High Intensity Interval Training (HIIT) is, in very simple terms, alternating intense exercise with less intense “rest” periods. For example, you can run as fast as you can across a football field and then walk around the field for 30 to 60 seconds before repeating.
Why does this work?
Exercise is like starting a fire for your metabolism. When you’re active, your metabolic rate and calorie burn increase to varying degrees. With traditional low- to moderate-intensity exercise, such as walking on a treadmill or using the elliptical for 30 minutes at a steady pace, you ignite the flame and it slowly builds to a gradual burn..
When the workout is over, the flame goes out quickly and abruptly… just like dousing it with water. On the contrary, In HIIT, high-intensity exercise creates a huge metabolic disturbance and the flame heats up quickly. Each interval is like throwing a lighter into the fire.
Also, after a HIIT workout, the flame gradually goes out and simmers for a long time. Have you ever lit a fire, left it burning all night, and found the embers still hot and glowing in the morning? This is HIIT and it’s the effect it has on your metabolism: it’s intense and you keep burning calories even when the workout is over.
This is called excess post-exercise oxygen consumption, or EPOC: after an exercise session, oxygen consumption (and thus caloric expenditure) remains elevated as active muscle cells reset physiological factors and cell metabolism to pre-exercise levels.
This is what traditional cardio cannot do: A review article published in the Journal of Sports Sciences notes that exercise intensity studies show higher EPOC values with HIIT training compared to low-to-moderate-intensity constant-speed cardiovascular training.
HIIT: The benefits don’t take long to show
A team from the University of Guelph in Canada showed that fat oxidation, or fat burning, was significantly higher after six weeks of interval training. Another study from the University of Guelph showed a similar change in just two weeks.
HIIT has also been shown to be better for building fitness or cardiovascular fitness than traditional cardio. Cardiovascular function is often measured by maximal oxygen consumption, commonly referred to as maximal aerobic capacity or VO2max (maximum volume of oxygen).
The body’s superior ability to consume, deliver and utilize oxygen to produce energy, VO2max is a good indicator of exercise performance. In what is the most comprehensive (and recent) study comparing HIIT and traditional cardio of longer duration, Jenna Gillen found that 12 weeks of speed training (three sessions per week for a total of 10 minutes per session) in a cycle consisting of just three 20-second full sprints separated by two-minute recovery periods produced exactly the same improvements (20 percent) in aerobic fitness and insulin resistance as three continuous 45-minute moderate-intensity sessions.
Think about this: the HIIT group trained for just six hours, compared to 27 hours for the traditional cardio group, and got the same results!
A French study measured VO2max responses between two groups of men and women; one group participated in an eight-week HIIT program; the other, in a traditional steady-rhythm cardio program.
The HIIT group saw a greater increase in VO2max (15%) than the group doing traditional steady-state cardio (9%).
Improving cardiovascular function and increasing VO2max are the main goals of patients suffering from heart disease. For that reason, some cardiac rehabilitation centers are beginning to incorporate interval training with heart disease patients.
The results show improvements similar to traditional low-intensity cardio, but in less time and with fewer sessions. The take home message? Compared to traditional low to moderate intensity sustained cardio, HIIT will allow you to:
- You burn fat faster.
- You burn more calories after you finish your workout.
- Build the same or better cardiovascular fitness in a fraction of the time.
The workouts work you really hard for less than a minute, and then you’ll be recovered enough to do them again. This format will build your cardiovascular health, which in turn can lower your blood pressure and cholesterol levels and protect you from heart disease. and diabetes, increase bone density, improve sleep quality and even help you live longer.