Effects of exercise intensity on postprandial improvement in glucose disposal and insulin sensitivity in prediabetic adults

Endothelial function following glucose ingestion in adults with prediabetes: Role of exercise intensity

OBJECTIVE

To determine whether high intensity exercise (HIE) would improve endothelial function more than an isocaloric bout of moderate intensity exercise (MIE) following glucose ingestion in adults with prediabetes.

METHODS

Twelve subjects with prediabetes completed all three conditions: time-course matched control and isocaloric exercise (∼200 kcal) at moderate (MIE; at lactate threshold) and high intensity (HIE; 75% of difference between lactate threshold and VO2 peak). Brachial artery flow-mediated dilation (FMD) was measured before exercise (baseline), within 30 min postexercise, and 1 and 2 hr following a 75 g oral glucose tolerance test (OGTT). Plasma F2-isoprostanes were also assessed during the protocol (i.e., baseline to 2 hr OGTT) as a biomarker of oxidative stress.

RESULTS

MIE reduced postexercise F2-isoprostanesAUC compared with time-course matched control and HIE. Although exercise had no statistical effect on FMD postexercise or during the OGTT, elevations in FMDAUC after MIE and HIE were associated with reduced postexercise F2-isoprostanesAUC .

CONCLUSIONS

Exercise at either intensity had no effect on FMD immediately postexercise following glucose administration. However, individuals with reduced oxidative stress responses to exercise had greater exercise-induced improvement in FMD. Further work is required to identify the mechanism by which exercise alters oxidative stress to enhance endothelial function.

A Systematic Review of the Prevalence and Outcomes of Ideal Cardiovascular Health in US and Non-US Populations

Several population-based studies have examined the prevalence and trends of the American Heart Association's ideal cardiovascular health (CVH) metrics as well as its association with cardiovascular disease (CVD)-related morbidity and mortality and with non-CVD outcomes. However, no efforts have been made to aggregate these studies. Accordingly, we conducted a systematic review to synthesize available data on the distribution and outcomes associated with ideal CVH metrics in both US and non-US populations. We conducted a systematic search of relevant studies in the MEDLINE and CINAHL databases, as well as the Cochrane Register of Controlled Trials (CENTRAL). Search terms used included "life's simple 7", "AHA 2020" and "ideal cardiovascular health". We included articles published in English Language from January 1, 2010, to July 31, 2015. Of the 14 US cohorts, the prevalence of 6 to 7 ideal CVH metrics ranged from as low as 0.5% in a population of African Americans to 12% in workers in a South Florida health care organization. Outside the United States, the lowest prevalence was found in an Iranian study (0.3%) and the highest was found in a large Chinese corporation (15%). All 6 mortality studies reported a graded inverse association between the increasing number of ideal CVH metrics and the all-cause and CVD-related mortality risk. A similar relationship between ideal CVH metrics and incident cardiovascular events was found in 12 of 13 studies. Finally, an increasing number of ideal CVH metrics was associated with a lower prevalence and incidence of non-CVD outcomes such as cancer, depression, and cognitive impairment. The distribution of ideal CVH metrics in US and non-US populations is similar, with low proportions of persons achieving 6 or more ideal CVH metrics. Considering the strong association of CVH metrics with both CVD and non-CVD outcomes, a coordinated global effort for improving CVH should be considered a priority.

Cardiometabolic Health Among Cancer Survivors: A 13-Week Pilot Study of a Combined Aerobic and Resistance Training Program

PURPOSE/OBJECTIVES

To explore the feasibility of combined aerobic and resistance training (CART) as a safe method of improving cardiometabolic health among cancer survivors.
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DESIGN

Descriptive and longitudinal pilot study for exercise intervention.
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SETTING

University campus in Los Angeles, California.
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SAMPLE

A multiethnic population of cancer survivors (N = 11) was recruited by convenience sampling and physician referral. 
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METHODS

Consenting participants were prescribed CART for one hour per day, three days per week for 13 weeks.
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MAIN RESEARCH VARIABLES

