Thesis (M.A.)--University of Northern Iowa, 2005. / Includes bibliographical references (leaves 23-24). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.A.)--University of Northern Iowa, 2005. / Includes bibliographical references (leaves 23-24).

Thesis (M.S.)--Kutztown University. / Source: Masters Abstracts International, Volume: 45-06, page: 2724. Typescript. Includes bibliographical references (leaves 39-41).

Thesis (M. Ed.)--University of Hong Kong, 1997. / Includes bibliographical references (leaf 82-89).

Thesis (M.Ed.)--University of Hong Kong, 1997. / Includes bibliographical references (leaves 82-89). Also available in print.

published_or_final_version / abstract / Human Performance / Doctoral / Doctor of Philosophy

abstract / Human Performance / Doctoral / Doctor of Philosophy

A Thesis Submitted to the Faculty of Education, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master in Education / This study aimed to assess selected physiological, osmoregulatory and thermoregulatory responses to tennis play in children, Twenty-four young male tennis players (X age; 13.3+ 1.31 years) were stndied while playing for 90 min under warm environmental conditions (WBGT index= 13-19). Ad libitum consumption of pure water was permitted. Questionnaires were used in order to elicit information regarding the health status, degree of aeelimatizationnnd pre-match trait and state anxiety of the subjects. The physiological variables assessed. included pre- and post-match rectal temperature (T), heart rate (HR) and oxygen consumption (02) during the match. The biochemical observations included pre- and postmatch blood glucose, haematoerit (Ret), haemoglobin (lIb), plasma electrolyte (Na", Cl', K+, Mg++) and total plasma protein (TPP) concentrations. The findings )q~ed that the young tennis players investigated in this study experienced, ~de!'ate levels of pre-competitive trait and state amdety. The estimated nie.m exercise intensity of 50-55% of VOzmax for a duration of 90 min resulted. in a Tre increase of 0.73 •C. Mean percentage dehydration was 0.MO+O.25. Plasma volume (PV) changes were insignificant and were positively related to TPP changes. Mean plasma. Na" and CI- concentrations increased by 0.88 mmol.r" and 2.2 mmol.r:' respectively. The subjects' mean H... response (145 bpm) of a subset or the sample(n=13) and estimated VOz (21.38 ml.kg-l.min-~ represented a 55% of the age adjusted HRmax reserve and approximately a 50-55% of V02 max respectively. The time spent within the target heart rate range (60-85% HR. max reserve) comprised only 33% of the match duration. Mean energy expenditure was estimated to be 1772 KJ dUl'ing the 90 min period. Itwas calculated that in order to prevent harmful levels of dehydration under warm environmental conditions and at an exercise intensity of tennis play of approximately 55% of the age adjusted HR max reserve or 50-55% of V02 max, consumption of 4.44-6.81 mI.Kg-1.br-1 or 200-360 ml.hr" of water is recommended in young tennis players possessing a body mass of 45-53 Kg. The precise quantity was concluded to be a function of the mass and exercise intensity of the subjects and the environmental heat stress index during play. / Andrew Chakane 2018

Exercise during growth may increase peak bone mass; if the benefits are maintained it may reduce the risk of fracture later in life (1). It is hypothesised that exercise will preferentially enhance bone formation on the surface of cortical bone that is undergoing bone modeling at the time (2). Therefore, exercise may increase bone mass accrual on the outer periosteal surface during the pre- and peri-pubertal years, and on the inner endocortical surface during puberty (3). An increase in bone formation on the periosteal surface is, however, more effective for increasing bone strength than medullary contraction (4). While exercise may have a role in osteoporosis prevention, there is little evidential basis to support this notion. It is generally accepted that weight-bearing exercise is important, but it is not known how much, how often, what magnitude or how long children need to exercise before a clinically important increase in bone density is obtained. In this thesis, the effect of exercise on the growing skeleton is investigated in two projects. The first quantifies the magnitude and number of loads associated with and in a moderate and low impact exercise program and non-structured play. The second project examines how exercise affects bone size and shape during different stages of growth. Study One: The Assessment of the Magnitude of Exercise Loading and the Skeletal Response in Girls Questions: 1) Does moderate impact exercise lead to a greater increase in BMC than low impact exercise? 2) Does loading history influence the osteogenic response to moderate impact exercise? 3) What is the magnitude and number of loads that are associated with a moderate and low impact exercise program? Methods: Sixty-eight pre-and early-pubertal girls (aged 8.9±0.2 years) were randomised to either a moderate or low impact exercise regime for 8.5-months. In each exercise group the girls received either calcium fortified (-2000 mg/week) or non-fortified foods for the duration of the study. The magnitude and number of loads associated with the exercise programs and non-structured play were assessed using a Pedar in-sole mobile system and video footage, respectively. Findings: After adjusting for baseline BMC, change in length and calcium intake, the girls in the moderate exercise intervention showed greater increases in BMC at the tibia (2.7%) and total body (1.3%) (p ≤0.05). Girl's who participated in moderate impact sports outside of school, showed greater gains in BMC in response to the moderate impact exercise program compared to the low impact exercise program (2.5 to 4.5%, p ≤0.06 to 0.01). The moderate exercise program included -400 impacts per class, that were applied in a dynamic manner and the magnitude of impact was up to 4 times body weight. Conclusion: Moderate-impact exercise may be sufficient to enhance BMC accrual during the pre-pubertal years. However, loading history is likely to influence the osteogenic response to additional moderate impact exercise. These findings contribute towards the development of school-based exercise programs aimed at improving bone health of children. Study Two: Exercise Effect on Cortical Bone Morphology During Different Stages of Maturation in Tennis Players Questions: 1) How does exercise affect bone mass (BMC) bone geometry and bone strength during different stages of growth? 2) Is there an optimal stage during growth when exercise has the greatest affect on bone strength? Methods: MRI was used to measure average total bone, cortical and medullary areas at the mid- and distal-regions of the playing and non-playing humerii in 47 pre-, peri- and post-pubertal competitive female tennis players aged 8 to 17 years. To assess bone rigidity, each image was imported into Scion Image 4.0.2 and the maximum, minimum and polar second moments of area were calculated using a custom macro. DXA was used to measure BMC of the whole humerus. Longitudinal data was collected on 37 of the original cohort. Findings: Analysis of the entire cohort showed that exercise was associated with increased BMC and cortical area (8 to 14%), and bone rigidity (11 to 23%) (all p ≤0.05). The increase in cortical bone area was associated with periosteal expansion in the pre-pubertal years and endocortical contraction in the post-pubertal years (p ≤0.05). The exercise-related gains in bone mass that were accrued at the periosteum during the pre-pubertal years, did not increase with advanced maturation and/or additional training. Conclusion: Exercise increased cortical BMC by enhancing bone formation on the periosteal surface during the pre-pubertal years and on the endocortical surface in the post-pubertal years. However, bone strength only increased in response to bone acquisition on the periosteal surface. Therefore the pre-pubertal years appear to be the most opportune time for exercise to enhance BMC accrual and bone strength

Bibliography: leaves 100-113.