1619544

ContentslistsavailableatScienceDirect

Journal of Science and Medicine in Sport

j o u r n a l ho me p ag e :w w w . e l s e v i e r . c o m / l o c a t e / j s a m s

Perspectives on resilience for military readiness and preparedness:

Report of an international military physiology roundtable

Bradley C. Nindl

, Daniel C. Billing

, Jace R. Drain

, Meaghan E. Beckner

,

Julie Greeves

, Herbert Groeller

, Hilde K. Teien

, Samuele Marcora

, Anthony Moffitt

, Tara Reilly

, Nigel A.S. Taylor

, Andrew J. Young

, Karl E. Friedl

aNeuromuscularResearchLaboratoryandWarriorHumanPerformanceResearchCenter,UniversityofPittsburgh,UnitedStates

bDefenceScienceandTechnologyGroup,Australia

cArmyPersonnelResearchCapability,HQ,Army,UK

dCentreforHumanAppliedPhysiology,SchoolofMedicine,UniversityofWollongong,Australia

eNorwegianDefenseResearchEstablishment,FFI,Norway

fSchoolofSportandExerciseScience,UniversityofKent,UK

gDepartmentofDefence,Australia

hCFWMSHumanPerformanceandDevelopmentCanadianArmedForces,Canada

iU.S.ArmyResearchInstituteofEnvironmentalMedicine,UnitedStates

a r t i c l e i n f o

Articlehistory:

Received16March2018

Receivedinrevisedform23April2018 Accepted8May2018

Availableonline19May2018

Keywords:

Adaptation Psychological Biological Stress

Extremeenvironment Taskperformance

a b s t r a c t

Modernwarfareoperationsoftenoccurinvolatile,uncertain,complex,andambiguous(VUCA)environ- mentsaccompaniedbyphysicalexertion,cognitiveoverload,sleeprestrictionandcaloricdeprivation.

Theincreasinglyfast-pacednatureoftheseoperationsrequiresmilitarypersonneltodemonstratereadi- nessandresiliencyinthefaceofstressfulenvironmentstomaintainoptimalcognitiveandphysical performancenecessaryforsuccess.Resiliency,thecapacitytoovercomethenegativeeffectsofsetbacks andassociatedstressonperformance,isacomplexprocessinvolvingnotonlyanindividual’sphysiology andpsychology,buttheinfluenceoffactorssuchassex,environment,andtraining.Thepurposeofthis moderatedroundtablewastoaddressfivekeydomainsofresiliencyinapoint/counterpointformat:phys- iologicalversuspsychologicalresiliency,sexdifferences,contributionsofaerobicandstrengthtraining, thermaltolerance,andtheroleofnatureversusnurture.Eachspeakerwasgiventhreeminutestopresent andthemoderatorfacilitatedquestionsanddiscussionfollowingthepanel’spresentation.Theintercon- nectednessofthefivedomainshighlightstheneedforaninterdisciplinaryapproachtounderstandand buildresiliencetoenhancemilitaryperformance.

©2018SportsMedicineAustralia.PublishedbyElsevierLtd.Thisisanopenaccessarticleunderthe CCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction

CharlesDarwinandLeonMegginsonshowedthatthespecies thatisbestabletoadaptandadjusttoachangingenvironmentisthe speciesthatwillprevail,notthestrongestnormostintellectual.¹ The same principle can be applied to Warfighters, as possess- ingahighlevelofphysicalfitnessandcognitiveabilityissimply not enough to succeed and to maintainovermatch superiority againstadversaries. Military operationsexpose servicemen and womentoavarietyofstressorsincludingdemandingworkloads, harshanddangerousenvironments,andambiguitythatdegrade performance.^2,3 TheArmiesthatprevailaretheonescomposed

∗Correspondingauthor.

E-mailaddress:bnindl@pitt.edu(B.C.Nindl).

ofresilientindividuals who canovercomethesechallenges and performwithgreateragility,tenacity,survivability,andlethality.

Militaryresiliencecanbedefinedasthecapacitytoovercomethe negativeeffectsofsetbacksandassociatedstressonmilitaryper- formanceandcombateffectiveness.Militaryoperationalstress cancomeinmanyformsviathesingularorcombinedeffectsof physicalexertion,cognitiveoverload,sleeprestriction,energy insufficiency,variationsintheoperationalenvironments,and emotionalandpsychologicalstress.Inthevolatile,uncertain, complex,andambiguous(VUCA)contemporaryoperatingenvi- ronment,bothcurrentandfutureoperationsdemandandplace ahigherpriorityonenhancingandsustainingthereadinessand resiliencyofmilitaryservicemembersinordertodecisivelywin inmulti-domainbattle.

AccordingtoRuiz-Casaresetal.,resilienceisadynamicprocess involvingtheinteractionbetweenriskandcompensatoryfactors

https://doi.org/10.1016/j.jsams.2018.05.005

1440-2440/©2018SportsMedicineAustralia.PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/

by-nc-nd/4.0/).

overthelifespan.⁴Despiteeverydaystressorsofpoverty,violence, and political instability, a studyby Eggermanand Panter-Brick reportedthatAfghanistudentsandcaregiverspossessresilience throughthebeliefthatadversitycanbeovercomebyadherenceto culturalvalues,lifegoals,anddailyperseverance.⁵Suchvaluesare alsonecessaryinthemilitaryasWarfightersmustmaintaindaily perseverancethroughoutintensemilitarytrainingandmustshare commongoalstoprotectandserveatallcosts.However,resilience ismorethanamindset.Studieshavereportedthatautonomicreg- ulation,measuredbyheartratevariability,maybeanindicatorof resiliencyandabilitytoadapttochangingenvironments.^6,7Fur- thermore,thereisgrowingevidencethatgenetic,epigenetic,and neurochemicalfactorsalsoplayakeyroleinthedevelopmentof resiliencethroughbiologicalresponsestostress.⁸

Beyondtheinter-andintra-personalinteractionsbetweenthe bodyandthemind,therearemanyotherfactorsthatcontribute toresiliency including sex, environment, and physical training.

