Minimizing Risks Of Acute Exercise In Chronic Multisymptom Illness: A Randomized, Controlled, Dose-response, Crossover Study

Chronic multisymptom illness (CMI) populations are prone to symptom worsening, increased experimental pain sensitivity, and decreased cognitive performance following acute exercise. They also report avoiding subsequent physical activity (PA) to recover from and/or prevent further exacerbation of these responses. Identifying exercise intensities which minimize the aforementioned risks and their effects on PA may inform the development of safe exercise prescriptions for CMI populations. PURPOSE: Examine the dose-response relationship between aerobic exercise intensity and (1) psychometrically measured risks and (2) PA in Veterans with Gulf War Illness (GWI). METHODS: Forty participants (age = 53 ± 4 yrs; BMI = 32 ± 5 kg/m2; %female = 10) completed 20 min of steady-state cycling at intensities corresponding to 35 ± 3% (light), 50 ± 3% (moderate), and 65 ± 3% (vigorous) of heart rate reserve (HRR) and seated-rest over four study visits, each separated by ≥7d. Symptoms (visual analog scales), experimental pain sensitivity (ratings of thermal stimuli between 43-49°C), and cognitive performance (continuous performance task) were measured before and within 1 hr after exercise and seated rest. PA was measured ≥7d following each study visit via actigraphy. Analysis of variance models tested the central hypothesis that higher intensity exercise would cause greater exacerbation of outcomes. RESULTS: Average heart rate (bpm) for seated rest, light, moderate, and vigorous exercise was 70 ± 10, 90 ± 8, 116 ± 7, and 130 ± 8, respectively. Significant condition-by-time interactions were not observed for symptoms (p = .63; ɳ2p = 0.01), pain sensitivity (p = .64; ɳ2p = 0.01), or cognitive performance (p = .80; ɳ2p = 0.01). Significant between-condition differences were not observed for PA (p = .98; ɳ2p = 0.001). CONCLUSIONS: On average, exercise-related exacerbation of psychometric or PA outcomes was not evident in the study sample. Thus, when exercising at intensities ≤65% HRR, these individuals may be relatively safe from risks that are associated with exercise in CMIs. Future research is needed to test the generalizability of these findings to the larger GWI population and other CMIs such as chronic fatigue syndrome, fibromyalgia, and long-COVID. Supported by VA CSRD Career Development Award #1K2CX001679