The purpose of this study was to identify the effects of gender and body adiposity on physiological responses to the stress of wearing body armor. Using a within-subject, repeated-measures design, 37 military personnel volunteered to undergo two experimental conditions, with body armor and without body armor. Female and male subjects with body armor, compared to those without body armor, had no significant differences in percentage increases in aerobic capacity, heart rate, or respiratory rate while walking at slow or moderate pace. However, women, as compared to men, had a significantly increased difference in the rating of perceived physical exertion between wearing and not wearing body armor at a slow pace. Fourteen subjects were not able to complete treadmill testing while wearing body armor because of volitional fatigue and/or limiting dyspnea. Body fat was the best single predictor of treadmill test completion.