One bout of exercise alters free-living postprandial glycemia in type 2 diabetes

Metabolic plasticity and obesity-associated changes in diurnal postexercise metabolism in mice

BACKGROUND

Circadian disruption is widespread and increases the risk of obesity. Timing of therapeutic interventions may promote coherent and efficient gating of metabolic processes and restore energy homeostasis.

AIM

To characterize the diurnal postexercise metabolic state in mice and to identify the influence of diet-induced obesity on identified outcomes.

METHODS

C57BL6/NTac male mice (6 wks of age) were fed a standard chow or high-fat diet for 5 weeks. At week 5, mice were subjected to a 60-min (16 m/min, 5 % incline) running bout (or sham) during the early rest (day) or early active (night) phase. Tissue and serum samples were collected immediately post-exercise (n = 6/group). In vivo glucose oxidation was measured after oral administration of 13C-glucose via 13CO2 exhalation analysis in metabolic cages. Basal and isoproterenol-stimulated adipose tissue lipolysis was assessed ex vivo for 1 h following exercise.

RESULTS

Lean mice displayed exercise-timing-specific plasticity in metabolic outcomes, including phase-specificity in systemic glucose metabolism and adipose-tissue-autonomous lipolytic activity depending on time of day. Conversely, obesity impaired temporal postexercise differences in whole-body glucose oxidation, as well as the phase- and exercise-mediated induction of lipolysis in isolated adipose tissue. This obesity-induced alteration in diurnal metabolism, as well as the indistinct response to exercise, was observed concomitant with disruption of core clock gene expression in peripheral tissues.

CONCLUSIONS

Overall, high-fat fed obese mice exhibit metabolic inflexibility, which is also evident in the diurnal exercise response. Our study provides physiological insight into exercise timing-dependent aspects in the dynamic regulation of metabolism and the influence of obesity on this biology.

Exercise Prescription for Postprandial Glycemic Management

The detrimental impacts of postprandial hyperglycemia on health are a critical concern, and exercise is recognized a pivotal tool in enhancing glycemic control after a meal. However, current exercise recommendations for managing postprandial glucose levels remain fairly broad and require deeper clarification. This review examines the existing literature aiming to offer a comprehensive guide for exercise prescription to optimize postprandial glycemic management. Specifically, it considers various exercise parameters (i.e., exercise timing, type, intensity, volume, pattern) for crafting exercise prescriptions. Findings predominantly indicate that moderate-intensity exercise initiated shortly after meals may substantially improve glucose response to a meal in healthy individuals and those with type 2 diabetes. Moreover, incorporating short activity breaks throughout the exercise session may provide additional benefits for reducing glucose response.

Is There an Optimal Time of Day for Exercise? A Commentary on When to Exercise for People Living With Type 1 or Type 2 Diabetes

Exercise is a cornerstone of diabetes self-care because of its association with many health benefits. Several studies that have explored the best time of day to exercise to inform clinical recommendations have yielded mixed results. For example, for people with prediabetes or type 2 diabetes, there may be benefits to timing exercise to occur after meals, whereas people with type 1 diabetes may benefit from performing exercise earlier in the day. One common thread is the health benefits of consistent exercise, suggesting that the issue of exercise timing may be secondary to the goal of helping people with diabetes establish an exercise routine that best fits their life.

The role of exercise and hypoxia on glucose transport and regulation

Muscle glucose transport activity increases with an acute bout of exercise, a process that is accomplished by the translocation of glucose transporters to the plasma membrane. This process remains intact in the skeletal muscle of individuals with insulin resistance and type 2 diabetes mellitus (T2DM). Exercise training is, therefore, an important cornerstone in the management of individuals with T2DM. However, the acute systemic glucose responses to carbohydrate ingestion are often augmented during the early recovery period from exercise, despite increased glucose uptake into skeletal muscle. Accordingly, the first aim of this review is to summarize the knowledge associated with insulin action and glucose uptake in skeletal muscle and apply these to explain the disparate responses between systemic and localized glucose responses post-exercise. Herein, the importance of muscle glycogen depletion and the key glucoregulatory hormones will be discussed. Glucose uptake can also be stimulated independently by hypoxia; therefore, hypoxic training presents as an emerging method for enhancing the effects of exercise on glucose regulation. Thus, the second aim of this review is to discuss the potential for systemic hypoxia to enhance the effects of exercise on glucose regulation.

