According to Medical News Today, the Department of Health and Human Services defines physical fitness as "a set of attributes people have or achieve that relates to the ability to perform physical activity." The five main components of physical fitness include muscular strength, muscular endurance, flexibility, body composition and cardiorespiratory endurance.
Muscular strength is an aspect of fitness that refers to the ability of a person's muscles to exert force during an activity, whereas muscular endurance is the ability of a muscle to continuously exert force without becoming exhausted. According to Medical News Today, lifting weights improves fitness by increasing muscular strength, and performing activities that require repetitive motions, such as jogging, improves muscular endurance.
A person's body composition refers to the ratio of muscles, bones and fat in his body. According to WebMD, staying active improves body composition by minimizing weight gain and increasing overall strength. The Mayo Clinic notes that gaining flexibility is an important aspect of fitness: Stretching increases the range of motion in joints and improves blood circulation.
Activities that improve cardiorespiratory fitness include walking, cycling, swimming or any activity that increases the heart rate. Cardiorespiratory endurance fuels the circulatory and respiratory systems, and this allows the heart and lungs to deliver oxygen to the body more efficiently during physical activities.