Components of cardiometabolic health were measured, including resting heart rate (HRrest), blood pressure, body mass index, waist circumference, body fat percentage, and android fat percentage at baseline and after 13 weeks of training. Fasting blood glucose, insulin, adiponectin, leptin, tumor necrosis factor alpha, and C-reactive protein (CRP) also were assessed at baseline and after 13 weeks of training.
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FINDINGS

More than half of the participants reported living with at least two other chronic diseases or conditions in addition to a cancer diagnosis. Five of six African American and Hispanic participants reported the presence of at least two risk factors for metabolic syndrome, compared to one of five Caucasian participants. After 13 weeks of training, participants experienced an average decrease in waist circumference. Decrease in waist circumference was associated with a decrease in CRP. A relationship also was suggested between number of exercise sessions attended and improvement in HRrest. 
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CONCLUSIONS

A CART intervention among cancer survivors should continue to be explored in a larger sample to establish efficacy and effectiveness at improving cardiometabolic health. Because of the higher risk of comorbidity among cancer survivors in comparison to cancer-free adults, improving cardiometabolic health is as important as monitoring cancer recurrence. A need exists for increased attention to the post-treatment cardiometabolic health of cancer survivors and also for examining potential cardiometabolic health disparities among non-Caucasian cancer survivors.
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IMPLICATIONS FOR NURSING

CART may be a plausible alternative to reduce the risk of metabolic syndrome and improve cardiometabolic health among cancer survivors. Additional studies that continue to explore the efficacy and effectiveness of CART may provide more information to help nurses and physicians determine whether the cancer survivorship care plan should include an exercise-based alternative to intervene on cardiometabolic health.

Exercise Intensity Modulates Glucose-Stimulated Insulin Secretion when Adjusted for Adipose, Liver and Skeletal Muscle Insulin Resistance

Little is known about the effects of exercise intensity on compensatory changes in glucose-stimulated insulin secretion (GSIS) when adjusted for adipose, liver and skeletal muscle insulin resistance (IR). Fifteen participants (8F, Age: 49.9±3.6yr; BMI: 31.0±1.5kg/m²; VO₂peak: 23.2±1.2mg/kg/min) with prediabetes (ADA criteria, 75g OGTT and/or HbA_1c) underwent a time-course matched Control, and isocaloric (200kcal) exercise at moderate (MIE; at lactate threshold (LT)), and high-intensity (HIE; 75% of difference between LT and VO₂peak). A 75g OGTT was conducted 1 hour post-exercise/Control, and plasma glucose, insulin, C-peptide and free fatty acids were determined for calculations of skeletal muscle (1/Oral Minimal Model; SM_IR), hepatic (HOMA_IR), and adipose (ADIPOSE_IR) IR. Insulin secretion rates were determined by deconvolution modeling for GSIS, and disposition index (DI; GSIS/IR; DI_SMIR, DI_HOMAIR, DI_ADIPOSEIR) calculations. Compared to Control, exercise lowered SM_IR independent of intensity (P<0.05), with HIE raising HOMA_IR and ADIPOSE_IR compared with Control (P<0.05). GSIS was not reduced following exercise, but DI_HOMAIR and DI_ADIPOSEIR were lowered more following HIE compared with Control (P<0.05). However, DI_SMIR increased in an intensity based manner relative to Control (P<0.05), which corresponded with lower post-prandial blood glucose levels. Taken together, pancreatic insulin secretion adjusts in an exercise intensity dependent manner to match the level of insulin resistance in skeletal muscle, liver and adipose tissue. Further work is warranted to understand the mechanism by which exercise influences the cross-talk between tissues that regulate blood glucose in people with prediabetes.