Exercise-induced responses in matrix metalloproteinases and osteopontin are not moderated by exercise format in males with overweight or obesity

PURPOSE

Matrix metalloproteinase-2 (MMP-2) and -3 (MMP-3), and osteopontin (OPN) are associated with adipose-tissue expansion and development of metabolic disease. The purpose of the current study was to assess the circulating concentration of these markers, along with adiponectin and glucose concentrations, in response to acute exercise in individuals with overweight or obesity.

METHODS

Fourteen sedentary males with overweight or obesity (29.0 ± 3.1 kg/m²) completed two separate, 3-day trials in randomised and counterbalanced order. An oral glucose tolerance test (OGTT) was performed on each day of the trial. Day two of each trial consisted of a single 30 min workload-matched bout of either high-intensity interval exercise (HIIE; alternating 100% and 50% of peak pulmonary oxygen uptake, [Formula: see text]O_2peak) or continuous moderate intensity (CME; 60% [Formula: see text]O_2peak) cycling completed 1 h prior to the OGTT. Glucose and physical activity were continuously monitored, while MMP-2, MMP-3, OPN and adiponectin were measured pre-, 0 h post-, 1 h post- and 25 h post-exercise.

RESULTS

Exercise transiently increased MMP-3 and decreased OPN (both p < 0.01), but not MMP-2 or adiponectin. There were no differences in the response of inflammatory markers to the different exercise formats. Exercise increased mean daily glucose concentration and area under the glucose curve during the OGTT on Day 2 and Day 3 (main effect of time; p < 0.05).

CONCLUSION

Acute cycling exercise decreased OPN, which is consistent with longer term improvements in cardiometabolic health and increased MMP-3, which is consistent with its role in tissue remodelling. Interestingly, exercise performed prior to the morning OGTT augmented the glucose concentrations in males.

TRIAL REGISTRATION

ACTRN12613001086752.

Acute effects of high intensity training on cardiac function: a pilot study comparing subjects with type 2 diabetes to healthy controls

This study evaluated acute cardiac stress after a high-intensity interval training session in patients with type 2 diabetes (T2D) versus healthy controls. High intensity aerobic exercise was performed by 4 × 4-min intervals (90-95% of maximal heart rate), followed by a ramp protocol to peak oxygen uptake. Echocardiography was performed before and 30 min after exercise. Holter electrocardiography monitored heart rhythms 24 h before, during, and 24 h after the exercise. Left atrial end-systolic volume, peak early diastolic mitral annular velocity, and the ratio of peak early to late diastolic mitral inflow velocity were reduced by approximately 18%, 15%, and 31%, respectively, after exercise across groups. Left ventricular end-diastolic wall thickness was the only echo parameter that significantly differed between groups in response to exercise. The T2D group had a rate of supraventricular extrasystoles per hour that was 265% greater than that of the controls before exercise, which remained higher after exercise. A single exhaustive exercise session impaired left ventricular diastolic function in both groups. The findings also indicated impaired right ventricular function in patients with T2D after exercise.ClinicalTrials.gov Identifier: NCT02998008.

Acute high intensity interval exercise is similarly effective as moderate intensity continuous exercise on plasma glucose control in type 2 diabetic men aged 30 to 50 years: a randomized controlled trial

BACKGROUND

This study aimed to compare the acute effects of high-intensity interval exercise (HIIE) versus moderate-intensity continuous exercise (MICE) on postprandial plasma glucose and insulin concentrations in men aged 30-50 years with type 2 diabetes (T2D), hoping to provide empirical evidence for the effects of different exercise types on glucose management in T2D patients.

METHODS

14 men with type 2 diabetes (T2D) underwent a randomized three crossover intervention: HIIE with cycling; energy expenditure matched MICE with cycling; and a sedentary control (CON)) in postprandial state. Plasma glucose and insulin levels were measured at pre-exercise, post-exercise, 1 h post-exercise, pre-lunch and 1 h post-lunch, respectively. Responses of areas under the curve (AUC) during 4 h from pre-exercise to 1 h post-lunch were also calculated.

