HIIT (high intensity interval training) is a very popular method of training when looking to maximize workout efficiency, improve cardiovascular fitness, and lose fat.
But, how long does it take for HIIT results?
If you are looking to increase cardiovascular fitness and VO2 max, HIIT can offer results in 6-8 weeks. If you are looking to lose fat using HIIT, the results are 100% dependent on your ability to place yourself in a calorie deficit, which HIIT can help with, but is not the only factor involved in weight loss.
In other words, to determine the most accurate time estimates on how long it will take for HIIT results, one must fully understand the mechanics behind HIIT, improving cardiovascular fitness, and losing body fat.
Here’s what you’ll learn in this article:
- 3 Ways HIIT Can Give Your Results
- What NOT to Expect from Doing HIIT
- What Results Can You Expect from HIIT in 7-30-90 Days?
- How Often Should You Do HIIT
- Other Factors to Consider to Increase Success
- FAQs Related To HIIT results
3 Ways HIIT Can Give You Results
In the below sections we will lay out why cardio is not as critical as people may think during a fat loss phase, and how to optimize fat loss through diet and resistance training methods so that you can successfully cut without cardio.
Increase Cardiovascular Fitness in Less Time
Repeated studies have shown that HIIT is a time-efficient method for increasing cardiovascular fitness, VO2 max, and anaerobic threshold. Furthermore, it has been shown to offer a more efficient way to decrease body fat when compared to steady state cardio (1).
These findings are predicated on the basis that training intensity is significantly higher than steady state cardio, meaning that during the same amount of time more calories or burned doing HIIT then steady state (hence greater results), or that the same amount of calories are expended when doing HIIT instead of steady state, just in less time (more time-efficient).
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Improve Your Workout Compliance
HIIT is a very time-efficient means to improving cardiovascular and metabolic outcome of exercise, that would otherwise be a challenge for some populations. One study found that HIIT is a very effective means at increasing workout compliance and improving cardiovascular health and fitness in less active individuals.
They concluded that the ability to have participants exercise at higher intensities (30 seconds to several minutes) with longer recovery periods (one to five minutes) with low or no exercise intensity increases workout compliance and is suitable for both healthy and unhealthy populations (2).
Potentially Increased Weight Loss
By increasing the workout efficiency, and improving your cardiovascular fitness, some researchers believe that HIIT may be more effective at decreasing body fat when compared to more traditional forms of exercise.
While the significance of this can be dependent on many factors such as workout compliance, diet, and exercise intensity, it is likely to think that the benefits of HIIT can be correlated with more weight loss for those individuals who are short on time and cannot commit to longer workouts and/or to individuals who find it difficult to train longer periods of time (3).
It is important to note that training intensity must be much higher during HIIT protocol, and that at the end of the day weight loss is 100% depending on being in a calorie deficit, regardless of the workout or diet methods.
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What NOT to Expect from Doing HIIT
Below are two main limitations of HIIT, in which you should be aware of if you are looking for HIIT to be an end all in your weight loss and fitness program.
A Shortcut to Your Goals
When we hear about HIIT training, some people may mistakenly think it means they can workout less and get more results.
While this is partially true, your workouts need to be intense. Furthermore, even if your workouts are intense, it won’t fix your diet or lifestyle behaviors contributing to your weight or lack of fitness.
The cold hard truth is that HIIT is simply a method of training that has some benefits, and some potentially detrimental effects when done in excess.
If you are not willing to address your diet, stick to a training program that incorporates weight training, and understand that HIIT is best used in small doses rather than every workout; expect your results to be limited.
Using HIIT properly will allow, however, to be more time efficient and even expedite the process, however that will require more intensity and effort than more traditional training programs.
Increased Muscle Mass and Strength
Research shows that HIIT can be a very effective and time-efficient method to increasing cardiovascular fitness, however the ability to increase muscle hypertrophy is limited when compared to more traditional weight training (4).
What Results You Can Expect After 7 Days of HIIT
In regards to improved cardiovascular fitness and body composition, seven days is not enough time to see significant improvements in either.
That said, you may find that mentally you are feeling better after a few workouts after establishing a routine, which will hopefully motivate you to continue training toward your goal.
What Results You Can Expect After 30 Days of HIIT
After 30 days of doing HIIT you should notice a difference in both your exercise performance and potentially body composition if you have been eating in a manner that allows for a caloric deficit (if fat loss was your goal).
