High-intensity interval training, also called HIIT, has become known in the fitness and health world as one of the most effective means of improving cardiovascular health as well as metabolic function.
HIIT workouts are known to be an exceptional way to burn fat in a short period of time and to help improve the physical performance of athletes, no matter what level. (1)
For most people, the biggest draw to a HIIT workout is its ability to change body composition due to its ability to raise your metabolic rate and keep the body burning fat long after the workout is over.
What is HIIT Training?
High-intensity interval training is a type of exercise that involves repeated short bursts of high-intensity exercises, followed by brief recovery periods. This sequence is repeated several times in a row usually for a duration between 20–30 minutes.
Considering the fact that many people use “not having enough time” as a popular reason to avoid regularly exercising, HIIT workouts are one of the best ways to overcome this block and get great results fast.
A HIIT protocol is a well-researched way to reap physical benefits as an alternative approach to steady-state exercise training but with less of a time commitment. (2)
For example, recently a study compared the impact of two different types of exercise training on body fat and muscle metabolism:
- HIIT workouts
- Steady-state exercise
The study investigated the effects of calorie expenditure and fat loss in young adults. It found that although HIIT workouts burned fewer calories during the actual workouts than did steady-state cardio exercise, likely due to their shorter duration, the HIIT program produced more fat loss than steady-state exercise did overall.
Additionally, the study concluded that while the HIIT workout helped build muscle, the steady-state workouts actually broke muscle down.
Researchers concluded that not only does HIIT burn more fat over the duration of the day, but it also builds more muscle and improves metabolic function. (3)
How to Perform HIIT
The exact type of exercise performed during the “intense” internal periods can vary, such as performing faster reps of a particular move, sprints or even circuit training. So, what stays the same throughout different types of HIIT programs? The act of alternating between periods of intense work and recovery.
A popular example of a HIIT workout can be running on the treadmill, alternating between a very fast pace and one that is easier and slower. In order to follow an interval schedule, you switch between sprints that require roughly 90 percent of your energy, followed by a slow jog to rest and recover.
Steady-state exercises, on the other hand, usually stay within the same type of “work” zone over time, with the amount of effort needed remaining consistent. (4)
HIIT Training Benefits
HIIT workouts have the ability to transform your body and physical abilities due to their effect on at least three important systems within the body:
- Your cardiovascular health
- Your body’s ability to use oxygen
- Your hormone levels
Studies have shown that resistance-based interval training specifically benefits blood flow and blood vessel dilation.
A study published in the American Journal of Physiology — Heart and Circulatory Physiology, found that resistance-based interval exercising improved endothelial function in individuals that previously exercised, those that didn’t and those with type 2 diabetes.
When researchers measured blood flow before, immediately following and at one and two hours after working out, participants with type 2 diabetes saw improvements at each time. The other two participant groups experienced improvements one and/or two hours after exercising. (5)
HIIT Training & Cardiovascular Health
Many studies are now showing that HIIT workouts promote greater improvements in VO2max and general fitness abilities than steady-state exercises do. In fact, VO2max is considered the best indicator of cardiovascular endurance. This is the measurement most commonly used in fitness studies to show the effects that the exercise is having on the body.
VO2 max is sometimes also called “max oxygen uptake” or “max aerobic activity” and is used to measure how well the body can use oxygen for energy.
Specifically, VO2max is defined as the maximum amount of oxygen (in milliliters) that a person can use in one minute per kilogram of their body weight. This measurement is important because the amount of oxygen that a person can utilize within one minute is an indicator of their lung and heart health in addition to their overall fitness level.
Due to the expansion of blood volume, the heart will undergo enlarging, or “hypertrophy,” during HIIT type of endurance exercises in order to allow the heart muscle to become bigger and stronger. (6)
By pushing your heart rate high during periods of intense work, you’ll be able to increase your cardiovascular ability and strengthen your heart. During the short rest intervals, you work on recovering more quickly and needing less time to rest. This is how you build stamina over time and increase your ability to perform physical exercises more effectively.
Performing short recovery segments in between the intervals where you’re working harder has the benefit of allowing you to keep the overall workout intensity high while still maintaining form.
While it’s hard to work very hard and maintain a high heart rate for an extended period of time because your body isn’t able to bring in enough oxygen, the rest/recovery periods of interval training allow you to catch your breath and for your heart rate to come down briefly.
HIIT Training & Post-Exercise Oxygen Effect (EPOC)
HIIT workouts trigger something known as excess post-exercise oxygen consumption (EPOC). EPOC is the phenomenon of an increased rate of oxygen that your body uses following strenuous activity (7).
Your body uses more oxygen after hard workouts like those performed during HIIT because it’s making up for the body’s oxygen shortage that occurred during the difficult burst exercise period.
EPOC has many functions for the body, including that following a HIIT workout, your body goes into a recovery phase. A higher level of oxygen is needed during recovery in order to facilitate in the rebuilding of hormone levels, refueling your glucose stores, and repairing your muscle fibers and tissue.
So, what’s the best part about EPOC?
It’s accompanied by an elevated need for body fuel or energy in addition to more oxygen. After intense exercise, fat stores within your body are actually broken down and free fatty acids are released into the bloodstream. During the post-workout recovery phase, these free fatty acids become oxidized and your body uses them for energy.
As your body uses more oxygen to bring itself back into a resting state, more calories are burned in the process, even while you are done working out. This means you continue to experience benefits and fat loss during the remainder of your day following a HIIT workout.
Another benefit of EPOC that results from HIIT workouts is new adenosine triphosphate (ATP) — which is the energy that your body’s cells work off of — is also synthesized. Additionally, post-exercise oxygen is used to reduce lactic acid, which is formed during exercise and is responsible for giving you the “burning” feeling in your muscles when they are working hard.
