High-intensity interval training with blood-flow restriction enhances sprint and maximal aerobic power in male endurance athletes

High-intensity interval training (HIIT) can improve endurance performance. We investigated the concurrent impact of HIIT and blood-flow restriction (BFR) as a novel approach to further enhance maximal aerobic and anaerobic physiology and performances in trained athletes. In a randomized controlled trial, eighteen endurance-trained males ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>V</mml:mi> <mml:mo>˙</mml:mo></mml:mover> </mml:math> O_2peak 65.6 ± 5.1 mL.min^-1.kg^-1) included three sessions of HIIT per week (sets of 15 s efforts at 100% maximal aerobic power, interspersed by 15 s recovery) into their usual training for 3 weeks, either with restriction imposed on both lower limbs at 50%-70% of arterial occlusion pressure (BFR group, <i>n</i> = 10) or without (CTL group, <i>n</i> = 8), and were tested for sprint and endurance exercise performance. The total mechanical work developed during a 30 s Wingate test increased only in BFR (3.6%, <i>P</i> = 0.02). During the Wingate, changes in near-infrared spectroscopy-derived vastus lateralis muscle oxygenation (Δ(deoxy[Hb + Mb]), % arterial occlusion) were attenuated after BFR training (-8.8%, <i>P</i> = 0.04). The maximal aerobic power measured during an incremental cycling test increased only in BFR (4.5%, <i>P </i>= 0.0004), but there was no change in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover><mml:mi>V</mml:mi> <mml:mo>˙</mml:mo></mml:mover> </mml:math> O_2peak among groups. Both groups improved 5 km cycling time trial performance, but BFR displayed a concomitant greater elevation in [H⁺] (11%, <i>P</i> = 0.02). Changes in other blood variables (e.g., pH, lactate, bicarbonate and potassium ion concentration, and hemoglobin) were not different between groups. Combining short-duration HIIT performed at 100% aerobic power with BFR elicited greater changes in sprint performance and maximal aerobic power in endurance athletes, associated with locomotor muscle metabolic adaptations but no meaningful effect on cardiorespiratory fitness.