Similar performance and muscle adaptations between intervals with and without blood flow restriction in well-trained cyclists

Blood flow restriction (BFR) allows exercise at a lower external load with similar or greater improvements compared with traditional training in nontrained individuals. However, the effect in well-trained competitive athletes is unclear. The aim of this study was to compare effort-matched high-intensity interval training (HIIT) microcycles performed with or without BFR on endurance performance and muscular adaptations in well-trained cyclists. Seventeen well-trained cyclists (31 ± 9 yr; V̇o_2max: 67 ± 6 mL × kg^-1 × min^-1) were randomized to groups performing five HIIT sessions (6 × 5 min intervals with 2.5 min of recovery) with (BFR) or without (HIIT) thigh cuffs occluding the legs. V̇o_2max, power output at 4 mmoL/L blood lactate (LT4), mean power output during 5-min maximal cycling (MPO_{5 min}), percentage of V̇o_2max used at LT4 (%V̇o_2max@LT4), hemoglobin mass, and blood volume (BV) were assessed. Muscle biopsies from <i>m. vastus lateralis</i> evaluated muscle cross-sectional area (CSA), capillaries, citrate synthase, hydroxyacyl-coenzyme A dehydrogenase, and cytochrome c oxidase subunit 4. The BFR group trained at a 42% lower power output than the HIIT group (177 ± 3 W vs. 307 ± 8 W, respectively, <i>P</i> < 0.01), but with no differences in heart rate or rate of perceived exertion. Both groups improved MPO_{5 min} by ⁓4%, with no changes in LT4, V̇o_2max, hemoglobin mass, and BV. HIIT showed a significant reduction in CSA for type 2 muscle fibers compared with BFR, whereas no changes were found in the other muscle analyses. BFR applied during a 6-day interval microcycle provides similar performance gains as traditional HIIT in well-trained cyclists.<b>NEW & NOTEWORTHY</b> Blood flow restriction training (BFR) enables well-trained cyclists to perform high-intensity interval training (HIIT) at lower power outputs while still achieving comparable improvements in performance and muscle adaptations after a 6-day interval microcycle training. By matching effort rather than power output, this approach could help manage training load without compromising physiological gains. These findings suggest that BFR could be a tool in the training program of competitive athletes, especially during periods requiring reduced mechanical stress.