Itis wellknownthat avarietyof anatomical,physiological and functionaldifferencesexistbetweenmenandwomen,including bodycomposition,cardiovascularandmusculoskeletalsystems,as wellashormonalsecretion,thatcaninfluenceinitialfunctioning aswell assubsequent resiliencein stressful environments.The environmentalonecanalsohaveanadverseeffectonstresstol- erance,regardlessofsex.Coldstresslimitsthefinemotordexterity andtouchsensitivity⁹andhasbeenshowntodecreasevigilance, moodandincreasetension.¹⁰Conversely,extremeheat,combined withphysicalexerciseandincreasedcoretemperature,canhave detrimentaleffectsoncardiovascularandendocrinefunctionthat resultindecreasedperformance.¹¹Inadditiontosexandenviron- ment,physicaltraininghasadirectimpactonthebody’sabilityto withstandphysicalandcognitivestressors.Loweraerobicpower hasbeenassociatedwithanincreaseinmusculoskeletalinjuries duringbasiccombattraining,¹²whereasloadcarriageandlifting areamongthemostfrequentactivitiesinwhichmusculoskeletal injuriesoccurduringdeployment.¹³Inbothinstances,theresult isreducedcapability.Withoutadequaterest,physicaltrainingcan diminishcognitiveperformance.Astudycomparingovertrained andcontrolathletesdemonstratedthatovertrainedathletesmade moremistakeswhen completingtheStroopColorWordTest.¹⁴ Similarly,sleeprestrictionhasbeenshowntonegativelyimpacts soldiers’reactiontimestoshootfoetargetsduringmarksmanship tasks.¹⁵

Therefore,theselectionandtrainingofservicemembersmust beusedtoidentifythosewhocanmaintainnormalphysiological andpsychologicalfunctioningunderstress.Suchfactorsdemon- stratethecomplexityofresilienceandtheneedtoidentifythebest meanstopromoteresiliencyamongmilitaryservicemembers.The needissohighthatimplementinghumanperformanceoptimisa- tionstrategiesaimedatenhancingmilitaryreadinessandlethality hasbeenidentifiedasatoppriorityforthemodernizationoffuture militaryoperations.^3,16,17However,themosteffectivestrategiesto enhanceresiliencyremainunclear.

Thispapersummarizesaroundtablediscussion,heldatthe4th InternationalCongressonSoldiers’PhysicalPerformanceassem- bledtoaddressfivekeydomainsofresiliencyrelativetoarduous military roles in a point/counterpoint format: 1) physiological versus psychological resiliency, 2)sex differences, 3)contribu- tionsofaerobicandstrengthtraining,4)thermal tolerance,and 5)theroleofnatureversusnurture.Apanelofteninternation- allyrecognisedscientistsandpractionerswasselectedtorepresent eachperspectiveasfollows:HildeTeien,physiologicalresilience;

SamMarcora,psychologicalresilience;DanBilling,maleresilience;

TaraReilly,femaleresilience;JaceDrain,aerobictraining;Herbert Groeller,strengthtraining;AndrewYoung,coldtolerance;Nigel Taylor,heattolerance;AnthonyMoffitt,nurturingresilience;Karl

Friedl,thenatureofresilience.Eachpresenterwasallottedthree minutestoeffectivelydefendtheperspective.BradleyNindlserved asthemoderator,facilitatingquestionsanddiscussionfollowing thepanel’spresentation.

1.1. Physiologicalorpsychologicalresilienceismostcriticalfor militaryreadiness

1.1.1. Physiologicalresilience(HildeK.Teien,Norway)

Employmentstandardsforsoldiersprimarilyevaluatephysio- logicalresilience.Ifyouconsiderasniper’ssuccesstohitthetarget, theabilitytohandlestresshasahugeimpactontheperformance.

However,thisfactor,whichmightbetrained,isalwaysasecondary consideration after thesniper’s physical performance, which is crucialforsuccessinmilitaryoperation.Inotherwords,psycho- logicalresilienceflowsfromthemorefundamentalphysiological resilience.

Soldier physiology underpins all soldier performance. Even psychologicalperformanceisdeterminedbyphysiologicalmecha- nismsandneurochemistry.Soldierresilienceisshapedbypersonal habitssuchasdailyphysicalexercise.Physicalexerciseimproves musculoskeletal and cardiovascular fitness. It also stimulates trophic factors suchas insulin-like growth factor 1 (IGF-I) and brain-derived neurotrophic factor (BDNF) withbenefits to sus- taining muscle and bone health.¹⁸ The same factors promote brainneurogenesisandsynaptogenesisandtheseeffectsimprove psychological resilience, including mood, cognition, and pain thresholds.¹⁸Hence,physiologicalresilienceisthebasisforpsy- chologicalresilienceratherthantheopposite.In thisrespectan importantresearchgapistounderstandthedifferentialeffectsof exercisemodeandintensityonneurobiologywithresilienceout- comesrangingfrommotivationandcognitiontoimmunefunction anddiseaseresistance.^19,20

Extremesoldier performance,where resiliencereallycounts, generallyinvolvesphysicalandmetabolicendurance.IntheNor- wegian Ranger School, male and female cadets must perform virtuallynonstopforoneweekwithnoorganizedsleep,andlim- itedornofood.²¹Metabolicresilienceisthedeterminantofsuccess, whereplummetingbloodglucoselevelsforlessresilientsoldiers canresultinphysicalcollapse,andwheremenmaybelessresilient thanwomenbecauseoftheirbiology.²¹Whenthesoldiersneedto performextremephysicalactivityincombinationwithdeprivation ofsleepandenergyintake,basiccomponentsofsurvival,physio- logicalresiliencewillbethepredominantfactorforsuccess.^22,23

Apreponderanceofdatademonstratesthattheabilitytoadjust toandovercometheeffectsofmilitaryoperationalstressorssuch asthermalextremes,highworkload,andinadequaterestisinflu- encedbyphysiologicalfitness.^24,25Thesecombinedstressorscan affectawiderangeofoutcomesrelatedtotheabilitytoperformthe militarymission.Susceptibilitytodiseaseisoneoutcomethathas beenwellinvestigatedinNorwegiansoldiers,wherephysiological resiliencefactorssuchastheabilitytomobilizebodyenergystores moderatesimmunefunction.^21,26Thishasalsobeendemonstrated intheU.S.ArmyRangercourse.^18,27,28

Thermaltoleranceinhot environmentsissignificantly influ- enced by fitness.²⁴ Musculoskeletal injury is also significantly predictedbyphysicalfitness.²⁵Sincemusculoskeletalinjuriesare theleadingcauseofinjuryandlostdutytimeinsoldiers,thismakes physiologicalresiliencethemostimportantfactorinoverallsoldier readiness.Thesinglemajorcontributortolossofsoldiersfromthe militaryisassociatedwithpoorphysicalfitness,includingover- weight,andpsychologicalresilienceisonlyasubsetofthisgroup becauseofthefundamentalimportanceofafitbodytocognitive readiness.

