (RT) exercise programs
are recommended for various chronic pain conditions. However, animal research has
focused on the utilization of aerobic based exercise programs. Therefore, the purpose
of this project was to determine if RT can protect against the development of activity-induced
muscle pain and to elucidate the analgesic mechanism. We hypothesized that RT would
produce analgesia in an activity-induced pain model through activation of androgen
receptors. Either sedentary or 8 week RT male and female mice were subjected to 2
pH 5.0 injections into the gastrocnemius muscle combined with fatiguing muscle contractions.
In this model, muscle withdrawal thresholds (MWT), assessed by withdrawal to pressure
applied to the gastrocnemius, are significantly decreased in sedentary mice; this
decrease in MWT did not occur in mice that performed RT (p=0.001; repeated measures
ANOVA). Strength, measured by maximal lifting load and grip force, significantly increased
after RT. Since RT increases testosterone and lactate in humans, we examined if lactate
and testosterone were elevated following RT by measuring serum concentrations using
either an ELISA kit or a lactate meter, respectively. Five minutes after RT, both
lactate and testosterone values were significantly higher compared with sedentary
animals in both male and female mice (p=0.03-0.05; one-way ANOVA)). To test if androgen
receptors mediate the analgesia produced by exercise, slow release flutamide (200mg)
or control pellets were implanted subcutaneously prior to initiation of training.
Animals that received flutamide pellets did not see the analgesic effects of exercise
when compared to animals who received control pellets (p<0.01; repeated measured ANOVA)
despite similar increases in strength. Thus, RT protects against the development of
activity-induced muscle pain through activation of androgen receptors in both male
and female mice. NIH AR061371 and AR061371-SI, AR073187, GM067795, Foundation for
Physical Therapy Research Promotion of Doctoral Studies (PODS I) and the Helen C.
Levitt Visiting Fellowship from the Carver College of Medicine at the University of
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