Interval training is any type of physical workout program that involves various intensities of exercise, going from short periods of high, intense work to longer periods of recovery in which only low- or no-intensity work is accomplished. The term can refer to any type of cardiovascular workout, such as running, bicycling, or swimming, in which brief spurts of maximum exertion, called sprint intervals, are intermingled with longer periods of much lower intensity activity, or rest intervals. This pair of intervals, or sets of high to low intensity activities are repeated several times to complete an interval training session.
For example, joggers include interval training within their weekly runs by alternating the use of walking and sprinting once or twice a week, in what is called sprint interval training (SIT). Similarly, swimmers can incorporate several fast-paced laps for every four or five slower laps.
The recent popularity of interval training over the past several decades has been due to its effectiveness in providing a good cardiovascular workout. Because the intensity of the workout is varied, it exercises the heart muscle, which improves the cardiovascular system of the body. Interval training helps to improve a person's aerobic capacity because, as one uses interval training on a regular basis, that person is able to exercise longer and at more intense levels. Interval training also provides a comprehensive workout plan for many types of athletes, along with people who just want to stay healthy and fit.
Interval training is appropriate for most people who are in generally good health. If one has problems with the cardiovascular system (such as heart disease), arthritis, or joint problems, then it is recommended that a doctor be consulted before beginning interval training. In addition, if one is over age 45 years for men and age 55 years for women, it is necessary to first check with a doctor before beginning such a program.
Interval training possibly originated in Sweden, where it is called fartlek, meaning “speed play.” As such, the basic idea of interval training is to vigorously exercise for a short amount of time and then slow down for a longer recovery time, only to resume the intensity for another short period followed by another longer break, and to do this many times in succession. This method improves a body's performance, specifically its endurance, speed, and strength.
Many different types of interval training are used. One example of interval training with a bicycle is:
Interval training can also be done with running. The high intensity portion of sprinting is called sprint intervals. They may consist of a time as short as 15 seconds or as long as 20 minutes. An example of sprint interval training is to run at a maximum speed for 30 seconds in a straight line. Running at such fast speeds for 15 minutes would simulate the climbing of a hill and is also a part of interval training.
Workout music is available that is specially designed to guide one through interval training. Such workout music is available on the Internet, and most tunes can be downloaded to a mobile device.
Medical research has proven over the years that interval training and HIIT, to a greater degree, has many benefits for its users. The American College of Sports Medicine (ACSM) states the benefits of interval training and HIIT, such as decreasing abdominal fat and body weight while preserving muscle mass, increasing aerobic and anaerobic fitness, improving endurance, lowering blood pressure, and improving cardiovascular health, cholesterol profiles, and insulin sensitivity
BURNING FAT. Studies involving interval training and the ability to effectively burn fat have been consistently reported by the medical community. For instance, a study from researchers at McMaster University (Hamilton, Ontario, Canada), along with those from the University of Stirling (Scotland) and the University of Guelph (Canada), reported on the use of interval training to improve cardiovascular fitness and the body's ability to burn fat. The researchers studied eight women in their early twenties. The women intensely cycled for ten sets of four-minute intervals each; which was then followed by periods of two minutes of rest. In a two-week period, these female participants completed seven of these HIIT sessions.
The researchers found that the amount of fat expended in one hour of continuous moderate cycling increased by 36% when compared to the control group, which did not participate in interval training. Overall, the ability of the women's heart and lungs to supply oxygen to their working muscles, or cardiovascular fitness, improved by 13%.
IMPROVING ENDURANCE. Medical studies have consistently shown similar results with endurance when experiments were conducted with human subjects participating in interval training versus a control group. For instance, Canadian researchers at McMaster University studied interval training and endurance in 2005. They looked at college students who bicycled for 30 seconds at sprint-type speeds and then stopped pedaling or greatly slowed their speeds for four minutes. This group and a control group (who did not do this interval training) also jogged, biked, and did aerobic exercise two to three times each week. After two weeks, 75% of the interval-training group doubled their endurance on the bicycles. That is, they were able to double the time that they sprinted at moderate intensities before becoming exhausted. None of the members of the control group showed any improvement in endurance over this two-week period. Because the size of the two groups was small, the researchers stated that further research studies were necessary to verify their conclusions.