In conclusion, a physiologically resilientsoldier will also be happy, motivated,and capableof good decision making under

stressbecausetheseareallmetabolicfunctionsthat dependon physiologicalresilience.

1.1.2. Psychologicalresilience(SamueleMarcora,United Kingdom)

Psychologicalresiliencereferstotheroleofmentalprocesses andbehaviorinprotectinganindividualfromthepotentialnega- tiveeffectofstressors.²⁹Itiswidelyacceptedthatpsychological resilience is critical for coping with the cognitive, emotional andsocialstressorsassociatedwithwarexposure.Psychological resilienceis most critical for militaryreadiness becauseit also playsanimportantroleforcopingwithphysiologicalstressors,and becauseapsychologicallystressedsoldier(i.e.asoldierthatcan- notcopewithpsychologicalstressors)willnotperformwellduring militaryoperationsnomatterhowphysiologicallycapablehe/she is.

Withregardstocopingwithphysiologicalstressors,scientists havefocusedontheautonomic,endocrineandimmuneresponses, andautoregulation.However,mentalprocessesandbehaviourare alsocriticaltomaintainbodilyhomeostasiswhenexposedtophysi- ologicalstressors.Forexample,copingwithphysicalactivityinthe heatisnotjustaboutsweatingandtheheatflow fromthecore totheskinviatheblood.³⁰Educationandself-monitoringaswell aspacingandappropriatedrinking(behaviouralthermoregulation) arealsoextremelyimportanttooptimiseperformance,andprevent exertionalheatstrokeandhyponatremia.³¹Furthermore,physio- logicalstressorshavepsychologicalmanifestations(e.g.subjective fatigueandthermaldiscomfort)thataddtothepsychologicalbur- denthesoldierhastocopewith.

Withregardstotheeffectsofpsychologicalstressorsonphys- icalperformance, a good example is provided by our workon mentalfatigue.³²Thisexperimentalworkhasdemonstratedthat prolongedanddemandingcognitiveactivityreducesperformance insubsequentaerobicexercisedespitenosignificantalterations inthephysiologicalfactorsthoughttodetermineenduranceper- formance,e.g.cardiacoutputandmusclefatigue.Inotherwords, mental fatigue (via an increase in perceived exertion)reduces enduranceperformance despitenoreduction inthephysiologi- calcapacity toperformprolongedaerobicexercise.Importantly, wehavealsoproducedsomeevidencethateliteenduranceath- letesaremoreresilientthanamateurstothenegativeeffectsof prolongedanddemandingcognitiveactivity.³³Thesefindingssug- gestthatbeingpsychologicallyresilientmayhelpsoldiersperform betterphysicallyaswellascognitively duringstressfulmilitary operations.

Insummary,thereisevidencesuggestingthatapsychologically resilientsoldierwouldcopebetternotonlywiththepsycholog- ical stressors associated with war exposure, but also with the physiologicalstressorsassociatedwithmilitaryoperations.There- fore,psychologicalresiliencehasimplicationsnotonlyformental health, but also for the physical health of a soldier. Further- more,thereisnowconsiderableexperimentalevidencereporting thatpsychologicalstressorslikemental fatiguecanhave aneg- ativeimpactonphysicalperformance andnotjust oncognitive performance.Therefore,selectinganddevelopingpsychologically resilientsoldierswould ensurethat theycanperformoptimally duringmilitaryoperationsthatrequirebothphysicalandcognitive tasks.Forallthesereasons,psychologicalresilienceismostcritical formilitaryreadiness.

1.2. Menorwomenaremorephysiologically/psychologically resilient

1.2.1. Menaremoreresilient(DanielBilling,Australia)

Womendisplaysuperiorperformanceinmanyrolesandwill continuetobeavitalelementofanarmedforce.However,thereare

certainrolesorassignmentswheretheproportionofmenlikelyto havetherequisitephysiologicalresiliencetosafelyandefficiently executetherequiredduties willbehigherthan thatofwomen.

Thispositioncanbeexplainedby discussingthepathwayfrom sexdifferencestomissionaccomplishment.Firstly,physiological sexdifferences indimensionssuchasstature, body mass,bone structure andgeometry, cardiacoutput,oxygenextraction, car- diopulmonaryendurance,musclestrengthandanaerobiccapacity, andmuscleendurancehavebeenwelldocumented.^34–36Secondly, asaresultofthesephysiological differences,theexecution ofa physicallydemandingsingletasksuchasloadcarriagerequires less capablepersonnel towork at a higher percentage of their maximalcapacity.³⁴Thirdly,whenphysicallydemandingtasksare performedinseries,which isreflective ofcontemporary opera- tions,cumulativefatigueensuesresultinginahigherpropensity formusculoskeletalinjuryandorreducedreservetorespondto emergencies.³⁵Fourthly,inadequatereservestorespondtoemer- genciesandortheincapacitationofindividualteammembersdue toinjuryhaveimportantimplicationsforsmallteamperformance andcohesion.Ultimately,areductioninthecapabilityandorcapac- ityoftheteammaycompromisemissionaccomplishment.³⁷

We know from my co-authors that the two dimensions of resilience(physiologicalandpsychological)areintrinsicallylinked sotohelpsupportthisthesis,twospecificcaseexamplesaredis- cussed. The assignments and tasks performedby some Special Forcespersonneldemandextremelyhighphysiologicalandpsy- chologicalresilience.Lessphysiologicallycapablepersonnelwill beunsuitablefortheserolesastheyhaveareducedreserveabove normalworkconditionstorespondtoemergenciesandareless resistanttofatigueandinjury.Anothercaseisextrememanualhan- dlingassignmentswhichdemandhighphysiologicalresilience.In manyinstances,thedemandsofthesetasksarebeyondthecapacity ofmanysoldiers.