RESULTS

Both HIIE and MICE decreased plasma glucose and insulin levels during 4 h experimental period compared to CON, with significant intervention × time interaction effects for glucose (P = 0.001) and insulin (P = 0.006) values evolution. Area under curve (AUCs) for glucose and insulin were reduced in HIIE and MICE compared to CON (P < 0.05), whereas no differences were found between HIIE and MICE.

CONCLUSIONS

Acute HIIE and the matched MICE improve plasma glucose control in the same magnitude in type 2 diabetic men aged 30-50 years.

Comparison of physiological and clinical markers for chronic sprint-interval training exercise performed either in the fasted or fed states among healthy adults

Sprint-interval training (SIT) and intermittent fasting are effective independent methods in achieving clinical health outcomes. However, the impact of both modalities when performed concurrently is unclear. The aim of this study was to compare the effects of 6 weeks of SIT performed in the fasted versus fed state on physiological and clinical health markers in healthy adults. Methods. Thirty recreationally-active participants were equally randomised into either the fasted (FAS; 4 males, 11 females) or the fed (FED; 6 males, 9 females) group. For all exercise sessions, FAS participants had to fast ≥10 h prior to exercising while FED participants had to consume food within 3 h to exercise. All participants underwent three sessions of SIT per week for 6 weeks. Each session consists of repeated bouts of 30-s Wingate Anaerobic cycle exercise. Pre- and post-training peak oxygen uptake (VO_2peak), isokinetic leg strength, insulin sensitivity, blood pressure and serum lipid levels were assessed. Results. There were no differences in baseline physiological and clinical measures between both groups (all p > 0.05). VO_2peak improved by 6.0 ± 8.8% in the FAS group and 5.3 ± 10.6% in the FED group (both p < 0.05), however the difference in improvement between groups was not statistically significant (p > 0.05). A similar pattern of results was seen for knee flexion maximum voluntary contraction at 300°·s⁻¹. SIT training in either fasted or fed state had no impact on insulin sensitivity (both p > 0.05). There was significant reduction in diastolic blood pressure (8.2 ± 4.2%) and mean arterial pressure (7.0 ± 3.2%) in the FAS group (both p < 0.05) but not FED group (both p > 0.05). Conclusion. VO_2peak and leg strength improved with SIT regardless of whether participants trained in the fasted or fed state. Chronic SIT in the fasted state may potentially reduce blood pressure to a greater extent than the same chronic SIT in the fed state.

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SIT in the fasted state leads to a significant decrease in blood pressure.

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VO_2peak and leg strength improves with SIT, regardless of nutrition status.

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SIT, performed in fasted or fed state, does not improve insulin sensitivity, body fat percentage or lipid profile.

Work, physical activity, and metabolic health: Understanding insulin sensitivity of long-haul truck drivers

BACKGROUND

Long-haul truck drivers are disproportionately exposed to metabolic risk; however, little is known about their metabolic health and the role of physical activity and other risk factors in metabolic outcomes.

OBJECTIVE

This study compares truck drivers' insulin sensitivity, and associations between metabolic risk factors and insulin sensitivity, with those of the general population.

METHODS

Survey, anthropometric, and biometric data were collected from 115 long-haul truckers, which were then compared to the general population data using the National Health and Nutrition Examination Survey (NHANES) dataset. The quantitative insulin sensitivity check index (QUICKI) was used to estimate insulin sensitivity.

RESULTS

Truck drivers had lower QUICKI scores than the general population cohort. Sagittal abdominal diameter and exercise were predictive for QUICKI among combined cohorts. Waist circumference and perceived health were more predictive for QUICKI among truck drivers, and sagittal abdominal diameter and income were more predictive for QUICKI among the general population.

CONCLUSIONS

Long-haul truckers appear to represent a subset of the general population regarding the impact of physical activity and other metabolic risk factors on QUICKI. Accordingly, comprehensive efforts which target these factors are needed to improve truckers' physical activity levels and other metabolic risks.

