Body Mass Index and Association of Psychological Stress with Exercise Performance in Military Members: The Cardiorespiratory Fitness and Hospitalization Events in Armed Forces (CHIEF) Study

Aims: To investigate the influence of body mass index (BMI) on the association between psychological stress and physical fitness. Background: Both obesity and psychological stress reduce exercise performance. Objective: It is unknown whether obesity may modify the relationship. Methods: A population of 4,080 military subjects in Taiwan was divided to three groups according to the BMI ≥27.0 kg/m2 (obesity), 24.0-26.9 kg/m2 (overweight) and 18.5-23.9 kg/m2 (normal weight). Normal, slight, and great psychological stress was evaluated by the Brief Symptoms Rating Scale (BSRS-5) score ≤5, 6-9, and ≥10, respectively. Aerobic and anaerobic fitness were respectively evaluated by time for a 3000-meter run and numbers of 2-minute sit-ups and 2-minute push-ups. Analysis of covariance (ANCOVA) with adjustments for age and sex was used to determine the relationship. Results: The mean time (sec) for a 3000-meter run (standard error) under slight and great stress differed from that under normal stress in the normal weight (881.0 (11.0) and 877.9 (5.8) vs. 862.2 (1.7), p=0.089 and 0.0088, respectively) and in the obesity (928.1 (16.8) and 921.8 (10.7) vs. 895.2 (1.6), p=0.054 and 0.016, respectively), while the differences were not significant in the overweight (877.1 (12.7) and 877.5 (7.1) vs. 867.1 (2.1), both p >0.5). The impacts of the BMI on 2-minute sit-ups had a similar pattern with that on a 3000-meter run whereas the impact of the BMI on 2-minute push-ups was insignificant. Conclusions: Mental stress may not affect physical fitness in overweight military personnel. The mechanism is not clear and should be further investigated.