This study involved a 28-week school-based exercise trial of single-leg drop-landing exercise with 42 girls (Tanner stage 1; 6-10 yr old) randomly assigned to control (C), low-drop (LD) or high-drop(HD) exercise groups. The latter two groups performed single-leg drop-landings (3 sessions.wk-1 and 50 landings.session-1) from 14cm and 28cm, respectively using the non-dominant leg. Single-leg peak ground-reaction impact forces (PGRIF) in a sub-sample ranged between 2.5 – 4.4 x body-weight (BW). No differences (p>0.05) among groups at baseline for age, stature, lean tissue mass (LTM - DXA - Lunar 3.6-DPX), leisure time physical activity or average daily calcium intake were detected. No significant within group changes for between leg differences from baseline to post-training and no significant differences among groups at baseline, or in magnitude of change for any of the dominant or non-dominant (loaded) leg bone mineral content (BMC g) measures determined by DXA – loaded leg total - 19.06, 25.5, 25.46 [p=.156], femoral neck - 0.14, 0.11, 0.15 [p=.959], greater trochanter - 0.37, 0.06, 0.26 [p=.733], mid femoral shaft - 3.87, 3.87, 3.42 [p=.677] for the C, LD and HD groups, respectively, after adjusting for the covariates baseline body and fat mass, and change in LTM (ANCOVA) were observed. Similarly, following ANCOVA adjustments no significant differences for changes in calcaneal speed of sound and broadband ultrasound attenuation (CUBA Clinical), DXA derived changes in femoral neck (-0.009, 0.033, -0.009; p=.189) and total MFS (0.029, 0.041, 0.053; p=.447) volumetric BMD (g.cm-3), or MFS cortical volumetric BMD, the latter derived by a new technique combining MRI and DXA were identified. TBBMC changed by 79.6g-C, 100.2g-LD and 91.9g-HD (p=.339). Combining data from both exercise groups to increase statistical power produced similar results. No significant within group changes for between leg differences from baseline to post-training and no significant differences among groups at baseline, or in magnitude of change for any of the dominant or non-dominant (loaded) leg bone geometrical (area cm2) determined by MRI using ANALYZE® software of proximal - 22.18, 12.91, 19.86 [p=.248], mid - 19.83, 15.91, 19.64 [p=.233], or distal - 14.78, 16.07, 13.35 [p=.792], slice cortical area for the C, LD and HD groups, respectively, after adjusting for the covariates baseline body and fat mass, and change in LTM (ANCOVA) were detected. Similarly there were no significant biomechanical cross sectional moment of inertia (CSMI cm4) changes determined by Scion Image® (Frederick, Maryland: Version-Beta 3B) and a custom macro program of proximal - 896, 815, 649 [p=.415], mid - 1054, 806, 1087 [p=.471], or distal - 1197, 1079, 966 [p=.606], slice CSMI for the C, LD and HD groups, respectively after adjusting for the same covariates. In contrast to some recent reports, our findings suggest that strictly controlled uni-modal; uni-directional single-leg drop-landing exercises involving low-moderate peak ground-reaction impact forces are not osteogenic in the developing prepubertal female skeleton.

This study examined links between adolescent depressive symptoms, actual pubertal development, perceived pubertal timing relative to one’s peers, adolescent-maternal relationship satisfaction, and couple sexual behavior. Assessments of these variables were made on each couple member separately and then these variables were used to predict the sexual activity of the couple. Participants were drawn from the National Longitudinal Study of Adolescent Health (Add Health; Bearman et al., 1997; Udry, 1997) data set (N = 20,088; aged 12-18 years). Dimensions of adolescent romantic experiences using the total sample were described and then a subsample of romantically paired adolescents (n = 1,252) were used to test a risk and protective model for predicting couple sexual behavior using the factors noted above. Relevant measures from the Wave 1 Add Health measures were used. Most of the items used in Add Health to assess romantic relationship experiences, adolescent depressive symptoms, pubertal development (actual and perceived), adolescent-maternal relationship satisfaction, and couple sexual behavior were drawn from other national surveys or from scales with well documented psychometric properties. Results demonstrated that romantic relationships are part of most adolescents’ lives and that adolescents’ experiences with these relationships differ markedly by age, sex, and race/ethnicity. Further, each respective couple member’s pubertal development, perceived pubertal timing, and maternal relationship satisfaction were useful in predicting sexual risk-promoting and risk-reducing behaviors in adolescent romantic couples. Findings in this dissertation represent an initial step toward evaluating explanatory models of adolescent couple sexual behavior.

