High intensity interval training (HIIT) consists of repeated, short bursts of exercise, completed at a high level of intensity. These sets of intense activity are followed by a predetermined time of rest or low intensity activity.[25] Studies have shown that exercising at a higher intensity has increased cardiac benefits for humans, compared to when exercising at a low or moderate level.[26] When your workout consists of an HIIT session, your body has to work harder to replace the oxygen it lost. Research into the benefits of HIIT have revealed that it can be very successful for reducing fat, especially around the abdominal region.[27] Furthermore, when compared to continuous moderate exercise, HIIT proves to burn more calories and increase the amount of fat burned post- HIIT session.[28] Lack of time is one of the main reasons stated for not exercising; HIIT is a great alternative for those people because the duration of an HIIT session can be as short as 10 minutes, making it much quicker than conventional workouts.[29]

The Physical Activity Guidelines for Americans were created by the Office of Disease Prevention and Health Promotion. This publication recommends that all adults should avoid inactivity to promote good health mentally and physically. For substantial health benefits, adults should participate in at least 150 minutes a week of moderate-intensity, or 75 minutes a week of vigorous-intensity aerobic physical activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity. Aerobic activity should be performed in episodes of at least 10 minutes, and preferably, it should be spread throughout the week.
There are different categories or types of physical fitness training. Each corresponds to a defined purpose or fitness goal such as the development and improvement of one or more of the five dimensions of physical fitness, or for participation in a particular type of sports and rehabilitation through physical training, among others. Note that the different types of training also correspond to the different categories or types of exercises.
To get in top physical shape, you’ll need to work on three different areas of cardiorespiratory fitness. Capacity is the amount of work you can do, such as how fast you can perform a sprint or dash. Stamina refers to how long you can exercise. For example, a sprinter is faster than a marathon runner, but probably can’t run as long or as far as the marathoner. Anaerobic conditioning helps you work at very high intensities and helps you recover more quickly afterward. For example, many basketball players have no problem making fast breaks down the court, but afterward, you see them grabbing their knees, gasping for breath as they try to recover. Interval training consists of many high-intensity bursts of activity, each followed by a recovery period. These recovery periods, which occur many times during an interval workout, help you improve your ability to catch your breath after a point or play and recover for the start of the next one. 

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Possibly one of the most important parts of fitness training is flexibility and mobility. Flexibility is the ability of your muscles to stretch, and mobility is being able to move your joints and tissues through their full range of motion. Both are important to athletic performance and for avoiding injury. Muscles and joints that are flexible and mobile — as well as strong — are much less susceptible to sprains and other injuries.
Studies have revealed that this type of physical fitness training is more efficient in burning calories over a shorter period than steady-state activity or performing the exercise routine repeatedly. Another benefit of this training is that it enables an individual to develop his or her routine by mixing and matching his or her choice of activities or exercises. Different mixes and matches can produce different results.
Eccentric training is another type of physical fitness training centered on improving eccentric muscle contraction. As a backgrounder, this type of muscle contraction occurs when the muscle elongates or lengthens from the influence of an opposing force. The contraction happens explicitly when a muscle gives in or goes with the flow or direction of an opposing force.
Centers for disease control and prevention provide lifestyle guidelines of maintaining a balanced diet and engaging in physical activity to reduce the risk of disease. The WCRF/ American Institute for Cancer Research (AICR) published a list of recommendations that reflect the evidence they have found through consistency in fitness and dietary factors that directly relate to cancer prevention.
For physical fitness activity to benefit an individual, the exertion triggers a response called a stimulus. Exercise with the correct amount of intensity, duration, and frequency can produce a significant amount of improvement. The person may overall feel better, but the physical effects on the human body take weeks or months to notice and possibly years for full development. For training purposes, exercise must provide a stress or demand on either a function or tissue. To continue improvements, this demand must eventually increase little over an extended period of time. This sort of exercise training has three basic principles: overload, specificity, and progression. These principles are related to health but also enhancement of physical working capacity.[24]
These recommendations are also widely supported by the American Cancer Society. The guidelines have been evaluated and individuals that have higher guideline adherence scores substantially reduce cancer risk as well as help towards control with a multitude of chronic health problems. Regular physical activity is a factor that helps reduce an individual’s blood pressure and improves cholesterol levels, two key components that correlate with heart disease and Type 2 Diabetes.[33] The American Cancer Society encourages the public to "adopt a physically active lifestyle" by meeting the criteria in a variety of physical activities such as hiking, swimming, circuit training, resistance training, lifting, etc. It is understood that cancer is not a disease that can be cured by physical fitness alone, however, because it is a multifactorial disease, physical fitness is a controllable prevention. The large associations tied with being physically fit and reduced cancer risk are enough to provide a strategy to reduce cancer risk.[32] The American Cancer Society asserts different levels of activity ranging from moderate to vigorous to clarify the recommended time spent on a physical activity. These classifications of physical activity consider the intentional exercise and basic activities are done on a daily basis and give the public a greater understanding of what fitness levels suffice as future disease prevention.
Endurance is your ability to perform physical activity over time. You might be able to serve aces and hit winning forehands and backhands, but if your muscles cramp or you run out of energy after a few games, you won’t win any matches. You build endurance by exercising for longer periods without stopping, working at a slower speed than when you interval train. This type of exercise is usually aerobic, calling on your slow-twitch muscle fibers and burning more fat than glycogen, depending on the speed you work. The slower you work, the higher percentage of your calories burned comes from fat.