Scientific research has shown that children:

• with better developed motor skills are more physically active from an early age, during school age (Williams et al., 2008; Lopez et al., 2001)
• who are physically active enough at a young age are more likely to be active when they grow up (Malina and Robert., 2012; Telama et al., 2005)
• with insufficiently developed general motor skills choose unhealthy ways of spending free time (Malina, 2012)

In addition, the quality of motor development and mastery of basic and advanced motor skills in early childhood:

• significantly determines the quality of life in later ages (Haubenstricker et al., 1986)
• largely determines physical form (e.g., cardiorespiratory function) in older ages (Barnett et al., 2008)
• directs children’s participation in fun and healthy activities, i.e. increases the level of their physical activity in society (Malina, 2012)

According to the children:

• Lack of playing skills is one of the most important reasons for giving up physical activity and sport (Canadian Sport for Life, 2014)
• If they have not developed basic movement skills by the age of 12, success in top sport seems out of reach (Moore et al. 1998; Oliver et al., 2011)

Strength and Conditioning program for children, young athletes and beginners is a specially designed system of knowledge and activities that takes into account the peculiarity, multiple specifics, characteristics as well as determining factors of growth, development, health, as well as motor progress of young athletes. The development of such a program requires and requires a thorough analysis, assessment, treatment and monitoring of all relevant and specific factors on which the effectiveness of sports of young athletes and beginners depends the most.

Such training differs significantly from the way top athletes train in a large number of organizational, training and structural principles and factors. At the same time, such a way of training is significantly different from all forms of physical exercise of young people outside the system of top sports (school lessons, school sports, playrooms, sports schools, etc.).

Strength and Conditioning training for children, young athletes and beginners is special and specific because the strength and conditioning coach , based on a thorough knowledge of the current issues of this very important and decisive period in the growth, maturation and development of a young individual, must have the full capacity of his ability to create and design the current conditioning training program, in the light of the required competitive result.

Therefore, there is a competitive result of the young athletebut it must be achieved as a reflection of his real and voluntary possibilities. Therefore, it must be continuously controlled and determined by all relevant factors of the normal and natural continuity of growth and development of the young person. Especially in such a training system, such an approach must be applied that will not compromise the health of the young athlete at any time. In the first place, it is the duty of coaches who implement such a system of training and competitions not to make unrealistic and inadequate demands on children that can compromise their psychological, mental, motor, morphological, functional capacities, and thus violate the social status of the young person within the framework of his need to affirm himself as an individual or as part of a collective (group, group, etc.) team, team). It is unquestionable to mention the possibility that inadequate training and improperly dosed loads can result in acute changes in the health of a young athlete, which, if they occur during this period, can produce various forms of reduced inadaptability to sports, with chronic, and often permanent consequences.

On the contrary, a studious, well-organized, functional training system for young athletes with constant control and monitoring of the effects of training work in the competition system, will minimize the possibility of injuries and setbacks, and enable continuous biological and sports development. It is a long-term process that systematically and timely deals with general and specific motor skills, which at each level of its specialization, through planned interventions in accordance with sensitive periods, affects their growth and development. Such a process must undeniably take into account:

• individual authenticity (cognitive, motor and functional abilities; conative, affective and morphological characteristics)
• on the general legality of psychophysical development of young athletes in accordance with sensitive periods
• The course and specifics of each individual stage of both the overall and sporting development of a young athlete
• the specific requirements of the current sport or discipline
• methodological and pedagogical principles of acquiring technical and tactical knowledge of the current sports branch, etc.

Proper treatment of a young person within the application of training loads implies the existence of phases, characteristics and sensitive periods in the current period of activity.
There are several phases of strength and conditioning training of young athletes during which it is necessary to adjust the content and modalities of training, in order to achieve the planned goals with the highest degree of certainty.

1. initiation (from 6th to 9th year)

At this stage, young athletes must apply low-intensity training with an emphasis on the development of a wide range of motor skills and elementary skills with nurogenic conditioning. The basic functional abilities, and above all the cardiorespiratory system, are adequately developed during this period for most low-intensity and low-capacity aerobic activities. This is a phase of multifaceted development of motor and functional abilities with a wide range of uses of natural forms of movement exercises, which include running, jumping, catching, balance, rolling.

2. shaping (11-14 years old)

At this stage, from the point of view of functional capabilities, there is a gradual increase in the intensity and capacity of training, due to a gradual increase in tolerance to acidification of the body, while anaerobic capacities are still compromised due to low tolerance to lactates, due to the underdevelopment of buffer systems. Conditioning training of young athletes of this age is directed towards multifaceted and basic sports preparation, with an increased degree of application and specific conditioning requirements with a positive transfer to sports technique.

3. specialization (from 15 to 18 years old)

At this stage, young athletes adapt to the higher demands of training in full capacity, whereby, after quality multilateral and basic preparation, they begin to apply many more fitness exercises that are specific to a particular sports branch from the aspect of time, space, intensity and complexity of movement organization. This increase in the intensity and capacity of specific conditioning exercises leads to an improvement in the level of competitive performance.

The general course of development of motor skills is characterized by:

• Heterochrony means that different motor skills are exhibited at different stages of development.
• Synchronicity means that the development of individual motor skills coincides with each other.
• Rhythmicity means that the development of motor skills goes through phases that vary in intensity and extent of change.
• Individuality means that the development of individual motor skills occurs in accordance with individually different adaptations.

By treating a young athlete within the mentioned phases, the strength and conditioning coach must condition his training activities on the existence of sensitive periods.
Sensitive periods are periods of special sensitivity (plasticity) for the development of certain functional systems and are characterized by the highest degree of reaction of the organism to adequate influences that stimulate the development of motor-functional abilities and the efficiency of motor action. From the perspective of long-term development of athletes, the development of basic motor skills during early childhood serves as a good basis for even more advanced and complex specific motor skills that naturally develop later.

Consequently, the greatest degree of importance in the realization of the previous has a comprehensive and studious analysis of the intensity and capacity of the realization of skills, general and specific motor skills in relation to the selective application of crucial factors, which are the basis for the creation and condition of the practical implementation of conditioning (motor) training for children and young athletes.