Threshold of Energy Deficit and Lower-Body Performance Declines in Military Personnel: A Meta-Regression

Nancy E. Murphy, Christopher T. Carrigan, J. Philip Karl, Stefan M. Pasiakos, Lee M. Margolis

Negative energy balance (EB) is common during military operations, diminishing body mass and physical performance. However, the magnitude of negative EB where performance would still be maintained is not well defined. Our objective was to explore relationships between EB and physical performance during military operations and define an acceptable negative EB threshold where performance may be maintained. A systematic search was performed for studies that measured EB and physical performance during military training. A total of 632 articles and technical reports were screened. Lower-body power and strength were the most common performance tests across investigations and were used as physical performance outcomes. Data were extracted from nine eligible studies containing 15 independent subgroups. Meta-regression assessed changes in performance in relation to study duration (days), average daily EB, and total EB (daily EB × duration). Changes in physical performance were not associated with average daily EB or training duration. Total EB was associated with changes in lower-body power (r2 = 0.764, P < 0.001) and strength (r2 = 0.836, P < 0.001) independently and combined (r2 = 0.454, P = 0.002). Predictive equations generated from the meta-regression indicated that, for a zero to small (2%) decline in performance, total EB should be limited to - 5686 to - 19,109 kcal, for an entire operation, whereas total EB of - 39,243 to - 59,377 kcal will result in moderate (7%) to large (10%) declines in performance. These data demonstrated that greater total negative EB is associated with declines in lower-body performance during military operations.