Strength training is one of the five types of physical fitness training that revolve around building muscle mass and bone density, as well as improving the strength and endurance of muscles by inducing muscle contraction through the use of resistance. It also enhances the functions of the joints and develops the sturdiness of tendons and ligament, thus reducing the risk of injuries from physical activities.
Before the industrial revolution, fitness was defined as the capacity to carry out the day’s activities without undue fatigue. However, with automation and changes in lifestyles physical fitness is now considered a measure of the body's ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic diseases, and to meet emergency situations.[4]
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.
^ Colbert LH, Visser M, Simonsick EM, Tracy RP, Newman AB, Kritchevsky SB, Pahor M, Taaffe DR, Brach J, Rubin S, Harris TB (July 2004). "Physical activity, exercise, and inflammatory markers in older adults: findings from the Health, Aging and Body Composition Study". Journal of the American Geriatrics Society. 52 (7): 1098–104. doi:10.1111/j.1532-5415.2004.52307.x. PMID 15209647.
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]

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.


Sam Ashe-Edmunds has been writing and lecturing for decades. He has worked in the corporate and nonprofit arenas as a C-Suite executive, serving on several nonprofit boards. He is an internationally traveled sport science writer and lecturer. He has been published in print publications such as Entrepreneur, Tennis, SI for Kids, Chicago Tribune, Sacramento Bee, and on websites such Smart-Healthy-Living.net, SmartyCents and Youthletic. Edmunds has a bachelor's degree in journalism.
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