Copyright 2002
Coaching Pitchers
By Michael G. Marshall, Ph.D.

     Chapter Five:   Variability of Adolescent Male Maturation Rates

     In my 1979 doctoral dissertation, I compared the chronological ages (CA) of 1571 adolescent males with my estimate of their skeletal ages (ESA).   (In the parentheses, I provide the percent of subjects at each chronological age.)

             Table 5.1: Estimated Skeletal Ages and Chronological Ages of 1571 Adolescent Males
|-------------------------------------------------------------------------------------|
| ESA\CA |   11.0    |    12.0    |    13.0    |    14.0    |    15.0    |    16.0    |
|-------------------------------------------------------------------------------------|
|  11.0  | 17(43.6%) |  45(20.7%) |  10(01.8%) |            |            |            |
|  12.0  | 20(51.3%) | 104(47.9%) | 140(25.1%) |  31(06.5%) |   4(01.7%) |            |
|  13.0  |  2(05.1%) |  50(23.0%) | 215(38.5%) | 109(22.9%) |  14(06.0%) |            |
|  14.0  |           |  15(06.9%) | 150(26.9%) | 173(36.3%) |  47(20.0%) |   4(08.7%) |
|  15.0  |           |   3(01.4%) |  38(06.8%) | 136(28.6%) | 110(46.8%) |  16(34.8%) |
|  16.0  |           |            |   4(00.7%) |  24(05.0%) |  53(22.5%) |  21(45.7%) |
|  17.0  |           |            |   1(00.2%) |   3(00.1%) |   7(03.0%) |   5(10.9%) |
|-------------------------------------------------------------------------------------|
| Totals |    39     |    217     |    558     |    476     |    235     |     46     |
|-------------------------------------------------------------------------------------|
         a.   Doctoral Dissertation Data

             1.   Eleven Year Olds

     Because the lowest possible value of my Sexual Maturation Indicator Value is 11.6 years, it is not possible to assess 11 year old males as skeletally delayed.   Skeletally delayed adolescent males have Chronological Ages greater than their Estimated Skeletal Ages.   Of thirty-nine 11 year old males, seventeen had 11 year old Estimated Skeletal Ages, twenty had 12 year old Estimated Skeletal Ages and two had 13 year old Estimated Skeletal Ages.

To summarize Table 5.1:
1. 51.3% of 11 year old males were one year skeletally advanced.
2. 5.1% of 11 year old males were two years skeletally advanced.

             2.   Twelve Year Olds

     Because the lowest possible value of my Sexual Maturation Indicator Value is 11.6 years, it is also not possible to assess 12 year old males as one year skeletally delayed.   Of two hundred and seventeen 12 year old males, forty-five had 11 year old Estimated Skeletal Ages, one hundred and four had 12 year old Estimated Skeletal Ages, fifty had 13 year old Estimated Skeletal Ages, fifteen had 14 year old Estimated Skeletal Ages and three had 15 year old Estimated Skeletal Ages.

To summarize Table 5.1:
1.   20.7% of 12 year old males were one year skeletally delayed.
2.   47.9% of 12 year old males were skeletally on time.
3.   23.0% of 12 year old males were one year skeletally advanced.
4.   06.9% of 12 year old males were two years skeletally advanced.
5.   01.4% of 11 year old males were three years skeletally advanced.

             3.   Thirteen Year Olds

     Because the lowest value of my Sexual Maturation Indicator Value is 11.6 years, it is not possible to assess 13 year old CA males as more than two years skeletally delayed.   Of five hundred fifty-eight 13 year old males, ten had 11 year old Estimated Skeletal Ages, one hundred forty had 12 year old Estimated Skeletal Ages, two hundred fifteen had 13 year old Estimated Skeletal Ages, one hundred fifty had 14 year old Estimated Skeletal Ages, thirty-eight had 15 year old Estimated Skeletal Ages, four had 16 year old Estimated Skeletal Ages and one had a 17 year old Estimated Skeletal Age.

To summarize Table 5.1:
1.   01.8% of 13 year old males were two years skeletally delayed.
2.   25.1% of 13 year old males were one year skeletally delayed.
3.   38.5% of 13 year old males were skeletally on time.
4.   26.9% of 13 year old males were one year skeletally advanced.
5.   06.8% of 13 year old males were two years skeletally advanced.
6.   00.7% of 13 year old males were three years skeletally advanced.
7.   00.2% of 13 year old males were four years skeletally advanced.