Exercise resistance across the prediabetes phenotypes: Impact on insulin sensitivity and substrate metabolism

Prediabetes is a heterogeneous term that encompasses different origins of insulin resistance and insulin secretion that contribute to distinct patterns of hyperglycemia. In fact, prediabetes is an umbrella term that characterizes individuals at high risk for developing type 2 diabetes (T2D) and/or cardiovascular disease (CVD). Based on current definitions there are at least 3 distinct phenotypes of prediabetes: impaired fasting glucose (IFG), impaired glucose tolerant (IGT), or the combination of both (IFG + IGT). Each phenotype is clinically relevant as they are uniquely recognized as having different levels of risk for progressing to T2D and CVD. Herein, we discuss the underlying pathophysiology that characterizes IFG, IGT and the combination, as well as examine how some of these phenotypes appear resistant to traditional exercise interventions. We propose that substrate metabolism differences between the prediabetes phenotypes may be a unifying mechanism that explains the inter-subject variation in response to exercise seen across obese, metabolic syndrome, pre-diabetic and T2D patients in the current literature. Ultimately, a better understanding of the pathophysiologic mechanisms that govern disturbances responsible for fasting vs. postprandial hyperglycemia and the combination of both is important for designing optimal and personalized exercise treatment strategies that treat and prevent hyperglycemia and CVD risk.

Vigorous exercise is associated with superior metabolic profiles in polycystic ovary syndrome independent of total exercise expenditure

OBJECTIVE

To characterize metabolic features of women with polycystic ovary syndrome (PCOS) by exercise behavior and determine relative health benefits of different exercise intensities.

DESIGN

Cross-sectional study.

SETTING

Tertiary academic institution.

PATIENT(S)

Three hundred and twenty-six women aged 14-52 years-old with PCOS by Rotterdam criteria examined between 2006 and 2013.

INTERVENTION(S)

International Physical Activity Questionnaire (IPAQ) administered to classify patients into three groups based on Department of Health and Human Services (DHHS) Guidelines of vigorous, moderate, and inactive, along with physical examination and serum testing.

MAIN OUTCOME MEASURE(S)

Blood pressure, body mass index (BMI), waist circumference, fasting lipids, fasting glucose and insulin, 2-hour 75-gram oral glucose tolerance, homeostatic model assessment of insulin resistance (HOMA-IR).

RESULT(S)

The DHHS guidelines for adequate physical activity were met by 182 (56%) women. Compared with moderate exercisers and inactive women, the vigorous exercisers had lower BMI and lower HOMA-IR; higher levels of high-density lipoprotein cholesterol and sex hormone-binding globulin; and a reduced prevalence of the metabolic syndrome. In a multivariate logistic regression analysis controlling for age, BMI, and total energy expenditure, every hour of vigorous exercise reduced a patient's odds of metabolic syndrome by 22% (odds ratio 0.78; 95% confidence interval, 0.62, 0.99).

CONCLUSION(S)

Women with PCOS who met DHHS guidelines for exercise demonstrated superior metabolic health parameters. Vigorous but not moderate activity is associated with reduced odds of the metabolic syndrome, independent of age, BMI, and total energy expenditure. PCOS patients should be encouraged to meet activity guidelines via vigorous physical activity.

Effect of the low- versus high-intensity exercise training on endoplasmic reticulum stress and GLP-1 in adolescents with type 2 diabetes mellitus

[Purpose] The primary objective of this study was to investigate the effect of low-intensity exercise training compare with high-intensity exercise training on endoplasmic reticulum stress and glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus. [Subjects and Methods] The low-intensity exercise training group performed aerobic exercise training at an intensity of ≤ 45% of the heart rate reserve. The high-intensity interval exercise training group performed interval exercise training at an intensity of ≥ 80% of the heart rate reserve. The exercise-related energy consumption was determined for both groups on a per-week basis (1,200 kcal/week). [Results] Both groups showed improvement in the glucose-regulated protein 78 and dipeptidyl peptidase-4, but the size of the between-group effect was not statistically significant. The high-intensity interval exercise training group showed a significant reduction in percentage body fat. The C-peptide level increased after the 12-weeks programs and was significantly different, between the groups. Fasting glucose, insulin resistance in the fasting state according to homeostasis model assessment, and leptin decreased after the 12-weeks exercise program and were significantly different between the groups, and glucagon-like peptide-1 increased after the 12-week exercise programs and was significantly different between the groups. [Conclusion] In conclusion high-intensity interval exercise training, as defined in this study, may lead to improvements in body composition, glycemic control, endoplasmic reticulum stress, and the glucagon-like peptide-1 in adolescents with type 2 diabetes mellitus.

