Strength refers to the ability of your muscles to perform work at one time, such as lifting a heavy barbell. You build strength by putting enough resistance against your muscles that you cause damage to them. When your muscles repair themselves in response to this damage, they grow bigger. Since your heart and lungs are muscles, some people refer to your cardio capacity as cardio strength.


Bioelectrical Impedance - This test measures body composition. Using either a hand-held or at-home scale, a slight electrical signal is sent through either the hands or feet. Body fat percentage is estimated based on the speed in which the signal passes through body tissues. According to the American Council on Exercise (ACE) men with a body fat percentage of 14-17% and women with a body fat percentage of 21-24% are considered to be in the 'fitness' category.
^ 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.
If you've ever fallen in the shower trying to wash one foot while standing on the other, you realize the importance of having good balance. But balance is important for so many other reasons. Especially as you age, improving your balance can help you avoid falls and stay active and independent. Better balance can also improve your performance in your favorite athletic activity.

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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