The Acute Effects of Short-Bout High-Intensity Interval Training on Physiological and Perceptual Outcomes: A...

Understanding the acute demands of short-bout high-intensity interval training can enhance training outcomes.

We aimed to examine the acute physiological and perceptual demands of short-bout high-intensity interval training in athletes and identify how they are moderated by programming variables, fitness level and competitive level.

We searched the databases PubMed, SPORTDiscus and CINAHL on 2 December, 2025 for original research articles investigating running-based, short-bout high-intensity interval training in healthy athletes, aged 16-40 years, of any sex, who were recreationally active or above. Outcomes were analysed using a multi-level mixed-effects meta-analysis. The analysed outcomes were: average heart rate (HR_avg), peak heart rate (HR_peak), peak and average oxygen consumption (VO₂), time > 90% of maximal oxygen consumption (T > 90% VO_2max), time > 95% of VO_2max (T > 95% VO_2max), T > 90% VO_2max/exercise time ratio (T₉₀/ET), T > 95% VO_2max/exercise time ratio (T₉₅/ET), blood lactate concentration (B[La]) and session ratings of perceived exertion (sRPE). To examine the influence of programming variables, fitness level, and competitive level, a meta-regression was performed on moderators with ten or more samples. Effects were evaluated based on coverage of their confidence limits against elected thresholds of practical importance.

From 139 data samples within 46 studies, the pooled demands (± 90% confidence limit) of short-bout high-intensity interval training were: HR_avg, 169 ± 4 b·min^-1 and 88 ± 2% of maximum heart rate; HR_peak, 184 ± 4 b·min^-1 and 94 ± 2% of maximum heart rate; average VO₂, 46 ± 3 mL·kg^-1·min^-1 and 78 ± 4% of velocity at VO_2max; peak VO₂, 55 ± 5 mL·kg^-1·min^-1 and 93 ± 7% of VO_2max; T > 90% velocity at VO_2max, 259 ± 57 s; time > 95% VO_2max, 125 ± 48 s; T₉₀/ET, 0.34 ± 0.9; T₉₅/ET, 0.15 ± 0.07; B[La], 8.3 ± 0.5 mmol·L^-1; and sRPE, 7.1 ± 0.5 au. When compared to an athlete VO_2max of 50-55 mL·kg^-1·min^-1, a VO_2max of 55-60 mL·kg^-1·min^-1 and > 60 mL·kg^-1·min^-1 were associated with a substantial decrease in sRPE (- 1.7 ± 1.3 au and -1.6 ± 1.1 au, respectively). Compared to a reference protocol of 1 set of 12 straight-line repetitions, performed at 120% of maximal aerobic speed for a 15-s work duration with 15 s of passive rest: shuttle runs were associated with a substantial increase in B[La] (1.9 ± 1.0 mmol·L^-1) and sRPE (1.7 ± 0.4 au); active rest was associated with a substantial increase in T₉₀/ET (0.21 ± 0.11); performing a 15-s longer repetition was associated with a substantial increase in T > 90% velocity at VO_2max (160 ± 113 s); completing one more set was associated with a substantial increase in B[La] (1.2 ± 0.1 mmol·L^-1); and a 5% increase in maximal aerobic speed was associated with a substantial increase in B[La] (1.0 ± 0.3 mmol·L^-1), HR_avg (3.2 ± 1.4 b·min^-1), and T₉₀/ET (0.05 ± 0.04), but a substantial decrease in T > 95% VO_2max (- 44 ± 28 s). All other moderators had compatibility with trivial effects or were inconclusive.

Short-bout high-intensity interval training elicits a substantial physiological stimulus, which is influenced by programming variables, athlete fitness level and competitive level. Implementing an active rest period, longer repetition duration and a higher running intensity are effective strategies to maximise the aerobic stimulus, while shuttle runs increase the anaerobic demand.