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<p> During exercise in a hot climate, it has been reported that children respond with a greater shift in blood volume from the central to the peripheral circulation, compared with adults. This can lead to inadequate central circulation, and early cessation of activity in children. No studies have considered if a transition in this hemodynamic response occurs during puberty in females. This study measured hemodynamic responses in pre/early (PEP), mid- (MP), and late- (LP) pubertal girls. Twenty-seven 9- to 16- year-old healthy girls (n=9, each group) cycled in a climatic chamber set at 35 ± 1°C and 50 ± 5% relative humidity for two 20-min bouts (10-min rest in between and a 10-min rest at the end). Cardiac output was measured upon chamber entry, in the middle and at the end of each exercise bout. Forearm blood flow (FBF) was measured upon chamber entry, 3 minutes after exercise bout 1 (E1) and bout 2 (E2) and at the end of rest 1 (R1) and rest 2 (R2). Overall, there was no significant group difference in the central hemodynamic (e.g. cardiac index, stroke volume index) responses to exercise in the heat. However, FBF among the three groups at R1 was almost significantly different (p=0.06), such that it was lower in LP than in PEP and MP. FBF in LP also tended to decrease from E1 to R1 (7.91±1.06 to 6.1±0.83 ml•100ml-1•min-1) and from E2 to R2 (9.47±1.47 to 8.26±1.20 ml•100ml-1•min-1). In contrast, PEP and MP showed little change in FBF at all time points. These findings strengthen the notion that there is a maturity-related decrease in forearm blood flow from pre- to late-puberty. In conclusion, under the conditions of the present study, there were very few differences in the hemodynamic responses of pre-, mid- and late- pubertal girls. It is possible that the transition to an adult-like hemodynamic response does not occur until later in a girl's physical development.</p> / Thesis / Master of Science (MSc)

<p> While several investigations have reported a higher proportion of lipid oxidation (lower carbohydrate oxidation) in females performing heavy endurance exercise at the same relative intensity as males, some studies have failed to support this. Possible factors contributing to the lack of agreement may be differences in subject training status and diet, or the hormonal status of female subjects related to menstrual phase. All these variables are known to affect substrate metabolism during submaximal exercise. These factors were controlled in the present study by selecting subjects who were matched for level of physical conditioning and performance experience and placing them on eucaloric identical diets for 3 days. The females were tested during the mid-follicular phase of their menstrual cycle. Six males and 6 females ran on a treadmill at 65% VO2 max for a total distance of 15.5 km (range in performance times, 90 to 101 min). Pre and post exercise needle biopsies of vastus lateralis were assayed for glycogen concentration. Plasma glycerol, glucose, free fatty acids and selected hormones (catecholamines, growth hormone, insulin and glucagon) were measured throughout and following the run by sampling from an indwelling venous catheter. Exercise protein catabolism was estimated from 24 hr (resting and exercise) urinary urea N excretion. </p> <p> Males were found to have significantly higher respiratory exchange ratios (X =0.94 vs 0.87), greater muscle glycogen utilization (by 25%) and greater urea nitrogen excretion (by 30%) than females. Changes in selected hormone concentrations could not explain the greater lipid utilization observed in females. The lower insulin and higher epinephrine levels seen in males could in part explain the greater glycogenolysis and protein catabolism observed inn this group. It is concluded that, during moderate intensity long duration exercise, females demonstrate greater lipid utilization and less carbohydrate and protein metabolism than equally trained and nourished males. </p> / Thesis / Master of Science (MSc)

