HIIT: Why It Works - insidefitnessmag.com
Written By Charlotte Sinclair
Every year, you’re probably wondering how high-intensity interval training (HIIT) is still popular? The buzz isn’t going anywhere. In 2020, HIIT came in at number two on the American College of Sports Medicine Health and Fitness Journal Worldwide Survey Fitness Trend.

Why is it popular?
During the pandemic, people are looking at ways to reduce their stress levels. Fitbit data found the activities which gained popularity were those typically associated with stress reduction. HIIT is known to reduce stress on a chemical level – in part because it’s stimulating endorphin levels in the brain in what is typically referred to as a “runners high” as it reduces stress hormones such as adrenaline and cortisol. This increasing trend won’t be going anywhere and is likely to continue as one of the most popular exercises well into 2021/2022.

What is HIIT?
HIIT is a popular fitness trend, which integrates cardiovascular and muscular effort using complex, partly loaded movement patterns with only minimal breaks in-between and has been shown to trigger positive adaptations in endurance and strength capacities. HIIT is a workout that alternates between intense bursts of activity and fixed periods of less-intense activity or even complete rest. HIIT Workouts can be performed on all exercise’s modes including cycling, swimming, walking, elliptical cross-training, and in many group exercise classes. It is often marketed as an efficient workout to achieve weight loss, explains Tom Cowan, an exercise physiologist at the Centre for Human Health and Performance on London’s Harley Street.

Science of HIIT
One of the reasons for HIIT’s popularity is the post-exercise calorie burn which makes it more of an efficient method than traditional steady-state exercise. The post-exercise period is called “EPOC”, which stands for excess postexercise oxygen consumption. This is generally about 2 hours after an exercise where the body is restoring itself to pre-exercise levels and therefore using more energy. The vigorous nature of HIIT Workouts makes the EPOC modestly greater, adding about 5-15% more calories to the overall workout energy expenditure. Besides its efficiency, studies have shown HIIT results in an increase in metabolism, improved cardiovascular fitness and improved muscle tone along with weight loss. More strikingly, according to a small study in Cell Metabolism in 2017, HIIT effectively halts ageing at the cellular level, by increasing the production of proteins for the mitochondria, your cells’ energy-releasing powerhouses, which otherwise deteriorates over the years. Other forms of exercise such as strength training do likewise, but HIIT is more effective. The study also stated that muscle cells, like those in the brain and heart, wear out and are not easily replaced, so if exercise prevents deterioration of mitochondria in muscle cells, or even restores them, then it likely does in other tissues too.

Similarly, HIIT beats continuous moderate-intensity exercise when it comes to releasing brain-derived neurotrophic factor (BDNF), a protein that protects nerve cells. This promotes plasticity (the forming of new connections, which aids learning and memory) and may even help regulate eating, drinking and body weight. Perhaps HIIT’s biggest selling point is its efficiency: a workout can last up to an hour, but it can also be completed in 20 minutes or less. Tabata, one of the most well-known HIIT protocols, consists of 20 seconds of work followed by 10 seconds of rest, repeated eight times for a total of just four minutes, not counting the warm-up and cool-down.

What is the impact on the body?
HIIT helps you burn calories quickly. A study published by the National Library of Medicine compared the calories burned during 30 minutes of each HIIT, weight training, running, and biking. The research found that HIIT burned 25-30% more calories than other forms of exercise. A HIIT workout elevates your metabolism. The workout quickly and thoroughly depletes the energy and strength of your muscles, depletes oxygen from your blood and increases your core temperature. Once the workout is completed your body beings to return to homeostasis. Your body begins repairing your muscles, resynthesizing, and replenishing the energy you depleted, replenishing oxygen in the blood and decreasing body temperature. As a result, your body breathes in greater levels of oxygen and therefore burns more calories to accomplish all of this. In other words, brief, intense exercise stresses your body more (in a good way.) This elevates your metabolism and makes you burn more calories, leading to better cardiovascular/metabolic health! HIIT has other additional benefits too. Another study published by the British Journal of Sports Medicine found that engaging in HIIT reduces heart rate and blood pressure in overweight and obese individuals, who often have high blood pressure. One study found that eight weeks of HIIT on a stationary bike decreased blood pressure as much as traditional continuous endurance training in adults with high blood pressure. In this study, the endurance training group exercised four days per week for 30 minutes per day, but the HIIT group only exercised three times per week for 20 minutes per day. Some researchers have found that HIIT may even reduce blood pressure more than the frequently recommended moderate-intensity exercise.

Getting Started
There are many ways to add high-intensity intervals to your exercise routine, so it isn’t hard to get started. To begin, you just need to choose your activity (running, jumping, skipping etc.). Then, you can experiment with different durations of exercise and recovery, or how long you are performing intense exercise and how long you are recovering.

Here is an example of a 30-minute HIIT workout without any equipment.

When warming up, jog on the spot, sprint as fast as you can for 15 seconds. Then, walk or jog at a slow pace for one to two minutes and rest for 30 seconds.
Jog in place, kicking your heels high to try to tap your butt. Complete this for 30 seconds and rest for 30 seconds.
Perform squat jumps as quickly as possible for 30 to 90 seconds. Then, stand or walk for 30 to 90 seconds.
Step back with your right foot and bend both knees to 90 degrees to sink into a lunge. Keep your core engaged, your hips tucked and your back straight. Repeat 10 times on each leg.
Jump your feet wide, sit back into a wide squat, engaging your glutes and bending both knees until your thighs are parallel to the floor, tap with your right hand. Jump your feet back together and repeat 20 times. Rest for 30 seconds.
Stand upright, walk your hands to a plank position, arms, and legs straight, core engaged and back flat, complete a push up and walk your hands back to your legs, push yourself up to standing repeat for 30-90 seconds, rest for 30 seconds.
Stand with your feet hip-width apart. Lift your right leg and jump to the right. Allow your left leg to straighten and follow. As you land on your right foot, swing your left foot behind you, keeping your left foot off the floor. Bring your left hand down as your right arm swings behind your back. Repeat for 30-90 seconds and rest for 30 seconds.
Place your forearms on the floor, elbows directly underneath your shoulders, hands facing forward so that your arms are parallel to each other. Hold for 30-60 seconds.
The key is to add short bursts of movement into any part of your exercise routine to help your body work harder and burn calories faster. You might find it hard at first, but one thing is for sure, you will see vast improvements in overall endurance, fitness, and weight levels in a short period of time.
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