HIIT Science
Increasing V̇O2max lowers all-cause mortality
Increasing V̇O2max by 3.5 mL/kg/min lowers all-cause mortality by 11%. Some caveats, see source.
Source: Objectively Assessed Cardiorespiratory Fitness and All-Cause Mortality Risk - Mayo Clinic Proceedings (2022)
HIIT increases V̇O2max
HIIT is more effective than endurance training at increasing V̇O2max. Some caveats, see source.
Source: Effectiveness of High-Intensity Interval Training and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials - Sports Medicine (2015)
More exercise ⇒ more V̇O2max gains
Exercising twice per week yields better V̇O2max gains than exercising once per week. The upper limit has yet to be found.
Source: Effects of High-Intensity Interval Training on Executive Functions in College Students: Evidence from Different Doses - Brain Sciences (2023)
HIIT is time-efficient
While endurance training yields similar V̇O2max gains, HIIT is more time-efficient. Linked study shows 28 minutes of HIIT yielded similar results to 38 minutes of endurance training.
Source: High-Intensity Interval Training Performed by Young Athletes: A Systematic Review and Meta-Analysis - Frontiers in Physiology (2018)
HIIT increases HDL-C
Increase in HDL-C of 0.2 mmol/L after 8 weeks of HIIT. Some caveats, see source.
Source: The Effect of a High-Intensity Interval Training Program on High-Density Lipoprotein Cholesterol in Young Men - Journal of Strength and Conditioning Research (2009)
V̇O2max is proportional to maximum heart rate over heart rate at rest
Measuing V̇O2max is difficult, but HR_max/HR_rest can be used as a proxy. Some caveats, see source.
Source: Estimation of VO2max from the ratio between HRmax and HRrest – the Heart Rate Ratio Method - European Journal of Applied Physiology (2004)