quantifying the effects of four weeks of lowvolume highintensity sprint interval training on vo2max through assessment of hemodynamics background sprint interval training is a popular workout modality studies have eluded to a positive effect on maximal oxygen uptake however little is known about the mechanistic basis of this adaptation therefore the purpose of this study was to determine the effects of a shortterm highintensity sprint interval training sit intervention on vo2max through quantification of both the respiratory and hemodynamic responsesmethods thirtysix physically active participants undertook 4 weeks of either cyclingbased sit 820 s at 170 pvo2max with 10 s recovery or continuous exercise training cet 30 min at 70 pvo2max 3 times per week vo2max bloodbased markers and hemodynamic responses were assessed pre and post the intervention period vo2max was assessed using breathbybreath open circuit spirometry while hemodynamic responses were monitored using thoracic impedance cardiographyresults vo2max exhibited a nonsignificant 41 increase es024 for sit with 70 p0007 es040 increase for cet hemodynamic responses maximal cardiac output maximal stroke volume displayed nonsignificant responses for cet and sit while avo2difmax increased from 15848 to 18329 ml100 ml p002 es063 in sitconclusions vo2max is a function of maximal cardiac output and avo2difmax so for a meaningful change to occur in cardiorespiratory fitness there must be a concomitant increase in o2 delivery this study demonstrates that a low volume sit intervention evokes peripherally mediated responses avo2dif and anaerobic substrate utilization rather than o2 delivery components future works should address the time course of the responses and when assessing vo2maxbased responses that due attention be given to the hemodynamic responses as means of quantification of the response