Differential Effects Of Exercise Induced Muscle Damage On Multiple Noxious Stimuli

Abstract

Chronic muscle pain (CMP) is a primary complaint of US Veterans of the Persian Gulf War (GWV) currently suffering from Gulf War illness, a chronic multisymptom condition. Although the research literature often characterizes Veterans as stoic, previous research in our lab has demonstrated that GWV with CMP report greater perceived exertion (RPE) and muscle pain during exercise compared to healthy GWV. Given the potential use of these ratings as tools for monitoring and prescribing exercise intensity in patient groups, it is important to quantify their dependability and relationships to symptoms as training progresses. PURPOSE: To evaluate the dependability (i.e., reliability) and sources of variance in RPE and muscle pain ratings across 16 weeks of resistance exercise training (RET), as well as their association with self-reported pain symptoms in GWV with CMP. METHODS: Twenty-six GWV with CMP completed 16 weeks of individualized RET initiated at a low intensity (25-35% of est. max.) with progression as tolerated. Each session consisted of 10 exercises with 2 sets of each. RPE (6-20) and muscle pain (0-10) were reported for each set at its completion. Ratings at weeks 2, 9, and 15 were evaluated separately using generalizability theory, a technique which quantifies the dependability of responses and apportions their variability to the conditions of the testing procedure (i.e., respondents, sets, and exercises). Daily pain symptoms were also recorded for each session. Associations between symptom scores and RPE and muscle pain were calculated using Spearman's rho. RESULTS: Generalizability coefficients were very high for both measures at each time point (ξρ 2 >0.89) indicating a high level of dependability. Respondents were the greatest source of variance throughout. Variance due to exercises, however, was reduced with training progression. No significant relationships between pain symptoms and RPE or muscle pain were noted at any time point (ρ: -0.28 -0.34; p>0.05). CONCLUSIONS: RPE and muscle pain ratings exhibit a high degree of dependability for GWV with CMP during exercise, even with training adaptations. This finding supports the use of these ratings as tools for monitoring and prescribing exercise intensity in this population.