Standardized Acute Exercise Does Not Affect Day-to-day Physical Activity In Veterans With Gulf War Illness

Post-exertional malaise (PEM) in patients is defined as a general worsening of symptoms following physical or mental effort. This response to exertion is a characteristic feature of several chronic multisymptom illnesses (CMI). Gulf War illness (GWI), a CMI affecting approximately 30% of US military Veterans of the Persian Gulf War (GWV), includes PEM as one of its core symptoms. Beyond symptom reports, changes in physical activity (PA) following exertion have been proposed as an additional indication of PEM. To date, however, research documenting the time course and magnitude of changes in PA following acute exercise in GWI has been lacking. PURPOSE: To evaluate the influence of an acute vigorous bout of aerobic exercise on sedentary behavior and PA in GWV with GWI. METHODS: GWV with GWI (n = 50) and healthy GWV controls (n = 39) completed PA monitoring prior to and following a 30-min submaximal (70% of heart rate reserve) cycle ergometer test. Participants wore a waist-mounted actigraphy monitor for 7 d during waking hours for each measurement period. Pre-exercise PA data was processed and analyzed to provide a baseline estimate of typical activity. Daily PA for 5 d following exercise was evaluated as separate time points coded for their proximity to the exercise test. Analyses were limited to participants with a valid baseline measure and at least two additional time points. Separate linear mixed models with group and time point as fixed effects were computed for counts/min/day and minutes spent in sedentary, light, moderate, and vigorous activity using baseline values as a covariate to control for initial differences. A Holm-Bonferroni correction for multiple comparisons was applied across the models (overall α = 0.05). RESULTS: With the correction applied, no significant main or interaction effects were observed for any of the models (p > 0.01). CONCLUSION: Our results indicate that sedentary behavior and PA in GWV, whether healthy or suffering from GWI, remained near usual levels across 5 d following an acute bout of vigorous aerobic exercise. This suggests that acute exercise of this type does not influence day-to-day physical activity, which in turn provides no indication of PEM, in Veterans with Gulf War illness. Supported by a grant from the U.S. Department of Veterans Affairs #I01 CX001329