Numerous studies have followed this one at McMaster University. In 2016, a study was published in Public Library of Science One (PLOS ONE). Titled “Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training Despite a Five-Fold Lower Exercise Volume and Time Commitment,” the study “investigated whether sprint interval training (SIT) was a time-efficient exercise strategy to improve insulin sensitivity and other indices of cardiometabolic health to the same extent as traditional moderate-intensity continuous training (MICT).”
As the title suggests, sprint interval training was considered equal to traditional endurance training but with much less commitment in volume and time. The authors concluded, “In summary, we report that a SIT protocol involving 3 minutes of intense intermittent exercise per week, within a total time commitment of 30 minutes, is as effective as 150 minutes per week of moderate-intensity continuous training for increasing insulin sensitivity, cardiorespiratory fitness, and skeletal muscle mitochondrial content in previously inactive men.”
GLUCOSE FUEL PRODUCTION. Studies have been conducted with regards to interval training, especially high-intensity interval training, and glucose/insulin. With regard to HIIT, medical researchers have found that it helps to improve the body's sensitivity to insulin. This means that when HIIT is performed regularly the muscles that are exercised become more readily able to use glucose for fuel to make energy. Glucose is a simple sugar that circulates within the blood as blood sugar. The reaction of insulin controls the concentration of glucose in the blood. Glucose is stored as glycogen and used when activity levels within the body need a boost of energy.
Any healthy person can do interval training for improved fitness, health, stamina, and speed. Due to the physical demands of interval training, adequate preparation is necessary. Participants should never go all out when first beginning interval training but gradually should increase performance to prevent injury. Warming up is critical because it gets extra blood into the muscles so they are prepared for the activity.
There is not one generally recommended way to prepare for interval training and to actually do interval training. A good warm-up period is always recommended before doing any exercise. A warm-up period may consist of about five minutes of light jogging or walking with a little extra quickness introduced from time to time to let the body get accustomed to exercising. Once interval training is started, many exercise experts recommend that the duration of intense activity and moderate activity or rest should be varied.
Once interval training is completed, it is a good idea to spend about five minutes cooling down. Light jogging or walking helps the body return to its regular routine. Some stretching exercises can also prevent muscle strain or soreness.
A chronic health condition, such as heart disease, respiratory disorder, or cancer, may prevent one from doing interval training. It is important to consult with a medical professional, such as a family doctor, before trying any type of interval training.
A risk of injury, such as with bones, muscles, or tendons, can occur with interval training, especially if one overexerts when first starting the training. Symptoms of overtraining include loss of endurance, strength, and speed; chronic aches and pains; loss of appetite; inability to sleep; overuse injuries such as tendinitis; irritability; irregular resting heart rate; and malaise, or a general feeling of fatigue, or ill feelings.
In general, the intensity of interval training sessions should be from 80% to 85% of the maximum heart rate, what is called the target heart rate. This rate differs from person to person, depending on such factors as age, genetics, fitness level, and gender. The American Heart Association provides advice on target heart rates on its webpage “How Do You Get Your Heart Rate on Target?” In addition, some high-blood pressure medications lower the maximum heart rate. Thus, if an individual is taking one of these medicines, then a lower target heart rate should be used. Before applying a maximum heart rate, individuals should contact a family physician or other medical professional for advice.
Interval training has great benefits for maintaining a healthy and physically fit body. It improves the body's aerobic capacity, which means the cardiovascular system will work more efficiently after interval training over a long period. In the long run, it improves cardiovascular fitness and also reduces the risk for many medical disorders, such as heart disease. A regular exercise program that includes interval training helps to maintain a healthy weight-to-height ratio, or body mass index (BMI), by raising the body's potential to expend (burn) fat.
See also EPOC (Excess Postexercise Oxygen Consumption) .
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William A. Atkins, BB, BS, MBA