Clash of the Titans – HIIT vs LISS – Part 1
The World Health Organisation’s current guidelines indicate that, in order to improve and maintain health levels, an adult at least needs to perform activities for muscular strengthening, two or more days per week so every main muscle groups is trained, and combine such activities with one of the following options:
- 150 minutes per week of moderate-intensity cardio activity (for example, walking the dog)
- 75 minutes per week of high-intensity cardio activity (meaning running after the dog!)
- a mix of moderate and high-intensity cardio activity, just like the previous activities (when you run after the dog and then both go for a walk).
This amount of exercise just represents the minimum recommendation, not the ideal amount. It is known that there are greater health benefits when you do more than 300 minutes of moderate-intensity cardio activity per week, or more than 150 minutes of high-intensity cardio activity per week.[1-3]
However, many people complain about not having time to exercise — and here is where high-intensity interval training (HIIT) comes in. This type of training alternates between maximum-effort periods of 10 to 60 seconds (90% of maximum cardio capacity), and lower-intensity recovery periods of 30 to 60 seconds. Learn more about this type of workout here and here.
Several studies have demonstrated surprising results in individuals doing HIIT workouts three times per week, for two weeks. Besides showing superior physiological results compared with Low-Intensity Steady State training (LISS), in just 1/3 of the time, HIIT brings a number of benefits to the organism.[5-7] So let’s see which changes actually take place.
About the cardiovascular and respiratory systems:
1 – Improvement of the cardiopulmonary function
Many studies have shown consistently that a superior cardiopulmonary function is related to a lower incidence of hypertension, and consequently a lower mortality risk.
HIIT promotes an increase in the VO2max (16% vs 8% with LISS) and improves several aspects of our cardio capacity and performance, such as the ventilatory threshold and the metabolic transition phases between the aerobic and anaerobic state.[8,9]
2 – A change in the endothelial function (regulatory and protective functions of the cardiovascular vessels against aggressions) and also in arterial stiffness.
The arterial stiffness is related to structural and functional changes, such as the loss of vascular elasticity that occurs naturally in each individual due to intrinsic factors, like ageing and atherosclerosis (a condition in which we see a thickening and loss of elasticity of the vessel wall).
We know that the practice of physical activity prevents and controls risk factors related to the cardiovascular system. But although LISS decreases the arteries’ rigidity in people with normal arterial pressure, surprisingly enough the studies could not demonstrate any benefit in hypertensive people. However, after 16 weeks of HIIT, it’s possible to find significant improvements in vascular rigidity, both in people with hypertension and in those with normal arterial pressure values.
3 – Maintenance and decrease in arterial pressure
Studies show that exercise intensity seems to have no significant effects on arterial pressure. Both HIIT and LISS are equally effective in reducing blood pressure values, being necessary at least 12 weeks of high-intensity training to register a significant decrease in the arterial pressure of people with levels previously high.
However, during the stress test for the diagnosis and prognostic evaluation of coronary disease in young women with normal levels of blood pressure, but with familiar history of hypertension, it was verified that HIIT, when compared with the LISS, can have some benefit in reducing the blood pressure after 16 weeks of training.[12,13]
Besides this breakthrough, and even though there are uncertainties about the exact mechanism through which the increase of our sympathetic nervous system activation plays a role in the hypertension problem, studies indicate that it might be related to the fact that HIIT induces a higher reduction of noradrenaline levels, when compared with LISS.
4 – A decrease in heart rate when in basal state (resting metabolic state)
Physical exercise has the effect of reducing the incidence of cardiovascular diseases, and one of the factors which contributes the most to that is related to the reduction of the heart rate values when resting.
By assessing the heart rate values in women with normal levels of blood pressure, but with a family history of hypertension, before and after an HIIT workout of 16 weeks, it was concluded that the heart rate recovers better into the basal state, than in case of LISS. The mechanism through which it is possible to maintain lower values suggest that, after more intense exercise , there is a quicker and sustained answer of the parasympathetic system (one of the components of the nervous system responsible for most functions of the body when resting), due to an higher sensibility of the carotid baroreflex (nerve cells responsible for blood pressure control). This is not the case when you do more moderate physical activity.
Incredible though it may seem, accelerating your heartbeat can actually be beneficial to your heart! But what about the famous fat loss associated with HIIT? Stay tuned for the next article, which will give more insight in this kind of training.
Inês Fernandes – She’s a medical doctor and passionate about fitness. Inês dedicates a lot of her time to her own workouts, based on the effectiveness of the exercises and on scientific study results, looking to mash up them with complex, unusual and challenging exercises. She wants to take a Personal Trainer course during her medical internship, combining the two things she likes to do most in life: heal people and help them achieve a good physical shape!
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13. Ciolac, E.G., et al., Effects of high-intensity aerobic interval training vs. moderate exercise on hemodynamic, metabolic and neuro-humoral abnormalities of young normotensive women at high familial risk for hypertension. Hypertens Res, 2010. 33(8): p. 836-43.
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15. Rennie, K.L., et al., Effects of moderate and vigorous physical activity on heart rate variability in a British study of civil servants. Am J Epidemiol, 2003. 158(2): p. 135-43.