Background: Little is known about the acute effects of exercise among individuals with clinical or sub clinical Generalized Anxiety Disorder (GAD).Purpose: Thus, this study examined worry, state anxiety, and feelings of energy and fatigue responses to acute aerobic exercise and quiet rest, and explored potential moderators of response among young adult women with worry scores indicative of GAD.Methods: Seventeen young women with Penn State Worry Questionnaire scores >45 (60 +/- 8) completed 30-min treadmill running at 65%-85% heart rate reserve (%HRR) and 30-min seated quiet rest in counterbalanced order. Outcomes included worry, state anxiety, and feelings of energy and fatigue. Two condition X two time repeated measures ANOVA examined differences across condition and time. Hedges' d effect sizes (95%CI) were calculated to quantify and compare the magnitude of change. Independent-samples t-tests explored potential moderators of outcome response.Results: Total exercise time was 35.8 3.4min with a mean 30.3 +/- 0.16 in-zone minutes (65%-85%HRR); participants exercised at similar to 72.9 +/- 0.03 %HRR (range 66%-79%). Compared with quiet rest, acute exercise significantly improved worry engagement, state anxiety, and feelings of energy and fatigue (all p <= 0.031). Moderate-to-large (d = 0.44 to 1.69) reductions in state anxiety and feelings of fatigue and improvements in feelings of energy were found. Exercise-induced reductions in worry engagement were significantly larger among non-high trait anxious participants. Compared to normal sleepers, quiet rest significantly increased feelings of fatigue among poor sleepers.Conclusion: Findings provide support for the positive effects of acute aerobic exercise on worry, state anxiety, and feelings of energy and fatigue among young women with worry indicative of GAD. (C) 2017 Elsevier Ltd. All rights reserved.