ArticlePDF AvailableLiterature Review

Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance

Authors:

Abstract

Elite athletic competitions have separate male and female events due to men’s physical advantages in strength, speed and endurance so that a protected female category with objective entry criteria is required. Prior to puberty, there is no sex difference in circulating testosterone concentrations or athletic performance but from puberty onwards sex difference in athletic performance emerges as circulating testosterone concentrations rise in men because testes produce 30 times more testosterone than before puberty with circulating testosterone exceeding 15-fold those of women at any age. There is a wide sex difference in circulating testosterone concentrations and reproducible dose-response relationship between circulating testosterone and muscle mass and strength as well as circulating hemoglobin in both men and women. These dichotomies largely accounts for the sex differences in muscle mass and strength and circulating hemoglobin levels resulting in at least an 8-12% ergogenic advantage in men. Suppression of elevated circulating testosterone of hyperandrogenic athletes results in negative effects on performance, which are reversed when suppression ceases. Based on the non-overlapping, bimodal distribution of circulating testosterone concentration (measured by liquid chromatography-mass spectrometry) and making allowance for women with mild hyperandrogenism including that of polycystic ovarian syndrome, who are over-represented in elite athletics, the appropriate eligibility criterion for female athletic events should be a circulating testosterone of less than 5.0 nmol/L. This would include all women other than those with untreated hyperandrogenic disorders of sexual development (DSD), testosterone-treated female-to-male (F2M) transgender, noncompliant male-to-female (M2F) transgender or androgen doping.
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CirculatingTestosteroneastheHormonalBasisofSex1
DifferencesinAthleticPerformance2
Shorttitle:HyperandrogenismandFemaleAthletics3
4
DavidJ.Handelsman1,AngelicaLindénHirschberg2,StephaneBermon35
6
1ANZACResearchInstitute,UniversityofSydneyandDepartmentofAndrology,7
ConcordHospital,Sydney,NewSouthWales,Australia,8
2DepartmentofWomen´sandChildren´sHealth,KarolinskaInstitutetand9
DepartmentofGynecologyandReproductiveMedicine,KarolinskaUniversityHospital,10
Stockholm,Sweden11
3UniversitéCôted'Azur,LAMHESSNice,FranceandInternationalAssociationofAthletics12
Federations,HealthandScienceDepartment,Monaco13
14
Keywords:testosterone,sexdifference,athleticperformance,muscle,hemoglobin,disordersofsex15
differentiation16
17
Words:13,172  References:161  Tables:5  Figures:818
19
20
Correspondence:21
ProfDJHandelsman22
ANZACResearchInstitute23
SydneyNSW213924
Australia25
E:djh@anzac.edu.au26
27
28
29
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Disclaimer:30
DJHisamedicalandscientificconsultantforInternationalAssociationofAthleticsFederations31
(IAAF)andmemberoftheInternationalOlympicCommittee(IOC)workinggroupon32
hyperandrogenicfemaleandtransgenderathletesandtotheAustralianSportsAntiDoping33
AgencyandisalsoamemberofWorldAntiDopingAgency(WADA)’sHealth,Medicineand34
ResearchCommittee.HehasreceivedinstitutionalgrantsupportfromBesinsHealthcareand35
Lawleyforinvestigatorinitiatedclinicalstudiesintestosteronepharmacologyandhasprovided36
experttestimonyintestosteronelitigation.37
ALHisamedicalandscientificconsultantfortheSwedishOlympicCommitteeandamemberof38
theIAAFandIOCworkinggroupsonhyperandrogenicfemaleathletesandtransgenderathletes.39
ShehasreceivedgrantsupportfromIAAFforastudyontestosteroneandphysicalperformancein40
women.41
SBisamedicalandscientificconsultantfortheIAAFandamemberoftheIAAFandIOCworking42
groupsonhyperandrogenicfemaleathletesandtransgenderathletes43
Theauthorshavenootherinvolvementwithanyentityhavingafinancialinterestinthematerial44
discussedinthemanuscript.Opinionsexpressedinthispaperarethepersonalviewoftheauthors45
anddonotrepresentthoseoftheIAAF,IOC,WADAorSwedishOlympicCommittee.46
47
48
49
Acknowledgements:TheauthorsaregratefulforhelpfulinsightsandcommentsfromAlan50
VernecandOsquelBarroso(WADA),PeterHarcourt(AFL,FIBA)andRichardBudgett(IOC).51
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Abstract52
Eliteathleticcompetitionshaveseparatemaleandfemaleeventsduetomen’sphysicaladvantagesin53
strength,speedandendurancesothataprotectedfemalecategorywithobjectiveentrycriteriaisrequired.54
Priortopuberty,thereisnosexdifferenceincirculatingtestosteroneconcentrationsorathletic55
performancebutfrompubertyonwardssexdifferenceinathleticperformanceemergesascirculating56
testosteroneconcentrationsriseinmenbecausetestesproduce30timesmoretestosteronethanbefore57
pubertywithcirculatingtestosteroneexceeding15foldthoseofwomenatanyage.Thereisawidesex58
differenceincirculatingtestosteroneconcentrationsandreproducibledoseresponserelationshipbetween59
circulatingtestosteroneandmusclemassandstrengthaswellascirculatinghemoglobininbothmenand60
women.Thesedichotomieslargelyaccountsforthesexdifferencesinmusclemassandstrengthand61
circulatinghemoglobinlevelsresultinginatleastan812%ergogenicadvantageinmen.Suppressionof62
elevatedcirculatingtestosteroneofhyperandrogenicathletesresultsinnegativeeffectsonperformance,63
whicharereversedwhensuppressionceases.Basedonthenonoverlapping,bimodaldistributionof64
circulatingtestosteroneconcentration(measuredbyliquidchromatographymassspectrometry)and65
makingallowanceforwomenwithmildhyperandrogenismincludingthatofpolycysticovariansyndrome,66
whoareoverrepresentedineliteathletics,theappropriateeligibilitycriterionforfemaleathleticevents67
shouldbeacirculatingtestosteroneoflessthan5.0nmol/L.Thiswouldincludeallwomenotherthanthose68
withuntreatedhyperandrogenicdisordersofsexualdevelopment(DSD),testosteronetreatedfemaleto69
male(F2M)transgender,noncompliantmaletofemale(M2F)transgenderorandrogendoping.70
71
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1.Background72
73
Virtuallyallelitesportsaresegregatedintomaleandfemalecompetitions.Themainjustificationistoallow74
womenachancetowin,aswomenhavemajordisadvantagesagainstmenwhoare,onaverage,taller,75
stronger,fasterandhavegreaterenduranceduetotheirlarger,strongermusclesandbonesaswellasahigher76
circulatinghemoglobin.Hence,elitefemalecompetitionformsaprotectedcategorywithentrythatmustbe77
restrictedbyanobjectiveeligibilitycriterionrelatedbynecessitytotherelevantsexspecificphysical78
advantages.Thepracticalneedtoestablishaneligibilitycriterionforelitefemaleathleticcompetitionledthe79