Workers experience combined physical and mental demands in their daily jobs, yet the contribution of these concurrent demands in the development of work-related musculoskeletal disorders (WMSDs) is not clearly understood. There is a need to understand how concurrent demands interact with different work parameters, such as force levels, muscles employed, and types of exertion, to influence physiological responses. Furthermore, whether muscle capacity is altered with these concurrent demands remains unclear. The current research was conducted to address these needs through three experimental studies that evaluated changes in physiological, performance, and subjective measures. The first study investigated muscle-specific responses to concurrent physical and mental demands during intermittent static work. Mental demands adversely affected physiological responses with increasing physical demand. Furthermore, greater motor and mental performance impairment was observed at either end of the physical demand spectrum. Finally, these interactions were muscle-dependent, with postural (shoulder and torso) muscles indicating a greater propensity to interference due to concurrent demands than executive (wrist) muscles. The aim of the second study was to evaluate differential effects of exertion type (static and dynamic) during concurrent physical and mental work. Concurrent physical and mental demands adversely affected physiological responses during static exertions compared to dynamic exertions. Furthermore, static exertions were more susceptible to decrements in muscle output and mental task performance than dynamic exertions, specifically at higher force levels. The last study quantified the effects of concurrent physical and mental demands on muscle capacity (endurance, fatigue, and recovery) during intermittent static work. Additional mental processing was associated with shorter endurance times, greater strength decline, increased fatigability, and slower cardiovascular recovery. Concurrent demand conditions were also associated with higher levels of perceived fatigue, and rapid increases in rates of perceived exertion, time pressure, mental load, and stress. Overall, the current research provides a comprehensive understanding of the interactive effects of physical and mental demands on physiological responses and task performance. These findings may facilitate the development of task design strategies to help reduce the risk of workplace injuries and to increase worker performance. Finally, outcomes from this research can contribute towards the revision of current ergonomic guidelines to incorporate concurrent assessment of physical and mental demands. / Ph. D.

Evaluated were correlated responses to 54-generations of divergent selection for 8-week body weight (BW) and of BW at other ages and reproductive traits. Evaluated first was the influence of scaling on phenotypic responses to selection, phenotypic correlations of means and standard deviations, and unadjusted vs. standardized responses. Measured was BW at 4 (BW4), 8 (BW8), 24 (BW24), and 38 (BW38) weeks of age. Correlations between means and standard deviations were positive and greater in the LWS than HWS. Scaling masked the degree more than the pattern of response and was line specific with the magnitude of response greater in the LWS than HWS. While BW ratios across ages were not influenced by scaling in LWS, they were evident in HWS. Also measured were correlated responses of reproductive traits in selected and relaxed lines. Traits were age at first egg (AFE), body weight at first egg (WFE), their ratio (WAFE), and hen-day normal egg production (HDP). Although sexual maturity was delayed, the effect was more pronounced in the low than high weight lines. Selection for low BW decreased WFE, WAFE and HDP. Selection for high BW resulted in lower HDP, while WFE and WAFE were generally higher. Minimum AFE, WFE and WAFE in relation to sexual maturity were line specific. Opposition between relaxed and artificial selection resulted in a higher reproductive performance and fitness with relaxed than artificial selection. Overall, results demonstrate that correlated responses to long-term divergent selection were masked by scaling and negative correlated reproductive responses. / Master of Science

Rats were used in an experiment which investigated the effects of partial and continuous reinforcement of the CER. A 2 x 2 mixed design provided for the factorial combination of 100% and 50% reinforcement schedules with two discrete conditioned stimuli. Analysis of bar press suppression revealed a significant within-subjects reversed PRE. A numerical, but not significant reversed PRE was obtained in the between-subjects comparisons. Further, suppression in the presence of the tone CS was greater than that in the presence of the light CS. The results were discussed in terms of a fear conditioning model and a predictability model. / Master of Science

This research uses a mixed methods approach to analyze recent climate and land use changes, and farmers\' perceptions of climate change and its impacts on traditional agriculture in the village of Keur Samba Guéye (KSG). This work looks at the influence of social beliefs in adoption of new strategies by small farmers in this region, a topic that has received little or no study to date. Traditional agriculture in KSG is not very productive at present because of the impoverishment of the area and traditional agricultures strong dependency on natural climatic conditions. In this research, I identified recent climatic trends, documented changes in land use/land cover (LULC) from 1989 to 2011, and assessed farmers\' perceptions of climate change and their responses to such changes. To document climate trends and LULC, I analyzed climate data of twelve meteorological stations located across the country and created a classification of satellite images of KSG for two time periods. To examine farmers\' perceptions and agricultural practices, I conducted surveys of the farmers of KSG and in surrounding villages. Most farmers reported negative impacts of climate change on their agriculture activities, and interest in adopting new agricultural strategies despite long-standing tradition. Increasing temperatures and irregularity of rainfall may have negatively impacted crop yields, but more climate data are needed to clarify this phenomenon. LULC has been influenced by both climate change and human pressure; agricultural land has declined, while bare soils have increased. Several recommendations are provided that may help farmers to cope with changing climate. / Master of Science