Exercise-nutrient interactions for improved postprandial glycemic control and insulin sensitivity

Type 2 diabetes (T2D) is a rapidly growing yet largely preventable chronic disease. Exaggerated increases in blood glucose concentration following meals is a primary contributor to many long-term complications of the disease that decrease quality of life and reduce lifespan. Adverse health consequences also manifest years prior to the development of T2D due to underlying insulin resistance and exaggerated postprandial concentrations of the glucose-lowering hormone insulin. Postprandial hyperglycemic and hyperinsulinemic excursions can be improved by exercise, which contributes to the well-established benefits of physical activity for the prevention and treatment of T2D. The aim of this review is to describe the postprandial dysmetabolism that occurs in individuals at risk for and with T2D, and highlight how acute and chronic exercise can lower postprandial glucose and insulin excursions. In addition to describing the effects of traditional moderate-intensity continuous exercise on glycemic control, we highlight other forms of activity including low-intensity walking, high-intensity interval exercise, and resistance training. In an effort to improve knowledge translation and implementation of exercise for maximal glycemic benefits, we also describe how timing of exercise around meals and post-exercise nutrition can modify acute and chronic effects of exercise on glycemic control and insulin sensitivity. Novelty: Exaggerated postprandial blood glucose and insulin excursions are associated with disease risk. Both a single session and repeated sessions of exercise improve postprandial glycemic control in individuals with and without T2D. The glycemic benefits of exercise can be enhanced by considering the timing and macronutrient composition of meals around exercise.

EFFECTS OF ACUTE EXERCISE WITH DIFFERENT INTENSITIES ON GLYCEMIC CONTROL IN PATIENTS WITH TYPE 2 DIABETES MELLITUS

OBJECTIVE

Exercise intensity is one of the most important factors that determines the effects of exercise; however, there is little known about the acute glycemic control of different exercise intensities on patients with Type 2 Diabetes Mellitus (T2DM). Here we aimed at exploring the influence of a single bout of exercise with different intensities on blood glucose levels in T2DM patients.

METHODS

Fifteen subjects (54.7 ± 5.8 years old) participated in a session of walking (WG), jogging (JG), or sedentary control (CG) in a randomized order on three different days. Distances in both WG and JG were set as 2 Km with a speed set as 4~4.5 Km/h for walking and 5~6 Km/h for jogging based on pretrial test. Blood glucose levels at fasting (~6:30am), pre-exercise (~8:30am), post-exercise (~9am), 11am and 4pm were detected.

RESULTS

Walking and jogging reached approximately moderate and high intensity based on the immediate post-exercise heart rate and RPE scores. Blood glucose levels at fasting, pre-exercise and 4pm were not substantially different among all groups (p > 0.05). JG had a significantly lower post-exercise blood glucose level (p < 0.05) when compared with CG and WG. The blood glucose level at 11am was notably lower in WG and JG than in CG (p < 0.05).

CONCLUSIONS

Both a single bout of jogging and walking can lower postprandial blood glucose levels in T2DM patients. When matched for exercise distance, jogging represents a more effective strategy to immediately lower postprandial glucose levels than walking.

Eight sessions of endurance training decrease fasting glucose and improve glucose tolerance in middle-aged overweight males

Exercise improves metabolic regulation and reduces the risk of developing type 2 diabetes and other metabolic diseases. The recommendations for exercise are rather general and the health benefits of controlled training studies are important to make better recommendations. In the present study, we report that eight endurance training sessions over 3 weeks reduced fasting glucose, and improved glucose tolerance and plasma lipids in sedentary middle-aged males (44-64 years) with overweight or obesity (BMI: 27-38). The decrease in fasting glucose was substantial (from 5.3 ± 0.3 to 4.8 ± 0.2 mM; p < .001). The training sessions consisted of 60-min indoor-cycling at ∼83% of peak heart rate divided in four blocks of 15 min cycling, with 2-min rest between blocks. Maximal oxygen uptake did not increase (38.8 ± 1.8 vs. 39.0 ± 1.6 ml kg^-1 min^-1). In conclusion, 3-weekly sessions of moderate-/high-intensity endurance training can be recommended for untrained males with overweight or obesity to improve glucose homeostasis.