InternationalAssociationofAthleticFederations(IAAF)toestablisharulein2011,endorsedbythe80
InternationalOlympicFederation(IOC)in2012,forhyperandrogenicwomen.ThefirstIAAFregulationstated81
thatforathletestobeeligibletocompleteinfemaleevents,theathletemustbelegallyrecognisedasafemale82
and,unlessshehascompleteandrogeninsensitivity,maintainserumtestosteronelessthan10nmol/L.That83
IAAFeligibilityrulewaschallengedbyanathletetotheCourtforArbitrationinSports(CAS)whichruledin201584
that,althoughaneligibilitycriterionwasjustified,thescientificgroundsfortheoriginalIAAFrulewas85
consideredinsufficient,notablyintheextentofthecompetitiveadvantageenjoyedbyhyperandrogenic86
athleteswhohadcirculatingtestosteronegreaterthan10nmo/L.TheCASsuspendedthehyperandrogenism87
eligibilityrulependingreceiptofsuchevidence.Inthatcontext,thepresentpaperreviewstheavailable88
evidenceonthehormonalbasisforsexdifferencesinathleticperformance.Itconcludesthattheevidence89
justifiedarevisedeligibilitycriterionofathresholdcirculatingtestosteroneconcentrationof5nmol/L90
(measuredbyamassspectrometrymethod).91
92
2.Sex,FairnessandSegregationinSport93
94
Ifsportisdefinedastheorganizedplayingofcompetitivegamesaccordingtorules(1),fixedrulesare95
fundamentalinrepresentingtheboundariesoffairsportingcompetition.Rulebreaking,whetherby96
breachingeligibilityorcompetitionrules,suchasuseofbanneddrugs,illegalequipmentormatchfixing,97
createsunfaircompetitiveadvantagesthatviolatesfairplay.Cheatingconstitutesafraudagainstnotjust98
competitorsbutalsospectators,sponsors,thesportandthepublic.Intheabsenceofgenuinefair99
competition,elitesportwouldloseitswidepopularappealandabilitytocaptivateandinspirewiththe100
authenticattractionofgenuinecontestbetweenhighlytrainedathletes.101
102
Nevertheless,fairnessisanelusive,subjectiveconceptwithmalleableboundariesthatmaychangeover103
timeassocialconceptsoffairnessevolve.Forexample,untilthelate19thcenturywhenorganizedsports104
trainersemerged,trainingitselfwasconsideredabreachoffairnesssincecompetitionwasenvisagedat105
thattimeasacontestbasedsolelyonnaturalendowments.Similarly,sportsoncedistinguishedbetween106
amateursandprofessionals.Theconceptoffairnesshasdeepandcomplexphilosophicalrootsmainly107
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focusedonnotionsofdistributivejustice.Theseconsiderationsimpactonsportthroughtheuniversal108
applicationofantidiscriminationandhumanrightslegislation.Lessattentionisgiventothephilosophical109
basisoffaircompetitioninelitesportwheretheobjectivesarenotegalitarianbutaimtodiscovera110
hierarchyofachievementderivedfromamixtureofunequalnaturaltalentandindividualtrainingeffort.111
Excellent,insightfuldiscussionofthelegalandmoralcomplexitiesofsexandfaircompetitioninelitesports112
fromalegalscholarandformerelitefemaleathleteisavailable(2).113
114
Thetermssexandgenderareoftenconfusedandusedasifinterchangeable.Sexisanobjective,specific115
biologicaltermwithdistinct,fixedfacets,notablygenetic,chromosomal,gonadal,hormonaland116
phenotypic(includinggenital)sex,eachofwhichhasacharacteristicdefinedbinaryform.Whileallfacets117
ofbiologicalsexarealmostalwaysalignedsothatassignmentofsexatbirthisstraightforward,rare118
instanceswhereanytwoormorefacetsofbiologicalsexconflictconstituteanintersexstate,nowreferred119
toasDisorders(orDifferences)ofSexDevelopment(DSD)(3).Bycontrast,genderisasubjective,malleable,120
selfidentifiedsocialconstructwhichdefinesaperson’sindividualgenderroleandorientation.Prompted121
bybiological,personalandsocietalfactors,volitionalexpressionofgendercantakeonvirtuallyanyform122
limitedonlybytheimaginationwithsomeindividualsassertingtheyhavenotjustasinglenatalgenderbut123
twogenders,none,adistinctthirdgenderorgenderthatvaries(fluidly)fromtimetotime.Hence,while124
genderisusuallyconsistentwithbiologicalsexasassignedatbirth,inafewitcandifferduringlife.For125
example,ifgenderwerethebasisforeligibilityforfemalesports,anathletecouldconceivablybeeligibleto126
competeatthesameOlympicsinbothfemaleandmaleevents.Thesefeaturesrendertheunassailable127
personalassertionofgenderidentityincapableofformingafair,consistentsexclassificationinelitesport.128
129
Thestrongestjustificationforsexclassificationinelitesportisthatafterpubertymenproduce20times130
moretestosteronethanwomen(47)resultingincirculatingtestosteroneconcentrations15timeshigher131
thaninchildrenorwomenofanyage.Agegradecompetitivesportingrecordsshownosexrelated132
advantagespriortopubertyonwards,whereasfromtheageofmalepubertyonwardsthereisastrongand133
ongoingmaleadvantage(8).Thestrikingmalepostpubertalincreaseincirculatingtestosteroneprovidesa134
major,ongoing,cumulativeanddurablephysicaladvantageinsportingcontestsbycreatinglargerand135
strongerbones,greatermusclemassandstrength,andhighercirculatinghemoglobinaswellaspossible136
psychological(behavioural)differences.Inconcert,theserenderwomen,onaverage,unabletocompete137
effectivelyagainstmeninpowerbasedorendurancebasedsports.138
139
Sexclassificationinsportthereforerequiresproofofeligibilityasonlywomenshouldcompeteinthe140
protected(female)category.Thisdeceptivelysimplerequirementforfairnessistakenforgrantedbypeer141
femalecompetitorswhoregardparticipationbymales,orathleteswithphysicalfeaturesclosely142
resemblingmales,asunfair.Thismakespolicingofeligibilityinescapableforsportstoavoidunfairmale143
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participationinfemaleevents.Yet,suchpolicinginevitablyintrudesintohighlypersonalmatterssothatit144
mustbeachievedwithrespectfordignityandprivacydemandinguseoftheleastinvasive,scientifically145
reliablemeans.Unsurprisinglythisdilemmahasalwaysbeenhighlycontentioussinceitfirstentered146
internationalelitesportsintheearly20thcenturyandithasbecomeincreasinglyprominentand147
contentiousinrecentdecades;nevertheless,therequirementtomaintainfairplayinfemaleeventswillnot148
disappearaslongasseparatefemalecompetitionsexist.Overrecentdecadestherehasbeenprogressively149
betterunderstandingofthecomplexbiologyofgeneticsexdeterminationandtheimpactofpubertal150
sexualmaturationinestablishingphenotypicsexualdichotomyinphysicalcapabilities.Thesesex151
dichotomousphysicalfeaturesformthebasisof,butremainquitedistinctfrom,adultgenderrolesand152
identity.Overthelastcenturyasknowledgegrewtheattemptstoformalizeascientificbasisforthe153
unavoidablenecessityofpolicingeligibilityforthefemalecategoryhavebeencontinuallychallenged.Most154
recently,theincreasingassertionofgenderselfidentificationasasocialcriterionhasfurtherchallenged155
thehegemonyofbiologyfordetermining“sportssex”,Coleman’saptterm(2).Allowingsubjectivegender156
