Physical fitness is a kind of ability of human movement, which generally refers to the functional abilities such as strength, speed, endurance, agility and flexibility in human movement. This ability depends on the anatomical and physiological characteristics of muscle, the energy supply of muscle work, the function of internal organs and the regulation of nervous system. Sports quality is closely related to the human body's completion of various activities and adaptation to the external environment, and it is also the basis for mastering sports techniques and improving sports performance.

(1) Strength quality

Strength refers to the ability to overcome resistance in the process of exercise and muscle activity. Muscle contraction is the driving force of human movement. Under the unified regulation of the central system, muscle activity is the core of human movement, and the activities of other organ systems in the body are all to ensure muscle work.

There are various manifestations of strength quality. Generally, it includes maximum power (pure power, absolute power), speed power (explosive power), endurance power (strength endurance) and so on.

Maximum strength is a typical form of strength quality, and its training principle can be regarded as the "basic" principle of strength training. There are two ways to develop maximum strength and achieve different results. The first is to increase strength by improving the internal coordination of muscles and the coordination between muscles. Adopting special training can greatly improve the ability of muscle fiber to work synchronously; Improve the coordination ability between muscles involved in work. This kind of training will not increase muscle mass, which is of great significance to projects that need to overcome their own resistance first. This kind of power is developing rapidly and fading rapidly. The second is to increase strength by increasing the cross-sectional area of muscles. This training is to promote the rapid decomposition of protein during muscle work, thus increasing the cross-sectional area of muscle.

In the process of training, different methods can be used to improve the strength of different sexes. Table 1-5 shows the different effects of load exercises with different weights.

(2) Speed quality

Speed quality refers to the ability to move quickly, including reaction speed and moving speed, which can be divided into action speed and moving speed.

There are many factors that affect the speed, besides the central nervous system, there are also the coordination of muscle contraction characteristics and abilities, as well as various skills and skill conditions of the body.

Different sports have different speed characteristics, so the training of speed quality has obvious particularity. For teenagers, because of their age characteristics, they have different emphasis on speed training at different age stages. For example, running speed mainly depends on pace frequency and step length, and one of the most important factors of pace frequency is the flexibility and coordination of nervous system. Because the nervous system develops early and matures early, the pace frequency should be increased as soon as possible, and generally it will not increase after 10 ~ 13 years old. The step length mainly depends on the back pedal force, and the strength develops rapidly after 10 ~ 13 years old.

(3) Endurance quality

Endurance is the ability of the body to overcome fatigue after working for a long time. Endurance is relative to fatigue. Fatigue in exercise has many manifestations, such as sensory, psychological and motor organ fatigue. However, all fatigue is ultimately related to the energy supply system of the body and the excitement of the nervous system. All endurance training and improvement should first be based on the energy reserve and supply needed for exercise, improve cardiopulmonary function and improve anti-fatigue ability such as lactic acid. For the endurance training of teenagers, we should pay attention to laying a solid foundation in an all-round way, starting with aerobic endurance and carrying out it according to their different age characteristics.

(4) flexibility

Flexibility refers to the range of joint activity and the stretching ability of muscle ligament. The main factors affecting the flexibility quality are the elasticity of muscles and ligaments, the bone structure of joints and so on. There are two kinds of flexibility training methods: active exercise and passive exercise, both of which can be static exercise and dynamic exercise. Teenagers are a good opportunity to improve their flexibility training, so we should pay attention to regular, moderate and gradual training.

(5) Sensitive quality

Agility refers to the ability of human body to change posture, action, posture and direction quickly. Sensitivity is closely related to the flexibility of neural processes in cerebral cortex. Start and stop suddenly, change direction, etc. , all need a quick transition between excitement and inhibition. Other factors affecting sensitivity are age, weight and fatigue.

Sensitive quality is the comprehensive expression of human body's various abilities. In the training of developing sensitive quality, we should start with cultivating various abilities of the human body and cultivate its ability to master movements, reactions and balance.

Wish you success!