Fasted exercise does not improve postprandial lipemia responses to different meals in lean and obese subjects: A crossover, randomized clinical trial

INTRODUCTION

Persistent episodes of postprandial hyperlipemia (PPL) and hyperglycemia (PPG) are considered risk factors for coronary heart disease (CHD) and premature death; whereas physical exercise improves lipid profile and glucose tolerance thus decreasing cardiovascular risks.

OBJECTIVE

To investigate the effects of low-intensity fasted aerobic exercise on the magnitude of the PPL and PPG responses to meals with different energy content, in normal and obese subjects.

METHODS

The study used a randomized crossover design. Twenty-one male (Lean: n = 9, BMI: 24.3 ± 2.2; and obese: n = 12, BMI 32.31 ± 2.1) volunteers aged 20-30 years, performed three interventions, separated by 7 days each: (i) 45 min at rest and isocaloric high-fat meal (60% lipids, 30% carbohydrates and 10% protein); (ii) fasted low-intensity aerobic exercise (50% VO_2max) for 45 min followed by an isocaloric or (iii) calorie deficit high-fat meal. Subjects were serially assessed for blood triglycerides, and glucose levels.

RESULTS AND CONCLUSIONS

Low-intensity fasted aerobic exercise had no acute effect on PPL in lean and obese subjects. Glucose concentrations were reduced only in lean subjects. There is a significant difference in PPL values when comparing lean to obese subjects, implying that the nutritional status influences lipid and carbohydrate after fasted low-intensity aerobic exercise. Registered under ClinicalTrials.gov Identifier no. NCT00929890.

Energy Deficit Required for Exercise-induced Improvements in Glycemia the Next Day

PURPOSE

This study determined the impact of an exercise-induced energy deficit on postprandial and 24 h glycemic control the day after a session of exercise.

METHODS

Fifteen healthy participants (m/f = 5/10, 27 ± 6 yr, body mass index = 24 ± 3 kg·m, peak oxygen consumption [V˙O2peak] = 36 ± 9 mL·kg·min) completed two separate 5-d experimental trials performed under "free-living" conditions. On day 1 of each trial, participants were fitted with a continuous glucose monitor and abstained from exercise. Day 2 served as a nonexercise control (NoEx). On day 3, participants exercised at 3:00 PM (65% V˙O2peak) until they expended 350 kcals (~45 min). The diet during both experimental trials was identical with the exception of meals after this exercise session. During one trial, the dinner after exercise did not replenish the 350 kcal expended during exercise, thereby establishing an exercise energy deficit (ExDEF). During the other experimental trial, the dinner after exercise contained an additional 350 kcal to compensate for the energy expended during exercise, and thereby maintained energy balance after exercise (ExBAL). Free-living glycemia was measured the day before exercise (NoEx) and the day after exercise under ExDEF and ExBAL conditions.

RESULTS

The day after exercise, 3 h postprandial area under the curve was lower after breakfast in ExDEF compared with ExBAL (16.0 ± 1.8 vs 17.0 ± 1.6 mmol·L·h per 3 h, P = 0.01), but did not differ between groups after lunch (P = 0.24), dinner (P = 0.39), or evening snack (P = 0.45). Despite differences in the glycemic response to breakfast, 24 h glycemia did not differ between ExDEF and ExBAL (area under the curve = 128 ± 10 vs 131 ± 10 mmol·L·h per 24 h, respectively; P = 0.54).

CONCLUSIONS

An exercise-induced energy deficit lowered the glycemic response to breakfast the next day-but this energy deficit did not impact total 24 h glycemia, the day after exercise in metabolically healthy adults.

Five Evidence-Based Lifestyle Habits People With Diabetes Can Use

Several evidence-based lifestyle habits focusing on the composition, timing, and sequence of meals and on pre- and postmeal exercise can improve diabetes management. Consuming low-carbohydrate, balanced meals and eating most carbohydrates early in the day are helpful habits. Eating the protein and vegetable components of a meal first and consuming the carbohydrates 30 minutes later can moderate glucose levels. Postmeal glucose surges can be blunted without precipitating hypoglycemia with moderate exercise 30-60 minutes before the anticipated peak. Short-duration, high-intensity exercise could also be effective. Premeal exercise can improve insulin sensitivity but can also cause post-exertion glucose elevations. Moreover, high-intensity premeal exercise may precipitate delayed hypoglycemia in some people. Glycemia benefits can be enhanced by eating a light, balanced breakfast after premeal exercise.

