HIIT, short for high intensity interval training, is often touted as a way to lose fat and improve your cardiovascular fitness with workouts that are short but extremely hard.
How long does it take to see results with HIIT?
If you want to improve your cardiovascular fitness and exercise performance, studies show that HIIT can deliver results in 2-3 weeks. While it can certainly contribute to the calorie deficit required for weight loss, most research shows that the fat burning powers of HIIT are relatively modest.
Read on, and I’ll show you what sort of results you can expect to see after weeks and months of regular HIIT training.
What Is HIIT?
HIIT is short for high-intensity interval training. The idea is that you get your heart rate up by working extremely hard for a short period of time, usually somewhere between 30 seconds and 4-5 minutes.
This is followed by a recovery period where you ease up on the intensity and allow your heart rate to drop.
Then you repeat the process, usually somewhere between 5-10 times, depending on your goals, fitness level and the time you have available to train.
Because you’re working at an intense level, most HIIT workouts usually take no longer than 30 minutes to complete.
What Results Can You Expect After Two Weeks of HIIT?
Studies show that sprint interval training, a form of HIIT involving repeated bouts of all-out exercise, can increase the oxidative capacity of skeletal muscle, as well as improve endurance performance, in just two weeks.
In one study, subjects performed six sessions of HIIT over a 2-week period .
The routine involved 4-7 bouts of “all-out” cycling lasting 30 seconds, separated by 4-minute rest periods, where the subjects cycled at a lower intensity.
After doing HIIT 3 times a week for just a couple of weeks, the results show that time trial performance improved by an average of almost 10 percent.
In another trial, HIIT generated identical improvements in time trial performance compared to lower intensity endurance exercise, despite the fact that the HIIT workouts required a lot less time to complete .
Here’s how the researchers sum up their findings:
“Given the large difference in training volume, these data demonstrate that sprint interval training is a time-efficient strategy to induce rapid adaptations in skeletal muscle and exercise performance that are comparable to continuous training in young active men.”
How Long Does It Take To Lose Weight With HIIT?
Do HIIT 2-3 times a week, paired with a solid diet that puts you in a calorie deficit, and you might lose around 2-4 pounds of body fat in your first two weeks.
Weight loss does tend to scale up with body weight, in the sense that the more weight you have to lose, the faster you tend to lose it.
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That is, smaller individuals with less fat to lose will see results near the lower end of that range, while larger individuals with more fat to lose will see results near the higher end.
The numbers you see on the scale may be even larger, because of the difference between weight loss and fat loss.
In the early stages of dieting, weight loss tends to happen more quickly than fat loss, mainly because of losses in fluid and glycogen (the name for carbohydrate stored in your body).
However, most of that weight loss will have been generated by the diet, rather than HIIT training per se.
To repeat a point I made earlier, no matter what form of exercise you do, your ability to lose fat hinges on being in a calorie deficit.
While high-intensity exercise, be it HIIT, strength training, or even just regular steady-state cardio done at a high intensity, can contribute to the energy deficit required for weight loss, it’s not going to produce radical changes in body composition by itself.
What Results Can You Expect After Six Weeks of HIIT?
After six weeks of HIIT, expect significant gains in cardiovascular fitness. In fact, studies show that regular training will increase your VO2max, a popular way to measure cardiovascular fitness, by around 8% in around six weeks .
VO2max is a way of measuring aerobic power. It tells you how much oxygen your body can use at a maximal level of effort and is usually expressed in milliliters of oxygen per kilogram of bodyweight per minute.
Some studies show even more impressive results.
However, the Tabata Protocol describes a very specific type of sprint interval training, in that it uses 20-second bouts of all out sprinting on a stationary bike separated by just 10 seconds of rest.
I’m not talking about a level of intensity that gets you a little out of breath — this type of training is brutally hard.
“If you feel OK afterwards you’ve not done it properly” says Izumi Tabata, the Japanese scientist who put the protocol to the test back in the 1990s.
“The first three repetitions will feel easy but the last two will feel impossibly hard. In the original plan the aim was to get to eight, but some [subjects] only lasted six or seven.”
And it’s not like the subjects taking part in Tabata’s study were complete novices, unaccustomed to the demands of high intensity exercise.
They were all physically active young men, and were members of varsity table tennis, baseball, basketball, soccer, and swimming teams.
Over the years, the Tabata Protocol label has been watered down, often being applied to any form of training that involves short 20-seconds of activity separated by 10 seconds of rest.
Don’t be taken in.