The aim of this article is to examine the relations between two approaches to the measurement of life history (LH) strategies: A traditional approach, termed here the biodemographic approach, measures developmental characteristics like birthweight, gestation length, interbirth intervals, pubertal timing, and sexual debut, and a psychological approach measures a suite of cognitive and behavioral traits such as altruism, sociosexual orientation, personality, mutualism, familial relationships, and religiosity. The biodemographic approach also tends not to invoke latent variables, whereas the psychological approach typically relies heavily upon them. Although a large body of literature supports both approaches, they are largely separate. This review examines the history and relations between biodemographic and psychological measures of LH, which remain murky at best. In doing so, we consider basic questions about the nature of LH strategies: What constitutes LH strategy (or perhaps more importantly, what does not constitute LH strategy)? What is gained or lost by including psychological measures in LH research? Must these measures remain independent or should they be used in conjunction as complementary tools to test tenets of LH theory? Although definitive answers will linger, we hope to catalyze an explicit discussion among LH researchers and to provoke novel research avenues that combine the strengths each approach brings to this burgeoning field.

Alcohol use in early adolescence is associated with numerous concurrent and future problems, including diagnosable alcohol use disorders. The trait of negative urgency, the tendency to act rashly when distressed, is an important predictor of alcohol-related dysfunction in youth and adults. The aim of this study was to test a model proposed by Cyders and Smith (2008) specifying a puberty-based developmental increase in negative urgency, which in turn predicts subsequent increases in early adolescent drinking. In a sample of 1,910 youth assessed semi- annually from spring of 5th grade through spring of 8th grade, we found support for this model. Pubertal onset was associated with both a mean increase and subsequent rises in negative urgency over time. Drinking frequency at any wave was predicted by prior wave assessments of drinking frequency, negative urgency, and pubertal onset. The slope of increase in drinking also increased as a function of pubertal onset. This model applied to negative urgency but not to other impulsivity-related traits. These findings highlight the importance of personality change in early adolescence as part of the risk matrix for early onset alcohol consumption.

Infertility among women has become a growing issue in the world requiring a significant number of women to seek treatment by means of assisted reproductive technologies (ART). One suggested reason for the fertility issue is modern diet, leading to diseases such as obesity and type II diabetes. In this study, twenty gilts three weeks in age, were placed on one of five dietary treatments (n=4 gilts per treatment) containing 15% fat (FAT), 35% fructose (FRU), both fat and fructose (HFHF), or two different controls: one standard industry (IND) diet meant to result in optimal lean growth and a second diet to account for the reduced lysine (LYS) intake in the treatment diets. Two experiments were performed to assess the reproductive outcomes of pre-pubertal gilts consuming a high fat and/or high fructose diet and to demonstrate interactions between diet and infertility using pigs as a model. In the first experiment, follicular fluid was collected from these gilts and introduced into porcine in vitro maturation system to determine whether characteristics of the follicular fluid affect oocyte competence and embryo development. The follicular fluid of females consuming high fructose and fat diets did not alter nuclear maturation of oocytes (p>0.10). There were, however, detrimental effects on subsequent development of embryos, especially blastocyst formation, with the gilts having consumed the HFHF diet having reduced day 5 and 6 blastocysts formation when compared to the IVM follicular fluid free (FFF) group (p=0.03 and p=0.01, respectively). In regards to embryo quality, blastocysts from the FAT group had greater cell number when compared to all other groups. In the second experiment, the reproductive tissues; ovary, oviduct, and uterus were analyzed for genes of interest: estrogen receptor alpha (ESR1), estrogen receptor beta (ESR2), insulin like growth factor I (IGFI), insulin like growth factor I receptor (IGFIR), and growth differentiation factor 9 (GDF9). Resulting data was analyzed in three ways: 1) across all 5 treatments, 2) with gilts grouped by whether or not they consumed fat, or 3) with gilts grouped by whether or not they consumed fructose. There were no differences detected between individual treatments for ESR1 and ESR2. In the ovary samples, the fructose diets decreases ESR2 (p=0.05). Also, GDF9 ovarian expression tended to decrease with fructose consumption (p=0.07). Furthermore in the ovary, there was a positive correlation between ESR2 and GDF9 expression (r=0.92 and p<0.01). GDF9 expression was lower in the oviducts of gilts consuming fat diets when compared to non-fat diets (p=0.01). Neither IGFI nor IGFIR were altered in the reproductive tissues analyzed. Based on the results from both experiments, the consumption of fat and fructose alters both the developing embryo and gene expression in the reproductive tissues that support the growing embryo. Further investigation will provide more insight on the impact nutrition has on pre-pubertal reproductive development and subsequent fertility. / Master of Science