High Intensity Interval Training Improves Glycaemic Control and Pancreatic β Cell Function of Type 2 Diabetes Patients

Physical activity improves the regulation of glucose homeostasis in both type 2 diabetes (T2D) patients and healthy individuals, but the effect on pancreatic β cell function is unknown. We investigated glycaemic control, pancreatic function and total fat mass before and after 8 weeks of low volume high intensity interval training (HIIT) on cycle ergometer in T2D patients and matched healthy control individuals. Study design/method: Elderly (56 yrs±2), non-active T2D patients (n = 10) and matched (52 yrs±2) healthy controls (CON) (n = 13) exercised 3 times (10×60 sec. HIIT) a week over an 8 week period on a cycle ergometer. Participants underwent a 2-hour oral glucose tolerance test (OGTT). On a separate day, resting blood pressure measurement was conducted followed by an incremental maximal oxygen uptake (V˙O_2max) cycle ergometer test. Finally, a whole body dual X-ray absorptiometry (DXA) was performed. After 8 weeks of training, the same measurements were performed. Results: in the T2D-group, glycaemic control as determined by average fasting venous glucose concentration (p = 0.01), end point 2-hour OGTT (p = 0.04) and glycosylated haemoglobin (p = 0.04) were significantly reduced. Pancreatic homeostasis as determined by homeostatic model assessment of insulin resistance (HOMA-IR) and HOMA β cell function (HOMA-%β) were both significantly ameliorated (p = 0.03 and p = 0.03, respectively). Whole body insulin sensitivity as determined by the disposition index (DI) was significantly increased (p = 0.03). During OGTT, the glucose continuum was significantly reduced at -15 (p = 0.03), 30 (p = 0.03) and 120 min (p = 0.03) and at -10 (p = 0.003) and 0 min (p = 0.003) with an additional improvement (p = 0.03) of its 1^st phase (30 min) area under curve (AUC). Significant abdominal fat mass losses were seen in both groups (T2D: p = 0.004 and CON: p = 0.02) corresponding to a percentage change of -17.84%±5.02 and -9.66%±3.07, respectively. Conclusion: these results demonstrate that HIIT improves overall glycaemic control and pancreatic β cell function in T2D patients. Additionally, both groups experienced abdominal fat mass losses. These findings demonstrate that HIIT is a health beneficial exercise strategy in T2D patients.

Type 2 diabetes alters metabolic and transcriptional signatures of glucose and amino acid metabolism during exercise and recovery

AIMS/HYPOTHESIS

The therapeutic benefit of physical activity to prevent and treat type 2 diabetes is commonly accepted. However, the impact of the disease on the acute metabolic response is less clear. To this end, we investigated the effect of type 2 diabetes on exercise-induced plasma metabolite changes and the muscular transcriptional response using a complementary metabolomics/transcriptomics approach.

METHODS

We analysed 139 plasma metabolites and hormones at nine time points, and whole genome expression in skeletal muscle at three time points, during a 60 min bicycle ergometer exercise and a 180 min recovery phase in type 2 diabetic patients and healthy controls matched for age, percentage body fat and maximal oxygen consumption (VO2).

RESULTS

Pathway analysis of differentially regulated genes upon exercise revealed upregulation of regulators of GLUT4 (SLC2A4RG, FLOT1, EXOC7, RAB13, RABGAP1 and CBLB), glycolysis (HK2, PFKFB1, PFKFB3, PFKM, FBP2 and LDHA) and insulin signal mediators in diabetic participants compared with controls. Notably, diabetic participants had normalised rates of lactate and insulin levels, and of glucose appearance and disappearance, after exercise. They also showed an exercise-induced compensatory regulation of genes involved in biosynthesis and metabolism of amino acids (PSPH, GATM, NOS1 and GLDC), which responded to differences in the amino acid profile (consistently lower plasma levels of glycine, cysteine and arginine). Markers of fat oxidation (acylcarnitines) and lipolysis (glycerol) did not indicate impaired metabolic flexibility during exercise in diabetic participants.

