Utility of Measuring Insulin-Like Growth Factor-I for Assessing Military Operational Stress: Supporting Future Force Warrior from the Bench Top to the Battlefield

Military training and operational stress can compromise health and performance of Soldiers. The availability of a sensitive biomarker of nutritional and physiological strain would have tremendous utility for monitoring soldier readiness as well as assessing the effectiveness of intervention and recovery strategies. Insulin-like growth factor-I (IGF-I) is sensitive to underfeeding and malnutrition; falling 50-60% during operational stress. It is a stable marker, minimally affected by circadian rhythms. IGF-I can be measured rapidly using minimally invasive techniques. IGF-1 monitoring offers the potential to reduce injury incidence and improve training effectiveness. 1. MILITARY RELEVANCE OF MONITORING INSULIN-LIKE GROWTH FACTOR-I Mission success in military tactical environments dictate that the warfighter be able to perform prolonged physical exertion in the face of food and sleep restriction (i.e., military operational stress). The physiological strain produced by these operational stressors can have deleterious effects on muscle mass, endocrine and metabolic function, as well as physical and mental performance (Friedl et al., 1994; Friedl, 1999; Friedl et al., 2000; Nindl et al., 1997; Nindl et al., 2002; Nindl et al., 2003a; Nindl et al., 2003b) (see Figure 1). A goal of the Army Medical Research and Materiel Command’s (MRMC) biomedical research program is to identify useful biomarkers that are indicative of nutritional and physiological status that can be assessed rapidly, with minimally or non-invasive collection methods. Once identified, these biomarkers will be used to sustain warfighter readiness and aid in assessing the effectiveness of intervention and recovery strategies. The growth hormone/insulin-like axis is a central endocrine axis and is thought to mediate many of the somatotrophic changes that are observed when warfighters are exposed to harsh field environments (Florini et al., 1996; Friedl et al., 2000; Nindl et al. 2003a; Rosen, 1999; Rosendal et al., 2002). For this reason, periodic assessment of the growth hormone/insulin-like growth factor axis may have utility for sustaining warfighter health and performance. In direct support of Objective Force Warrior's (OFW) vision of revolutionizing soldier performance by aggressively employing science and technology efforts that enhance the warfighter's survivability, lethality, sustainment, and mobility on the modern battlefield, The Military Performance and Military Nutrition Division U.S. Army Research of Institute of Medicine have been evaluating IGF-I as a candidate biomarker for assessing nutritional stress. Our research has focused on 1) characterizing temporal response patterns of IGF-I and its family of binding proteins during military operational stress, 2) the influence of macronutrient and energy intake on the circulating IGF-I system responses to stress, and 3) assessment of minimally invasive and field expedient collections methods for determination of IGFI. Sleep Deprivation Sleep eprivation Under feeding nder feeding Physical Overexertion Physical verexertion