Can We Determine the Genetic, Physiologic, & Behavioural Predictors of Cardiorespiratory Fitness in Specialised Military Men?

Research Paper Title

Genetic, Physiologic, and Behavioral Predictors of Cardiorespiratory Fitness in Specialized Military Men.

Background

Cardiorespiratory fitness (CRF) is a crucial performance requirement of specialised military occupations. Age and physical activity are established predictors of CRF, but it is not clear how these predictors combine with each other and/or with genetic predisposition.

The goal of this study was to derive inclusive explanatory models of CRF in US Navy Explosive Ordnance Disposal (EOD) operators, synthesising conventional (e.g., age, body composition, and physical activity) and novel influences (e.g., genetic variance).

Methods

In this cross-sectional study, 40 male, active duty EOD operators completed a graded exercise test to assess maximal oxygen consumption and ventilatory threshold (VT) using the Bruce protocol. Aerobic performance was further quantified via time of test termination and time at which VT was achieved. Body composition was determined via dual x-ray absorptiometry, and physical activity was assessed by self-report.

Genetic variants underlying human stress systems (5HTTLPR, BclI, -2 C/G, and COMT) were assayed. Descriptive analyses were conducted to summarise subject characteristics. Hypotheses were tested with linear regression models. Specifically, separate univariate regression models first determined associations between each of the independent and dependent variables. This protocol was approved by the Naval Health Research Centre Institutional Review Board (NHRC.2015.0013).

Results

In univariate regression models, age, body composition, physical activity, and 5HTTLPR consistently predicted CRF and/or aerobic performance (R2 range 0.07-0.55). Multivariate regression models routinely outperformed the univariate models, explaining 36-62% of variance.

Conclusions

This study signifies a shift toward inclusive explanatory models of CRF and aerobic performance, accounting for combined roles of genetic, physiologic, and behavioural influences. Although the researchers were able to quantify combined effects, they were unable to evaluate interaction effects (e.g., gene-gene, gene-behaviour) due to limited statistical power. Other limitations are that this specialised military population may not readily generalise to broader populations, and the current sample was all male.

Considering these limitations, the researchers aim to replicate this study in various populations, both male and female. Despite its limitations, this study reflects a shift toward more comprehensive predictive models of CRF, explaining the unique and shared contributions of genetic predisposition, physiology, and behaviour.

These findings have implications for assessment, selection, and training of specialised military members, and may also impact mission success and survivability. Future studies are needed to better characterise additive, interactive, and mediated effects.

Reference

Taylor, M.K., Hernández, L.M., Schoenherr, M.R. & Stump, E.J. (2019) Genetic, Physiologic, and Behavioral Predictors of Cardiorespiratory Fitness in Specialized Military Men. Military Medicine. pii: usz033. doi: 10.1093/milmed/usz033. [Epub ahead of print].

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