CONCLUSIONS/INTERPRETATION

Type 2 diabetic individuals showed specific exercise-regulated gene expression. These data provide novel insight into potential mechanisms to ameliorate the disturbed glucose and amino acid metabolism associated with type 2 diabetes.

Effects of prior exercise on glycemic responses following carbohydrate inges on in individuals with type 2 diabetes

BACKGROUND

Exercise is effective in reducing glycemia, especially when it is performed in the postprandial period. However, no consensus exists in the literature about the effect of exercise on postprandial glucose control when it is performed before carbohydrate consumption.

AIMS

The main aim was to determine whether 20 min of exercise performed prior to carbohydrate consumption reduces postprandial glycemic and insulinemic responses. A secondary aim was to analyze the effectiveness of short-term (10 min) exercise bout with respect to postprandial glycemia reduction.

METHODS

Nine individuals with type 2 diabetes (54.9 ± 1.7 years; 30.7 ± 1.8 kg/m²; glycemia level of 167.0 ±10.6 mg/dL) participated in the study and underwent the following procedures: (a) an incremental test to determine the lactate threshold; (b) an exercise session for 20 minutes at moderate intensity (90% of the lactate threshold); and c) a control session. The last two sessions were randomized, and the participants were monitored during 135 minutes of post-exercise recovery. A standard meal was consumed two hours before the experimental procedures started. A dextrose solution was administered at 45 minutes of post-exercise recovery while monitoring glucose and insulin concentrations. At 135 min of post-exercise recovery, eight of the participants performed an additional 10-min exercise bout following induced hyperglycemia.

RESULTS

Exercise reduced glycemia (-46.6 ± 7.9 mg/dL) and the insulin/glucose ratio (from 1.73 ± 0.59 to 0.93 ± 0.22 µU/mL/mmol/L) during the first 45 minutes of post-exercise recovery. Glycemia was significantly increased after carbohydrate consumption, reaching its peak value at 105 minutes of post-exercise recovery (261.8 ± 15.8 mg/dL) or control (281.3 ± 13.4 mg/dL). There was no effect of the previous exercise in attenuating glycemia or reducing the area under the curve for glucose and insulin after carbohydrate consumption. However, the effectiveness of exercise in reducing glycemia was shown again when it was performed at the end of the experimental session, even in case of only a 10-min exercise (reduction of -44.5 ± 4.9 mg/dL).

CONCLUSIONS

Twenty minutes of moderate exercise does not alter the kinetics or the area under the curve in terms of glycemia and insulinemia after subsequent carbohydrate consumption. However, moderate exercise, even if performed for only 10-20 minutes, is effective in reducing postprandial glycemia in individuals with type 2 diabetes.

RELEVANCE FOR PATIENTS

Moderate-intensity exercise, even of short duration, may benefit individuals with type 2 diabetes on blood glucose control. A fast reduction in postprandial glycemia can be obtained with only ten minutes of exercise that, in turn, may ameliorate some of complications associated with the disease.

Brain-derived neurotrophic factor and substrate utilization following acute aerobic exercise in obese individuals