One of the fundamental concerns of developmental psychology is the nature of continuity and change across development. The present study investigated the continuity of social competence across developmental periods, paying special attention to the transition from middle childhood to adolescence. Using a birth cohort of youths (277 males, 315 females), I examined the stability of social competence across developmental periods, assessed the relation between quality of early parenting and later competence, and tested how timing of pubertal maturation and school transition impact the stability of social competence, using both variable-centered and person-centered analyses. It was expected that social competence would be highly stable across development, but less stable across the transition to adolescence, and that higher quality parenting would predict greater competence among males and females. Furthermore, I expected that pubertal maturation and school transition would deflect trajectories of social competence over time, accentuating individual differences (e.g., socially competent youths would become more competent, whereas incompetent youths would become less competent). As expected, the nature of social competence was fairly stable from early childhood to adolescence, although there is evidence that social competence is less stable as youth transition from early childhood to middle childhood and from middle childhood to adolescence. Moreover, individuals with warm parenting evinced greater social competence across time. Consistent with my hypothesis, off-time pubertal maturation and school transition accentuated individual differences in social competence, increasing social competence among more competent youths, and further diminishing social competence among less competent youths. Finally, I find evidence that experiencing both off-time pubertal maturation and a school transition simultaneously incurred more risk for females, particularly among less competent females, than experiencing only off-time maturation or a school transition. / Psychology

Puberty is the process of becoming sexually mature and it has fundamental somatic and psychosocial implications. The focus of this dissertation was the short and long term developmental significance, concerning both soma et psyche, of female pubertal timing. Four studies were designed to accomplish these aims. Six samples of different ages from different countries and from different time points, comprising several thousand females some of which were followed longitudinally, were used. Age at menarche was used as the primary measure of pubertal maturation. The first main aim of this dissertation was to explore the mechanisms that might explain the well-established link between female pubertal timing and problem behavior, and to identify contextual conditions at which associations are stronger or weaker. Existing explanations are unsatisfactory and little is known about conditions that might affect the strength of the associations. In Paper I, we tested and confirmed a peer socialization hypothesis as a satisfactory explanation for the link between early puberty and problematic adjustment. In short, this hypothesis posits that early developing girls associate with older peers and boyfriends because they feel more mature than their same age peers, and through these peers and boyfriends the early developed girls are channeled into more socially advanced behaviors, including normbreaking. This should be particularly true in contexts where heterosexual relationships are sanctioned and where there is an abundance of deviant youth. In Paper II, I used a biopsychosocial approach and studied pubertal timing along with self-perceptions of maturity and early romantic relationships. The findings revealed that early puberty had very different implications depending on the psychological and social contexts in which it was embedded. For instance, when early puberty was coupled with feeling mature and having early romantic relationships, it was associated with adjustment problems. When early puberty was coupled with neither, it was not linked to particularly high levels of problem behavior. In stark contrast to the vast literature on the role of female pubertal timing in adolescence, the literature on long-term implications is remarkably limited. For this reason, the second main aim of this dissertation was to study the adult implications of female pubertal timing. In Papers III and IV, we examined long term implications of pubertal timing, particularly as it relates to somatic development. The findings suggested that pubertal timing does have future implications for women’s body perception and composition, with early developing females having higher body mass indexes in adulthood, but only under certain circumstances. The findings of this dissertation help further understanding of the soma et psyche implications of female pubertal timing. They indicate that pubertal timing has concurrent and future implications. It seems, however, that timing is not everything. The developmental significance of female pubertal timing appears to be very different under different contextual conditions. Thus, it is only when girls’ psychological and social contexts are considered that fruitful predictions can be made. As such, the findings have important implications for prevention, policy, and practice.

The aim of this project is to examine the relationships between two approaches to the measurement of life history strategies. The traditional method, termed here the biodemographic approach, measures developmental characteristics like birthweight, gestation length, inter-birth intervals, pubertal timing, and sexual debut. The alternative method under exploration, termed here the psychological approach, measures a suite of cognitive and behavioral traits such as altruism, sociosexual orientation, personality, mutualism, familial relationships, and religiosity. Although both approaches are supported by a large body of literature, they remain relatively segregated. This study draws inspiration from both views, integrating measures that assess developmental milestones, including birthweight, prematurity, pubertal timing, and onset of sexual behavior, as well as psychological life history measures such as the Mini-K and a personality inventory. Drawing on previous theoretical work on the fundamental dimensions of environmental risk, these measures are tested in conjunction with several scales assessing the stability of early environmental conditions, including both "event-based" measures that are defined with an external referent, and measures of internal schemata, or the predicted psychological sequelae of early events. The data are tested in a three-part sequence, beginning with the measurement models under investigation, proceeding to an exploratory analysis of the causal network, and finishing with a cross-validation of the structural model on a new sample. The findings point to exciting new directions for future researchers who seek to integrate the two perspectives.

