High Intensity Interval Training (HIIT) is a popular cardiovascular training approach that involves alternating bouts of high-intensity effort and rest/recovery periods.
The high intensity bouts are performed at varying exercise intensities and length of time. These typically range from 5 seconds to 8 minutes long, at an exercise intensity of 80-95% of the maximum Heart Rate.
You might be wondering what all these percentages and terminology are all about. Well, it’s a rather simple concept:
The term “Maximum Heart Rate (HRmax)” refers to the maximum number of times that your Heart can beat per minute during high intensity physical activity. It’s a really helpful measure of exercise intensity as it directly correlates with how your body is responding to physical activity. Researchers have managed to come up with a clever formula for estimating your HRmax. Just subtract your age from 220 and you’re good to go.
To sum it up:
Estimated Maximum Heart Rate (HRmax)= 220-age
An exercise intensity of 80-95% of Maximum Heart Rate (HRmax) means being involved in an exercise that elevates your Heart Rate to somewhere between 80-95% of your Maximum Heart Rate.
The “Recovery Periods” involve dialing down the effort to 40-50% of the Maximum Heart Rate.
These bouts of high-effort and recovery periods continue in a linear sequence, totaling to about 20-60 minutes.
Key Benefits
Current scientific evidence documents numerous benefits of HIIT, which fall under three main categories:
- Improved Physical Capacity
In basic terms, physical capacity refers to your ability to carry out various physical tasks. This is influenced by a number of factors, including strength, endurance/stamina, balance, and flexibility. HIIT comes with positive effects on all these factors to varying degrees. However, the highest effect is seen in physical endurance. This is possible through its effect on cardiorespiratory fitness, which is basically your body’s ability to transport and utilize oxygen to sustain physical activity.
Based on 2015 and 2021 major research reviews of previous studies on the effects of HIIT, it has proven to be a superior form of exercise for enhancing cardiorespiratory fitness in both younger and older populations.
- Improved body Composition
Results from numerous studies show that HIIT is a highly effective strategy for improving key parameters of body composition i.e. Body Fat Percentage and Lean Mass. A 2023 research review, published in the Journal of Clinical Medicine, furnishes one of the most recent pieces of evidence on the effect of HIIT on Body Fat Percentage and Lean Mass. The researchers analyzed 36 studies and compared body compositional changes between participants on various forms of HIIT, and those who weren’t on any exercise routine.
In the end, there was a substantial difference between the two groups in terms of Body Fat Percentage and Lean Mass. Interestingly, the authors observed that HIIT strategies performed for at least 8 weeks (3 sessions/week); with high-intensity bouts lasting for up to 60 seconds, and rest intervals of 90 seconds or less, produced the best results.
But why is this the case?
There are two main underlying reasons for this:
- The high-intensity exercise bouts mean more energy expended per unit time.
- Studies associate HIIT with enhanced Oxygen consumption after exercise sessions. The body still uses a lot of Oxygen even after exercise as it restores itself to pre-exercise consumption levels. This tends to hang around for about 2 hours. Recent evidence shows that total overall Oxygen consumption tends to be greater during this period after HIIT. According to the American College of Sports Medicine’s positional stand on HIIT, this translates to around 6-15% more energy expenditure/calories overall.
- Improved Cardiovascular Health and metabolic Disease Risk Profile
Researchers have delved into the effect of HIIT on blood lipid profile. In case this is new to you, blood lipid profiles indicate concentrations of different types of fats in your blood. These include key players in the development of cardiovascular disease such as Low-density Cholesterol and Triglycerides.
A 2023 research review in the International Journal of Exercise Science compared blood lipid profiles in individuals on HIIT against a sedentary population, and another group on a moderate-intensity training method known as MCIT (moderate Continuous Interval Training). HIIT proved the most effective training method for reducing concentrations of LDL-Cholesterol, which is heavily associated with a high risk of Heart Disease.
Beyond cardiovascular disease, HIIT has been shown to lower the risk of Diabetes, and improve Diabetes treatment outcomes through its effect on the body’s ability to control blood sugar levels (Glycemic Control). Another 2023 research review investigated the effect of HIIT on Glycemic Control in patients with Type 2 Diabetes in comparison with Moderate training and sedentary individuals. In the end, HIIT did not only prove to be superior in terms of improving Glycemic control, but also cardiorespiratory fitness in general.
How to Develop an HIIT Routine
HIIT can be adapted to various types of aerobic exercise, i.e. cycling, jogging, elliptical training, brisk walking, and swimming. The first principle is to identify exercises which you’re more likely to enjoy and stick to in the long run.
Exercise Intensity and Recovery Periods
As pointed out earlier, high intensity intervals should be within 80-90% if the Maximum Heart Rate(220-age), while recovery periods can range from 15-60 seconds. Practically, this would involve a 5-minute warm up of the exercise of choice, before amping up the speed or effort in general to push the Heart Rate to the recommended zone.
A reliable wrist Pulse Reader may prove handy when it comes to tracking the Heart Rate. However, pulse readers may not really be accessible to everyone, and poor accuracy can be a big challenge.
Alternatively, you can use your subjective feeling, or perceived physical exertion to gauge your exercise intensity levels. Working at high intensities should feel like working hard-very hard, or 80-100% of your all-out effort. Using the conversation test, this is the level where you can hardly string words together to carry out a conversation.
The recovery period exercise intensity should be somewhere between 30-40% of the maximum Heart Rate. This is basically the point where you dial it down to a rather comfortable level, which serves as a preparatory phase before the next high-intensity bout.
There's a number of simple HIIT protocols you can draw inspiration from. 1:1 interval workout offers the simplest HIIT variation based on workout and recovery period ratio. In simple terms, the high-intensity bouts are followed by recovery periods of the same length of time. For instance, 4 minutes of a high-intensity bout followed by 4 minutes of recovery period.
The "Sprint Interval" approach offers another great option to get started with. In basic terms, this involves very short bursts of all-out effort followed by longer recovery periods. Typically, the high intensity intervals last for about 30 seconds while the recovery period lasts between 4-4.5 minutes.
Precautions
The high intensity nature of HIIT routines comes with its risks, especially for individuals with a history of certain medical conditions. These include High Blood Pressure, Diabetes, and Heart Disease. To keep things safe, it's imperative to seek medical clearance before getting involved in any HIIT routine.
Another point worth noting is that HIIT can be a risky endeavor for starters in general, especially those who're severely deconditioned. The best way to go about this is to start with a moderate intensity aerobic exercise plan to establish base/foundational fitness levels for HIIT.
Final Word
High intensity Interval Training is a highly effective aerobic exercise approach with a wide range of proven health and aesthetic benefits. These include enhanced physical capacity, improved body fat percentage, and better risk profile of common cardiovascular and metabolic diseases. Just like any sound physical exercise approach, success boils down to applying the key principles in light of personal and contextual factors. Check out one of our experienced trainers in the expert’s section for a personalized HIIT plan for optimal results.