Brain-derived neurotrophic factor (BDNF) serves as a vital regulator of neuronal proliferation and survival, and has been shown to regulate energy homeostasis, glucose metabolism and body weight maintenance. Elevated concentrations of plasma BDNF have been associated with obesity and type 2 diabetes mellitus. Acute aerobic exercise transiently increases circulating BDNF, potentially correcting obesity-related metabolic impairment. The present study aimed to compare acute aerobic exercise elicited BDNF responses in obese and normal-weight subjects. Furthermore, we aimed to investigate whether acute exercise-induced plasma BDNF elevations would be associated with improved indices of insulin resistance, as well as substrate utilization [carbohydrate oxidation (CHOoxi) and fat oxidation (FAToxi)]. Twenty-two healthy, untrained subjects [11 obese (four men and seven women; age = 22.91 ± 4.44 years; body mass index = 35.72 ± 4.17 kg/m(2)) and 11 normal-weight (five men and six women; age = 23.27 ± 2.24 years; body mass index = 21.89 ± 1.63 kg/m(2))] performed 30 min of continuous submaximal aerobic exercise at 75% maximal oxygen consumption. Our analyses showed that the BDNF response to acute aerobic exercise was similar in obese and normal-weight subjects across time (time: P = 0.015; group: P = not significant) and was not associated with indices of IR. Although no differences in the rates of CHOoxi and FAToxi were found between both groups, total relative energy expenditure was significantly lower in obese subjects compared to normal-weight subjects (3.53 ± 0.25 versus 5.59 ± 0.85; P < 0.001). These findings suggest that acute exercise-elicited BDNF elevation may not be sufficient to modulate indices of IR or the utilization of either carbohydrates or fats in obese individuals.

Differential impact of acute high-intensity exercise on circulating endothelial microparticles and insulin resistance between overweight/obese males and females

Background

An acute bout of exercise can improve endothelial function and insulin sensitivity when measured on the day following exercise. Our aim was to compare acute high-intensity continuous exercise (HICE) to high-intensity interval exercise (HIIE) on circulating endothelial microparticles (EMPs) and insulin sensitivity in overweight/obese men and women.

Methods

Inactive males (BMI = 30 ± 3, 25 ± 6 yr, n = 6) and females (BMI = 28 ± 2, 21 ± 3 yr, n = 7) participated in three experimental trials in a randomized counterbalanced crossover design: 1) No exercise control (Control); 2) HICE (20 min cycling @ just above ventilatory threshold); 3) HIIE (10 X 1-min @ ∼90% peak aerobic power). Exercise conditions were matched for external work and diet was controlled post-exercise. Fasting blood samples were obtained ∼18 hr after each condition. CD62E⁺ and CD31⁺/CD42b^- EMPs were assessed by flow cytometry and insulin resistance (IR) was estimated by homeostasis model assessment (HOMA-IR).

Results

There was a significant sex X exercise interaction for CD62E+ EMPs, CD31+/CD42b- EMPs, and HOMA-IR (all P<0.05). In males, both HICE and HIIE reduced EMPs compared to Control (P≤0.05). In females, HICE increased CD62E+ EMPs (P<0.05 vs. Control) whereas CD31+/CD42b- EMPs were unaltered by either exercise type. There was a significant increase in HOMA-IR in males but a decrease in females following HIIE compared to Control (P<0.05).

Conclusions

Overweight/obese males and females appear to respond differently to acute bouts of high-intensity exercise. A single session of HICE and HIIE reduced circulating EMPs measured on the morning following exercise in males but in females CD62E+ EMPs were increased following HICE. Next day HOMA-IR paradoxically increased in males but was reduced in females following HIIE. Future research is needed to investigate mechanisms responsible for potential differential responses between males and females.

Examination of Lifestyle Behaviors and Cardiometabolic Risk Factors in University Students Enrolled in Kinesiology Degree Programs

Preventing physical inactivity and weight gain during college is critical in decreasing lifelong obesity and associated disease risk. As such, we sought to compare cardiometabolic risk factors and lifestyle behaviors between college students enrolled in kinesiology and non-kinesiology degree programs to assess whether health and exercise degree programs may influence health behaviors and associated disease risk outcomes. Anthropometrics, fasting blood glucose, insulin, lipid profiles and HbA1c%, blood pressure, and peak oxygen consumption (V[Combining Dot Above]O2peak) were assessed in 247 healthy college students. The homeostasis model assessment of insulin sensitivity (HOMA) was calculated using glucose and insulin levels. Self-reported physical activity from the Paffenbarger questionnaire was collected to estimate the average caloric expenditure due to different types of physical activities. Despite no significant differences in body mass index or waist circumference between groups, kinesiology majors presented with ∼20% lower fasting insulin levels and HOMA (p = 0.01; p < 0.01, respectively) relative to nonmajors. Kinesiology majors reported increased weekly participation in vigorous-intensity sport and leisure activities and, on average, engaged in >300 metabolic equivalent-h·wk, whereas non-kinesiology majors engaged in <300 MET-h wk (p = 0.01). Our data suggest that students enrolled in kinesiology degree programs display improved healthy behaviors and associated outcomes (parameters of glucose homeostasis). Practical outcomes of this research indicate that implementing components of a comprehensive kinesiology curriculum encourages improved health behaviors and associated cardiometabolic risk factors.

