Short-term exercise training reduces insulin resistance and improves insulin action. The purpose of this research was to examine how short-term training, defined as 5–10 consecutive days of exercise, reduces insulin resistance. A preliminary study investigated the effects of short-term exercise training on substrate utilization during exercise to explore the relationship of fuel selection and insulin action. The primary study examined the role of energy balance in mediating improved insulin action following short-term exercise training and how that affected risk factors for type 2 diabetes and cardiovascular disease. Prior to this study, the importance of generating a caloric deficit was unclear. Replacing the energy expended during exercise to prevent negative energy balance might oppose the insulin-sensitizing effects of exercise. The purpose of this study was to establish the role of negative energy balance in mediating improved insulin action after short-term exercise training. Design. Previously sedentary, overweight/obese subjects were randomly placed in an energy balance group, in which energy expended during exercise was promptly replaced (BAL, n = 8) or in a caloric deficit group in which the energy was not replaced (NEG, n = 8). The groups were similar at baseline in age, BMI, trunk fat, lean mass, VO2 peak and insulin resistance. Training consisted of 6 consecutive days of treadmill walking (60–65% VO2 peak) to expend ∼500 kcals (duration = 62 ± 6.5 min/d). Insulin action pre- and post-training was measured by glucose rate of disappearance per unit insulin. Results. As designed, daily energy expenditure increased by ∼500 kcal/d during training in each group (NEG = 469 ± 45, BAL = 521 ± 48). Insulin action increased 40% in NEG (p = 0.032) but was unchanged in BAL (−8.4%, p = 0.107). Suppression of hepatic glucose production during the glucose infusion increased significantly only in NEG (+30.2 ± 9.5%, p = 0.037) but not in BAL (−10.0 ± 7.4%, p = 0.417). Mean changes in fasting plasma insulin, leptin, triglycerides, adiponectin and C-reactive protein tracked charges in insulin action but only changes in leptin were statistically significant. Conclusions. Short-term exercise training without energy replacement significantly reduced insulin resistance. Feeding back the 500 kcal of energy expended during exercise negated the effect of training. These findings suggest that subtle changes in energy balance that precede measurable fat loss play a key role in mediating the beneficial effects of exercise on whole-body insulin action.

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 50-71). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://proquest.umi.com/pqdweb?index=0&did=1299815841&SrchMode=1&sid=3&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1195667700&clientId=5220

Recently published federal public health initiatives have called for research to “develop better methods for analysis and quantification of (physical) activity” behaviors and to better understand the most important “features of physical activity (total amount, intensity, duration, frequency, pattern, or type) that confers health benefit”. Accordingly, this dissertation examined measurement issues related to the sources of variance in daily physical activity, as well as the types and features (e.g., dose) of physical activity that were associated with the cardiovascular disease risk factors body mass and blood lipids. Three investigations from within the Seasonal Variation of Blood Cholesterol Study (Seasons) cohort were conducted. Seasons was an observational study of 641 healthy adults that collected longitudinal assessments of body mass, blood lipids, physical activity, and dietary intake over 12 months of follow-up. The first investigation found that day-to-day variability was the major source of variance (65–80%) in activity, and that seasonal and day-of-the-week effects were minimal (<2%). Between-subject differences accounted for 20–35% of the variance observed, and 14 to 21 days of assessment were required to reliably measure non-occupational activity. The second investigation found that men increased (0.5 kg, p < 0.05) and women maintained (–0.2 kg, p > 0.05) their body mass levels over follow-up, and that both sexes had lower body mass (0.4 to 0.6 kg, p < 0.09) and higher activity levels (0.7 to 1.1MET-hrs·d–1, p < 0.05) in spring/summer compared to winter months. Total, occupational, and leisure activities were associated with lower cross-sectional body mass levels, and household and leisure activities were associated with longitudinal reductions in body mass. The final investigation revealed that individuals who were below recommended levels of moderate-vigorous physical activity ([special characters omitted]2 MET-hrs·d–1) had lower high-density lipoprotein cholesterol and higher triglyceride levels, placing them at increased risk of coronary heart disease. Additionally, total activity and duration of activity, but not intensity, were associated with lower levels of, or changes in blood lipids, particularly among men. These findings have important implications for the measurement of physical activity in epidemiologic studies, and they underscore the notion that naturally occurring changes in physical activity levels are directly related to disease risk.