selfidentificationtobecomethesolecriterionofsportssexwouldallowforgamingandperceptionsof157
systematicunfairnesstogrow.Thecaseforwomen’ssportsbeingdefinedbysexratherthangender,158
includingtheconsequencesofaccedingtogenderbasedclassificationhavebeenoutlined(9)inarguingthe159
importanceofpropermedicalmanagementofathletesintendingtocompeteinfemaleevents.160
161
Separatemaleandfemaleeventsinsportisadominantformofclassificationthatissuperimposedon162
othergraduatedagegroupandweight(e.g.weightlifting,powerlifting,wrestling,boxing,rowing)163
classifications,whichreflectdifferencesinstrength,power,speedtoensurefairnessintermsof164
opportunitytowinand,additionally,safetyincontactsports.Ageandweightclassificationsrelyon165
objectivecriteria(birthdate,weighinweight)foreligibilityasnecessarilyshouldsexclassification.166
Nevertheless,somepowersportsdependentonexplosivestrengthandpower(egthrowingevents,167
sprinting)donotsegregateweightclasses,whileothersportswhereheightisanadvantage(egbasketball,168
jockeys)donothaveheightclassifications.Thesesportsdisproportionatelyattractathleteswithgreater169
weightand/orpowertoweightratiooradvantageousstature,respectively.Ifsexclassificationwere170
eliminatedsuchopenormixedcompetitionswouldbedominatedalmostexclusivelybymen.Ittherefore171
seemshighlyunlikelythatsexclassificationwouldeverbediscardeddespitecallsonphilosophicalor172
sociologicalgroundstoend“gender”classificationinsport(10).173
174
3.Sexdifferenceincirculatingtestosteronelevels175
3.1Testosteronebiosynthesis,secretionandregulationinmenandwomen176
Anandrogenisahormonecapableofdevelopingandmaintainingmasculinecharacteristicsinreproductive177
tissues(notablythegenitaltract,andothertissuesandorgansassociatedwithsecondarysexual178
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characteristicsandfertility)andcontributingtotheanabolicstatusofnonreproductivebodytissues(11).179
Thetwodominantbioactiveandrogenscirculatinginmaturemammals,includinghumans ‐‐testosterone180
anditsmorepotentmetabolite,dihydrotestosterone(DHT)‐‐accountforthedevelopmentandmaintenance181
ofallandrogendependentcharacteristics,andtheircirculatinglevelsinmenandnonpregnantwomenarise182
fromsteroidssynthesizeddenovointhetestes,ovaryoradrenals(12).183
Thesexuallyundifferentiatedgonadsintheembryodevelopintoeitherovariesortestesaccordingto184
whetheraychromosome(oratleastthesrygene)ispresent.Afterbirthanduntilpubertycommences,185
circulatingtestosteroneconcentrationsareessentiallythesameinboysandgirls,otherthanbrieflyinthe186
neonatalperiodofboyswhenhigherlevelsprevail.Theonsetofmalepuberty,abraindrivenprocess187
triggeredbyastillmysterioushypothalamicorhighercerebralmechanism(13),initiatesthehormonal188
cascadeofpuberty.Inmalesthisleadstoenhancedpituitaryluteinizinghormone(LH)secretionthat189
stimulatesthe500millionLeydigcellsinthetestestosecrete310mg(mean7mg)oftestosteronedaily(4,190
6,7,14,15).Thiscreatesaveryhighlocalconcentrationoftestosteronewithinthetestisaswellasasteep191
downhillconcentrationgradientintothebloodstreamthatmaintainscirculatingtestosteronelevelsatadult192
malelevels,whicharetightlyregulatedbystrongnegativehypothalamicfeedbackofcirculating193
testosterone.However,intheabsenceoftestesthesemechanismsdonotoccurinfemales.Ingirls,serum194
testosteroneincreasesduringpuberty(16),peakingatage2025yearsbeforedeclininggraduallywithage(17,195
18)butitremainslessthan2nmol/Latallages,asdeterminedbyareliablemethod(seebelow).Inadult196
women,circulatingtestosteroneisderivedfromthreeroughlyequalsourcesdirectsecretionfromtheadrenal197
glandortheovaryaswellasindirectlyfromextraglandularconversion(inliver,kidney,muscle,fat,skin)from198
testosteroneprecursorssecretedbytheadrenalandovary.However,incombinationthesedifferentsources199
produceabout0.25mgoftestosteronedailysothatthroughoutlifewomenmaintaincirculatingtestosterone200
levelsoflessthan2nmol/L.Circulatingtestosteroneconcentrationsinwomenaresubjecttolittledynamic201
physiologicalregulation.Asaresult,circulatingtestosteroneconcentrationsinhealthypremenopausal202
womenarestable(nonfluctuating)andnotsubjecttostrongnegativefeedbackbyexogenoustestosterone203
likemen.Eventhesmallrise(50%)atthetimeofthemidcycleLHsurgetriggeringovulation(19),remains204
withinthephysiologicalrangeforpremenopausalfemales.Insummary,onlywhencirculatingtestosterone205
concentrationsinmaleadolescentsrisesabovethecirculatingprepubertalconcentrationsdoesthe206
virilisationcharacteristicofmencommence,progressandremainthroughoutadultlifeatleastuntiloldage207
(18).208
209
3.2Maleandfemalereferencerangesforcirculatingtestosterone210
211
Areliablethresholdforcirculatingtestosteronemustbesetusingmeasurementbythereferencemethodof212
liquid(orgas)chromatographymassspectrometry(LCMS)ratherthanusingoneofthevariousavailable213
commercialtestosteroneimmunoassays.Thenecessaryrelianceonsteroidmassspectrometryforclinical214
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applicationsinendocrinology,reproductivemedicineandsportsmedicineiswidelyrecognized.Ithasbeen215
standardfordecadesinantidopingscience(20)andthegrowingconsensusisthatitisrequiredforhigh216
qualityclinicalresearchandpracticerecognizedbycognateprofessionalsocieties(21,22)andeditorialsin217
leadingclinicalendocrinology(23)andreproductivemedicine(24)journals.Theinherentlylimitedspecificity218
oftestosteroneimmunoassaysarisesfromantibodycrossreactivitywithstructurallyrelatedsteroids(suchas219
precursorsandmetabolites)otherthantheintendedtarget.Asaresult,allsteroidimmunoassaysincluding220
fortestosteronedisplaymethodspecificbiaswhereby,forexample,thelowerlimitofatestosterone221
referencerangeinhealthyyoungmenvariesfrom7.3to12.6nmol/Laccordingtotheimmunoassayused,so222
thatnoconsensusdefinitionofalowerlimitcouldbeobtainedindependentofthecommercialimmunoassay223
methodused(25).Further,testosteroneimmunoassaysareoptimizedforcirculatinglevelsinmenbutdisplay224
increasinginaccuracyatthelower,byanorderofmagnitude,circulatingtestosteroneconcentrationsin225
womenorchildren.Incontrasttoimmunoassays,LCMSbasedmethodsarehighlyspecificanddonot226
dependonproprietaryantibodies.UsingLCMSbasedmeasurements,methodspecificbiascanbeavoided227
andafixedconsensuslowerreferencelimitdefined(seetable1).Hence,fortheprecisionrequiredin228
sportsmedicine,whetherforeligibilitycriteriaorantidopingapplications,testosteroneinserummustbe229
measuredbyLCMSmethods.230
231
Priortopuberty,levelsofcirculatingtestosteroneasdeterminedbyLCMSarethesameinboysandgirls232
(16)aswellasremaininglowerthan2nmol/Linwomenofallages.However,fromtheonsetofmale233
