What are the cardiovascular benefits of high-intensity interval training (HIIT)?

What are the cardiovascular benefits of high-intensity interval training (HIIT)?

Guidelines of most medical societies recommend 150 minutes of moderate intensity or 75 minutes of vigorous intensity physical activity per week for health benefits. High-intensity interval training (HIIT) is another efficient exercise protocol with short sessions, being increasingly recognized to have benefits for general health as well as primary and secondary cardiovascular prevention. HIIT has been classified into aerobic HIIT and anaerobic HIIT. The latter is also known as sprint interval training (SIT) [1].

SAINTEX-CAD study compared aerobic interval training with moderate continuous training [2]. Two hundred patients with coronary artery disease and left ventricular ejection fraction above 40% were randomized to a supervised cardiac rehabilitation program of three weekly sessions of either aerobic interval training at 90-95% of peak heart rate or aerobic continuous training at 70-75% of peak heart rate on a bicycle. Primary outcome was VO_2peak and secondary outcomes were peripheral endothelial function, cardiovascular risk factors, quality of life and safety. Similar improvements in exercise capacity and peripheral endothelial function was noted in both groups. Quality of life and cardiovascular risk factors including diastolic blood pressure and high density lipoprotein cholesterol improved significantly after training in both groups [2].

An earlier, smaller study in 27 stable post infarction heart failure patients on optimal medical treatment had also come to similar conclusions. They had a mean left ventricular ejection fraction of 29%. Mean age of the patients was  75.5+/-11.1 years. They were randomized to either moderate continuous training or aerobic interval training 3 times per week for 12 weeks or to a control group that received standard advice regarding physical activity. Increase in VO_2peak was 46% in aerobic interval training while it was 14% in the moderate continuous training (P<0.001). This was associated with reverse left ventricular remodeling. Improvement in endothelial function and quality of life was also documented in that study [3].

These HIIT protocols require a shorter exercise duration to obtain the same benefit as that provided by moderate intensity exercise. Aerobic HIIT consists of intermittent bursts of vigorous activity of 70-90% of VO_2peak, or 85%-95% of the peak heart rate interspersed with active rest periods [3]. 4 x 4 minute or 10 x 1 minute protocols are commonly used for HIIT. One Wingate-type protocol of SIT is four to seven sessions of all-out vigorous intensity exercise for 30 seconds interspersed with 4 minutes of complete rest [4]. Anaerobic SIT protocol involves exercise intensity 350% of VO_2peak. Obviously, these high intensity protocols are quite demanding, even though the intensity is adapted to the individual’s aerobic capacity.

The risks of these high intensity protocols are a concern and certainly more studies are needed. Supervised workout is mandatory initially in the case of HIIT till the participants are accustomed to the intensity. Heart rate is measured with a wearable heart rate monitor during the exercise to make sure that the permitted limits are not exceeded. In aerobic HIIT, the recommended peak heart rate is 85-90% of the age predicted maximal heart rate. Age predicted maximal heart rate is calculated as 220-age of the person in years. Medical opinion from the regular physician is mandatory before starting supervised HIIT programs in those with existing heart disease or any other significant medical problem. Home based HIIT programs are possible if sufficient support is provided by experienced centers.

References

1. Ito S. High-intensity interval training for health benefits and care of cardiac diseases – The key to an efficient exercise protocol. World J Cardiol. 2019 Jul 26;11(7):171-188. doi: 10.4330/wjc.v11.i7.171. PMID: 31565193; PMCID: PMC6763680.
2. Conraads VM, Pattyn N, De Maeyer C, Beckers PJ, Coeckelberghs E, Cornelissen VA, Denollet J, Frederix G, Goetschalckx K, Hoymans VY, Possemiers N, Schepers D, Shivalkar B, Voigt JU, Van Craenenbroeck EM, Vanhees L. Aerobic interval training and continuous training equally improve aerobic exercise capacity in patients with coronary artery disease: the SAINTEX-CAD study. Int J Cardiol. 2015 Jan 20;179:203-10. doi: 10.1016/j.ijcard.2014.10.155. Epub 2014 Oct 25. PMID: 25464446.
3. Wisløff U, Støylen A, Loennechen JP, Bruvold M, Rognmo Ø, Haram PM, Tjønna AE, Helgerud J, Slørdahl SA, Lee SJ, Videm V, Bye A, Smith GL, Najjar SM, Ellingsen Ø, Skjaerpe T. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study. Circulation. 2007 Jun 19;115(24):3086-94. doi: 10.1161/CIRCULATIONAHA.106.675041. Epub 2007 Jun 4. PMID: 17548726.
4. Burgomaster KA, Hughes SC, Heigenhauser GJ, Bradwell SN, Gibala MJ. Six sessions of sprint interval training increases muscle oxidative potential and cycle endurance capacity in humans. J Appl Physiol (1985). 2005 Jun;98(6):1985-90. doi: 10.1152/japplphysiol.01095.2004. Epub 2005 Feb 10. PMID: 15705728.