Effects of metabolic state on the regulation of melanocortin circuits

Dysfunction in neurophysiological systems that regulate food intake and metabolism are at least partly responsible for obesity and related comorbidities. An important component of this process is the hypothalamic melanocortin system, where an imbalance can result in severe obesity and deficits in glucose metabolism. Exercise offers many health benefits related to cardiovascular improvements, hunger control, and blood glucose homeostasis. However, the molecular mechanism underlying the exercise-induced improvements to the melanocortin system remain undefined. Here, we review the role of the melanocortin system to sense hormonal, nutrient, and neuronal signals of energy status. This information is then relayed onto secondary neurons in order to regulate physiological parameters, which promote proper energy and glucose balance. We also provide an overview on the effects of physical exercise to induce biophysical changes in the melanocortin circuit which may regulate food intake, glucose metabolism and improve overall metabolic health.

Does Exercise Timing Affect 24-Hour Glucose Concentrations in Adults With Type 2 Diabetes? A Follow Up to the Exercise-Physical Activity and Diabetes Glucose Monitoring Study

OBJECTIVES

It is well known that exercise can improve the glycemic profile in individuals with type 2 diabetes (T2D). However, the optimal timing of exercise is often debated. Our aim in this study was to compare the effects of exercise performed at different times of the day and different timing in relation to meals on 24-hour glucose profiles in people with T2D.

METHODS

Fourteen individuals with T2D were recruited and wore continuous glucose monitors for 12 days. During the 12 days, participants completed 4 conditions according to a randomized, crossover design: i) morning (fasting) exercise (MorEx), ii) afternoon exercise (AftEx), iii) evening exercise (EveEx) and iv) seated control. Exercise consisted of 50 minutes of walking at 5.0 km/h.

RESULTS

Eight men and 6 women (age, 65±9.0 years; T2D duration, 10.5±6.8 years; mean glycated hemoglobin, 6.7±0.6%) were included in the analysis. Mean 24-hour continuously monitored glucose was 7.4±0.7 mmol/L, 7.3±0.7 mmol/L, 7.5±0.8 mmol/L and 7.5±0.7 mmol/L in the MorEx, AftEx, EveEx and control conditions, respectively, with no significant differences among the 4 conditions (p=0.55). MorEx had a lower respiratory exchange ratio compared with AftEx and EveEx (p<0.01). The decrease in glucose during exercise was less pronounced for MorEx compared with AftEx (p<0.05).

CONCLUSIONS

Fifty minutes of walking at 3 different times of day and at different timing in relation to meals did not lower 24-hour glucose concentrations in people with T2D. The reasons why exercise was not effective at lowering glucose remain unclear.

The Effect of Timing of Exercise and Eating on Postprandial Response in Adults: A Systematic Review

Type 2 diabetes is a major public health concern. Management of this condition has focused on behavior modification through diet and exercise interventions. A growing body of evidence has focused on temporality of dietary intake and exercise and potential effects on health. This review summarizes current literature that investigates the question "how does the timing of exercise relative to eating throughout the day effect postprandial response in adults?" Databases PubMed, Scopus, Cochrane Library, CINAHL, and SPORTDiscus were searched between March-May 2019. Experimental studies conducted in healthy adults (≥18 y) and those with type 2 diabetes were included. Full texts were examined by at least two independent reviewers. Twenty studies with a total of 352 participants met the inclusion criteria. The primary finding supports that exercise performed post-meal regardless of time of day had a beneficial impact on postprandial glycemia. There was insufficient evidence regarding whether timing of exercise performed pre- vs. post-meal or vice versa in a day is related to improved postprandial glycemic response due to inherent differences between studies. Future studies focusing on the investigation of timing and occurrence of meal intake and exercise throughout the day are needed to inform whether there is, and what is, an optimal time for these behaviors regarding long-term health outcomes.