Niacin increased glucose, insulin, and C-peptide levels in sedentary nondiabetic postmenopausal women

The current study examined the effects of niacin and a single bout of aerobic exercise on plasma glucose, insulin, and C-peptide in sedentary, nondiabetic postmenopausal women. As a crossover design, 17 participants underwent four different trials: rest during the no-niacin condition (R), exercise during the no-niacin condition (E), rest during the with-niacin condition (RN), and exercise during the with-niacin condition (EN). All participants took 1,000 mg/day of extended-release niacin for 4 weeks during the with-niacin conditions (RN and EN). The exercise treatment consisted of a single bout of treadmill walking at 60% heart rate reserve until 400 kcal were expended. Blood samples were collected at 24 hours after each trial and analyzed for changes in plasma glucose, insulin, and C-peptide. A two by two analysis of variance was used to examine the changes in dependent variables, and the Bonferroni adjustment was employed as the post hoc test. The level of statistical significance was set at P<0.05. There was no significant interaction between exercise and niacin, nor was there a main effect of exercise for changes in glucose, insulin, or C-peptide. However, there was a significant main effect for niacin as mean glucose, insulin, and C-peptide values significantly increased with niacin; glucose increased 10.6% (P=0.001), from 95.03±10.67 mg/dL to 105.07±13.56 mg/dL; insulin increased 61.8% (P=0.001), from 16.98±12.49 μU/mL to 27.48±14.84 μU/mL; and C-peptide increased 46.1% (P=0.001), from 1.65±0.75 ng/mL to 2.41±0.97 ng/mL. Although niacin was generally well tolerated, given its adverse effects on glucose, insulin, and C-peptide profiles, the use of niacin should be done so with caution and under medical supervision.

High intensity interval exercise is an effective alternative to moderate intensity exercise for improving glucose tolerance and insulin sensitivity in adolescent boys

OBJECTIVES

High-intensity interval exercise (HIIE) may offer a time efficient means to improve health outcomes compared to moderate-intensity exercise (MIE). This study examined the acute effect of HIIE compared to a work-matched bout of MIE on glucose tolerance, insulin sensitivity (IS), resting fat oxidation and exercise enjoyment in adolescent boys.

DESIGN

Within-measures design with counterbalanced experimental conditions.

METHODS

Nine boys (14.2 ± 0.4 years) completed three conditions on separate days in a counterbalanced order: (1) HIIE; (2) work matched MIE, both on a cycle ergometer; and (3) rest (CON). An oral glucose tolerance test (OGTT) was performed after exercise or rest and the area under curve (AUC) responses for plasma [glucose] and [insulin] were calculated, and IS estimated (Cederholm index). Energy expenditure and fat oxidation were measured following the OGTT using indirect calorimetry. Exercise enjoyment was assessed using the Physical Activity Enjoyment Scale.

RESULTS

The incremental AUC (iAUC) for plasma [glucose] was reduced following both MIE (-23.9%, P = 0.013, effect size [ES] = -0.64) and HIIE (-28.9%, P=0.008, ES = -0.84) compared to CON. The iAUC for plasma [insulin] was lower for HIIE (-24.2%, P = 0.021, ES = -0.71) and MIE (-29.1%, P = 0.012, ES = -0.79) compared to CON. IS increased by 11.2% after HIIE (P = 0.03, ES = 0.76) and 8.4% after MIE (P = 0.10, ES = 0.58). There was a trend for an increase in fat oxidation following HIIE (P = 0.097, ES = 0.70). Both HIIE and MIE were rated as equally enjoyable (P > 0.05, ES < 0.01).

