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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.

^ Osawa Y, Azuma K, Tabata S, Katsukawa F, Ishida H, Oguma Y, Kawai T, Itoh H, Okuda S, Matsumoto H (2014). "Effects of 16-week high-intensity interval training using upper and lower body ergometers on aerobic fitness and morphological changes in healthy men: a preliminary study". Open Access Journal of Sports Medicine. 5: 257–65. doi:10.2147/OAJSM.S68932. PMC 4226445. PMID 25395872.
A comprehensive fitness program tailored to an individual typically focuses on one or more specific skills,[7] and on age-[8] or health-related needs such as bone health.[9] Many sources[10] also cite mental, social and emotional health as an important part of overall fitness. This is often presented in textbooks as a triangle made up of three points, which represent physical, emotional, and mental fitness. Physical fitness can also prevent or treat many chronic health conditions brought on by unhealthy lifestyle or aging.[11] Working out can also help some people sleep better and possibly alleviate some mood disorders in certain individuals.[12]

Physical activity boosts the immune system. This is dependent on the concentration of endogenous factors (such as sex hormones, metabolic hormones and growth hormones), body temperature, blood flow, hydration status and body position.[37] Physical activity has shown to increase the levels of natural killer (NK) cells, NK T cells, macrophages, neutrophils and eosinophils, complements, cytokines, antibodies and T cytotoxic cells.[38][39] However, the mechanism linking physical activity to immune system is not fully understood. 
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