You could lose anywhere between 2-4 lbs of fat for most individuals per week, or slightly more for heavier individuals.
Note, that for most people, a weight loss of 0.5 to 1.0lbs per weeks is advised. Anything faster than that and you may be losing weight at the expense of retaining muscle, i.e. you’ll lose muscle along with losing fat, which will just make you look “skinny fat”.
What Results You Can Expect After 90 Days of HIIT
At this stage, you will notice improvements in resting heart rate, increased exercise performance, workout economy (improvements in movement efficiency specific to your modality), and improved blood pressure.
Additionally, after 90 days (12 weeks), you could lose 8-12lbs of weight, hopefully the vast majority of that is fat (especially if you trained with weights during this fat loss phase).
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How Often Should You Do HIIT To See Results
When looking to see results from HIIT, you first need to determine what results are attached to the act of performing HIIT, versus the results of adhering to a diet and being in a calorie deficit.
General recommendations for improving cardiovascular fitness and decreasing certain metabolic disease risk factors is to perform 2.5 hours or 150 minutes of general (steady state, interval based, or HIIT) cardiovascular exercise a week to be sufficient for most individuals.
For HIIT, the guidelines are less clear, however most suggest that three workouts per week lasting 30-60 minutes will suffice for most if the intensity is high enough to elicit the benefits of HIIT (5).
If you are looking to increase your cardiovascular fitness and health, one study indicated that doing HIIT three times a week (four sets of four minute work intervals with a three minute recovery interval) in very small doses can be an effective means at increasing cardiovascular fitness (6).
If you are looking to decrease body composition, this is entirely dependent on your diet and your energy balance. HIIT is a means of improving fitness and in part also expending more calories, however research has repeatedly shown that that weight loss is 100% depending on being in a calorie deficit, and is 100% independence of the means at which you use to get there (7).
Assuming you are eating in a calorie deficit and are not crash dieting, it is likely to think that you could lose .5lbs to 1.0lbs per week, for up to 12-16 weeks before you would need to think about a maintenance diet (or until you lose 10% of your bodyweight).
Other Factors To Consider To Increase Your Chance Of Success
You can increase the likelihood of reaching your goals by also addressing some of the biggest limitations of HIIT based training.
Below is a list of some of the most important aspects of training, diet, and lifestyle modifications that can be made to ultimately help you increase your chances of success.
Stick to Your Diet
As discussed above, your diet plays a key role in losing body fat and performance. If you are doing HIIT with the goals of losing weight, it is important that you understand HIIT does not replace sticking to a diet. In fact, cardio is not even a necessary part of weight loss and muscle retention…
Training with Weights
Weight training is key if you are looking to lose body fat and preserve as much muscle as possible.
If your goal is to also improve cardiovascular fitness, making sure to lift with weights regularly will also help you increase power output, aid in injury prevention, and help keep your bone density and metabolism from getting beat down with excessive high-impact, non-load bearing exercise.
Adopting a Physically Active Lifestyle
Increasing your physical activity, such as taking daily walks, is a great way to increase your daily calorie epidural, decrease stress, and improve blood flow to the body and brain.
These low-impact, lower-intensity forms of movements are great ways to also decrease your risks of metabolic disease and health concerns like high blood pressure, weight gain, and stress.
Get Enough Sleep
Sleep is critical to recovery, brain function, stress reduction, and hirmal production. If you are not sleeping, there is a strong chance your body is not recovering from the HIIT workouts.
Furthermore, if you are in a calorie deficit during this time, your body is already under high amounts of stress and poor sleep, which only compounds the negative effects of overtraining (muscle loss, increased resting heart rate, sleep and mood disturbances, decreased physical performance, etc).
Monitor Your Recovery Between Workouts
During a diet, your performance may slip some as your body is under increased stress from dieting. Decreasing your calorie intake often means the body has less readily available fuel and energy to train hard and recover properly.
While this is a very normal part of losing body fat, you want to be sure that if you are focused on losing fat and improving fitness that you are not placing yourself in too large of an energy deficit.
If you notice that your performance is slipping from workout to workout, and you are feeling more worn down the longer you go, you either need to increase your calories and slow the rate of weight loss down, or you need to cut back the amount of workouts or the overall intensity.
This is why HIIT may not be sustainable for people who are cutting for longer periods of time).