Although operational roles or assignments’ will continue to changewiththe ever-evolvingbattlefield, at this point in time thehighdemandsofthemoreextremecaseexamplescannotbe madeeasier.Asaresult,therewillremainalowerpercentageof womenthanmenwhoarecapableofservingintheseoccupations.

However,throughresearchandimplementationoffemalespecific bestpracticetrainingtoenhancemodifiablecharacteristic,suchas muscularstrength,andtheintroductionofnewperformanceaug- mentationtechnologies,suchasexoskeletons,themagnitudeofthe observedsexdifferenceswillcontinuetodiminishorpotentially becomeirrelevantandtherebyenablemorefemales(andmales) toparticipatefullyintheseroles.³⁸Further,abetterunderstanding onthepsychologicalprofileofwomenwhoaresuccessfulinphys- icallystrenuousoccupationswillalsoassistinprovidingtargeted support.Inconclusion,whenitcomestosomeofthemostarduous rolesinthemilitary,atthispresentpointintimemenhaveahigher physiologicalcapacityandaremoreresistanttofatigueandinjury andtherebymoreresilientthanwomen.

1.2.2. Womenaremoreresilient(TaraReilly,Canada)

Historydemonstratesthatintimesoffamineandextremeenvi- ronmental conditions, women are more likely to survive than men.Assumingresilienceequatestosurvival,womendemonstrate lowermortalityratesthan menatallages,resultingin women outlivingmentypicallybya10yearmargin.Between15and24 years oldmenare threetimes morelikely todiethan women, andmostofthesemalefatalitiesareself-inflicted,causedbyreck- lessbehaviororviolence,afindingthatisreflectedinothermale primatesaswell.³⁹Asmenage,theirchoicescontinuetopropel themtowardshigherrisk ofdeath.Illnessesrelatedtosmoking andalcoholconsumptionkillmorementhanwomen,andintheir 40scardiovasculardiseaseandcancerkillsfarmoremalesthan females.³⁹

Specifictothedemandsofcombat,womenarebetteratmaking logicaldecisionsunderstressfulconditionswithoutthenegative interactions caused by testosterone which increases activity of brain areas associated withimpulse control and distractibility.

Researchdemonstratesthatwomenincombatroleswouldresultin farfeweraccidents,assaults,andcasesoffratricide.⁴⁰Biomechani- cally,womenhavealowercenterofgravity,whichinherentlygives thembetterbalance,usefulforhandtohandcombat,climbingand traversingdifficultterrain.⁴¹

Interms ofmental resilience,aftercontrollingforreports of priorlifestressorsandsexualharassmentduringdeployment,Vogt etal.reportednogenderdifferencesintheassociationbetweensev- eraltypesofdeploymentstressorsincludingcombatexposureand PTSD.⁴²Infact,menare5timesmorelikelytousealcoholasacop- ingmechanism,andbecomealcoholdependentordiagnosedwith antisocialpersonalitydisorder.

Insummary,withlowerlevelsofoxygenfreeradicals,higher body fat,lower needfor caloricintake,and betterlipidutiliza- tion for energy metabolism while sparing muscle protein and glycogen,⁴³womenhaveahigheraveragesurvivalratethanmenin timesofgreatmetabolicstress,likeseverefamine.Additionally,the greatertheseverityofthestress,thegreaterthedifferenceinsur- vivalnumbersbetweenmenandwomen.⁴⁴Women,aredesigned tohavechildren, and evolutionaryadaptationstobear children haveenabledwomentodealbetterwithdeprivation.⁴⁴Thesephys- iologicaladvantages thatwomen haveover menforsurvival in adverseenvironmentsremain,andthisadvantageisfurthersup- portedbytherapidreductioninthemaletofemalegapinathletic performance,aresultofthescaleupofathleticprogramstargeting girlsandwomen.⁴⁵

1.3. Aerobicorstrengthtrainingbestbuildsmilitary physiologicallyresilience

1.3.1. Aerobictrainingbestbuildsmilitaryphysiological resilience(JaceDrain,Australia)

It is well understood that many military occupational tasks involveprolongedand/orrepeatedperformance,e.g.packmarches, digging, sand-bagging, fire and movement, material manual handling.Typically,cardiovascularenduranceunderpinstheper- formance of these tasks. An individual with a higher aerobic capacity (VO_2max)willtherefore beworkingata lower relative intensity(%VO_2max),whencomparedtolessaerobicallyfitindivid- uals.Areducedrelativetaskintensitywillinturnallowforlonger taskperformanceand/oragreatercapacityforrepeatedefforts.⁴⁶ Beyondoccupationalperformance,aerobicfitnessisalsostrongly correlatedwithinjuryratesandattritionduringmilitarytraining.⁴⁷ Infact,aerobicfitnessisoneofthemostcommonriskfactorsfor musculoskeletalinjuryduringmilitarytraining.¹²

Aerobictraining canalso help militarypersonnel bufferthe allostaticstressassociatedwithmilitarytraining.Specifically,aer- obicfitnesshasbeenassociated withattenuatedhormonal and subjective stressreactivity in response tomilitarytraining.^48,49 Importantly in a military context, aerobic training helps to moderate reactivity to psychological stressors, in the absence of physical stress. Furthermore, evidence indicates that aero- bic training can help to attenuate age-related increases in the hypothalamic-pituitary-adrenal axis reactivity to psychological stress.⁵⁰Improvedaerobicfitnessisalsoassociatedwithreduced cardiometabolicriskfactorsandimportantly,canhelptoattenuate stress-relatedincreasesincardiovascularriskfactors.⁵¹

Insummary,aerobictrainingcanconferanarrayofbenefitsto militarypersonnelincludingincreasedphysicalandphysiological abilitytotolerateoccupationaltaskdemands,decreasedinjuryrisk, improvedoverallhealth(includingpsychological),andenhanced ability to bufferstress. These benefits are realized in both the

short-term(e.g.improvedabilitytoexecuteatask/mission)and thelonger-term(e.g.improvedinjuryresistanceandstressbuffer- ingduringsustainedtraining/deployment,anddecreaseddisease risk).Whilsttherequirementforphysicalconditioningisovertfor militarypersonnelinphysicallydemandingroles/occupations(e.g.

infantry,artillery),physicalfitnessshouldalsobeconsideredatool tomanagecapability(andresilience)acrossanageinganddiverse workforce.Itissuggestedthattherecanbelittledoubtthataero- bictrainingisessentialtobuildingmilitaryphysiologicalresilience.