pubertythetestessecrete20timesmoretestosteroneresultingincirculatingtestosteronelevelsthatare234
15timesgreaterinhealthyyoungmenthanagesimilarwomen.UsingLCMSmeasurement,circulating235
testosteroneinadultshasastrikingly,nonoverlappingbimodaldistributionwithwideandcomplete236
separationbetweenmenandwomen.Table1summarisesdatafromappropriatereportedstudiesusing237
MSbasedmethodstomeasureserumtestosteroneinhealthymenandwomen.Basedonanumber238
weightedpoolingwithconventional95%twosidedconfidencelimitsoftheeightavailablestudiesusingLC239
MSmeasurementsofserumtestosterone,thelimitsofthereferencerangeforhealthyyoungmen(18to240
40years)is7.7nmol/Lto29.4nmol/L.Similarly,summarisingthenineavailablestudiesforhealthy241
menstruatingwomenunder40years,the95%(twosided)referencerangeis0to1.7nmol/L.These242
referencelimitsneglectfactorssuchasoralcontraceptiveuse(26,27),menstrualphase(19),SHBG(28,243
29),overweight(30,31),fastingandsmoking(32),aswellasdiet(31)andphysicalactivity(33,34)in244
womenandmen,allofwhichhavesmalleffectsoncirculatingtestosteronebutwithoutmaterially245
influencingthedivergencebetweenthenonoverlappingbimodaldistributionofmaleandfemale246
referencerangesofcirculatingtestosterone.247
248
Increatingathresholdforeligibilityforfemaleeventsitisalsonecessarytomakeallowancefor249
hyperandrogenicwomenincludingwomenwithpolycysticovarysyndrome(PCOS)andnonclassical250
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adrenalhyperplasia.PCOSisarelativelycommondisorderamongwomenofreproductiveageswitha251
prevalenceof610%,dependingonthediagnosticcriteriaused(35),inwhichmildhyperandrogenismisa252
keyclinicalfeatureandhashigherthanexpectedprevalenceamongelitefemaleathletes(26,3638).Non253
classicaladrenalhyperplasiaisamilderandlater(adult)onsetvariantofclassicalcongenitaladrenal254
hyperplasia(39)withamuchhigherbutstillrarepopulationprevalence(1:1000vs1:16,000fortheclassical255
variant(40).Table2summarisesclinicalstudies(n=16,≥40women)reportingserumtestosterone256
concentrationsmeasuredbyLCMSinsamplesfromwomenwithPCOS.Thepooleddatarevealsthatthe257
upperlimitofserumtestosteroneinwomenwithPCOSis3.1nmol/L(95%confidenceinterval,onesided)258
or4.8nmol/L(usinga99.99%confidenceinterval,onesided)(table3).Henceaconservativethresholdfor259
circulatingtestosteroneof5nmol/LmeasuredbyLCMSwouldidentifyfewerthan1:10,000womenwith260
PCOSasfalsepositives,basedoncirculatingtestosteronemeasurementalone.Circulatingtestosterone261
higherthanthisthresholdislikelytobeduetotestosteronesecretingadrenalorovariantumors,262
intersex/DSD,badlycontrolledornoncompliantM2Ftransgenderathletesortestosteronedoping.263
264
3.3Thephysiologicaleffectsoftestosteronedependonthecirculatingtestosterone,notitssource265
(endogenousorexogenous)266
Testosterone,whetherofnaturalendogenousormanufacturedexogenoussource,hasanidenticalchemical267
structureandbiologicaleffects,asidefromminordifferencesinisotopiccompositionwhicharebiologically268
insignificant.Regardlessofitssource,atequivalentdosesandcirculatinglevels,exogenoustestosterone269
exertsthesamebiologicalandclinicaleffectsoneveryknownandrogenresponsivetissueororgan,apart270
fromeffectsonspermatogenesis,whichasdiscussedbelowisonlyamatterofdegree.Consequently,271
exogenoustestosteroneisafullyeffectivesubstituteforendogenoustestosteroneintherapeuticuse,272
counteringtheeffectsoftestosteronedeficiencyduetohypogonadism(reproductivesystemdisorders).Any273
purporteddifferencesbetweenendogenousandexogenoustestosteroneare,likethedifferencesbetween274
menandwomen,duetocorrespondingdifferencesintheendogenousproductionrateorexogenousdose.275
Suchdifferencesineffectiveexposureleadtocorrespondingdifferencesincirculatingtestosteronelevels276
anditseffectsaccordingtothedoseresponsecurvesfortestosterone.277
Likeallhormonesanddrugs,overtheireffectiverangeofbiologicalactivitythedoseresponserelationship278
fortestosteroneisusuallyasigmoidalcurvewithlowerandupperplateausjoinedbyamonotonicallyrising279
middleregion,whichmaybelinearinthenaturalscalebutmoreoftenloglinear(linearonthelogorsimilar280
transformedscale).Inthemiddleportionofthetypicalsigmoidaldoseresponsecurveforthesameincrease281
intestosteronedose(orconcentration),theresponsewouldbeincreasedinsimpleproportional(ielinear)282
butmoreoftenonalogarithmicscale.Bycontrast,atthelowerandupperplateausofdoseorconcentrations,283
changesintestosteroneexposuremayevokeminimalornoresponseontheendpoint.Forexample,in284
womenofanyagecirculatingtestosteroneconcentrationsarealongthelowerplateauofthedoseresponse285
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curve,sothatincreasesincirculatingtestosteroneconcentrationswithinthatlowerplateaumayhave286
minimalornoeffect.InfemaleathleteswiththemildhyperandrogenismofPCOS,higherperformancehas287
beenshown(38)withtheirmusclemassandpowerperformancecorrelatingwithandrogenlevels(26).288
However,beyondtheseeffectswhereendogenoustestosteroneconcentrationsareinthehighnormaladult289
femalerange,itisonlywhentheincreasesincirculatingtestosteroneconcentrationssubstantiallyand290
consistentlyexceedthoseprevailinginchildhood(<2nmol/L)andamongwomenincludingthosewithPCOS291
(<5nmol/L)thattheeffectswouldreplicaterisingtestosteroneconcentrationsofboy’sinmid‐ tolate292
puberty(typically>8nmol/l)whichcausethemasculinizingeffectsofincreasedmuscle,boneand293
hemoglobincharacteristicsofmen.Asshownabove,thecirculatingtestosteroneofmostwomennever294
reachesconsistentlyabove5nmol/L,alevelwhichboysmustsustainforsometimetoexhibitthe295
masculinizingeffectsofmalepuberty.296
Secondarily,theeffectsoftestosteronearemodulatedinaformoffinetuningbythepatternsofexposure,297
suchaswhetherthecirculatingtestosteroneisdeliveredintheunphysiologicalsteadystateformat(e.g.298
quasisteadystatedeliverybyimplantortransdermalproducts)orbythepeakandtroughdeliveryof299
injectionsasopposedtothenaturalstateofendogenousfluctuationsinserumtestosteronearoundthe300
averageadultmalelevels.However,theselatterpatterneffectsaresubtleandthedominanteffectremains301
thatofdoseandaveragetestosteroneconcentrationsinblood,howevertheyarise.Furthermore,thereis302
evidencethattheandrogensensitivityofresponsivetissuesdifferandmaybeoptimalatdifferentcirculating303
testosteroneconcentrations(41).304
Malesexualfunctionismaintainedbyendogenoustestosteroneatadultmalecirculatingconcentrations.305
Theseeffectscanbereplicatedbyexogenoustestosteroneifandonlyifitachievescomparablecirculating306
testosteroneconcentrations.Forexample,inawellcontrolledprospectivestudyofoldermenwithprostate307
cancer(42),androgendeprivationachievingcastratelevelsofcirculatingtestosteronesustainedover12308