             4.   Fourteen Year Olds

     Of four hundred seventy-six 14 year old males, thirty-one had 12 year old Estimated Skeletal Ages, one hundred nine had 13 year old Estimated Skeletal Ages, one hundred seventy-three had 14 year old Estimated Skeletal Ages, one hundred thirty-six had 15 year old Estimated Skeletal Ages, twenty-four had 16 year old ESAs and three had 17 year old Estimated Skeletal Ages.   Because highest value of my Sexual Maturation Indicator Value is 15.6 years, it is not possible to assess 14 year old males as more than three years skeletally advanced.

To summarize Table 5.1:
1.   06.5% of 14 year old males were two years skeletally delayed.
2.   22.9% of 14 year old males were one year skeletally delayed.
3.   36.3% of 14 year old males were skeletally on time.
4.   28.6% of 14 year old males were one year skeletally advanced.
5.   05.0% of 14 year old males were two years skeletally advanced.
6.   00.1% of 14 year old males were three years skeletally advanced.

             5.   Fifteen Year Olds

     Of two hundred thirty-five 15 year old males, four had 12 year old Estimated Skeletal Ages, fourteen had 13 year old Estimated Skeletal Ages, forty-seven had 14 year old Estimated Skeletal Ages, one hundred ten had 15 year old Estimated Skeletal Ages, fifty-three had 16 year old Estimated Skeletal Ages and seven had 17 year old Estimated Skeletal Ages.   Because the highest value of my Sexual Maturation Indicator Value is 15.6 years, it is not possible to assess 15 year old males as more than two years skeletally advanced.

To summarize Table 5.1:
1.   01.7% of 15 year old males were three years skeletally delayed.
2.   06.0% of 15 year old males were two years skeletally delayed.
3.   20.0% of 15 year old males were one year skeletally delayed.
4.   46.8% of 15 year old males were skeletally on time.
5.   22.5% of 15 year old males were one year skeletally advanced.
6.   03.0% of 15 year old males were two years skeletally advanced.

             6.   Sixteen Year Olds

     Of forty-six 16 year old males, four had 14 year old Estimated Skeletal Ages, sixteen had 15 year old Estimated Skeletal Ages, twenty-one had 16 year old Estimated Skeletal Ages and five had 17 year old Estimated Skeletal Ages.   Because the highest value of my Sexual Maturation Indicator Value is 15.6 years, it is not possible to assess 16 year old males as more than one year skeletally advanced.

To summarize Table 5.1:
1.   08.7% of 16 year old males were two years skeletally delayed.
2.   34.8% of 16 year old males were one year skeletally delayed.
3.   45.7% of 16 year old males were skeletally on time.
4.   10.9% of 16 year old males were one year skeletally advanced.

         b.   Adolescent Male Maturational Rate Differences

     To demonstrate the degree of adolescent male delayed and advanced biological maturation, we need to discuss the ranges of delayed skeletal maturers and advanced skeletal maturers.

             1.   Three Year Delayed Skeletal Maturers

     Because my sample did not include 8, 9 or 10 year old males and my Estimated Skeletal Age requires some primary or secondary sexual characteristic development, we cannot investigate whether 11, 12 or 13 year old males had three years delayed skeletal maturation.   Nevertheless, four 15 year olds had 12 year old Estimated Skeletal Ages.   No 16 year old had 13 year old Estimated Skeletal Ages.   Therefore, only approximately 0.25% of the subjects demonstrated three years of delayed skeletal maturation.

             2.   Two Year Delayed Skeletal Maturers

     Because my sample did not include 9 or 10 ten year old males and my Estimated Skeletal Age requires some primary or secondary sexual characteristic development, we cannot investigate whether 11 or 12 year old males had two years delayed skeletal maturation.   Ten 13 year olds had 11 year old Estimated Skeletal Ages.   Thirty-one 14 year olds had 12 year old Estimated Skeletal Ages.   Fourteen 15 year olds had 13 year old Estimated Skeletal Ages.   No 16 year old subjects had 14 year old Estimated Skeletal Ages.   Therefore, only approximately 3.5% of the subjects demonstrated two years of delayed skeletal maturation.

             3.   One Year Delayed Skeletal Maturers

     Because my sample did not include 10 year old males and my Estimated Skeletal Age requires some primary or secondary sexual characteristic development, we cannot investigate whether 11 year olds had one year delayed skeletal maturation.   Forty-five 12 year old had 12 year old Estimated Skeletal Ages.   One hundred and forty 13 year olds had 12 year old Estimated Skeletal Ages.   One hundred and nine 14 year olds had 13 year old Estimated Skeletal Ages.   Forty-seven 15 year olds had 14 year old Estimated Skeletal Ages.   Sixteen 16 year olds had 15 year old Estimated Skeletal Ages.   Therefore, only approximately 23% of the subjects showed one year of delayed skeletal maturation.