CONCLUSION

A single bout of time efficient HIIE is an effective alternative to MIE for improving glucose tolerance and IS in adolescent boys immediately after exercise.

Physiological mechanisms of vascular response induced by shear stress and effect of exercise in systemic and placental circulation

Physiological vascular function regulation is essential for cardiovascular health and depends on adequate control of molecular mechanisms triggered by endothelial cells in response to mechanical and chemical stimuli induced by blood flow. Endothelial dysfunction is one of the main risk factors of cardiovascular pathology, where the imbalance between the synthesis of vasodilator and vasoconstrictor molecules is common in the development of vascular disorders in systemic and placental circulation. In the placenta, an organ without autonomic innervations, the local control of vascular tone is critical for maintenance of fetal growth and mechanisms that underlie shear stress response induced by blood flow are essential during pregnancy. In this field, shear stress induced by moderate exercise is one of the most important mechanisms to improve vascular function through nitric oxide synthesis and stimulation of mechanical response of endothelial cells triggered by ion channels, caveolae, endothelial NO synthase, and vascular endothelial growth factor, among others. The demand for oxygen and nutrients by tissues and organs, especially in placentation and pregnancy, determines blood flow parameters, and physiological adaptations of vascular beds for covering metabolic requirements. In this regard, moderate exercise versus sedentarism shows potential benefits for improving vascular function associated with the enhancement of molecular mechanisms induced by shear stress. In this review, we collect evidence about molecular bases of physiological response to shear stress in order to highlight the relevance of moderate exercise-training for vascular health in adult and fetal life.

The immediate effects of a single bout of aerobic exercise on oral glucose tolerance across the glucose tolerance continuum

We investigated glucose tolerance and postprandial glucose fluxes immediately after a single bout of aerobic exercise in subjects representing the entire glucose tolerance continuum. Twenty‐four men with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes (T2D; age: 56 ± 1 years; body mass index: 27.8 ± 0.7 kg/m², P > 0.05) underwent a 180‐min oral glucose tolerance test (OGTT) combined with constant intravenous infusion of [6,6‐²H₂]glucose and ingestion of [U‐¹³C]glucose, following 1 h of exercise (50% of peak aerobic power) or rest. In both trials, plasma glucose concentrations and kinetics, insulin, C‐peptide, and glucagon were measured. Rates (mg kg⁻¹ min⁻¹) of glucose appearance from endogenous (R_aEndo) and exogenous (oral glucose; R_aOGTT) sources, and glucose disappearance (R_d) were determined. We found that exercise increased R_aEndo, R_aOGTT, and R_d (all P < 0.0001) in all groups with a tendency for a greater (~20%) peak R_aOGTT value in NGT subjects when compared to IGT and T2D subjects. Accordingly, following exercise, the plasma glucose concentration during the OGTT was increased in NGT subjects (P < 0.05), while unchanged in subjects with IGT and T2D. In conclusion, while a single bout of moderate‐intensity exercise increased the postprandial glucose response in NGT subjects, glucose tolerance following exercise was preserved in the two hyperglycemic groups. Thus, postprandial plasma glucose responses immediately following exercise are dependent on the underlying degree of glycemic control.

This study shows that following an exercise bout, plasma glucose concentrations during an oral glucose tolerance test are increased in subjects with normal glucose tolerance, but unchanged in subjects with impaired glucose tolerance or type 2 diabetes. While rates of glucose disappearance and rates of glucose appearance from endogenous sources and from orally ingested glucose were all increased following exercise, there was a 20% greater peak value for the rate of orally ingested glucose appearance in normal glucose tolerant subjects, when compared to IGT and T2D subjects. In summary, postprandial plasma glucose responses immediately following exercise are dependent on the underlying level of glycemic control.