High-intensity interval training (HIIT) provides a number of health benefits, according to the American College of Sports Medicine. The benefits include reduced blood pressure, improved cardiovascular health, healthy cholesterol levels, better insulin sensitivity, loss of abdominal fat and excess weight while maintaining muscle mass. High-intensity interval training can also improve your fitness performance by helping you build endurance, increase your strength, and boost the amount of oxygen flowing to your working muscles.
In short, HIIT features short bursts of intense aerobic exercise followed by less intense recovery periods. The theory behind HIIT is that engaging in rest intervals allows the body to do more work at a higher intensity than engaging solely in high intensity exercise.
The total HIIT workout typically lasts 20 to 60 minutes, alternating between bouts of intense exercise and recovery periods. The bursts of intense exercise may last anywhere from 5 seconds to 8 minutes. The individual engages in exercise that raises his or her heart rate to 80 to 95 percent of the person’s maximum heart rate. Recovery periods, done at 40 to 50 percent of the individual’s maximum heart rate, usually last as long as the work periods.
As far as calorie burn, one study shows that high-intensity interval training can burn 25 to 30 percent more calories than other types of exercise. HIIT can increase metabolic rate after exercise, according to research, even more than jogging and weight training can. This approach to exercise can help burn fat, reduce blood sugar, and provide other health benefits.
High-intensity interval training can also improve fitness performance, which means it can help individuals perform better during daily exercise and while engaging in sports. HIIT does this by optimizing the cardiovascular system to improve the flow of oxygen- and nutrient-rich blood to muscles.
HIIT Improves Fitness Performance By Optimizing The Cardiovascular System
The cardiovascular system supplies muscles with the oxygen, sugar, and other nutrients they need to function during exercise. Muscles use oxygen to turn blood sugar, otherwise known as blood glucose, into energy. Insulin helps the muscles absorb all the glucose they need from the bloodstream.
Each beat of the heart pushes about 4.5 to 5.5 liters of blood through the arteries, veins, and capillaries of the human body. The heart consists of four chambers – two ventricles and two atria. Veins deliver blood from around the body to the two atria, which pump the blood into the two ventricles. The ventricles then pump the blood to the lungs and to the rest of the body.
The heart relaxes in between heartbeats. During the relaxation phase of the heart, blood fills the ventricles in a process known as preloading. The flow of blood causes the muscle tissue in the ventricle to stretch so that the chamber can hold as much blood as possible, somewhat like a balloon, which allows the heart to pump out a large amount of blood with the next heartbeat. High-intensity exercise expands the ventricle to allow the heart to pump the maximum amount of blood possible.
HIIT improves oxygen flow to complete longer exercise sessions. During the high-intensity portion of HIIT, the cardiovascular system speeds up to deliver more oxygen to the muscles to improve fitness performance. The intense cardiovascular workout increases heart rate to push blood through arteries and veins faster. Increased heart rate delivers more oxygen-rich blood to working muscles each minute. The more oxygen and nutrients muscles receive from the blood, the better they will be able to perform.
The high-intensity activity increases heart contractility, which is the forcefulness of each contraction of the heart. Heart contractility allows the heart to pump oxygen-rich blood into arteries, even when the blood pressure inside the arteries is already high.
An aerobic workout, such as the intense exercise portion of the HIIT cycle, also increases the amount of blood pumped per heartbeat, known as stroke volume. A high stroke volume delivers a large amount of blood to working muscles to improve fitness performance.
Increased heart rate, forcefulness of contractility and the extra blood pumped with stroke volume increase the flow of oxygen- and nutrient-rich blood to the exercising muscles; the extra oxygen and nutrients help muscles function at peak performance.
Exercising the skeletal muscles, such as those in the arms and legs, also improve cardiovascular function. Each time skeletal muscles contract, they push blood through veins back towards the heart. The repeated muscle contractions associated with exercise causes a large volume of blood to flow towards the heart and create a generous amount of blood available for preload.
HIIT can trigger adaptations in the structure of the heart muscle. Bursts of exercise can help thicken heart muscles and expand the left ventricle to improve heart function during activity. In other words, HIIT improves your endurance by strengthening the muscles of your heart.
HIIT also increases strength to improve fitness performance. In a 2017 study, researchers assigned male participants between the ages of 25 and 70 to two groups. Participants in the test group performed HIIT along with strength training, while participants in the control group did only strength training. After 12 weeks, the test participants who did HIIT experienced increases in VO2 max, insulin sensitivity, mitochondrial function, fat-free mass, and muscle strength. Those in the control group did not experience these benefits.
VO2 max is the maximum amount of oxygen a person uses during exercise. Increasing VO2 max provides more oxygen to the cells, which use the oxygen to turn glucose into fuel. Increased insulin sensitivity means the cells can absorb greater amounts of glucose to use as fuel.
HIIT has been around since the early 1900s, according to the International Sports Sciences Association (ISSA), created as a tool to help endurance athletes. In the decades since, athletes from a number of other sports adopted the training technique. Today, fitness enthusiasts of all athletic levels use HIIT to improve their fitness performance.