A very good source on this thread and possibly still available through Dr. Yessis are the early Soviet Sports Reviews. As I have been reviewing many of the issues from the mid 1960
's and later there are numerous articles on the training of youth. The following is an example:
“Stages of Training: Long-Term Preparation of Young Runners”, Legkaia Atletika, 8:13, 1977 G. Bukharina
"The acceleration, noted in recent decades in the speeding up of "biological maturing" of young sportsmen, has served as one of the reasons for re-examining the age groups in which athletes compete with each other.
At the present time, serious sports training is attracting tall, healthy, sturdy boys and girls who possess better morpho-functional capabilities than their contemporaries. The fast maturers also have a higher level of intellectual development and associated abilities.
All of these factors have a definite effect on the process of developing high-class sportsmen. According to data from complex pedagogical and medico-biological studies, athletes as young as 13 years of age have morphological and functional attributes that make it possible to use effective modern methods of sports training.
This acceleration nevertheless has both positive and negative aspects in regard to the development of high-caliber athletes. On the one hand, the athletic accomplishments of fast maturers are generally markedly higher than of their contemporaries. On the other hand, it is precisely this fact that stirs many coaches to train young athletes according to adult standards--which often is the cause of functional breakdown and stagnation of sports results at a certain stage of training (19-20 years).
Looking at the preparation of young athletes through the prism of "adult" concepts, most coaches specialize too much, restrict the means of training, and achieve high results at a youthful age, not providing a solid foundation of all-round physical preparedness.
A comparative analysis of the progress of Soviet and GDR athletes showed that the GDR athletes have a faster rate of progress of sports results. The reason for the lag in rate of progress in USSR sportsmen is insufficient utilization of effective means and methods of training, aimed at development of the necessary physical qualities.
Repeated studies of the national junior team by the polydynamometry method have shown a significant lag in development of absolute and relative strength in the whole team in comparison with adult athletes.
Analysis of the training loads executed by youngsters in all age groups (up to adult) showed that a significant number of the sprinters are extremely limited in their means of preparation. They do not give sufficient attention to strength preparation, which facilitates an increase in the general level of physical development and growth of absolute and relative strength of the muscles bearing the main loads. Although there is no great difference in the yearly volumes of running at different intensities between the GDR and USSR juniors, the difference in the number of hours devoted to general physical preparation is enormous.
According to data obtained from surveys, the beginning of the active training process for sprinters is around the age of 13-14 years. However, in order to go from novice to master in 5-7 years, 13-14-year-old sportsmen need to have a good background of game playing and general physical preparation in school before taking up track and field training.
The long-term prepartion of sprinters and the stages in the general scheme of the athlete's sports life are as follows:
SUB-TEEN GROUP (12-13 YEARS)
Purpose–all-round physical education, mastery of a large repertoire of movements, fortification of health, “hardening” (overall strengthening), development of motor qualities: speed, strength, dexterity, endurance. Outdoor (movement) and sports games are utilized in this period, but they consume no more than 50% of total workout time.
In the yearly cycle, at least 36 weeks are preparatory and 12 are competitive.
JUNIOR YOUTH GROUP (14-15 YEARS)
At this age, youngsters have high work capcity. Founded on the preceding base of preparation, they continue to accomplish the task of all-round physical training. The ratio of means of general and special preparation is 70:30%. In the yearly cycle, 36 weeks are prepatory and 12 are competitive.
SENIOR YOUTH GROUP (15-16 YEARS)
This is a transitional age–an age of active formation of the body, of increasing body weight. There must be careful dosing of the amount of strength training, an increase in hours of technical training, instruction and formation of technique. The main problems are development of character, striving for systematization in training sessions, preparation for high sports accomplishments. The ratio of means of general, special, and technical preparation is 50:25:25%. The number of preparatory weeks is 36-40; competitive weeks are 12.
JUNIORS (17-18 YEARS)
The main tasks in the preparation of athletes at this age are: above all else, organization of their training process, adoption of a new life style in connection with finishing school and taking up new responsibilities (technical studies, work, etc.). Also important are nutrition and the body’s recovery from training loads. Preparation of sprinters is based on the principle of 2 cycles. Autumn-winter–23 weeks, spring-summer–29 weeks.
SUBADULT AGE (19-20 YEARS)
The main tensdencies here are as follows: further increase of training loads of the main training methods. The leading factor at the present time is the quality (intensity) of exercises, in relation to today’s volume of key training means. In the last 4 years, the volume of the top track men has increased 1.5 times, but the percentage of exercises executed at high intensity has increased 2 times. The main means of training are used concurrently and are distributed more evenly over the span of all periods and stages of training.
In preparatory periods, one includes more exercises for improvement of movement technique, for accomplishing stabilization of movement in the competitive period, for mastering faster movement from foundation of higher special physical preparation, for continuous improvement of rhythm. At this age, expanding the means of restoration is important along with increasing the training loads. Throughout the year, tapering-off phases should be provided for. At least 50 sessions should include swimming and gymnastics: there should be at least 40 steam baths, and from 80 to 100 general and therapeutic massages.
In the long-term preparation of young athletes, we should be striving for one main, special goal–sports improvement. The period of training during the youth years should be considered a preparatory stage, and the main purpose of this stage should be to create maximum prerequisites for sports progress later in life." 
