During the growth spurt (GS) which forms part of the mid-adolescence period of boys (13-17 years), considerable changes take place in the body composition of boys. It is therefore an unstable period where imbalances in body proportions (muscle mass, fat mass, neurological development) occur, that might have an effect on sport performance. It is also accompanied by changes in physical and motor fitness. The study firstly aimed to determine anthropometric growth changes in stature, arm span, mass, sitting height and sitting height ratio during mid-adolescence over a period of three years. The study secondly aimed to investigate the developmental changes in physical fitness (muscle strength, aerobic endurance) and motor fitness abilities (speed, agility, hand- eye coordination, explosive power) during the mid-adolescence phase of boys and finally to investigate possible relationships between anthropometric and physical and motor fitness abilities over the course of three years. A convenience sample consisting of all the grade 8 learners (n=182) of a quintile 5 high school in Potchefstroom in the North-West province of South Africa was selected to participate in a longitudinal growth research project over a three year period. Only the boys, with a mean age of 13.58 years in grade 8, of whom 95.4 % were white, 2.3% black and 2.3% colored boys, were part of the study. In 2010, 87 boys had complete measurements, while the final group in 2012 with completed follow-up measurements, were 73 boys. The physical and motor fitness components were measured according to the Australian Sport Search Program consisting of 10 tests (4 anthropometrical tests, 5 motor fitness tests, 1 physical fitness test). The cricket ball throwing test was added as an additional test. The anthropometrical measurements were made using the protocol of ISAK, while sitting height was measured according to the Canadian Sports for Life protocol. Sitting height ratio was calculated according to the formula (sitting height/stature x 100). The data was processed by “Statistica for Windows” Statsoft-computer program package. Descriptive statistics that included means (M), standard deviations (SD) and minimum and maximum values were used. A repeated measures over time analysis of variance (ANOVA) with a Bonferonni adjustment was done to analyze the differences over a period of 3 years within the group for all variables, where p<0.05 indicates a statistically significant difference. A partial correlation analysis was used to determine correlations between variables. Practical significance of correlations was determined according to Cohen’s d-value (0.1=small, 0.3=medium, 0.5=large). The results showed that during mid-adolescence in the period 13.58-14.58 years, boys grow considerably in stature, body mass, arm span and sitting height with accompanying improvement in motor and physical fitness abilities while sitting height ratio showed the greatest increase from 14.58-15.57 years. Stature, mass and arm span showed a parallel development up to 15 years after which further development leveled off, while mass increase showed no leveling off. Speed, agility, coordination and isometric-dynamic shoulder strength (basketball throw) also showed the biggest and significant improvement from 13.58-15.57 years, while explosive leg power and upper body arm and shoulder strength (vertical jump, cricket ball throw) showed the biggest and significant improvements during the period from 14.58 to 15.57 years. Significant correlations up to r=0.74; p<0.05, were found between changes in physical and motor fitness abilities and anthropometric variables, although the correlations become smaller over the 3-year period. Hand-eye coordination showed no correlation with any anthropometrical changes, while upper body strength correlated with all the anthropometrical measurements except sitting height ratio throughout the three years. It was concluded that the most accelerated growth and development took place from 13.58- 15.57 years in boys when they are in their first high school year and which falls within the mid-adolescent period (13-15 years). Furthermore, clear relationships were found between anthropometric, motor- and physical fitness variables. This knowledge of the rate of growth and motor fitness development and the relationships between these variables during the midadolescence period can provide a better understanding of changes that boys underwent during the mid-adolescent period, and can help monitoring the level of physical maturity in adolescents in order to develop training, competition and rehabilitation programs according to their developmental and not their chronological age. This cannot only prevent injuries, but also prevent early burnout in sport. / MA (Sport Science), North-West University, Potchefstroom Campus, 2014

During the growth spurt (GS) which forms part of the mid-adolescence period of boys (13-17 years), considerable changes take place in the body composition of boys. It is therefore an unstable period where imbalances in body proportions (muscle mass, fat mass, neurological development) occur, that might have an effect on sport performance. It is also accompanied by changes in physical and motor fitness. The study firstly aimed to determine anthropometric growth changes in stature, arm span, mass, sitting height and sitting height ratio during mid-adolescence over a period of three years. The study secondly aimed to investigate the developmental changes in physical fitness (muscle strength, aerobic endurance) and motor fitness abilities (speed, agility, hand- eye coordination, explosive power) during the mid-adolescence phase of boys and finally to investigate possible relationships between anthropometric and physical and motor fitness abilities over the course of three years. A convenience sample consisting of all the grade 8 learners (n=182) of a quintile 5 high school in Potchefstroom in the North-West province of South Africa was selected to participate in a longitudinal growth research project over a three year period. Only the boys, with a mean age of 13.58 years in grade 8, of whom 95.4 % were white, 2.3% black and 2.3% colored boys, were part of the study. In 2010, 87 boys had complete measurements, while the final group in 2012 with completed follow-up measurements, were 73 boys. The physical and motor fitness components were measured according to the Australian Sport Search Program consisting of 10 tests (4 anthropometrical tests, 5 motor fitness tests, 1 physical fitness test). The cricket ball throwing test was added as an additional test. The anthropometrical measurements were made using the protocol of ISAK, while sitting height was measured according to the Canadian Sports for Life protocol. Sitting height ratio was calculated according to the formula (sitting height/stature x 100). The data was processed by “Statistica for Windows” Statsoft-computer program package. Descriptive statistics that included means (M), standard deviations (SD) and minimum and maximum values were used. A repeated measures over time analysis of variance (ANOVA) with a Bonferonni adjustment was done to analyze the differences over a period of 3 years within the group for all variables, where p<0.05 indicates a statistically significant difference. A partial correlation analysis was used to determine correlations between variables. Practical significance of correlations was determined according to Cohen’s d-value (0.1=small, 0.3=medium, 0.5=large). The results showed that during mid-adolescence in the period 13.58-14.58 years, boys grow considerably in stature, body mass, arm span and sitting height with accompanying improvement in motor and physical fitness abilities while sitting height ratio showed the greatest increase from 14.58-15.57 years. Stature, mass and arm span showed a parallel development up to 15 years after which further development leveled off, while mass increase showed no leveling off. Speed, agility, coordination and isometric-dynamic shoulder strength (basketball throw) also showed the biggest and significant improvement from 13.58-15.57 years, while explosive leg power and upper body arm and shoulder strength (vertical jump, cricket ball throw) showed the biggest and significant improvements during the period from 14.58 to 15.57 years. Significant correlations up to r=0.74; p<0.05, were found between changes in physical and motor fitness abilities and anthropometric variables, although the correlations become smaller over the 3-year period. Hand-eye coordination showed no correlation with any anthropometrical changes, while upper body strength correlated with all the anthropometrical measurements except sitting height ratio throughout the three years. It was concluded that the most accelerated growth and development took place from 13.58- 15.57 years in boys when they are in their first high school year and which falls within the mid-adolescent period (13-15 years). Furthermore, clear relationships were found between anthropometric, motor- and physical fitness variables. This knowledge of the rate of growth and motor fitness development and the relationships between these variables during the midadolescence period can provide a better understanding of changes that boys underwent during the mid-adolescent period, and can help monitoring the level of physical maturity in adolescents in order to develop training, competition and rehabilitation programs according to their developmental and not their chronological age. This cannot only prevent injuries, but also prevent early burnout in sport. / MA (Sport Science), North-West University, Potchefstroom Campus, 2014