The Science Behind High-Intensity Interval Training (HIIT)

Has your workout ever felt like it isn’t intense enough? Are you tired of performing steady-state cardio for hours on end?

If so, a great way to up the intensity of your training is to try a type of exercise known as High-Intensity Interval Training (HIIT).

What Exactly is HIIT?

HIIT entails interspersing short bursts of very high-intensity exercise with periods of rest or lower-intensity exercise. For example, one session might require sprinting as fast as possible on a treadmill for 30 seconds, followed by 60 seconds of jogging at a light pace to recover.

Then you repeat this sequence several times, keeping your heart rate up the whole time.

The intense exercise intervals during HIIT are done at 80-100% of your max heart rate, meaning you push yourself to the limit. This allows you to burn way more calories and fat in a short amount of time compared to steady-state cardio at 60-70% of your maximum heart rate.

The Many Benefits of HIIT

Studies have shown HIIT has a ton of benefits:

• Burns More Calories in Less Time: Evidence suggests that HIIT can burn 25-30% more calories during the same session as other aerobic training and workouts.
• Improves Cardiovascular Fitness: The hard intervals boost VO2 max, a measure of how much oxygen your body can utilize when you exercise, indicating increased cardiovascular efficiency.
• Burns More Fat: HIIT draws on body fat to power the intense bursts of exercise and burns more glycogen than steady-state cardio. One study found that, when equal numbers of calories were burned, HIIT decreased body fat twice as much as steady-state cardio.

Why Does HIIT Work So Well?

There are some key scientific reasons why HIIT is so effective:

Excess Post-Exercise Oxygen Consumption (EPOC)

This is the supercharged rate of oxygen uptake once you stop working hard. Depending on the HIIT workout you choose, you can get more of this boost after the workout than you ever could from steady-state cardio.

Your body needs the extra oxygen to bring all your systems—heart rate, temperature, breathing, blood pressure, etc.—back down to pre-exercise levels. In other words, you keep burning calories after the workout too.

Increased Metabolic Rate

HIIT programs have been shown to boost your resting metabolic rate, which means that you burn more calories during normal daily activities, even when you’re at rest. This effect is attributed to the fact that your muscles require more energy to return to their normal state of equilibrium; the metabolic boost after a HIIT workout can last 24-48 hours.

Improved VO2 Max

The continuous high-intensity intervals increase your VO2 max. Your heart and lungs become more efficient, and your muscles become better at utilizing oxygen.

Muscle Fiber Recruitment

Different muscle fiber types are recruited at different intensities. HIIT forces your body to utilize high proportions of fast-twitch muscle fibers on top of the slow-twitch fibers that carry you through easier exercises. Fast-twitch fibers are metabolically more active, meaning they spark more calories being burned during and long after your workout.

Increased Growth Hormone

Human Growth Hormone (HGH) peaks following HIIT, effectively combining calorie and fat burning with muscle building. More growth hormone means more calorie and fat burn.

Sample HIIT Workouts to Try

Treadmill HIIT

1. Warm-Up: Warm up with a 5-minute walk at an easy pace.
2. Intervals: Sprint for 1 to 2 minutes as fast as you can (roughly 10 mph), then slow down for 1-2 minutes of brisk walking (3-4 mph).
3. Repeat: Complete 10 sprint/walk intervals for a 20-minute workout.

Cycling HIIT

1. Warm-Up: Warm up for 2 minutes at an easy pace (about 50 rpm).
2. Intervals: Reduce the resistance and alternate 30 seconds of intense pedaling (80-100 rpm) with 30 seconds of slow pedaling (50-60 rpm).
3. Repeat: Complete 20 intervals for a total of 10 minutes of HIIT.
4. Cool Down: Finish with 2 minutes of easy cycling to cool down.

Bodyweight HIIT Circuit

1. Warm-Up: Jog in place for 1 minute to warm up.
2. Push-Ups: Do 10 push-ups, rest for 30 seconds.
3. Squats: Do 15 bodyweight squats, rest for 30 seconds.
4. Mountain Climbers: Do 20 mountain climbers (10 per leg), rest for 30 seconds.
5. Plank: Hold a 30-second plank, rest for 30 seconds.
6. Repeat: Repeat the circuit 3 times.

There are literally endless possibilities for doing HIIT with any sort of cardio or bodyweight exercises. Begin with gentler intervals to perfect proper form and intensity.

By incorporating HIIT into your fitness routine, you can maximize your workouts and achieve better results in less time. Always remember to consult with a fitness professional or healthcare provider before starting any new exercise program, especially if you have any underlying health conditions.