Exercise Intensity and Duration as Factors Contributing to Hypoalgesia Among Nocioceptive C-Fibers

Abstract

Exercise Induced Hypoalgesia (EIH) is characterized by a temporary desensitization of the nocioceptive system both during and after physical exertion. Although EIH is well documented in the literature, the underlying mechanisms responsible for this phenomenon remain somewhat unclear. PURPOSE: To observe the changes in nocioception of the C-Pain fibers both during and after moderately intense exercise. METHODS: Fourteen healthy collegiate female athletes volunteered for this study. After an initial V02 peak assessment, subjects returned to the laboratory approximately one week later to exercise for 20 minutes on a cycle ergometer at a workload corresponding to 70%-75% of their V02 peak. Electrodiagnostic Pain (EP) assessment and Heart Rate (HR) were collected at time points corresponding to: pre-exercise (Baseline), 10 and 20 minutes into exercise, as well as 10 and 20 minutes into recovery. EP scores were collected using a Neurometer and were normalized by expressing each subjects scores as a multiple of their baseline value. HR was collected using a Polar HR monitor. Each dependent variable was analyzed using a repeated measures ANOVA with a significance level of p<0.05. RESULTS: A table with the means and standard deviations for each variable can be found below.TableCONCLUSIONS: Based upon these data, it appears that exercise duration is an important factor in eliciting EIH. Although there are several physiological mechanisms that may be responsible for the temporary desensitization of the nocioceptive system, these findings suggest that there may be an accumulating effect of circulating opiates that may be responsible for at least some of the pain variations observed both during and after exercise.