monthsmarkedlysuppressedsexualdesireandfunction,whereasthoseeffectsdidnotoccurinagematched309
menhavingnonhormonaltreatmentforprostatecancerorthosewithoutprostatecancer.Inhealthy310
youngermenwhoseendogenoustestosteroneisfullysuppressed,theirsexualfunctioncompletelyrecovers311
whencirculatingtestosteronewasrestoredtothephysiologicalmalerangebyadministrationofexogenous312
testosterone(43).Similareffectswerealsoobservedinhealthy,middleagedmeninwhommalesexual313
functionwasfullymaintained(comparedwithplacebo)during2yearsoftreatmentwithanexogenous314
androgen(DHT)despiteitcausingsustained,completesuppressionofendogenoustestosterone(44).This315
furthersupportsthekeyinterpretationthatthebiologicaleffectsofexogenousorendogenoustestosterone316
arethesameatcomparablecirculatinglevels.317
318
Clinically,exogenoustestosteronereplicatesfullyalleffectsofendogenoustestosteroneonevery319
reproductiveandnonreproductiveorganortissue,withthesoleexceptionofthetestis.Spermproduction320
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inthetestisrequiresaveryhighconcentrationoftestosterone(typically100timesgreaterthaninthegeneral321
bloodstream),whichisproducedinnatureonlybytheactionofthepituitaryhormoneLH.LHstimulatesthe322
Leydigcellsintheinterstitialspaceofthetestisbetweenseminiferoustubulestoproducehighintratesticular323
concentrationsoftestosterone,whicharenecessaryandsufficienttoinitiateandmaintainspermproduction324
intheadjacentseminiferoustubules.Thishighconcentrationoftestosteronealsoprovidesadownhill325
gradienttosupplytherestofthebody,wherecirculatingtestosteroneactsonandrogenresponsivetissues326
tomaintainmasculinepatternsofandrogenization.Whenexogenoustestosterone(oranyotherandrogen)327
isadministeredtomen,pituitaryLHissuppressedbynegativefeedbackandthespermproductionhaltsfor328
aslongasexogenoustestosteroneorandrogenexposurecontinues,afterwhichitrecovers(45).However,329
eventhereductioninspermatogenesisandtestissizewhenmenaretreatedwithexogenoustestosteroneis330
onlyamatterofdegree.Itiswellestablishedinrodents(46,47)thatspermatogenesisisinducedby331
exogenoustestosteroneifthetestosteroneconcentrationsinthetestisarehighenoughtoreplicatewhat332
occursnaturallyviaLHstimulation(48).However,directreplicationthathighdosetestosteronealsoinitiates333
andmaintainsspermatogenesisinhumansisnotfeasibleasthesetestosteronedosesare10100times334
higherthancouldbesafelygiventohumans.Nevertheless,confirmatoryevidenceinhumansisavailable335
fromrarecasesofmenwithanactivatingmutationoftheCG/LHreceptor(49,50).Thismutationcauses336
autonomoustesticulartestosteronesecretionleadingtoprecociouspubertyarisingfromthepremature337
adultmalecirculatingtestosteroneconcentrationswhichleadtocompletesuppressionofcirculating338
gonadotropin(LH,FSH)secretion.Inthisillustrativecasethetestiswasexposedtononphysiologicallyhigh339
testosteroneconcentrations(butwithoutanygonadotropinstimulation)whichinducedspermproduction340
andallowedfornaturalpaternity(49).Thisindicatesthatevenforspermatogenesis,exogenoustestosterone341
canreplicateallbiologicaleffectsofendogenoustestosteroneinaccordancewiththerelevantdoseresponse342
characteristics.343
Themostrealisticviewisthatincreasingcirculatingtestosteronefromthechildhoodorfemalerangetothe344
adultmalerangewillhavethesamephysiologicaleffectswhetherthesourceoftheadditionaltestosterone345
isendogenousorexogenous.Thisisstronglysupportedbywellestablishedknowledgeabouttherelationship346
ofcirculatingtestosteroneconcentrationswiththetimingandmanifestationsofmalepuberty.The347
characteristicclinicalfeaturesofmasculinisation(musclegrowth,increasedheight,increasedhemoglobin,348
bodyhairdistribution,voicechangeetc)appearonlyifandwhencirculatingtestosteroneconcentrationsrise349
intotherangeofmalesatmidpubertywhicharehigherthaninwomenatanyageevenaftertherisein350
circulatingtestosteroneinfemalepuberty.Ifandonlyifthepubertalriseincirculatingtestosteronefails,351
themalesaffectedareclinicallyconsideredhypogonadal.Suchafailureofmalepubertymayoccurfor352
geneticreasons(arisingfrommutationsthatinactivateanyofthecascadeofproteinswhoseactivityiscritical353
inthehypothalamustotriggermalepuberty)orasaresultofacquiredconditions,causedbypathological354
disordersofthehypothalamusorpituitaryorfunctionaldefectsarisingfromseveredeficitsofenergyor355
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nutrition(egextremeovertraining,undernutrition),thelatterbeingcomparablewithhypothalamic356
amenorrheaoranorexianervosainfemaleathletes/balletdancers.Ifmalepubertyfails,testosterone357
replacementtherapyisfullyeffectiveinreplicatingtheallthedistinctivemasculinefeaturesapartfrom358
spermatogenesis.359
360
361
3.4ElevatedcirculatingtestosteroneconcentrationcausedbyDSDs362
RaregeneticintersexconditionsknownasDSDscanleadtomarkedlyincreasedcirculatingtestosteronein363
womenand,whencoupledwithambiguousgenitaliaatbirth,appearingasundervirilizedmale,orvirilized364
females.Thiscancauseathleteswhowereraisedandidentifyaswomentohavecirculatingtestosterone365
levelscomparablewithmenandmuchexceedingthatofnonDSD(andnondoped)women,includingthose366
withPCOS.Keycongenitaldisordersinthiscategoryare46XYDSDsnamely5αreductasedeficiency(51),367
17β‐hydroxysteroiddehydrogenasetype3deficiency(52),androgeninsensitivity(53,54)aswellas368
congenitaladrenalhyperplasia(55),whichisa46XXDSD.Thereisevidencethatthefirstthreeconditions,369
componentsof46XYDSDs,are140timesmoreprevalentamongelitefemaleathletesthanexpectedinthe370
generalpopulation(56).371
Genetic5αreductasedeficiencyisduetoaninactivatingmutationinthe5αreductasetypeIIenzyme(51).372
ThisleadstoadeficitofDHTduringfetallifewhenDHTisrequiredforconvertingthesexundifferentiated373
embryonicandfetaltissuetoformthesexdifferentiatedmasculineformexternalgenitalia.Althoughgenetic374
males(46XY)with5αreductasedeficiencywilldeveloptestes,theyusuallyremainundescendedandlabial375
fusiontoformascrotumandphallicgrowthdoesnotoccur.Henceatbirththeexternalgenitaliamayappear376
feminine,leadingtoafemaleassignednatalsex.Thus,individualswith5α reductasedeficiencymayhave377
malechromosomalsex(46XY),gonadalsex(testes),andhormonalsex(adultmaletestosterone378
concentrations),butsuchseverelyundervirilizedgenitaliathataffectedindividualsmayberaisedfrombirth379
asfemalesratherthanasundervirilizedmales.However,fromtheonsetofmalepuberty,testicularLeydig380
cellsstartproducinglargeamountsoftestosterone,andthesteepriseincirculatingtestosteronetoadult381
malelevels(withthepermissiveroleof5αreductaseactivity)leadstomasculinevirilisation,includingmale382
patternsofmuscleandbonegrowth,hemoglobinlevelsandothermasculinebodyhabitusfeatures(hair383
