DISCUSSION
INFLAMMATION, PHYSIOLOGICAL STRESS, SECONDARY
The current analysis used a 20‐day, simulated sustained military operation as a model for studying changes in raw BIA metrics and the utility of correlating these measures with physical performance during, and in recovery from severe physiological stress in healthy, young males. Additionally, the potential protective effects of administering a single dose of testosterone undecanoate (750 mg) prior to the simulated sustained military operation on non‐invasive measures of muscle cellular integrity were examined. We report significant decreases in all raw BIA parameters measured (R, Xc, Z, and PhA) in both the whole body and legs from PRE to POST, which were not different between TEST and PLA. With the exception of PhATo our knowledge, this is the first study to report changes in raw BIA parameters in response to military operations or training. It is also the first study to examine longitudinal BIA changes in response to TA in healthy, young males. Importantly, R, Xc, Z, and PhA are variables measured directly by the BIA device, and, unlike other BIA‐derived variables that require prediction equations to estimate/quantify [e.g., FFM, fat mass, percent body fat, total body water (TBW), ECW, ICW], they do not rely on inherent assumptions that may be inappropriate for certain individuals, increasing the chance of measurement error (Campa, Colognesi, et al., Changes in physical performance have been previously reported in the larger cohort of subjects included in this study (Varanoske et al., However, contrary to our hypothesis, reductions in R, Xc, Z, and PhA from PRE to POST were not attenuated in TEST compared to PLA. As research suggests that lean body mass is positively associated with PhA (Francisco et al., Significant positive associations were observed between PhADespite these findings, performance on the ruck march time trial task was not significantly associated with any BIA measure, and VOAlthough significant reductions in both physical performance and BIA parameters were observed from PRE to POST, no significant correlations were observed between these metrics at POST, ΔPhA was not correlated with changes in any physical performance variable, and only ΔZWe observed greater reductions in BIA parameters measured in the Legs compared to those measured in Whole (RStrengths of this investigation included the use of a controlled environment eliciting significant physiological stress, in which energy intake, energy expenditure, and sleep duration were meticulously designed and monitored. Additionally, this study appears to be the first to examine changes in raw BIA vectors in response to military operations as well as TA in young, healthy males, demonstrating that cellular membrane integrity is impaired during sustained military operations, but these effects are not attenuated by TA. The use of raw BIA parameters, rather than those that are calculated from prediction equations (ex: TBW, FFM, ICW, ECW), enhances our confidence in the accuracy of the measures as these are not based on assumptions of cellular hydration. Nevertheless, several limitations should be noted. The observational study design prevents us from drawing conclusions regarding causality, and we are unable to definitively state that longitudinal changes in PhA contribute to changes in physical performance. Additionally, as this was a secondary investigation of a larger study, this analysis may be underpowered to detect relationships between some physical performance metrics and bioelectrical impedance parameters. Also, the number of correlations included in this analysis increase risk for type II error, and this investigation should therefore be considered preliminary and hypothesis‐generating. Furthermore, this study recruited only male participants, so the findings are likely not generalizable to females, and future research examining the effects of sustained military operations on cellular integrity in females is warranted. Finally, the use of a single timepoint for BIA analyses during REC, where most variables did not return to PRE values by the end of this period, does not allow us to provide a time course of recovery. The smallest relative decrement reported in any BIA variable from PRE to POST was PhAIn conclusion, this analysis demonstrated that sustained simulated, sustained military operations elicit significant disruptions to cellular membrane integrity, as evidenced by decreases in PhA in both the whole‐body and legs. The shift in PhA was a result of decreases in Xc and increases in R, indicating reduced cellular mass, an inability of cells to store energy, and inflammation. TA (administered once, 750 mg testosterone undecanoate) did not attenuate changes in any of these parameters despite the maintenance of FFM, as previously reported (Varanoske et al., 