The Effects of Repeated Operational Stress and Limited Recovery on Resilience Capacity

Operational stress inherent of military training and operations is largely unavoidable and jeopardizes Warfighter readiness and performance. Operational stressors, including high physical activity, severe energy deficiency, and restricted sleep, challenge Warfighter resilience. The characterization of physiological factors contributing to maintained or declining resilience during repeated stress exposures with limited recovery is therefore required to enable development of new, targeted interventions that maintain or enhance resilience. Previous efforts have characterized the regulation of physiological status, including muscle recovery and endocrine function, during operational stress. However, no studies have directly assessed the effects of limited recovery (i.e., 48h) on physiological and performance decrements associated with repeated operational stress or resilience capacity. It is possible that repeated missions and limited recovery will drive progressive declines of physiological status and performance. The effects of operational stress on nutrition status also negatively impact readiness and performance. Absorption of key dietary nutrients, such as iron, is required to sustain nutritional status; and iron status, specifically, has been associated with performance declines. Laboratory and field-based studies from our group have shown declines in iron status and absorption following a single simulated sustained operation. However, no studies have directly assessed the effects of limited recovery (i.e., 48h) on physiological and performance decrements associated with repeated operational stress or resilience capacity. It is possible that repeated missions and limited recovery will drive progressive declines of physiological status and performance. Beyond characterizing the effects of repeated cycles of operational stress, there is potential value in determining whether body composition phenotypes (i.e., "energy deficiency-sensitive" and "energy deficiency-resistant") may modulate resilience during energy deficiency. Should phenotype-based differences be determined and suggest more beneficial/resilient vs. less beneficial/less resilient body composition phenotypes, guidance to maintain or interventions to achieve optimal body composition are potential individualized strategies to enhance resilience. This longitudinal study will examine the effects of repeated operational stress and limited recovery on integrated muscle protein synthesis, whole-body protein balance, iron absorption, and aerobic performance. Adults (n=24) representative of normal weight and overweight phenotype (n=12/phenotype) will complete a 48h balance phase preceding two repeated rounds of 72h energy deficit (increased physical activity and reduced dietary intake) with sleep restriction followed by a 48h recovery phase.