growthpattern,voicechange),aswellasphallicgrowth(56).Suchchangesofmalepubertypromptaround384
halfaffectedindividualswhohadfemalesexassignedatbirthanddevelopedasgirlspriortopubertytoadopt385
amalegenderidentityandrole(57).Spermareformedinthetestessothat,usinginvitrofertilization,these386
individualsmayfatherchildren(58).387
Seventeenβhydroxysteroiddehydrogenasetype3deficiency(52)hasasimilarnaturalhistoryto5α388
reductasedeficiency.Thisdisorderisduetoinactivatingmutationsinasteroidogenicenzymeexpressedonly389
inthetestisandwhichisessentialfortestosteroneformationinthefetus.Intheabsenceofafunctional390
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enzyme,thetestismakeslittletestosteronebutinsteadsecreteslargeamountsofandrostenedione,the391
steroidimmediatelypriortotheenzymaticblock.Inthecirculation,theexcessofandrostenedioneis392
convertedtotestosterone(mainlybytheenzymeAKR1C3(12)).Althoughthecirculatingtestosteroneisthen393
convertedtocirculatingDHT,insufficientDHTisformedlocallywithintheurogenitalsinustovirilisegenitalia394
atbirth.Thiscausesthesamesevereundervirilisationoftheexternalgenitaliaofgeneticallymale395
individuals,leadingtoambiguousgenitaliaatbirthdespitemalechromosomal,gonadalandhormonalsex.396
Whenpubertyarrives,thetestesstartproducingtheadultmaletestosteroneoutputthisleadstomarked397
virilisationandsubsequentassumptionofamalegenderidentitybysomeaffectedindividuals,conflicting398
withafemaleassignednatalsexandchildhoodupbringing.399
Androgeninsensitivity,whicharisesfrommutationintheandrogenreceptor(AR),posesdifferentbut400
complexchallengesforeligibilityforfemaleathleticevents.AstheARislocatedontheXchromosome,401
geneticmales(46XY)arehemizygous,sothataninactivatingmutationintheARcanbepartiallyorfully402
insensitivetoandrogenaction.Affectedindividualshavemaleinternalgenitalia(testesintheinguinalcanal403
orabdomenwithWolffianducts)andconsequentlyadultmalecirculatingtestosteroneconcentrationsafter404
puberty.Thesenonlethalmutationshaveawidespectrumoffunctionaleffects,rangingfromfullresistance405
toallandrogenactionincompleteandrogeninsensitivitysyndrome(CAIS)whereindividualshaveafull406
femalephenotypewithnormalfemaleexternalgenitalia,topartialandrogeninsensitivitysyndrome(PAIS)407
wheresomeandrogenactionisstillexertedleadingtovariousdegreesofambiguousgenitalia,ortomild408
androgeninsensitivitywhichproducesaverymild,undervirilisedmalephenotype(normalmalegenitaland409
somaticdevelopmentbutwithlittlebodyhairandnomalepatternbalding)(53).Testosterone(and410
dihydrotestosterone)havenoconsistenteffectofinducingnormalnitrogenretention(anabolic)responses411
inpatientswithCAIS(5962)althoughsomereducedandrogenresponsivenessisretainedbypatientswith412
PAIS(60,6366).AthleteswithCAIScanfairlycompeteasfemalesbecausethecirculatingtestosterone,413
althoughatadultmalelevels,hasnophysiologicaleffectsothat,intermsofandrogenactionandtheensuing414
physicalsomaticadvantagesofmalesex,affectedindividualsareindistinguishablefromfemalesandgainno415
benefitsofthesexdifferencearisingfromunimpededtestosteroneaction.Amorecomplexissueariseswith416
athleteshavingPAISreflectingthedegreeofincompleteimpairmentofARfunction.Residualandrogen417
actioninsuchARmutationsishardertocharacterisequantitativelyasthereisnostandardized,objectivein418
vitrotesttoquantifyARfunctionality.Hence,althoughindividualswithPAISmayhaveadultmalecirculating419
testosteroneconcentrationsbutvariableandrogensensitivity,atpresentthisrequiresacasebycase420
evaluation,primarilybasedonthedegreeofvirilisation.Thecurrentbestavailableclinicalapproachto421
determiningthefunctionalimpact(degreeoffunctionality/sensitivity)ofanARmutationisbasedonthe422
degreeofsomatic,primarilygenital,virilisationassessedaccordingtotheQuigleyclassificationofgradeof423
androgensensitivity(67).424
Congenitaladrenalhyperplasia(CAH)isarelativelycommondefectinadrenalsteroidogenesisinthe425
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enzymaticpathwayleadingtosynthesisofcortisol,aldosteroneandsexsteroidprecursors.Thedisease426
variesinseverityfromlifethreatening(adrenalfailure)tomild(hirsutismandmenstrualirregularity),oreven427
asymptomaticandundiagnosed.ThemostcommonmutationscausingCAHoccurinthe21hydroxylase428
enzyme,accountingfor95%ofcases(55).Thedefectleadstoabottleneck,creatingamajorbackingupof429
precursorsteroidswhichthenoverflowintoothersteroidpathways,leadingtodiagnostichighlevelsof17430
hydroxyprogesteroneand,infemalepatients,excessivecirculatingtestosteroneorotheradrenalsource431
androgenprecursors(egandrostenedione,DHEA)whichmaybeconvertedtotestosteroneintissues.A432
commonclinicalproblemwithmanagementofCAHisthatglucocorticoid/mineralocorticoidtreatmentisnot433
alwaysfullyeffectivepartlyduetovariablecompliance,whichmayleavehighcirculatingtestosterone,434
includingwellintoorevenabovethenormalmalerange(68).Itisunlikelythatmildnonclassicalcongenital435
adrenalhyperplasiaisamajorcontributortothemildhyperandrogenismprevalentamongelitefemale436
athletes.TheprevalenceofPCOS(616%)isabout100timeshigherthanmildnonclassicalcongenitaladrenal437
hyperplasia(0.1%,(40))whileadisproportionatelyhighnumberofelitefemaleathletes(especiallyinpower438
sports)havePCOS(36).Inonestudyofhyperandrogenicfemaleathletes,evenmildNCAHwasruledoutby439
normal17hydroxyprogesterone(26)andinanother(38)reportedserumandrostenedioneandcortisoldid440
notdifferfromcontrols,rulingoutsignificantcongenitaladrenalhyperplasia..441
442
4.Sexdifferenceinmuscle,hemoglobin,boneandathleticperformancerelatingtoadult443
circulatingtestosteroneconcentrations444
445
Followingpuberty,testosteroneproductionincreases(16)butremainsbelow2nmol/Linwomenwhereas446
inmentestosteroneproductionincreases20fold(from0.3mgadayto7mgaday)leadingtoa15fold447
highercirculatingtestosteroneconcentrations(15vs1nmol/L).Thegreatermagnitudeofsexdifferencein448
testosteroneproduction(20fold)comparedwithcirculatinglevels(15fold)isduetowomen’shigher449
circulatingSHBG,whichretardstestosteroneclearancecreatingaslowercirculatinghalftimeof450
testosterone.Thisorderofmagnitudedifferenceincirculatingtestosteroneconcentrationsisthekeyfactor451
tomen’ssuperiorathleticperformanceduetoandrogeneffectsprincipallyonmuscle,boneandhemoglobin.452
453
4.1Muscle454
4.1.1Biology:455
Ithasbeenknownsinceancienttimesthatcastrationinfluencesmusclefunction.Modernknowledgeofthe456
molecularandcellularbasisforandrogeneffectsonskeletalmuscleinvolveseffectsduetoandrogen457
(testosterone,DHT)bindingtotheandrogenreceptorwhichthenreleaseschaperoneproteins,dimerizes458
andtranslocatesintothenucleustobindtoandrogenresponseelementsinthepromoterDNAofandrogen459