Age at the initiation of puberty and at menarche are key maturational indicators. They reflect health both within and between populations; in that a declining average age is associated with improving health, nutrition, and socio-economic conditions. Knowledge of the timing of pubertal development and menarche is important as earlier development within a population, in particular, has been linked with an increased risk of negative sequelae including overweight and obesity, development of risk factors for non-communicable diseases such as hypertension and insulin resistance, and engagement in risk behaviours such as early sexual debut and substance abuse. The main aims of this study were to investigate the timing of, and the early life factors (such as body composition and growth velocities) associated with pubertal development and age at menarche in Black and White urban South African adolescents. Mixed-longitudinal data (n = 401) from the Birth to Twenty (Bt20) birth-cohort study, initiated in 1990 and set in SowetoJohannesburg, South Africa were used. Median age at the initation of puberty and at menarche was derived by fitting logistic curves to cumulative frequency plots. Logistic regression models were constructed to examine the early life predictors of the timing of puberty and menarche. Data were also collected from adolescents and Bt20 staff (n = 72) using focus groups to explore views on the pubertal development questionnaire used in the Bt20 study. Median age at the initiation of genitalia development was 10.4 years (95% Cl = 8.4, 12.4) for Black boys and 9.8 years (95% Cl = 9.4, 10.2) for White boys. Median age for the initiation of pubic hair development for Black males was 10.8 years (95% Cl = 9.6, 12.0) compared to White males, which was 10.2 years (95% Cl = 8.4, 12.0). Median age at the initiation of breast development in Black females was 10.1 years (95% Cl = 9.3, 10.9) compared to White females which was 10.2 years (95% Cl = 8.2, 12.2). Median age for the initiation of pubic hair was 10.3 years (95% Cl = 9.3, 11.3) and 10.5 years (95% Cl = 8.7, 12.3) for Black and White girls, respectively. Results from logistic regression showed that a greater weight and height velocity in late childhood significantly increased the odds of achieving early breasU genitalia development. Furthermore, a low socio-economic status (SES) index at 9/10 years significantly reduced the odds of achieving early breasUgenitalia development. A greater weight, height, body mass index (BM I), and growth rate during infancy and childhood significantly increased the odds of achieving early pubic hair development. Median age at menarche for Black females was 12.4 years (95% Cl = 12.2, 12.6) and 12.5 . years (95% Cl = 11.7,13.3) for White females. Average menarcheal age for Black girls has declined by 0.56 years per decade and 0.32 years for White girls in South Africa, when comparing the current study findings with those from previous studies. Results from logistic regression showed that being taller, fatter and heavier in late childhood significantly increased the odds of achieving earlier menarche. The focus groups provided a range of opinions relating to the Bt20 pubertal development questionnaire and procedure. The majority of views were positive and included the ease of understanding and completion of the tool. Negative views revolved around the language used and privacy issues. These qualitative results provided a unique insight into the way in which pubertal development data are assessed and how these methods can potentially be improved to enhance the reliability and accuracy of pubertal development data collection. The results from this study provide the most recent estimates of age at the. initiation of puberty and age at menarche for urban Black and White South African adolescents. This is particularly important given the social, nutritional, and economic transition currently occurring in this country as these key maturity indicators reflect population health. This study has also added to our knowledge of the factors that are associated with pubertal development, showing that proximate rather than distal factors are the most sensitive indicators in this urban transitioning environment. In addition, the results from the focus groups provided a unique insight into how pubertal development data are assessed and how these methods could be improved. The negative health outcomes which have been associated with earlier pubertal development and age at menarche are major public health concerns, particularly in the South African context given the HIV/AIDS epidemic and rising levels of obesity. This study highlights the need for renewed research and resources for intervention strategies and policy programmes which target appropriate sex and obesity education in urban South African children.

STUDENT NUMBER: 0301561E MASTERS OF EDUCATION FACULTY OF HUMANITIES-DISCIPLINE OF SPECIALISED EDUCATION / The purpose of this study was to examine whether: actual and ideal body mass index (BMI) scores, perception of a weight problem, racial identity, physical exercise, weight control behaviour and stage of pubertal development predict levels of global self-esteem in average academic achieving English speaking middle-class adolescent females. The sample consisted of 90 females, ranging in age from 13 years 3 months to 18 years 7 months who were attending Benoni High School. BMI was measured and desired BMI based on self-reported weight and height. Self-perception of having a weight problem was evaluated by one question: “Do you see yourself as having a weight problem?” Self-esteem was measured in two ways: firstly participants completed the Rosenburg Self-esteem Scale and secondly homeroom teachers were asked to give a score of global self-esteem. A significant association was found between global self-esteem and: a perceived weight problem, actual BMI and race. No significant association was found between global self-esteem and: weight control behaviour; physical exercise, age of menarcheal onset and ideal BMI. KEY WORDS Global self-esteem, adolescent females, BMI, racial identity, weight control behaviour, physical exercise and pubertal development