Exercise-Induced Improvements in Postprandial Glucose Response Are Blunted by Pre-Exercise Hyperglycemia: A Randomized Crossover Trial in Healthy Individuals

BACKGROUND

Exercise improves glycemic control but the magnitude, and in some cases, the direction of this effect is variable. Ambient hyperglycemia has been implicated in this exercise response heterogeneity. The current study investigated whether pre-exercise hyperglycemia directly impacts the effect of exercise on glycemic control.

METHODS

Twelve healthy normal glucose-tolerant males completed four trials in a randomized, crossover design. Each trial consisted of 24-h pre-intervention monitoring, a 7-h intervention, and 24-h post-intervention monitoring. Glycemic control was measured throughout the study by continuous glucose monitoring. The four interventions were no exercise (CON) or 45 min of cycling exercise (70%HRmax) preceded by 3.5 h of either normoglycemia (NG-Ex), steady-state hyperglycemia induced by constant glucose infusion (HG-Ex) or fluctuating glycemia induced by repeated glucose bolus infusions (FG-Ex).

RESULTS

Physical activity and diet were similar between trials, and energy expenditure during exercise was matched between exercise trials (all P > 0.05). Mean glucose during the 3.5 h ± infusion period was higher in HG-Ex (mean ± SEM; 7.2 ± 0.4 mmol/L) and FG-Ex (7.3 ± 0.3 mmol/L) compared to CON (4.8 ± 0.2 mmol/L) and NG-Ex (5.0 ± 0.2 mmol/L) trials (P < 0.01). Glycemic variability was greatest in FG-Ex (P < 0.01). Following the interventions, the postprandial glucose response (iAUC) was reduced by exercise in NG-Ex compared to CON (321.1 ± 38.6 vs. 445.5 ± 49.7 mmol/L.8h, P < 0.05, d=0.81). This benefit was blunted when exercise was preceded by steady-state (HG-Ex, 425.3 ± 45.7 mmol/L.8h) and fluctuating (FG-Ex, 465.5 ± 39.3 mmol/L.8h) hyperglycemia (both P > 0.05 vs. CON).

CONCLUSION

Pre-exercise hyperglycemia blunted the glucoregulatory benefits of acute exercise upon postprandial glucose response, suggesting that exposure to hyperglycemia contributes to exercise response heterogeneity.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT03284216.

Acute and Chronic Effects of Exercise on Continuous Glucose Monitoring Outcomes in Type 2 Diabetes: A Meta-Analysis

Objective: To examine the acute and chronic effects of structured exercise on glucose outcomes assessed by continuous glucose monitors in adults with type 2 diabetes. Methods: PubMed, Medline, EMBASE were searched up to January 2020 to identify studies prescribing structured exercise interventions with continuous glucose monitoring outcomes in adults with type 2 diabetes. Randomized controlled trials, crossover trials, and studies with pre- and post-designs were eligible. Short-term studies were defined as having exercise interventions lasting ≤2 weeks. Longer-term studies were defined as >2 weeks. Results: A total of 28 studies were included. Of these, 23 studies were short-term exercise interventions. For all short-term studies, the same participants completed a control condition as well as at least one exercise condition. Compared to the control condition, exercise decreased the primary outcome of mean 24-h glucose concentrations in short-term studies (-0.5 mmol/L, [-0.7, -0.3]; p < 0.001). In longer-term studies, mean 24-h glucose was not significantly reduced compared to control (-0.9 mmol/L [-2.2, 0.3], p = 0.14) but was reduced compared to pre-exercise values (-0.5 mmol/L, [-0.7 to -0.2] p < 0.001). The amount of time spent in hyperglycemia and indices of glycemic variability, but not fasting glucose, also improved following short-term exercise. Among the shorter-term studies, subgroup, and regression analyses suggested that the timing of exercise and sex of participants explained some of the heterogeneity among trials. Conclusion: Both acute and chronic exercise can improve 24-h glucose profiles in adults with type 2 diabetes. The timing of exercise and sex of participants are among the factors that may explain part of the heterogeneity in acute glycemic improvements following exercise.

Safety of Blood Glucose Response Following Exercise Training After Bariatric Surgery

INTRODUCTION

Safety of exercise training in relationship with the risk of hypoglycemia post-bariatric surgery is unknown.

