Traditionally,cognitive,motivational,andvolitionaldeterminantshavebeenusedtoexplainandpredicthealthbehaviorssuchasphysicalactivity.Recently,theroleofaffectininfluencingandregulatinghealthbehaviorsreceivedmoreattention.Affectsasinternalcuesmayautomaticallyactivateunconsciousprocessesofbehaviorregulation.Theaimofourstudywastoexaminetheassociationbetweenaffectandphysicalactivityindailylife.Inaddition,westudiedtheinfluenceofthehabitofbeingphysicallyactiveonthisrelationship.Anambulatoryassessmentstudyin89persons(33.7%male,25to65years,M=45.2,SD=8.1)wasconducted.Affectwasassessedintheafternoonon5weekdaysusingsmartphones.Physicalactivitywasmeasuredcontinuouslyobjectivelyusingaccelerometersandsubjectivelyusingsmartphonesintheevening.Habitstrengthwasassessedatthebeginningofthediaryperiod.Theoutcomeswereobjectivelyandsubjectivelymeasuredmoderate-to-vigorousphysicalactivity(MVPA)performedafterwork.MultilevelregressionmodelswereusedtoanalyzetheassociationbetweenaffectandafterworkMVPA.Inaddition,thecross-levelinteractionofhabitstrengthandaffectonafterworkMVPAwastested.Positiveaffectwaspositivelyrelatedtoobjectivelymeasuredandself-reportedafterworkMVPA:thegreaterthepositiveaffectthemoretimepersonssubsequentlyspentonMVPA.Aninverserelationshipwasfoundfornegativeaffect:thegreaterthenegativeaffectthelesstimepersonsspentonMVPA.Thecross-levelinteractioneffectwassignificantonlyforobjectivelymeasuredMVPA.Astronghabitseemstostrengthenboththepositiveinfluenceofpositiveaffectandthenegativeinfluenceofnegativeaffect.Theresultsofthisstudyconfirmpreviousresultsandindicatethataffectplaysanimportantrolefortheregulationofphysicalactivitybehavioridailylife.Theresultsforpositiveaffectwereconsistent.However,incontrasttopreviousreportsofnooraninverseassociation,negativeaffectdecreasedsubsequentMVPA.Theseinconsistenciesmaybe—inpart—explainedbythedifferentmeasurementsofaffectinourandotherstudies.Therefore,furtherresearchiswarrantedtogainmoreinsightintotheassociationbetweenaffectandphysicalactivity.