Many of the so-called Tabata workouts promising to make all your physical fitness dreams come true with less than 10 minutes of exercise are nothing like what was done in the original study.
What Results Can You Expect After Three Months of HIIT?
In one study, 10 minutes of HIIT, done three times a week for three months, delivered many of the same benefits as 150 minutes of traditional moderate intensity exercise .
After warming up for two minutes, the participants pedaled fast for three 20-second intervals. Each interval was followed by two minutes of slow pedaling. The workout finished with a three-minute cool-down.
From start to finish, the workout lasted 10 minutes. Only 60 seconds of that time was spent working hard.
By the end of the three-month study, subjects in the continuous moderate intensity group had ridden for 27 hours. However, the interval group spent a little over five hours on the bike.
Despite a five-fold lower time commitment, various measures of cardiometabolic health improved to a similar extent in both the HIIT and steady-state groups.
- VO2 peak, a measure of aerobic fitness, increased by 15-20% in both groups.
- Insulin sensitivity, a marker of blood sugar control, improved to a similar extent in both groups.
- Muscle mitochondrial content also increased similarly after HIIT and steady-state exercise.
What about fat loss?
A review published in the British Journal of Sports Medicine reports that after 30-35 workouts (around three months if you’re training three times a week), the average amount of fat lost with HIIT training was 3.5 pounds (1.6 kilograms), compared to 2.5 pounds (1.1 kilograms) with steady-state cardio .
Granted, the HIIT workouts didn’t last as long. But still, the overall difference in results – one pound of additional fat loss over a 10-12 week period – was relatively small.
Where HIIT Doesn’t Live Up to the Hype
One of the main selling points of HIIT is its so-called “afterburn effect,” which refers to the fact that your body is still burning calories in the hours and days after a workout is over.
Unfortunately, the size of the afterburn effect, as well as the extent that post-exercise changes in metabolism and fat burning contributes to weight loss, is not as great as was once believed.
Most research comparing the effect of HIIT and steady-state cardio on fat loss show little difference in results between the two types of exercise .
In a 2017 review published in the journal Obesity Reviews, researchers could find “no evidence to support the superiority of either high-intensity interval training or steady-state cardio for body fat reduction.”
A separate research team came to much the same conclusion after doing their own analysis of the research .
HIIT and moderate-intensity continuous training (MICT) are similarly effective, they say, and both elicit “modest improvements, and of similar magnitude, in body fat levels and waist circumference in overweight and obese adults.”
They do note, however, that HIIT is a more efficient alternative to steady-state cardio, delivering similar fat-loss benefits with less time spent in the gym.
Compared to strength training, HIIT isn’t a particularly effective way to build muscle mass either.
If you’re completely deconditioned and out of shape, HIIT is likely to stimulate some kind of increase in muscle mass.
In novices, virtually any stimulus represents an unusual challenge to muscle tissue, which will adapt to that challenge, in part at least, by getting bigger.
But if you’ve got a few years of training behind you, your muscles will already have adapted to such a low level of stress, and HIIT is unlikely to provide a significant stimulus for growth.
Frequently Asked Questions
How much weight can I lose in a month with HIIT?
Combine regular HIIT with a diet that puts you in a calorie deficit, and you’ll lose anywhere between 4-8 pounds of fat in a month. However, most of that weight loss will have been generated by the diet, rather than the HIIT.
Is HIIT 3 times a week enough?
Research shows that doing HIIT 3 times a week is enough to boost your VO2max (a measure of cardiovascular fitness), improve exercise performance, as well as enhance various measures of cardiometabolic health, such as insulin sensitivity and skeletal muscle mitochondrial content.
What happens if I do HIIT everyday?
Doing HIIT every day will ultimately lead to a physiological state known as overreaching, a term used to describe temporary overtraining. Some of the symptoms include persistent tiredness, heavy, sore muscles, and a reduction in exercise performance. You’ll see better results doing HIIT 2 or 3 times a week, rather than every day.
Should you do HIIT on an empty stomach?
Doing HIIT on an empty stomach is no more effective for fat loss than doing it after a meal. Ultimately, training in a fed or fasted state is a decision that can be left to personal preference. As far as improving your body composition is concerned, there’s no great harm or benefit to one or the other.
Can you lose weight just doing HIIT?
HIIT can certainly contribute to the calorie deficit required to lose weight. However, just doing HIIT without making any changes to your diet isn’t going to deliver much in the way of weight loss. No matter what form of exercise you do, be it HIIT, steady-state cardio or resistance training, your ability to lose weight depends on you being in a calorie deficit.
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