The effect of fitness level on cardiac autonomic regulation, IL-6,total antioxidant capacity, and muscle damage responses to a single bout of high-intensity interval training

Purpose：Theaimofthisstudywastoinvestigatetheinfluenceofthecardiorespiratoryfitnesslevelontheresponsetohigh-intensityintervaltraining（HIIT）withanindividuallyadjustedrunningspeedofthesamerelativeintensity.Theevaluationfocusedonacutecardiorespiratoryresponse,postexercisecardiacautonomicmodulation（heartratevariability（HRV））andbiochemicalmarkersofinflammation,oxidativestress,andmuscledamage.Methods：Thirtyparticipantsweredividedinto3subgroups：welltrained,moderatelytrained,anduntrained.Alltheparticipantsperformed30minHIITcomposedof6×2minintervalexercisewithwork-to-reliefratio=1andworkintensity100%ofindividualvelocityatmaximaloxygenconsumption（VO2max）.Acutecardiorespiratoryvariables,postexerciseHRV,lactate,interleukin-6（IL-6）,totalantioxidantcapacity（TAC）,creatinekinase,andmyoglobinupto4hafterHIITweremonitored.Results：Thedifferencesinrelativelyexpressedcardiorespiratoryvariables（heartrate,VO2）duringHIITwereatmostmoderate,withthemostpronouncedbetween-groupdifferencesinabsoluteVO2values.ThedisruptionofthepostexerciseHRVwasthemostpronouncedinuntrainedindividuals,andthisdifferencepersisted1hafterHIIT.ThehighestpostexerciseIL-6andTACconcentrationsandthelowestchangesincreatinekinaseandmyoglobinwererevealedinwell-trainedindividuals.Conclusion：Thehigherfitnesslevelwasassociatedwiththelesspronouncedpostexercisecardiacautonomicchangesandtheirfasterrestoration,evenwhenthereweresimilaracutecardiorespiratoryresponses.ThesefindingsweresimultaneouslyaccompaniedbythehigherpostexerciseIL-6andTACconcentrationsandlesssignificantchangesinmuscledamagebiochemicalmarkersinwell-trainedindividuals.