Association Of Strength And Aerobic Activity To Body Composition And Performance In Active Adults

Background: Soldiers must have high physical fitness (PF) and healthy body fat (%BF) levels. Self-directed physical activity (PA) is often part of their program to maintain PF and %BF in compliance with regulatory standards. To better understand the efficacy of that approach, the relationship between self-directed PA, %BF and PF needs to be investigated. Purpose: To examine the relationship between self-reported PA with body composition (BC) and PF levels in active healthy adults. Methods: Study population was a statistically representative (age, sex, race) sample of the modern Army (1327 Total, 958 men; 369 women). %BF and lean body mass (LBM) were measured by dual energy x-ray absorptiometry and PF scores as measured by the Army Combat Fitness Test (ACFT), attained from Army records. A self-reported survey cataloging demographics and types of self-directed PA, was classified as hours per week (h/w) of strength training and aerobic activities separately, and summed for total PA. Linear regression models, adjusted for age, sex, race, and ethnicity were used to estimate the change in LBM and %BF. Results: Mean (±SD) total PA was 7.4 ± 4.4 h/w and 6.5 ± 3.9 h/w for men and women respectively. Men reported 4.6 ± 3.2 and women 3.8 ± 2.7 h/w of strength training. Men reported 2.9 ± 2.2 h/w and women 2.7 ± 2.0 h/w of aerobic exercise. A one-hour increase in total PA was associated with 0.25 kg (95% CI: 0.16, 0.35) LBM increase, a 2.38-point (1.76, 3.01) ACFT increase, and a 0.25 percentage points (-0.32, -0.18) %BF decrease. A one-hour increase in strength PA showed a stronger association with changes in LBM, ACFT and %BF: 0.43 kg (0.30, 0.56), 3.47 points (2.64, 4.30), and -0.38 (-0.47, 0.28) respectively, than a one hour increase in aerobic PA: 0.08 kg (-0.10, 0.27) 1.78 points (0.57, 3.00) and -0.21 percentage points (-0.35, -0.07), respectively. Conclusion: Self-directed PA is associated with increased LBM, decreased %BF, and increased PF performance with greater increases in LBM and PF from strength PA. This is likely due to the ACFT emphasizing explosive movements to assess PF. Outcomes suggest that encouraging Soldiers to engage in PA can improve Army physical readiness. U.S. Army Medical Research and Materiel Command