sensitivegenes.Thisleadstoincreasesin(a)musclefibrenumbersandsize,(b)musclesatellitecellnumbers,460
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(c)numbersofmyonuclei,and(d)sizeofmotorneurons(69).Additionallythereisexperimentalevidence461
thattestosteroneincreasesskeletalmusclemyostatinexpression(70),mitochondrialbiogenesis(71),462
myoglobinexpression(72)andinsulinlikegrowthfactor(IGFI)content(73)whichmayaugmentenergetic463
andpowergenerationofskeletalmuscularactivity.464
Customizedgeneticmousemodelscanprovideuniquephysiologicalinsightintargetingspecificmoleculesor465
theirreceptorstoprovideexperimentalinsightintomammalianphysiologywhichisunobtainablebyhuman466
experimentation.Thetightevolutionaryconservationofthemammalianreproductivesystemexplainswhy467
geneticmousemodelshaveprovidedconsistent,highfidelityreplicationofthehumanreproductivesystem468
(74,75).Geneticmales(46XY)withandrogeninsensitivitydisplayingsimilarfeaturesoccurthrough469
spontaneouslyoccurringinactivatingARmutationsinallmammalianspeciesstudiedincludinghuman,where470
theyareknownaswomenwithCAIS.Theconverse,geneticfemales(46XX)resistanttoallandrogenaction,471
cannotoccurnaturallyinhumansorothermammals.Thisisbecausefullyandrogenresistantfemalesmust472
havebothXchromosomescarryinganinactivatedAR.InturnthisrequiresacquiringoneXchromosomefrom473
theirfather.However,thepotentialfathersaresterileashemizygousmalesbearingasinglecopyanX474
chromosomewithaninactiveARproducenosperm,asafunctionalARisbiologicallyindispensablefor475
makingsperminanymammal.However,androgenresistantfemalescanbebredbygeneticengineering476
usingtheCreLoxsystem(76).Animportantfindingfromsuchstudiesisthatandrogenresistantfemalemice477
haveessentiallythesamemusclemassandfunctioncomparedwithwildtypeandrogensensitivefemales478
bearingnormalARwhereasandrogenresistantmalemicehavesmallerandweakermusclemassand479
functionthanwildtypemalesbutarecomparableinsteadwiththemuscleofwildtypefemales(77).This480
indicatesthatandrogenaction,representedbycirculatingtestosterone,isthekeydeterminantofthehigher481
musclemassandstrengthcharacteristicofmalescomparedwithfemales.Furthermore,endogenous482
circulatingtestosteronehasminimaleffectsonskeletalmusclemassandstrengthinfemalemice.Although483
theseexperimentscannotbereplicatedinhumans,theirkeyinsightisthatthehighercirculatingtestosterone484
inmalesisthedeterminantofthemale’sgreatermusclemassandfunctioncomparedwithfemales.485
Nevertheless,thereisalsoevidencethathyperandrogenicwomen,mostlywithPCOS,haveincreasedmuscle486
massandstrengththatcorrelateswithmildlyincreasedcirculatingtestosteroneinthehighnormalfemale487
range(26,38).488
489
4.1.2Observationaldata:490
Thereisaclearsexdifferenceinbothmusclemassandstrength(7880)evenadjustingforsexdifferencesin491
heightandweight(80,81).Onaverage,womenhave5060%ofmen'supperarmmusclecrosssectional492
area(CSA)and6570%ofmen'sthighmuscleCSA;andwomenhave5060%ofmen'supperlimbstrength493
and6080%ofmen'slegstrength(82).Youngmenhaveonaverageaskeletalmusclemassofover12kg494
greaterthanagematchedwomenatanygivenbodyweight(80,81).Whilenumerousgenesand495
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environmentalfactors(includinggenetics,physicalactivityanddiet)maycontributetomusclemass,the496
majorcauseofthesexdifferenceinmusclemassandstrengthisthesexdifferenceincirculating497
testosterone.498
Agegradecompetitivesportsrecordsshowminimalornofemaledisadvantagepriortopuberty,whereas499
fromtheageofmalepubertyonwardsthereisastrongandongoingmaleadvantage.Correspondingtothe500
endogenouscirculatingtestosteroneincreasinginmalesafterpubertyto1520nmol/L(sharplydiverging501
fromthecirculatinglevelsthatremain<2nmol/Linfemales),maleathleticperformancesgofrombeingequal502
onaveragetothoseofagematchedfemalesto1012%betterinrunningandswimmingevents,and20%503
betterinjumpingevents(8)(figure1).CorroborativefindingsareprovidedbyaNorwegianstudythat504
examinedperformanceofadolescentsincertainathleticeventsbutwithoutreferencetocontemporaneous505
circulatingtestosteroneconcentrations(83).Thestrikingpostpubertalincreaseinmalecirculating506
testosteroneprovidesamajor,ongoing,cumulativeanddurableadvantageinsportingcontestsbycreating507
atleastgreatermusclemassandstrengthsuchthatthesesexdifferencesrenderwomenunabletocompete508
effectivelyagainstmen,especially(butnotonly)inpowersports.509
Thesefindingsaresupportedbystudiesofnonathleticwomenshowingthatmusclemassisincreasedin510
proportiontocirculatingtestosteroneinwomenwithmildlyelevatedtestosteronelevelsduetoPCOS(84,511
85),aconditionwhichismoreprevalentamongelitefemaleathleteswhoexhibitthesefeatures(26,36,38),512
oftenundiagnosed(37),butwhichmayprovideanergogenicadvantage(38),consistentwiththegraded513
effectsofcirculatingtestosteroneonexplosiveperformanceinmenandwomen(86).514
Studiesofelitefemaleathletesfurthercorroboratethesefindings.Onestudydemonstratesdoseresponse515
effectsofbetterperformanceinsome(400m,400mhurdles,800mrunning,hammerthrow,polevault)but516
notallathleticeventscorrelatedwithsignificantlyhigherendogenoustestosteroneinfemale,butnotmale,517
athletes.Evenwithinthelowcirculatingtestosteronelevelsprevailingwithinthenormalfemalerange,in518
theseeventstherewasasignificantadvantageof1.8%to4.5%amongthoseinthehighestcomparedwith519
thelowesttertileofendogenoustestosterone(27).Afurtherstudyofelitefemaleathletescorroboratesand520
extendstheseobservationsinthatendogenousandrogensareassociatedwithamoreanabolicbody521
compositionaswellasenhancedmuscularperformance(26).Inthisstudy106SwedishOlympicfemale522
athleteswerecomparedwith117age‐andweight(BMI)matchedsedentarycontrolwomenfortheirmuscle523
andbonemass(bydualenergyXrayabsorptiometry,DEXA),theirmuscularstrength(squatand524
countermovementjumps),andtestosteroneandDHT,aswellasandrogenprecursors(DHEA,525
androstenedione)andurinaryandrogenglucuronidemetabolites(androsterone,etiocholanolone,3and17526
3α‐diols)measuredbyliquidchromatographymassspectrometry(26).Theathletesdisplayedhighermuscle527
(andbone)massthanthesedentarycontrolwomen,withstrengthtestscorrelatingstronglywithmuscle528
masswhetherintotalorjustinthelegs.Inturn,musclemassandstrengthwerecorrelatedwithandrogens529
andandrogenprecursors.Consideringthatsuchstudiesmaybeconfoundedbyfactorssuchasmenstrual530
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phaseanddysfunction,andheterogeneoussportsdisciplines,whichweakenthepowerofthestudy,these531
findingscanberegardedasquiterobust.532
4.1.3Interventionaldata:533
Doseresponsestudiesshowthat,inmenwhoseendogenoustestosteroneisfullysuppressed,addback534
administrationofincreasingdosesoftestosteronethatproducegradedincreasesincirculatingtestosterone,535
