Aerobic Training Effects on Glucose Tolerance in Prediabetic and Normoglycemic Humans
ABSTRACT It is generally accepted that if prediabetic individuals adopt healthy lifestyle habits, the progression to type 2 diabetes mellitus can be prevented or delayed. However, the role of exercise training independent of other lifestyle factors has not been determined. Furthermore, patients with type 2 diabetes mellitus have been shown to experience greater training-induced changes in glucose and insulin metabolism compared with healthy subjects, but the adaptations of prediabetic individuals have not been adequately examined. We hypothesized that (i) prediabetic subjects would have greater endurance training-induced changes in plasma glucose and insulin responses to an oral glucose challenge compared with age- and body mass index-matched normoglycemic subjects and (ii) training would completely reverse the abnormal glucose metabolism of prediabetic subjects.
Plasma glucose and insulin responses to oral glucose tolerance tests (OGTTs) were examined in normoglycemic (n = 119) and prediabetic (n = 47) older men and women before and after a 6-month standardized endurance exercise training program.
Prediabetic subjects had greater glucose and insulin OGTT responses than normoglycemic subjects both before and after training (P < 0.05). Prediabetic subjects had greater training-induced changes in glucose and insulin areas under the glucose tolerance curve, as well as greater changes in glucose and insulin concentrations at several points of the OGTT. However, these changes did not eliminate the baseline differences in glucose tolerance between normoglycemic and prediabetic subjects. The between-group differences in changes in glucose and insulin variables were largely independent of changes in body weight or composition.
Our data indicate that prediabetes is associated with greater training-induced changes in glucose tolerance. However, 6 months of endurance training alone was not sufficient to completely reverse prediabetes.
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ABSTRACT: To review the responses of the liver to acute and chronic physical activity and to summarize relationships between physical activity and liver health. A systematic search of HealthStar/Ovid from 1975 through June of 2013, supplemented by articles from other sources. 351 of 8,010 articles identified by HealthStar/Ovid were supplemented by 92 other papers; after focussing, the review was reduced to 435 citations. Prolonged acute exercise reduces hepatic blood flow, stimulating hepatic glycogenolysis, gluconeogenesis and synthesis of some proteins; however, lipid metabolism shows little change. Glutathione depletion suggests oxidative stress. Enzymes affecting carbohydrate metabolism are up-regulated, and lipogenic enzymes are down-regulated. The main triggers are humoral, but hepatic afferent nerves, cytokines, reactive oxygen species, and changes in hepatic blood flow may all play some role. Regular aerobic exercise training improves blood glucose control during exercise by increasing glycogen stores and up-regulating enzymes involved in gluconeogenesis and carbohydrate metabolism. Resistance to oxidant stress is generally increased by training. Lipogenic enzymes are down-regulated, and lipid metabolism is augmented. Modulations of insulin, insulin-like growth factor, glucagon and interleukin-6 may trigger the adaptive responses to training. Cross-sectional and longitudinal studies show that regular exercise can reduce hepatic fat, but the effect on circulating aminotransferases is unclear and the modality and dose of physical activity optimizing health benefits need clarification. Regular moderate physical activity enhances liver health. Adverse functional changes can develop if habitual activity is inadequate, and extremely prolonged competitive exercise may also be harmful, particularly under harsh environmental conditions.Arbeitsphysiologie 11/2014; 115(1). DOI:10.1007/s00421-014-3031-6 · 2.30 Impact Factor
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ABSTRACT: High-intensity interval training (HIIT) offers a practical approach for enhancing cardiorespiratory fitness, however its role in improving glucose regulation among sedentary yet normoglycemic women remains unclear. Herein, multi-segment injection capillary electrophoresis-mass spectrometry is used as a high-throughput platform in metabolomics to assess dynamic responses of overweight/obese women (BMI > 25, n = 11) to standardized oral glucose tolerance tests (OGTTs) performed before and after a 6-week HIIT intervention. Various statistical methods were used to classify plasma metabolic signatures associated with post-prandial glucose and/or training status when using a repeated measures/cross-over study design. Branched-chain/aromatic amino acids and other intermediates of urea cycle and carnitine metabolism decreased over time in plasma after oral glucose loading. Adaptive exercise-induced changes to plasma thiol redox and orthinine status were measured for trained subjects while at rest in a fasting state. A multi-linear regression model was developed to predict changes in glucose tolerance based on a panel of plasma metabolites measured for naïve subjects in their untrained state. Since treatment outcomes to physical activity are variable between-subjects, prognostic markers offer a novel approach to screen for potential negative responders while designing lifestyle modifications that maximize the salutary benefits of exercise for diabetes prevention on an individual level.Scientific Reports 08/2014; 4:6166. DOI:10.1038/srep06166 · 5.08 Impact Factor
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ABSTRACT: The aim of the present study was to determine which of the available glucose tolerance tests (oral (OGTT) vs. intravenous (IVGTT)) could more readily detect the insulin sensitizing effects of a bout of continuous exercise. Ten healthy moderately fit young men (VO2peak of 45.4 ± 1.8 mL·kg−1·min−1; age 27.5 ± 2.7 yr) underwent 4 OGTT and 4 IVGTT on different days following a standardized dinner and overnight fast. One test was performed immediately after 55 min of cycle-ergometer exercise at 60% VO2peak. Insulin sensitivity index was determined during a 50 min IVGTT according to Tura (CISI) and from a 120 min OGTT using the Matsuda composite index (MISI). After exercise, MISI improved 29 ± 10% without reaching statistical significance (p = 0.182) due to its low reproducibility (coefficient of variation 16 ± 3%; intra-class reliability 0.846). However, CISI significantly improved (50 ± 4%; p ISI compared with MISI suggests the preferential use of IVGTT to assess the effects of exercise on insulin sensitivity when using a glucose tolerance test.Applied Physiology Nutrition and Metabolism 07/2014; 39(7). DOI:10.1139/apnm-2013-0507 · 2.23 Impact Factor