Abstract
High-intensity interval exercise (HIIT) is performed widely. However, there is a gap in knowledge regarding the acute cerebrovascular response to low-volume HIIT. Our objective was to characterize the middle cerebral artery blood velocity (MCAv) response during an acute bout of low-volume HIIT in young healthy adults. We hypothesized that MCAv would decrease below the baseline (BL), 1) during HIIT, 2) immediately following HIIT, and 3) 30 min after HIIT. As a secondary objective, we investigated sex differences in the MCAv response during HIIT. Twenty-four young healthy adults completed HIIT [12 males, age = 25 (SD = 2)]. HIIT included 10 min of 1-min high intensity (∼70% estimated maximal Watts) and active recovery (10% estimated maximal Watts) intervals on a recumbent stepper. MCAv, mean arterial pressure (MAP), heart rate (HR), and end-tidal carbon dioxide ([Formula: see text]) were recorded at BL, during HIIT, immediately following HIIT, and 30 min after HIIT. Contrary to our hypothesis, MCAv remained above BL during HIIT. MCAv peaked at minute 3 then decreased concomitantly with [Formula: see text]. MCAv was lower than BL immediately following HIIT (P < 0.001). Thirty minutes after HIIT, MCAv returned to BL (P = 0.47). Compared with men, women had a higher MCAv at BL (P = 0.001), during HIIT (P = 0.009), immediately following HIIT (P = 0.004), and 30 min after HIIT (P = 0.001). MCAv did not decrease below BL during low-volume HIIT. However, MCAv decreased below BL immediately following HIIT and returned to resting values 30 min after HIIT. MCAv also differed between sexes.NEW & NOTEWORTHY We are the first, to our knowledge, to characterize the cerebrovascular and hemodynamic response to low-volume high-intensity interval exercise (HIIT, 1-min intervals) in young healthy adults. Middle cerebral artery blood velocity (MCAv) decreased during the HIIT bout and rebounded during active recovery. Women demonstrated a significantly higher resting MCAv than men and the difference remained during HIIT. Here, we report a novel protocol and characterized the MCAv response during an acute bout of low-volume HIIT.
Highlights
High intensity interval exercise (HIIT) is performed widely
Temporal changes in cerebral blood flow, measured by middle cerebral artery blood velocity (MCAv), have been well-characterized during submaximal continuous exercise.[1,2,3,4] During steady-state low and moderate intensity continuous exercise, MCAv remains at a consistent rate.[2, 5] As exercise intensifies, many physiological factors including cardiac output, sympathetic activity, blood pressure, and metabolism contribute to MCAv increasing in tandem up to anaerobic threshold. [1, 6, 7] Beyond the anaerobic threshold, MCAv decreases with high intensity exercise.[1, 4, 6] One possible explanation of MCAv decreasing after the anaerobic threshold could be due to hyperventilation, resulting in hypocapnia or decreased partial pressure carbon dioxide (PaCO2).(8) To attenuate the decrease in PaCO2, downstream arteriole vasoconstriction occurs resulting in a reduced MCAv.[9]
MCAv did not decrease below BL.[18]. The same study investigated high-volume The longer recovery intervals of 3 to 4.5 minutes during sprint interval exercise and high-volume high intensity interval exercise (HIIT) may have allowed for stabilization of PaCO2, maintaining MCAv above baseline.[18]
Summary
High intensity interval exercise (HIIT) is performed widely. there is a gap in knowledge regarding the acute cerebrovascular response to low-volume HIIT. HIIT has been stated to be counterintuitive due to decreases in PETCO2.(19) While the 3 to 4.5 minutes of active recovery during sprint interval and high-volume HIIT may have allowed for recovery of PETCO2, low-volume HIIT with an active recovery of 1-minute may not be enough time to recover PETCO2.(17) Decreasing PETCO2 may lead to further reductions of MCAv below baseline, which was previously shown during an acute 12-minute HIIT bout.[20] This has been suggested, no studies have reported the effects of low-volume HIIT on MCAv in young healthy adults. MCAv recovery immediately following low-volume HIIT has not been previously studied in young healthy adults, previous work has shown reduced MCAv immediately following a HIIT exercise bout.[20] To address the gap in cerebrovascular knowledge in young healthy adults, we proposed to characterize the MCAv response during a single bout of lowvolume HIIT, with 1-minute intervals of high intensity and active recovery, immediately after
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