causesadosedependent(whetherexpressedaccordingtotestosteronedoseorcirculatinglevels)increase536
inmusclemass(measuredasleanbodymass)andstrength(41,87).Takentogether,thesestudiesprovethat537
testosteronedosesleadingtocirculatingconcentrationsfromwellbelowtowellabovethenormalmale538
rangehaveunequivocaldosedependenteffectsonmusclemassandstrength.Thesedatastronglyand539
consistentlysuggestthatthesexdifferenceinleanbodymass(muscle)islargely,ifnotexclusively,dueto540
thedifferencesincirculatingtestosteronebetweenmenandwomen.Thesefindingshavestrongimplications541
forpowerdependentsportperformanceandlargelyexplainthepotentefficacyofandrogendopinginsport.542
Thekeyfindingsprovidingconclusiveevidencethattestosteronehasprominentdoseresponseeffectsin543
menarereportedinstudiesbyBhasinetalthatprovedamonotonicdoseresponse,extendingfromsub‐to544
supraphysiologicalrangeformenfortestosteroneeffectsonmusclemass,sizeandstrengthinhealthy545
youngmen,findingsthathavebeenreplicatedandconfirmedbyanindependentgroup(41).Bothsetsof546
studiesusedacommondesignoffullysuppressingallendogenoustestosterone(tocastratelevels)forthe547
fulldurationoftheexperimentbyadministeringaGnRHanalog.IntheBhasinstudies,participantswerethen548
randomizedtofivegroupswhoreceivedweeklyinjectionsof25mg,50mg,125mg,300mgor600mgof549
testosteroneenanthatefor20weeks.Ineffectthiswastwosub‐andtwosupraphysiologicaltestosterone550
doses.Inthesestudies,thelowesttestosteronedoseproducedameanserumtestosteroneof253ng/dl(8.8551
nmol/L)inyoungermenand176ng/dl(6.1nmol/L)inoldermen.Thestudiesshowedaconsistentdose552
responseformusclemassandstrengththatwasclearlyrelatedtotestosteronedoseandconsequentialblood553
testosteroneconcentrations(upperpanel,figure2).554
ThestudyofFinkelsteinetalinvolvedthesamedesignandinvolved400healthymenaged20to50yearsof555
agewhohadcompletesuppressionofendogenoustestosteroneforthe16weeksofthestudywith556
testosteroneaddedbackusingdailydosesof0,1.25g,2.5g,5gor10gofatopical1%testosteronegel(41).557
Thisagaincreatedagradeddoseresponsecurveforserumtestosteroneandformusclemassandstrength.558
Theinclusionofazero(placebo)dosealloweddifferentiationbetweenthezeroandlowesttestosterone559
dose.Theplacebo(zero)doseproducedaserumtestosteroneof0.7nmol/L,thetypicalmeanforcastrated560
men,childhood,andwomenofanyage.Meanwhilethelowesttestosteronedose(1.25ggelperday)561
producedaserumtestosteroneof6.9nmol/L,whichisequivalenttothatofamaleinearlytomidpuberty.562
Akeyfindingforthisreviewisthat,fromthisstudyofmen,theincreaseinserumtestosteronefrommean563
ofnormalfemaleconcentration(0.9nmol/L)tosupraphysiologicalfemaleconcentrations(6.9nmol/L)564
producedsignificantincreasesof2.3%fortotalbodylean(muscle)mass,3.0%forthighmusclearea,and565
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5.5%increaseinlegpressstrength(digitiseddatapoolingbothcohortsfromlowerpanel,figure2).566
Studiesoftheergogeniceffectsofsupraphysiologicalconcentrationsofcirculatingtestosteronerequire567
studiesadministeringgradeddosesofexogenoustestosteroneformonths.Duetoethicalconcerns568
regardingrisksofunwantedvirilisationandhormonedependentcancers,however,fewstudieshave569
administeredsupraphysiologicaltestosteronedosestohealthywomen.Onewelldesigned,randomized570
placebocontrolledstudyofpostmenopausalwomeninvestigatedtheeffectsofdifferenttestosteronedoses571
onmusclemassandperformanceandphysicalfunction(88).Sixtytwowomen(meanage53)allhada572
standardestrogenreplacementdoseadministeredduringa12weekruninperiod(toeliminateany573
hypotheticalconfoundingeffectsofestrogendeficiency),afterwhichtheywererandomizedtooneoffive574
groupsreceivingweeklyinjectionsoftestosteroneenanthate(doses:0,3mg,6.25mg,12.5mg,and25mg575
respectively)for24weeks.Theincreasingdosesoftestosteroneproducedanexpecteddoseresponsein576
serumtestosteroneconcentrations(byLCMS)withthehighesttestosteronedose(25mg/week)produced577
ameannadirconcentrationof7.3nmol/L.Thewomenwhosetestosteroneconcentrationswereincreased578
to7.3nmol/Lachievedsignificantincreasesinmusclemassandstrength(table4),rangingfrom4.4%for579
muscle(lean)masstobetween12%and26%formeasuresofmusclestrength(chestandlegpress,loaded580
stairclimb).Asmusclestrengthmeasurementiseffortdependent,theplacebocontrolleddesignofthe581
Huangstudysupportthefurtherinterpretationthatthehighestdoseoftestosteronealsohadprominent582
mentalmotivationaleffectsintheeffortdependenttestsofmusclestrength.Thesefindingsprovidesalient583
directevidenceoftheergogeniceffectsofhyperandrogenisminfemaleathletesconfirmingthatatleastup584
toaveragecirculatingtestosteroneconcentrationsof7.3nmol/L,womendisplayasimilardoseresponse585
relationshipasdomenforsupraphysiologicaltestosteronewithsignificantgainsinmusclemassandpower.586
587
Theseeffectsoftestosteroneadministrationoncirculatingtestosteroneconcentrationsinfemalesmaybe588
comparedwiththeeffectsinmalesfromtheFinkelsteinandBhasinstudies.Inmen,thelowesttestosterone589
dose(1.25g/day)increasedmeanserumtestosteroneto6.9nmol/Lequivalenttoearlytomidmalepuberty590
resultinginsignificantincreasesoftotalbodylean(muscle)mass(2.3%),thighmusclearea(3.0%),andleg591
pressstrength(5.5%)comparedwiththeplacebodosewhichresultedinaserumtestosteroneof0.7nmol/L.592
IntheHuangstudy(figure3),musclemassandstrengthinpostmenopausalwomendisplayedaflatresponse593
atthe3lowerdoses,whencirculatingtestosteroneconcentrationsremainbelow5nmol/L,anddisplayeda594
significantincreaseonlywhenthemeancirculatingtestosteroneconcentrationproducedbythehighest595
testosteronedosefirstincreasedcirculatingtestosteroneconcentrationsabove5nmol/L.Thispattern,flat596
atlowerdosesandrisingathighestdose,representsthelowerplateauandtheearliestrisingportion,597
respectively,ofthesigmoidaldoseresponsecurveoftestosteroneformuscle.598
DatacorroboratingtheHuangstudyresultscomesfromanotherwellcontrolledstudyinwhichpost599
menopausalwomenwhowereadministeredmethyltestosteronefollowingaruninperiodofestrogen600
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replacementdisplayedasignificantincreaseinlean(muscle)massaswellasupperandlowerlimbpower601
duringa16weekdoubleblind,parallelgroupstudy(89).602
Similarly,twoprospectivestudiesofthefirst12monthstreatmentoftransmen(F2Mtransgender)showsa603
consistentmajorincreaseinmusclemassandstrengthduetotestosteroneadministration.Inonestudy604
testosteronetreatmentof17transmenachievingadultmalecirculatingtestosteronelevels(mean31nmol/L)605
increasedmusclemassby19.2%(90)whereas,conversely,testosteronesuppression(usinganestrogen606
basedtreatmentregimen)in20transwomenreducedcirculatingtestosteronelevels