Lactic acid travels via the bloodstream to the kidneys, heart and liver during workouts where an increased amount of oxygen is then necessary to convert the lactic acid back to pyruvic acid so that your pain subsides and body enters a resting state.
Additionally, EPOC fuels the body’s increased metabolism that results from the increase in body temperature experienced during exercise.
Due to all of these vital tasks that the body must undergo during a period of EPOC, you can see why HIIT workouts have such a huge effect on your strength, body composition, stamina and health.
Building Your Own HIIT Training Routine
No matter what your exercise preference is — whether running, biking, swimming or lifting weights, for example — you can practice HIIT workouts to improve your abilities. Even seasoned athletes use HIIT workouts to gain stamina and bust through plateaus that they are experiencing after practicing one particular type of exercise for a long time.
HIIT workouts are a great way to shock your muscles and to kick your body into high gear, allowing you to continue experiencing results and improvements after your body has become accustomed to your usual workout routine.
According to studies, it’s believed that an optimal HIIT workout produces maximum cardiovascular benefits when athletes spend at least several minutes per session in their “red zone” — this generally means reaching at least 80 to 90 percent of maximal oxygen uptake (VO2max).
In order to estimate when you are working at 90 percent of your VO2max, you can think about your level of perceived effort on a 1 to 10 scale; you should be aiming to give it “your all” and reach a score of 9 for at least a few minutes during a 20 to 30-minute HIIT workout. (8)
Other Variables to Note
The amount of time you spent in your “intense” working interval
The longer you spend in your intense zone, the more of an effect the exercise will have. Start off with shorter bursts of intense periods and increase the duration as you build strength and stamina.
The amount of time you spent in your “rest” and recovery interval
You will likely notice that you need less time to recover as your body adapts to HIIT workouts. Pay attention to how long of rests you are taking and aim to shorten the restful period duration as your abilities improve.
The amount of reps you perform during your intense bursts
Instead of aiming to improve the duration of time you spend in an intense interval, you can also focus on how many reps you are able to do in a row, for example, or your speed of work.
You will likely notice your ability to do reps quickly improves as you become accustomed to HIIT workouts and that you need less recovery time in between sets. You may also notice that your sprints get quicker or your cycling pace gets faster if you choose to run or bike during your HIIT workout.
The total number of interval series you are able to perform
It’s a good idea to start out with about 15 to 20 minutes of HIIT intervals and work your way up to 25 to 30 minutes. The more your body gets used to the intensity, the more series you’ll be able to perform and your total workout length will increase.
The time needed between HIIT workouts
Most experts recommend practicing HIIT workouts 2 to 3 times per week, but not much more than this. The body needs an adequate break period between HIIT workouts to fully repair and grow stronger.
In fact, this is just as important as the workout itself and if you fail to properly give yourself enough rest, you miss out on some of the benefits of HIIT.
That being said, you will improve your ability to practice HIIT workouts closer to each other as your recovery periods become shorter. Even after you’ve seen great improvements, it’s still best to allow 48 hours in between HIIT workouts and avoid practicing them multiple days in a row.
3 HIIT Workouts to Get You Started
Keeping all of the above factors in mind, you can start practicing HIIT workouts using one of these examples:
HIIT Circuit Training
The 3 exercises below will make up your “intense interval phase”, then performing an easier form of cardio afterwards will make up your “rest interval phase”.
Perform the following 3 exercise moves back-to-back according to these reps:
- Start by doing 10 lunges, push-ups, and jumping jacks
- Then repeat the cycle doing 15 reps of each
- Then repeat the cycle doing 20 reps of each
Don’t take any breaks until after you’ve gone through all three sets.
In place of these 3 moves, you could also try performing fast alternating Burpees, Mountain Climbers or kettlebell swings.
After you’ve completed these 3 sets, do a form of steady-state cardio for about three minutes. This can mean jogging, running in place, hopping on an exercise bike, etc. You want to be performing at about 50 to 60 percent of your ability during this cycle.
Treadmill Running HIIT Workout
Start with a warm up by lightly jogging for three minutes.
Next, move into your interval period for about 10 minutes.
Each minute you will do 20 seconds of intense work followed by 40 seconds of recovery.
Do this for 10 minutes to start out, and as you become more fit you can increase it to 15 minutes and beyond.
If you’d like to challenge yourself more, do 30 seconds of intense bursts (90 percent of your maximum capacity) followed by 30 seconds of recovery (50 to 60 percent of your maximum capacity).
Finally, cool down with a 3-minute jog.
Cycling HIIT Workout
This cycling interval workout is based on the “Tabata style” of exercise, which usually consists of 20 seconds of hard work followed by 10 seconds of rest or recovery.
In order to do interval training, this same ratio can be used in any other form of exercise as well.
Start by cycling at a restful pace for three minutes to warm up.
Move into your interval period for the next 10 minutes, where you will be cycling as hard as you possibly can for 20 seconds and then slowing your pace for 10 seconds. You can use a timer to keep track of the time or count in your head.
Repeat this interval schedule 10 to 20 times depending on your abilities and current fitness level.
Cool down with a slow, restful three minutes of cycling.
An exercise plan that includes consistent high-intensity interval exercise has been shown to improve body composition, boost cardio-metabolic health, lessen the risk for heart disease, and help improve exercise tolerance, even in obese and overweight participants. (9)
Research has shown that HIIT training is safe, efficient, well-tolerated and could help to improve adherence to exercise training given the limited time commitment that they require.
As long as you practice HIIT training responsibly and ease your way into a HIIT program, you can experience great results using HIIT workouts in combination with other forms of exercise that you enjoy.