| dc.description.abstract | Success in sport is influenced by controllable factors, including coaching, facilities, nutrition and training programs. Less controllable factors during childhood and adolescence include influences of growth and maturation such as the onset of menarche. The timing and the magnitude of these processes affect each individual differently. Based on individual differences in development, menarche is reached earlier or later, resulting in the phenomenon of early, average and late maturing girls. This difference in maturity status affects the anthropometric growth and physical fitness and motor performance of girls in different ways.
This thesis is based on four objectives of which all were studied by means of two years of follow-up longitudinal data that included a period of three school years (Grade eight to Grade ten). The first aim was to determine growth differences in mass, sitting height, sitting height ratio, arm span, leg length and body mass index (BMI) of pre- and post-menarche adolescent girls over a three-year school period, and the implications of these differences on sport performance. The study aimed to determine secondly and thirdly, the differences between pre- and post-menarche girls’ physical fitness capabilities (muscle strength, cardio respiratory endurance) and motor fitness capabilities (speed, agility, hand-eye coordination and power) over a period of three school years. The fourth aim was to investigate the classification agreement between self-reported age at menarche and calculated maturity off-set in adolescent girls. The study made use of a convenience sample within the three school year longitudinal study titled Growth and sport psychological characteristics of talented adolescent boys and girls (Growth study). This study included the high school’s years (Grade eight to Grade ten) and included participants from one Quintile five school within Potchefstroom, South Africa. The school had a boarding facility and all Grade 8 learners that enrolled in 2010 represented 46 different primary schools. Anthropometric measurements were taken at 9 time points (three times annually, 4 months apart) while motor- and physical capabilities were measured longitudinally at 3 time points (once annually in Feb 2010 until 2012). In 2010, 95 girls were enrolled in the study with a mean age of 13.73±0.48 years at baseline. Of these, 37 (38%) were lost to follow-up, resulting in the final group consisting of 58 girls during the final measurements with a mean age of 16.26±3.58 years in November 2012. The age of menarche was determined by the Status Quo method which was used to categorize the group at baseline into a pre- (n=13) and post-menarche group (n=45). The protocol of the International Standards for Anthropometric Assessment (ISAK) was used to measure stature, arm span, body mass, sitting height and leg length while sitting height ratio and BMI were calculated. Maturity offset was calculated by means of a set gender specific equation for girls that is based on chronological age, growth related measures, growth interactions and ratios. Physical- and motor fitness capabilities were tested using the Australian Sport Search Program. Physical fitness capabilities included muscle strength (cricket ball throw for distance) and aerobic capacity (beep test). Motor fitness capabilities included speed (0-10m and 0-40m speed), agility (10m agility test), hand-eye coordination (throw and catch) and power (vertical jump and basketball chest press). Statistical analyses of objectives one to three were similar. For descriptive purposes, means, standard deviations (sd) and minimum and maximum values were calculated. To analyse the changes over time in each group, a repeated measures ANOVA with a Posthoc Bonferonni adjustment was used to determine statistical significance (p<0.05) of differences between time point measurements. Independent t-testing was also done to investigate group differences with p<0.05 set as the level of significance. Effect sizes were calculated to determine practical significance of differences with cut-off values of d>0.2 indicating a small practical significance, d>0.5 a medium practical significance and d>0.8 a large pracical significance. Statistical analysis for objective four included a Receiver Operating Characteristic (ROC curve) analysis to determine maturity offset cut-off points for early and late maturing girls. An asymptotic level of p< 0.05 was used as the set criterion for statistical significance where an area value of 1 indicated a strong/accurate prediction potential. Cross-tabulation and a Chi-square analysis was used to determine the association between the Status Quo and maturity offset results. Cut-off points for Chi-square (Cramer’s V) were V>0.1 indicating a small predictive effect, V>0.3 a medium predictive effect and V>0.5 a strong predictive effect. The results with regards to objective one showed that post-menarche girls were taller and heavier, had a higher BMI and longer body segments at a younger age. These differences were significant at 13.51 years but declined to similar values (p>0.05) at the end of the study at 16.25 years when most of the girls have reached menarche. The results of objective two showed no statistical significant differences (p>0.05) between the groups at the end of the study (15.51 years). However, post-menarche girls had practical significantly higher muscle strength with the pre-menarche girls showing a practical significant higher aerobic capacity and relative V̇O2max over the follow-up period, with differences between maturational groups (p>0.05) becoming smaller with increased age. Post-menarche girls initially displayed better absolute V̇O2max (p>0.05) values although performance of pre-menarche girls caught up and surpassed them at 15.51 years (p>0.05). With regard to objective three, differences between maturity groups were only significant in the strength tests during baseline measurements (13.51 years). Explosive upper body strength differed significantly between the groups, favoring post-menarche girls during baseline measurements. Pre-and post-menarche girls also showed similar changes in motor fitness. Pre-menarche girls performed non-significantly (p>0.05) better in agility and explosive leg strength and post-menarche girls significantly better in explosive upper body strength (p<0.05), although non-significantly in hand-eye coordination and speed (p>0.05) at 13.51 years. At 15.51 years no statistical significant group differences were found. Performance of pre-menarche girls surpassed post-menarche girls in hand-eye coordination and 0-40 m speed while post menarche girls displayed higher leg strength scores after 2 years of follow-up.
The results regarding objective four showed that there was a level of classification agreement between the actual age of onset of menarche and the results derived from a maturity off-set equation. The results indicated an area value (AUC) of 0.757 where a score of 1 indicate accurate prediction, which shows that the prediction capability of the maturity offset equation is of relative high accuracy. Classification of girls as early or late developers at a younger age (13.51 years) nearer to their PHV were higher, while validity and accuracy of classification declined with increasing age possibly because most girls reached menarche and moved further away from PHV as was confirmed with cross-tabulation. It was concluded that the use of a set equation outside the population that it was developed for, should rather be limited to categorizing girls in different maturity groups and not as a tool to predict maturity offset. The accuracy of the equations also declined with increasing maturity, therefore it should only be used a few years before and after reaching PHV. Based on the above findings, it can be concluded that the timing of the onset of menarche contribute to significant differences between pre- and post-menarche girls’ anthropometric growth during mid- to late adolescence. These include changes in body proportions and extremities and body composition including fat deposition and distribution. However, except for muscle strength differences (p<0.05), no statistical significant differences in physical and motor fitness capabilities of girls of differing menarcheal status during mid- to late adolescence, were found. Some differences were however of small practical significance. It is still concluded that the time of reaching menarche is an unstable developmental period and girls will consequently, only be homogeneous in their physical and motor fitness abilities one to two years after all girls of the same chronological age have reached menarche. It is recommended that the knowledge that was generated by this thesis should be used to improve sports development and talent identification processes by incorporating the understanding of the temporary weaknesses but also the strengths associated with early or late development, and by applying this knowledge in appropriate short- and long-term motor performance goals. | en_US |
