# Six weeks of high-intensity interval training to exhaustion attenuates dynamic cerebral autoregulation without influencing resting cerebral blood velocity in young fit men PMID: 31373166 Journal: Physiological Reports Published: 2019-08-01 Authors: Drapeau A, Labrecque L, Imhoff S, Paquette M, Le Blanc O, Malenfant S, Brassard P ## Question Does 6 weeks of HIIT to exhaustion at 85% or 115% maximal aerobic power alter resting cerebral blood velocity and dynamic cerebral autoregulation in fit young men? ## Summary In young endurance-trained men, 6 weeks of exhaustive cycling HIIT improved VO2max and lowered resting heart rate, but did not change resting middle cerebral artery blood velocity. Dynamic cerebral autoregulation phase during squat-stand testing decreased after training, suggesting a subtle attenuation in cerebral blood-pressure buffering. The study was small, male-only, and lacked a non-training control group. ## Population - Seventeen young fit men completed training: HIIT85 n=8 and HIIT115 n=9; dynamic cerebral autoregulation analysis n=15 because of technical artifacts. Participants trained 5-12 h/week for at least 2 years and were free from diagnosed medical, cardiovascular, and cerebrovascular conditions. - Sample size: 17 - Age: HIIT85 26 +/- 6 years; HIIT115 28 +/- 6 years - Sex: 17 men completed - Fitness level: Endurance-trained, 5-12 h/week for at least 2 years - Health status: Free from diagnosed medical/cardiovascular/cerebrovascular conditions ## Methodology - Single-blind randomized training substudy - 6 weeks - Laboratory-supervised cycling training - Randomized and controlled study design. ## Protocol - Cycling HIIT to exhaustion at 85% or 115% MAP; details: HIIT85: repeated 1-7 min cycling bouts at 85% maximal aerobic power, with active recovery at 150 W or 50% MAP if MAP was below 300 W, continued until exhaustion. HIIT115: repeated 30 sec to 1 min cycling bouts at 115% maximal aerobic power with the same active recovery approach, also to exhaustion. Both groups trained 3 times/week for 6 weeks with 48-72 h between sessions. - Modality: Cycle ergometer HIIT. - Work intervals: HIIT85: 1-7 min bouts; HIIT115: 30 sec to 1 min bouts. - Recovery: Active recovery between bouts. - Sets or repetitions: Repeated intervals until inability to complete an effort bout. - Intensity: 85% maximal aerobic power or 115% maximal aerobic power. - Session duration: To exhaustion; reported average exercise duration 36.6 +/- 14.4 min/session for HIIT85 and 19.3 +/- 4.7 min/session for HIIT115. - Frequency: 3. - Program length: 6 weeks. - Progression: Intervals were performed to exhaustion rather than a fixed progressive prescription. - Alternate cycling HIIT intensity group; details: Active comparator was the alternate HIIT intensity/interval-duration protocol; there was no non-training control group. - Modality: Cycle ergometer HIIT. - Work intervals: HIIT85: 1-7 min bouts; HIIT115: 30 sec to 1 min bouts. - Recovery: Active recovery between bouts. - Sets or repetitions: Repeated intervals until inability to complete an effort bout. - Intensity: 85% maximal aerobic power or 115% maximal aerobic power. - Session duration: To exhaustion; reported average exercise duration 36.6 +/- 14.4 min/session for HIIT85 and 19.3 +/- 4.7 min/session for HIIT115. - Frequency: 3. - Program length: 6 weeks. - Progression: Intervals were performed to exhaustion rather than a fixed progressive prescription. ## Outcomes ### VO2max Status: improved VO2max increased in both groups: HIIT85 56.0 +/- 6.0 to 59.3 +/- 4.7 and HIIT115 55.9 +/- 4.0 to 59.2 +/- 1.1 mL/kg/min; time effect p=.002. p=.002 ### Resting heart rate Status: improved Resting heart rate decreased in both groups, by 8% in HIIT85 and 5% in HIIT115; p=.02. p=.02 ### Resting cerebrovascular measures Status: no clear change Resting mean arterial pressure, middle cerebral artery blood velocity, cerebrovascular conductance, and resistance did not change. ### Dynamic cerebral autoregulation Status: improved Transfer-function phase during 0.10 Hz squat-stands decreased after training irrespective of intensity; p=.048. Gain and coherence were not affected. p=.048 ## Practical Insights - Similar aerobic fitness gains occurred with shorter, lower-volume 115% MAP intervals and longer 85% MAP intervals in already-fit men. - Resting cerebral blood velocity should not be claimed to improve from this 6-week exhaustive HIIT protocol. - Exhaustive athlete protocols may carry fatigue burden and are not directly suitable for broad consumer app programming. ## Limitations - Small sample and only young fit men. - No non-training time-control group. - Training volume differed between intensity groups. - Transcranial Doppler assumes stable middle cerebral artery diameter. - Technical artifacts reduced dynamic cerebral autoregulation sample size. ## Safety And Adherence - No study-related adverse events were explicitly reported. - One participant was excluded after illness/absence from more than 3 sessions. - One participant was excluded after excessive fatigue during HIIT115. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/31373166/) (pubmed) - [DOI](https://doi.org/10.14814/phy2.14185) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6675921/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.