             4.   Equated Skeletal Maturers

     Seventeen 11 year olds had 11 year old Estimated Skeletal Ages.   One hundred and four 12 year olds had 12 year old Estimated Skeletal Ages.   Two hundred fifteen 13 year olds had 13 year old Estimated Skeletal Ages.   One hundred seventy-three 14 year olds had 14 year old Estimated Skeletal Ages.   One hundred ten 15 year olds had 15 year old Estimated Skeletal Ages.   Twenty-one 16 year olds had 16 year old Estimated Skeletal Ages.   Therefore, approximately 41% of the subjects showed equated chronological age and skeletal maturation.

             5.   One Year Advanced Skeletal Maturers

     Twenty 11 year olds had 12 year old Estimated Skeletal Ages.   Because my Estimated Skeletal Age regression equation inflates the Estimated Skeletal Ages for 11 year old males, it is possible to have higher Estimated Skeletal Ages for 11 year olds than true.   Fifty 12 year olds had 13 year old Estimated Skeletal Ages.   One hundred fifty 13 year olds had 14 year old Estimated Skeletal Ages.   One hundred thirty-six 14 year olds had 15 year old Estimated Skeletal Ages.   Fifty-three 15 year olds had 16 year old Estimated Skeletal Ages.   Five 16 year olds had 17 year old Estimated Skeletal Ages.   Therefore, approximately 26% of the subjects showed one year of advanced skeletal maturation.

             6.   Two Year Advance Skeletal Maturers

     Two 11 year olds had 13 year old Estimated Skeletal Ages.   Because my Estimated Skeletal Age regression equation inflates the Estimated Skeletal Ages for 11 year old males, it is possible to have higher Estimated Skeletal Age for 11 year olds.   Fifteen 12 year olds had 14 year old Estimated Skeletal Ages.   Thirty-eight 13 year olds had 15 year old Estimated Skeletal Ages.   Twenty-four 14 year olds had 16 year old Estimated Skeletal Ages.   Seven 15 year olds had 17 year old Estimated Skeletal Ages.   Because my sample did not include 18 or 19 year olds and because the highest value my Sexual Maturation Indicator Value is 15.6 years, it is not possible to investigate whether 16 year olds showed two years of advanced skeletal maturation.   Therefore, only approximately 5.5% of the subjects showed two years of advanced skeletal maturation.

             7.   Three Year Advanced Skeletal Maturers

     No 11 year old had a 14 year old Estimated Skeletal Age.   Three 12 year olds had 15 year old Estimated Skeletal Ages.   Four 13 year olds had 16 year old Estimated Skeletal Ages.   Three 14 year olds had 17 year old Estimated Skeletal Ages.   Because my sample did not include 18 or 19 year olds and the highest value of my Sexual Maturation Indicator Value is 15.6 years, it is not possible to investigate whether 15 and 16 year olds showed three years of advanced skeletal maturation.   Therefore, only approximately 0.6% showed three years of advanced skeletal maturation.

             8.   Four Year Advanced Skeletal Maturers

     One 13 year old had a 17 year old Estimated Skeletal Age.   Because my sample did not include 18 or 19 year olds and the highest value of my Sexual Maturation Indicator Value is 15.6 years, it is not possible to investigate whether 15 and 16 year olds showed four years of advanced skeletal maturation.   Therefore, only approximately 0.0006% showed four years of advanced skeletal maturation.

             Table 4.2: Biological Variability of Adolescent Males
|-------------------------|
|    Percent of Sample    |
|---------------------------------------------------------------------|
|         00.25%          |  Three Year Delayed Skeletal Maturers     |
|---------------------------------------------------------------------|
|         03.50%          |  Two Year Delayed Skeletal Maturers       |
|---------------------------------------------------------------------|
|         22.70%          |  One Year Delayed Skeletal Maturers       |
|---------------------------------------------------------------------|
|         40.70%          |  Equated Skeletal Maturers                |
|---------------------------------------------------------------------|
|         26.30%          |  One Year Advanced Skeletal Maturers      |
|---------------------------------------------------------------------|
|         05.40%          |  Two Year Advanced Skeletal Maturers      |
|---------------------------------------------------------------------|
|         00.60%          |  Three Year Advanced Skeletal Maturers    |
|---------------------------------------------------------------------|
|         00.0006%        |  Four Year Advanced Skeletal Maturers     |
|---------------------------------------------------------------------|

FREE BOOK!!!                          Chapter Six