In recent years athletes, coaches, and fitness enthusiasts have dramatically increased their use of interval training, especially high-intensity interval training (HIIT). This trend is evidenced by the sheer number of interval-training classes being offered at local gyms and health clubs. Additionally, in the past several years consumers have been bombarded with information about extreme conditioning programs through the Internet, television, and other forms of media. Although these programs may differ in structure, types of exercises and drills, and duration, one thing is relatively consistent: purpose. That purpose is to gain the benefits of aerobic training, anaerobic training, and even strength training in a short, intense period.
The purpose of this book is to help readers develop optimal maximum interval training (MIT) sessions to meet their specific fitness and performance goals in a safe and effective manner. To allow readers to individualize their MIT sessions, a wide variety of modalities and training options are presented so that readers can tailor their training program to their specific needs, preferences, and constraints.
MIT uses short, intense exercise periods with a variety of exercise modes combined with brief bouts of recovery to improve performance and body image. Typically, exercise bouts are performed at a high intensity level. To allow performance at high intensity, the exercise session has to be brief; otherwise, the person would not be able to maintain the effort. For example, many of the programs in this book have exercise bouts between 20 and 60 seconds in length.
The length of the rest periods is dictated by the intensity of the work bout, meaning that the more intense the work bout is, the greater the amount of recovery is needed before the next work bout begins. In simple terms, intensity and volume are inversely related. If one of these training variables increases, the other must decrease and vice versa. The selected duration and intensity depend on the primary energy system being emphasized, the mode of training being used, and the adaptational responses desired.
MIT differs dramatically from traditional steady-state, cardiorespiratory training, in which a relatively constant intensity at or below the lactate threshold is maintained for the duration of the exercise session.
Although athletes have used interval training for over a century, it is now becoming a mainstream concept for developing overall fitness. You only have to turn on the TV or go on to social media to see examples of these programs. This model is in contrast to the old view of fitness, which held that long-term aerobic exercise was required to work the heart, lungs, and circulatory system. But many of the cardiorespiratory benefits produced by traditional aerobic training methods are also provided by interval training. These benefits include improved ability to consume oxygen, greater ability to transport oxygen to exercising muscles, and an increase in mitochondrial size and density, allowing greater production of energy.
Besides improving cardiorespiratory performance, MIT may serve as an effective tool for weight loss and weight management. The old thinking was that to burn fat, people needed to exercise at a low intensity. The problem with this line of thinking is that low-intensity exercise doesn’t burn as much fat! Although low- to moderate-intensity, steady-state cardio burns a greater percentage of fat during a workout, the total amount of fat burned and the total caloric expenditure are significantly greater when using a HIIT training program (Tremblay, Simoneau, and Bouchard 1994; Boutcher 2011). Thus, for those attempting to lose weight or maintain a healthy weight, performing MIT may be more beneficial than doing traditional steady-state aerobic training.
Energy system development (ESD) for explosive and intermittent-style sports is another benefit associated with MIT. We ultimately use a substance called ATP, or adenosine triphosphate, to fuel movement. When we want to exercise or perform in sport, we break down the ATP to release energy. We rely on three primary energy pathways to create ATP—two anaerobic pathways (the ATP–PCr system and the fast-glycolytic system) and one aerobic pathway (the oxidative system). The ATP–PCr system provides energy for explosive activities that last approximately 7 to 15 seconds, which would include activities such as the 40-yard dash, pro-agility, or vertical jump. For moderate- to high-intensity activities of longer duration, such as a 400- or 800-meter run, we start to rely more on the fast-glycolytic energy system to provide energy through glycolysis. Finally, for activities performed at a lower intensity for greater than 2 or 3 minutes, we start to rely on the aerobic energy system for ATP production. Although each of these energy systems are working to some degree at any given time, the one that dominates in ATP production is dictated by the intensity and duration of the activity as well as our ability to use oxygen (Baechle and Earle 2008).
During intermittent, or discontinuous, team and court sports, such as basketball, hockey, and tennis, the anaerobic energy pathways are called on to provide energy to sustain performance. Thus, to yield the greatest carryover to performance, the training method selected must reflect the metabolic demands of the sport and challenge the energy systems that supply athletes with fuel during competition. The athlete should engage in training that requires intermittent bouts of high intensity performed over short durations and allows brief recovery bouts using active or complete rest. This form of training also stimulates aerobic adaptations because the athlete will have an increase in oxygen consumption in an attempt to recover from the stressors between work bouts (Brewer 2008). The athlete would have a similar experience during a game or match: high-intensity bouts (acceleration and deceleration, rapid changes of direction, jumping, and so on) followed by lower-intensity bouts (jogging, time-outs, waiting for the next play, and so on) that rely heavily on the oxidative system for recovery.
MIT stimulates an increase in anaerobic enzymes, allowing greater anaerobic energy turnover and more efficient use of lactate as a fuel source during exercise. Athletes can thus work at a higher intensity for a longer time, which provides them with a distinct advantage over their competition. From a physiological standpoint, higher-intensity bouts of training also provide greater stimulation to explosive muscle fibers (Type II) than traditional steady-state aerobic training does. Athletes are thus able to preserve a greater amount of lean muscle mass tissue, allowing greater force production. Those attempting to manage their weight may benefit as well because this method promotes the preservation of lean mass while stimulating fat loss.
MIT can be done using a variety of training modalities and equipment, such as calisthenics, repeat sprints, and kettlebells. Many of these options are discussed in greater detail in chapter 2. Users have many training options; they are not limited to long, slow distance training or whatever cardio equipment is available at the local gym or health club. Having more options helps combat the boredom that many people experience when performing continuous-style cardiorespiratory training; the various alternatives may increase exercise adherence, self-efficacy, self-esteem, and enjoyment.
Finally, MIT is a time-efficient method of training. In general, MIT sessions last approximately 10 to 20 minutes (including rest periods). For example, 15 minutes of intense exercise, performed in as few as six sessions over a 2-week period, has been shown to have a positive effect on oxidative capacity during aerobic-based exercise (Gibala and McGee 2008). Furthermore, performing seven HIIT sessions over 2 weeks has been shown to produce a significant improvement in fatty acid oxidation during exercise (Talanian et al. 2007). Also, because MIT does not necessarily require a lot of expensive equipment, a session can be performed practically anywhere, so not having time to get to the gym is no longer a barrier. Therefore, MIT may provide the perfect solution for those with limited time to work out.