Onthisbasis,theestablishmentandmaintenanceofaerobicfitness shouldbeanimperativeformilitaryorganizations.

1.3.2. Strengthtrainingbestbuildsmilitaryphysiological resilience(HerbertGroeller,Australia)

Physicalfitnessclearlyinfluencestheabilityofindividualsto manageandadaptwelltostressors.⁵²Higherlevelsofphysicalfit- ness(cardiorespiratoryfitnessandlocalmuscleendurance)prior toentryintobasiccombatandseveremilitarytrainingwasasso- ciatedwithaloweredstressresponseandimprovedpsychological outcomesinsoldiers.^53,54However,theoptimaltypeandamountof exercisetofacilitatetheprotectivebenefitsofphysicalfitnesshas notasyetbeenestablished.⁵⁴Furthermore,oftherangeofphys- icalregimeninvestigated,moreisknownoftheeffectofaerobic exercisetrainingandresponsivenesstophysicalandpsychological stress.Thereforewhatrolemightstrengthtraininghaveuponthe physiologicalresilienceofsoldiers?

Thecharacteristicsofthestressorareanimportantconsidera- tion,asintermittentexposuretostresswithsufficientrecoveryis knowntofacilitatetoughness,masterythatcanprovidedapro- tectionfunctionforthesoldier.Giventhecarriageandliftingof externalloadsisassociatedwiththehighestincidenceofinjurydur- ingdeployment,¹³intermittentandfunctionalexposuretophysical stressorstoimproveperformanceinthisareawouldappeartohave thegreatestutilitywithrespecttophysiologicalresilience.Indeed, themoderndaybattlefieldrequireshighintensityandexplosive movement, often withsoldiersburdened by the carriageof an externalmass; physicalperformancecharacteristicsthatbenefit fromincreasedmuscularstrengthandpower.^55,56Yet,cardiores- piratoryendurancetrainingisstillasignificantbiaswithinmodern militarytrainingregimen.⁵⁵

However,theincorporationofresistancetrainingtoimprove physiologicalresilienceinsoldiersshouldbecarefullyconsidered.

Afocusuponphysicalgainstoincreaseforceproductioncapacityor skeletalmusclemassthathaspoorutilitywiththeessentialphysi- caldemandsofdeploymentandcombatmayservetodecreasethe physiologicalresilienceofthesoldier.Thus,acriticalevaluationof theendstaterequirementsofthesoldiershouldbeacknowledged andusedtoinformtheapplicationofresistancetrainingregimen, toimprovenotonlymuscularstrengthandpowerforfunction- allyrelevanttasks,butalsoenhanceenduranceperformanceand movementcompetencyandquality.Nonetheless,thisstrategyin isolationislikelytohavelimitedefficacywithrespecttothedevel- opment of physiological resilience.The totalityof the physical stressshouldbeconsidered;whereparadoxicallyincreasedabso- lutephysicaltrainingloadswhenprogressivelyappliedload,can increaseresiliencetomusculoskeletalinjury.⁵⁷

1.4. Thermalresilienceisessentialformilitarypreparedness 1.4.1. Coldenvironmentalresilienceismostessentialformilitary preparedness(AndrewYoung,UnitedStates)

PreparationstoimproveWarfightertolerance/resiliencetocold exposureduringmilitaryoperationsareprobablymoreimportant toundertakethanpreparationstoenhancetoleranceofheatstress.

Foronething,thelikelihoodthatmilitaryforceswillbedeployed inthecold,northernlatitudesforpeacekeepingandnationalsecu-

rityoperationsisincreasingasglobalwarmingcausessealanes in theArcticOcean to open, and nations compete for thenat- uralresourcesin that region.⁵⁸ Also, the incidencerateof cold injuries⁵⁹ is much higher thantheincidence ofheat injuries.⁶⁰ MostWarfightersandtheirleadershavepriorexperiencecoping withheat-stressconditionsduringmilitarymissions,whereasfar fewerhaveexperiencewithcold-weatheroperations.Further,itis widelyappreciatedbymilitaryleadersthatphysiologicalmech- anisms underlying human heat tolerance can be optimized in theirWarfightersrelativelyeasily,simplybyhavingthemperform increasinglystrenuousboutsofphysicalworkinthehot-weather conditionsfor progressivelylongerperiodsof time over fiveto tenconsecutivedays(i.e.,inductionofheatacclimatization),and ensuringthattheyconsumeadequateamountsofwatertomain- tain homeostasis.In contrast,the primaryhumanphysiological responsestocoldexposure,shiveringandperipheralvasoconstric- tion,providelittlemeaningfulprotectionevenafterinductionof coldacclimatization,whichisslowertodevelopandlesseffective forimprovingthermaltolerancethanheatacclimatization.⁶¹Opti- mizingbehavioralresponsestocoldismoreeffectiveforenhancing coldtolerance/resiliencethanoptimizingphysiologicalresponses.

Developingoptimalbehavioralresponsestooperateeffectivelyin coldconditionswithoutsufferingcoldinjurieswillentaillearning andpracticebytheindividualWarfighter,aswellasspecialized clothingandequipment,andwillthereforerequiremoretimeand resourcesthanneededtooptimizeheattolerance.