This is one of the biggest issues with HIIT training, is that it is instnese, and it often can lead people to overtrain if they are not adequately feeling their body and recovery properly.
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Frequently Asked Questions
Below are two very common questions asked regarding HIIT and how to know whether or not it is working for you.
How Do You Know If HIIT Is Working?
If you are looking to see if your cardiovascular fitness is improving, one of the easiest ways to do so is to track your resting heart rate every morning. If your resting heart rate starts to decrease over the course of a few weeks, you are headed in the right direction.
Another way to determine if HIIT is working is to track your performance during repeated workouts.
Are you running faster than previous workouts, with the same amount of rest periods?
Are you able to cover the same amount of ground with shorter intervals?
All these, when also taking your heart rate variability into account, all can suggest HIIT is working.
How Long Does It Take To Lose Fat From HIIT?
If you are looking to see if HIIT is working in regards to your fat loss efforts, again, this has more to do with your diet than doing HIIT. If you are losing .5lbs to 1lbs of body weight per week, that is a good starting point for most individuals who want to lose fat but not lose muscle.
It cannot be stressed enough that if you are looking to lose fat, this is 100% dependent on being in a calorie deficit, and 100% independent of the method used to accomplish that. HIIT could be a time efficient method for improving fitness and increasing calorie expenditure.
HIIT is a highly efficient method of improving fitness and increasing energy expenditure for initials who may have time limitations and/or are unable to train at hard intensities for long durations.
Research has repeatedly shown that HIIT is very effective at increasing cardiovascular health and has been correlated with increasing exercise compliance in healthy and at-risk individuals; making it a great option for all levels.
For individuals who look for HIIT to help improve their fat loss, research shows that the most critical and sole factor at decreasing body fat is to be in a caloric deficit.
Furthermore, research has shown that those results are 100% independent of the workout method, meaning that HIIT is not necessary for fat loss or any more effective than other means if calories are equated.
If you are looking for a time-efficient workout method that can help you burn as many calories as you would in longer sessions AND improve cardiovascular fitness, HIIT may be a good option.
Schoenfeld, B., & Dawes, J. (2009). High-intensity interval training: Applications for General Fitness training. Strength & Conditioning Journal, 31(6), 44–46. https://doi.org/10.1519/ssc.0b013e3181c2a844
Shiraev, T. (2012). Evidence based exercise: Clinical benefits of high intensity interval training. Australian Family Physician, 41(12), 960–962.
SHEHATA, A. Y. M. A. N., & MAHMOUD, I. S. L. A. M. (2018). EFFECT OF HIGH INTENSITY INTERVAL TRAINING (HIIT) ONWEIGHT, BODY MASS INDEX AND BODY FAT PERCENTAGE FOR ADULTS. Science, Movement and Health, 18(2), 125–130.
Callahan, M. J., Parr, E. B., Hawley, J. A., & Camera, D. M. (2021). Can high-intensity interval training promote skeletal muscle anabolism? Sports Medicine, 51(3), 405–421. https://doi.org/10.1007/s40279-020-01397-3
Garzon, R. (2018). Why and How to Do Aerobic Training, Including High-intensity Interval Training. COLLEGE OF AGRICULTURAL, CONSUMER AND ENVIRONMENTAL SCIENCES. https://doi.org/aces.nmsu.edu/pubs
Ramos, J. S., Dalleck, L. C., Tjonna, A. E., Beetham, K. S., & Coombes, J. S. (2015). The impact of high-intensity interval training versus moderate-intensity continuous training on vascular function: A systematic review and meta-analysis. Sports Medicine, 45(5), 679–692. https://doi.org/10.1007/s40279-015-0321-z
Strasser, B., Spreitzer, A., & Haber, P. (2007). Fat loss depends on energy deficit only, independently of the method for weight loss. Annals of Nutrition and Metabolism, 51(5), 428–432. https://doi.org/10.1159/000111162
About The Author
Mike holds a Master’s in Exercise Physiology and a Bachelor’s in Exercise Science. He’s a Certified Strength and Conditioning Specialist (CSCS), USA Weightlifting Advanced Coach, and has over 10+ years of experience working with collegiate athletes, national level lifters, and beginners alike. Mike is Founder of J2FIT Strength and Conditioning, a growing global training company with gyms in New York City, Cincinnati, and online offering personal training, online custom coaching programs.