Comparison of Acute Responses to Two Different Cycling Sprint Interval Exercise Protocols with Different Recovery Durations.

: Knowledge of acute responses to different sprint interval exercise (SIE) helps to implement new training programs. The aim of this study was to compare the acute physiological, metabolic and perceptual responses to two different SIE cycling protocols with different recovery durations. : Twelve healthy, active male participants took part in this study and completed four testing sessions in the laboratory separated by a minimum of 72h. Two SIE protocols were applied in randomized order: SIE-six "all-out" repeated 10-s bouts, interspersed with 4-min recovery; and SIE-two series of three "all-out" repeated 10-s bouts, separated by 30-s recovery and 18-min recovery between series. Protocols were matched for the total work time (1 min) and recovery (20 min). In SIE, peak oxygen uptake and peak heart rate were significantly higher ( < 0.05), without differences in peak blood lactate concentration and mean rating of perceived exertion compared to SIE. There were no differences in peak power output, peak oxygen uptake and peak heart rate between both series in SIE. : Two series composed of three 10-s "all-out" bouts in SIE protocol evoked higher cardiorespiratory responses, which can provide higher stimulus to improve aerobic fitness in regular training.