Keybehavioralresponsesthatmustbelearnedandpracticed during cold-weather operations to improve Warfighter toler- ance/resilience include understanding how to wear, use and maintain cold-weather protective clothing, shelters, tools, and mobilityequipment.Properwearofcold-weatherprotectivecloth- ing, will be highly variable between and within individuals, depending on weather conditions, physical activity levels and individualanthropometriccharacteristics.⁶²IndividualWarfight- ersshouldbeallowedtochoosetheirownclothingcombinations to achieve optimal environmental protection. This skill cannot be mastered in a classroom, and requires training in different cold-weatherconditionsatdifferentactivitylevelssoWarfighters learn to appreciate their own individual requirements.⁶³ Simi- larly,Warfightersmusttraintoperformtheirdutieswearingtheir cold-weatherclothingusingtheirweaponsandequipmentdur- ingdifferentcold-weatherconditions,sotheycanappreciatehow thatclothing and thecold weather conditions affecttheirdex- terity and ability tofunction inthe environment. Comparedto optimizingheattolerance/resilience,itisessentialthatWarfight- erscompletemuchmoreextensiveexperientiallearningtodevelop behavioralresponsestocoldexposurethatoptimizeenvironmental tolerance/resilience.

1.4.2. Heattoleranceisanessentialpartofmilitarypreparation (NigelTaylor,Australia)

Homoeothermicspecies are vulnerable toclimatic extremes thatchallengetemperatureregulationandelicitsignificantchanges intissuetemperatures.Humansarenoexception,withthosein militaryandemergency-serviceoccupationsfacingregularthermal challenges.Fromamilitaryperspective,operationsinbothhotand coldextremesarelikely,withtheprobabilitydictatedbynational prioritiesandinternationalobligations.Forinstance,Asia–Pacific countriesroutinelypreparefordeploymentintotropicalandequa- torialregions.Sincehumansevolvedinhot-dryclimates,itmay bearguedthatwearemorepronetocold-relatedinjuries,andthe evidencesupportsthatproposition.^64–66

Coldpersedoesnotexist;itismerelyasubjectivedescription assignedtostatesoflowerthermalenergy(heat).Sinceenergycon- stantlymovesfromhighertolowerenergeticstates,thensome solutionstothesethermalchallengescomeintheformofprotective

barriers.Designers,manufacturersandprocurersofpersonalpro- tectiveclothingandequipmentforthemilitaryandfirstresponders facesignificantchallenges.Inthecold,thermalprotectiveclothing mustresistheatloss,whilsttheinfluxofthermalenergymustbe minimisedwhenexternaltemperaturesexceedbodytemperature.

Furthermore, protective clothing should enhance heat dissipa- tionduringstatesofhighmetabolicheatproduction, regardless ofenvironmentaltemperature.Thermalproblemsalsochallenge physiologistsseekingtoidentifystrategiestoenhancethetolerance andresilienceofwarfightersandemergencypersonnel.

Withtheexceptionofextremeradiant-heatexposures,itisthe deeptissuesthataremostsusceptibleduringheatstress,giving risetoillnessesrangingfromcrampstoheatstroke.Forthemili- taryandfirstresponders,thosedisordersareassociatedasmuch,if notmoreso,withphysicalexertionandmetabolicallyderivedheat, largelyduetooccupationalrequirementsmandatingthewearing ofprotectiveclothing,equipmentandbodyarmour.Suchensem- blescanencapsulatethewearer,particularlyduringchemicaland biologicalthreats,isolatingthatpersonfromtheambientmedium.

Inthatstate,limitedexchangeoccursbetweenthebodyandthe externalenvironment.⁶⁷Thus,heatproducedwithin,andfluidlost into,thatclosedsystemremainswithintheprotectiveensemble, andthemicroclimateapproximatesbodytemperatureandrapidly becomessaturatedwithwatervapor.Thatstate,whencombined withelevatedheatproduction,isnotconducivetoprolongedsur- vival,regardlessofpriorphysicalandthermalconditioning.

Threeapproacheshavebeenusedtominimisetheriskofexer- tionalheatillness:heatadaptingpersonnel,⁶⁸developingfabrics thatfacilitateheatandmoistureremoval⁶⁷andsupplementalcool- ing. The first two are beneficial to minimally clothed athletes.

However,heatadaptationelevatessweatsecretion,atleastinthe shortterm,mostofwhich remains unevaporated,and provides negligiblecoolingforthosewearingprotectiveclothing.Suchsweat lossesacceleratedehydrationandcompromisethermalinsulation oftheprotectiveclothing.Smartfabrics,ifwornbeneathprotective clothingandequipment,offernorespite.⁶⁷Thelessexoticsolu- tionmust,justlikeinthecold,centeraroundsoundeducational andmanagerialpractices,incombinationwithampleexperiential opportunities.

1.5. Themilitarycan(nurture)orcannot(nature)buildand instillphysiological/psychologicalresilience

1.5.1. Themilitarycanbuildandinstillphysiologicaland psychologicalresilience(AnthonyMoffitt,Australia)

“Mancan (nurture) only onexternal and visible characters:

naturecaresnothingforappearances,exceptinsofarastheymay beuseful.”IfDarwin’sallusiontothefutilityofinfluencingeonsof randomvariationsandinfinitesimal‘nature’adaptationsiscorrect,

“whichasfarasourignorancepermits”itis,shouldweconsume ourselveswiththe‘nurture’ofmanatall?

Howmanycitizenswouldneedtobetrainedtocounterapoten- tiallycatastrophic threattoAustralia–hundredsofthousands?

Ifso,ourmilitarywillessentially‘getwhatweget’.We canno longertakeforgrantedthe‘hardiness’ofpastgenerationsgiven theprofoundbiopsychosocialdevelopmentalchallengesthatthe emergingdigitalnativegenerationareexperiencing.⁶⁹Certainly, thebrutalityofcombatisprofoundlydivorcedfromacontemporary youngwesterner’sreality.So,howpreparedisthecurrentfighting agedgeneration?⁷⁰Buildingandinstillingresilience(nurture)in

‘whatweget’(nature)isnotsomuchaquestionasitisacritical vulnerability.

Amilitary’sfirstobjectistodefenditspeopleandterritories.

Wehavesuccessfullymadesoldiersofourcitizensforever.During WW1&2pressureforbootsonthegroundultimatelymeantthat geneticsmatteredlittle.Sincethistime,Australia’scommitmentto

warfarehasbeenmodestandsafeincomparisonandwehavebeen abletobuildenviablemilitarycapability.

