High Intensity Interval Training (HIIT)
High Intensity Interval Training (HIIT)
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Interval training involves bursts of intense exercise separated by periods of recovery, which can involve complete rest or lower-intensity exercise.
Go hard...Relax...Go hard...Relax...
Why would someone want to do high intensity exercise? After all, it's hard!
New research is showing that high intensity exercise is much more beneficial for your health than light or moderate intensity exercise. For example, consider a recent study in Nature Communications that analyzed data from wearable devices for ~73,000 adults aged 40-69.
Across different outcomes, the study found that 1 minute of vigorous activity typically matches 4–9 minutes of moderate activity. Specifically:
All-cause mortality: 1 minute of vigorous = 4.1 minutes of moderate
CVD mortality: 1 minute of vigorous = 7.8 minutes of moderate
MACE: 1 minute of vigorous = 5.4 minutes of moderate
Type 2 diabetes: 1 minute of vigorous = 9.4 minutes of moderate
Cancer mortality: 1 minute of vigorous = 3.5 minutes of moderate
In other words, vigorous activity is often 4x, 5x, even 9–10x "more valuable" minute-for-minute than moderate when it comes to actual health outcomes.
While this is a new study, there have been many studies showing the benefits of high intensity exercise.
More Evidence
More Evidence
Most of the research summarized here was included in Martin Gibala's book The One Minute Workout.
Study conducted by Martin Gibala at McMaster University in 2005.
8 subjects
6 training sessions over 2 weeks
Each session: 4-6 rounds of cycling all-out for 30 seconds each, with 4 minutes of rest in between
Assessment: Pedal a stationary bike set to a fixed workload for as long as possible (before and after the training period).
Results
Results
On average, before the training, the 8 subjects could pedal the bike for 26 minutes until exhaustion. Following the 2 weeks of internal training, the average time was 51 minutes - a doubling of endurance capacity.
These results were achieved with a total of approximately 15 minutes of intense exercise time across all sessions in 2 weeks!
Designed to directly compare HIIT with more traditional endurance training.
6 week study
20 subjects divided into two groups
Endurance training (ET) group - rode stationary bike 5 days/week for 40-60 minutes/day (at 65% of max aerobic capacity)
Interval training (IT) group - rode stationary bike 3 days/week, 4-6 rounds of cycling all-out for 30 seconds each, with 4 1/2 minutes of rest in between
If you count only the intervals, the IT group worked out for just under 10 minutes a week. Compare that with the ET group's 4 1/2 hours of continuous moderate-intensity exercise per week. The IT group exercised less than 5% of the total time of the endurance group.
Results
Results
The improvements were the same between the groups for every fitness parameter measured.
Approximately 10 minutes of hard exercise a week boosted overall fitness to the same extent as 4 1/2 hours per week of traditional endurance training!
Led by Ulrik Wisløff and colleagues at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway, it is one of the largest and longest randomized controlled trials examining the effects of exercise on health and longevity in older adults.
It was a three-arm randomized controlled trial (RCT) with a HIIT group, a moderate intensity continuous training (MICT) group, and a control group which was instructed to follow national physical activity guidelines (but not supervised).
The study provided high-quality evidence that following public health physical activity guidelines is sufficient to achieve similar longevity benefits as structured supervised training in healthy older adults. However, HIIT was superior for improving and maintaining cardiorespiratory fitness—a strong predictor of health and survival—and may offer advantages for functional capacity and quality of life*.
*Participants in HIIT reported higher self-perceived well-being, including aspects like vitality, emotional health, and overall life satisfaction.
12 week study with 27 men
Three-arm RCT - SIT, MICT, and control group
SIT: 3 x 20second all-out sprints
MICT: 45 minutes of continuous cycling at 70% max heart rate
Control: No training
Results
Results
This demonstrated that ultra-low-volume SIT (five-fold less time and volume than MICT) elicits comparable cardiometabolic benefits over 12 weeks, including enhanced insulin action and mitochondrial biogenesis—key for preventing metabolic diseases like type 2 diabetes—highlighting intensity's role over volume in longer-term adaptations.
Key Takeaways
The harder you go, the shorter the duration and the fewer intervals you need to achieve the same benefits of a much longer endurance-training workout.
Whether you're talking endurance training or interval training, the goal is the same: cardiorespiratory fitness.
Cardiorespiratory fitness or aerobic fitness refers to the ability of your body to transport and utilize oxygen. Scientists have found that it's one of the best predictors of overall health. It also happens to be the form of fitness that helps you live longer and live better by reducing your chance of developing ailments like cardiovascular disease and diabetes.
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