Inthefaceofapotentiallycatastrophicthreat,‘nature’willagain belargelyirrelevant.Inthecontextofasoftening modernAus- traliansociety,buildingresilienceinasustainablelethalcapability willbemoreimportantthanever.However,thechallengetobuild resilientcombateffectivesoldierstooperateinVUCAbattlefield environmentsappearstobeunprecedented.For example,more sedentarylifestylesandtheincreasein‘knowledgework’maybe conspiringagainstusintermsofaworstcasenationaldefenseper- spective.Further,thereappearstobeanoveremphasisonwhatwe putonoursoldiersratherthanwhatweputinthem.⁷¹

Thenature/nurturedebatehasoutlasteditsusefulness.Tech- nologyanddevelopmentsinpedagogy,psychologyandphysiology haverevolutionizedhowwe‘build’humans.Developmentswemay wellleveragedeliberatelytoinfluenceepigeneticfactors⁷²andthe biopsychosocialplasticityofoursoldierstoassistinthebuild.Many thingsweconsideredfixedinhumans,arenot.Forexample,our understandingofhowsocialstimuli aretranslatedintophysical characteristicsinthebrain⁷³;or,thesignificantpsychological(cog- nitive)benefitsofphysiologicaltraining.^74–76Interestingly,both raisequestionsaroundthemaintenanceofresilience.

Thiscanbeachievedbyimmersingthescientistswithoursol- diersin what mustberealitybased trainingenvironments. We mustresisttheriskadversityof thebureaucraticpolicymakers thatpredominatemoderntrainingserials.Indeed,manyseniorsol- dierswouldagreethatthisriskadversityisathreattooursoldier’s resilience.Itistimetoreturntheancients’approach⁷⁷ofalocally coordinated,multidisciplinary,multifaceted‘HumanPerformance’

programs that are wellresourced and foundedin practitioner- academiaalliances.

We havesuccessfully builtresilienceinourmilitaryforever, withfew exceptions.Through training and by organizingthem intogroupingsandindoctrinationswehavealsobuiltsocialand nationalresilience.However,inlessdeterminabletimeswemust modernizedeliberatelyandrapidly.Ratherthanpolicyoursoldiers needadaptivehumanperformanceprogramssupportedbylocal academicalliances.Oursoldiers’,andindeedournation’s,resilience profoundlydefinesusall,andthereforewe‘must’buildonwhatwe get.

1.5.2. Themilitarycannotbuildandinstillphysiologicaland psychologicalresilience(KarlFriedl,UnitedStates)

Everyonecandotheirpartfornationaldefense,butnoteveryone isborntobeasoldier.Soldierresilienceisdeterminedbygenetics andearlychildhoodexperiences;buildingresilienceratherthan selectingindividualswhoalreadypossessitisgenerallynotfeasi- ble.Bythetime17or18yearoldrecruitsreportforduty,thedie hasbeencastandtherearepracticallimitstohowmuchbiology canbemodifiedtobestmeetsoldierperformanceneeds.

Earlyinfluenceshavebeenwellentrainedbythetime young men and women report to military training and the resulting resilienceattributes arenot easilymodifiable. In 1946,theU.S.

Congressenactedtheschoollunchprogrambecauseofnational securityconcerns.Toomanychronicallymalnourishedconscripts hadbeenunsuitableformilitaryserviceinWorldWarII,andthe Armycouldnotbuildorinstillresilienceintheseindividualsafter thefact.Today,reversingthefirsttwo decadesofnutrition and exercisehabitshasalsobeenunsuccessfulforobeseyoungmen andwomen;obeserecruitswhosuccessfullyloseweightduring basictraining arestill likelytobeeliminatedas fitnessfailures beforetheendoftheirfirstenlistment.⁷⁸Duringbasictrainingaddi- tionalselectionoccursbecausetrainabilitygenesdeterminewho canachieveminimumphysicaltrainingstandardsandcontinueas asoldier.⁷⁹

Geneticandepigeneticinfluencesdetermineresiliencefactors suchashardinessandmetabolicflexibility.InastudyoftheU.S.

ArmyRangercourse,thetwoleanestindividualsoutof50young soldierswhocompletedthefulleightweeksinvolvinghighwork- loadandhypocaloriaillustratedoppositeextremes ofmetabolic response.Oneofthesesoldierslosttheleastamountofweight(only 9%ofbodyweight)andrelativelylittleleanmass,whiletheother lostthelargestamountofweight(23%)andconsumedanestimated 40%ofmusclemass(andwasnotawardedtheRangertab,basedon patrolleadershipperformance).⁸⁰U.S.ArmyRangersareselected onthebasisofdemonstratedresilience.

Epigenetics can determine psychological resilience.Trauma- induced stress responsivity can be passedto offspring, putting theseindividualsatincreasedriskforPTSDandothermaladaptive responsestofuturetraumaticexposures.⁸¹Otherrecentfindings showthatmindfulcontrolofanxietyismoderatedbythestrength of theconnectionbetweenprefrontalcortexand theamygdala.

Traitanxietyislowerinindividualswithathickerfibertractcon- nectiontofrontalcortex,thecenterofpsychologicalresilience.⁸² Gutmicrobiotaalsoplayanimportantroleinstressandanxiety.⁸³ Untilthereisaprogramtoreverseepigeneticeffectsorsuccessfully reconfigurethegutmicrobiomeofrecruits,thesefactorsaffectkey resiliencetraitsthatshouldbepartofsoldierselection.

Artificialattemptstoenhancesoldierperformancemayactu- allyreduceresilience.Forexample,pharmaceuticalenhancement ofalertnessremovestheflexibilityforrestorativesleepopportuni- ties,anddrugmanipulationofmyostatinactiontocreatemassively muscled hulks reduces the opportunity to run fast and toler- atehotenvironments.Armiesshouldselectindividualswithhigh resiliencegenesfromthemostpromisingpoolsofrecruits;warrior culturessuchasSikhs,Gurkhas,NewZealandM ¯aori,andHighland Scotsareexamplesofsuchindividualswhoarepurposelyoverrep- resentedinmilitaryservice.Selectionispreferabletoextraordinary training,drug,andgeneticenhancementofaverageindividuals.

2. Discussion

Resilience is the ability to maintain normal psychological andphysiologicalfunctioninginthepresenceofhighstressand trauma.^8,84 Asdemonstratedinthis roundtable,therearemany co-dependentlayerstoresiliencethatbuildupononeanotherto ultimatelyenhancemilitaryreadinessandpreparedness(Fig.1).

Resilienceisinitiallyinstilledwithinsoldiersthroughtrainingand preparation aimedtoenhance physiological toleranceto stress.

Aerobictraininghaslongbeenthecornerstoneofmilitarytraining duetothephysiologicaladaptationsincludingincreasedcardiac output,decreased peripheralvascular resistance, and increased numberofmitochondriainmusclecellsthatarevitaltooptimal performanceofmanymilitarytasks.⁸⁵Certainlytheseadaptations areadvantageousinthepresenceofhighphysiologicalstress.How- ever,themodern battlefieldrequireshigher levelsofanaerobic fitness,involvinghighforceandquickexplosivemovements,and failuretoprepareforsuchdemandscanleadtoincreaseininjury ordeath.⁸⁵

Asmorecombatrolesbecomeopentowomen,theimportance of anaerobic and strength training become increasingly essen- tialforwomentodeveloptheadaptationsnecessarytomeetthe demandsof thebattlefield.Thediscernablephysiologicaldiffer- encesbetweenmenandwomencanpromoteandhinderresiliency foreithersex.Thoughmenhaveseveralphysiologicaladvantages overwomen,includinghigheraveragecardiacoutputandmuscle strength,testosterone cannegativelyaffectimpulsecontroland decisionmakingincombat.⁴⁰Incontrast,despitethephysiolog- icalshortcomingsrequiringwomentoperformatahigherlevel of theirmaximumcapacity duringsomemilitary-specifictasks,

Fig.1.Fivekeydomainsofresiliencyresiliencecanbepromotedthroughavarietyofdomainstoenhancethereadiness,lethality,andmodernizationofarmedforces.While performanceisultimatelygroundedincellularbiologyandphysiology,itisenhancedthroughdevelopingpsychologicalcopingmechanismsthatnurturesoldierstotolerate discomfortandstress.Foryearsaerobictraininghasbeenthecornerstoneofmilitarytrainingduetotheadvantageousphysiologicaladaptations.However,themodern battlefieldrequireshigherlevelsofstrengthandanaerobicfitness.Thoughmenhaveseveralphysiologicaladvantagesoverwomen,betterlipidutilizationprovideswomen aresilientadvantageovermeninadverseenvironments.Regardlessofsex,soldierscanprepareforextremeheatandcoldbytraininginprotectiveclothingwhileexposed totheelements.

theirdecreasedcaloricrequirementsandbetterlipidutilization⁴³ providearesilientadvantageovermeninadverseenvironments.

Whilethe capabilityof asoldier’sperformance is ultimately groundedatthecellularlevel,performancewillbesuboptimalif thesoldierisunabletodevelopcopingmechanismstohandlea changingoperationalenvironment. Therefore, buildingadaptive resilienceinsoldiersisthenextlayernecessarytopromotemili- taryreadiness.Consideringtheresponsetothesamepsychological stressorcanvaryimmenselyfrompersontoperson,resilienceis consideredanindividualtrait.⁸⁶However,humanshave proven tobeahighlyadaptablespecies.Throughbehavioraladaptations andrealitybasedtrainingenvironments,resiliencehasthepoten- tialtobeinstilledinsoldiers,justasithasbeenhistoricallyduring wartimewithminimalselectioncriteriaforsoldiers,i.e.conscrip- tion. The Comprehensive Soldier Fitness (CSF) program is one exampleofhowtheUS Armyis takingaproactiveapproachto buildingresiliencyinsoldiers.⁸⁷Basedonpositivepsychology,the CSFprogramtakesasimilarapproachtotheArmy’sphysicalfit- nesstraining.Adaptiveresilienceisnotsolelybasedinpsychology asasoldiermustalsobephysicallypreparedtoadapttoextreme climates.A combination ofphysiological training usingspecial- izedequipmentforextremeenvironments,performingtaskswhile wearingappropriateprotectiveclothing,andexposuretotheele- ments,inconjunctionwithpsychologicaltrainingsuchaspacing, self-monitoring,andmanagingdiscomfort,arenecessarytobuild resilienceinthepresenceofextremeheatorcold.

Natures versus nurture tradeoffs are completely dependent ontheneedsofthemilitary.Though someaspects surrounding resilienceare solelygrounded innature,suchas biologicalsex, geneticpredisposition,and environmentalconditions,resilience hasthepotentialtobenurturedthroughphysicalandpsycholog- icaltrainingcombinedwiththeuseofspecializedequipmentfor extremeconditions.In times ofnational emergency,everyable bodiedindividualmaybecalledtoserveindefenseoftheircoun- tryandselectionstandardsareeasedoreliminated.Inconscript armiesaroundtheworld,individualsarepreparedinbasictrain- ingtodotheirpartfornationaldefense.Professionalarmiesand specializedeliteperformersaremorelikelytobeselectedfortheir performance,includingdemonstratedresiliencetraits.

Oncethelayersoffoundationaland adaptiveresiliencehave beenestablished,thefinallayershouldaimtoreducethedemands for resilience in the modern battlefield to enhance readiness andpreparedness.Forinstance,theapplicationofnewtechnolo- gies,suchastheuseofexoskeletonsforcarryingheavycombat loads,⁸⁸orinnovativeapproachestodeterminereadiness,suchas biomarkeranalysis,¹⁶canfurtherenhancethelevelofprepared- ness.Furthermore,forecastingtheoperationalenvironment and buildingappropriate techniquesand countermeasureswillopti- mizethereadinessofoursoldiers.

Ultimately,theinterrelationsofthelayersofresilienceindicate thereisnosingularorevenbinaryapproachthatismostadvan- tageousforbuildingresiliencetoenhancemilitarypreparedness.

Rather, a hybrid approach may be superior. Combiningstrate-