OBJECTIVE

To evaluate the safety and magnitude of changes in blood glucose levels during exercise training following bariatric surgery.

MATERIAL AND METHODS

Twenty-nine severely obese patients undergoing either sleeve gastrectomy (SG) (n = 16) or biliopancreatic diversion with duodenal switch (BPD-DS) (n = 13) were prospectively enrolled. Three months after surgery, patients participated in a 12-week supervised exercise training program, (35-min aerobic training with a 25-min resistance exercises) three times a week. Capillary blood glucose (CBG) levels were measured immediately before and after each exercise session.

RESULTS

Seven patients (24%) had type 2 diabetes before surgery (mean duration: 10 years); four patients still have type 2 diabetes 3 months post-bariatric surgery. A total of 577 exercise training sessions with CBG monitoring were recorded. Only seven sessions (1.2%) were associated with an episode of asymptomatic hypoglycemia (CBG ≤ 3.9 mmol/L). Patients with type 2 diabetes at baseline showed a larger decrease in CBG with pre-exercise CBG being between 6.1 and 8.0 mmol/L (- 1.6 ± 1.2 vs. - 1.1 ± 0.9 mmol/L, p = 0.02). BPD-DS patients with CBG ≥ 6.1 mmol/L showed higher reduction in CBG following exercise vs. SG patients (- 1.7 ± 1.0 vs. - 1.1 ± 1.1 mmol/L; p < 0.001 and - 4.3 ± 1.0 vs. - 2.2 ± 1.4 mmol/L, p < 0.001, respectively).

CONCLUSION

Three months after bariatric surgery, exercise training program in patients without and with type 2 diabetes is safe, and is associated with a desirable glycemic profile, with few episodes of asymptomatic hypoglycemia.

Minimal effect of walking before dinner on glycemic responses in type 2 diabetes: outcomes from the multi-site E-PAraDiGM study

AIM

To examine the effect of walking before dinner on 24-h glycemic control in individuals with type 2 diabetes using the standardized multi-site Exercise-Physical Activity and Diabetes Glucose Monitoring (E-PAraDiGM) Protocol.

METHODS

Eighty participants were studied under two conditions (exercise vs. non-exercise control) separated by 72 h in a randomized crossover design. Each condition lasted 2 days during which standardized meals were provided. Exercise consisted of 50 min of treadmill walking at 5.0 km/h before the evening meal, while control involved 50 min of sitting. The primary outcome measure was mean glucose during the 24-h period following exercise (or sitting) measured by continuous glucose monitoring.

RESULTS

Of the 80 participants who were initially randomized, 73 completed both exercise and control. Sixty-three participants [29 males, 34 females; age = 64 ± 8 years, body mass index = 30.5 ± 6.5 kg/m² and HbA1c = 51 ± 8 mmol/mol (6.8 ± 0.7%), mean ± SD] complied with the standardized diets and had complete continuous glucose monitoring data. Exercise did not affect mean 24-h glucose compared to control (0.03 mmol/L; 95% CI - 0.17, 0.22, P = 0.778) but individual differences between conditions ranged from - 2.8 to +1.8 mmol/L. Exercise did not affect fasting glucose, postprandial glucose or glucose variability. Glucose concentrations measured by continuous glucose monitoring were reduced during the 50 min of walking in exercise compared to sitting in control (- 1.56 mmol/L; 95% CI - 2.18, - 0.95, p < 0.001).

CONCLUSION

Contrary to previous acute exercise studies, 50 min of walking before dinner in the E-PAraDiGM protocol did not affect 24-h glucose profiles. However, highly heterogeneous responses to exercise were observed.

TRIAL REGISTRATION

NCT02834689.

Pilot Study of Impact of a Pedal Desk on Postprandial Responses in Sedentary Workers

Physical inactivity has been linked to rates of obesity, diabetes, and heart disease through insulin resistance and other mechanisms. Although sedentary workplace environments have unintentionally contributed to the risk for chronic diseases, innovations in the workplace environment could potentially rectify this public and occupational health problem.

PURPOSE

To evaluate the effects of light-intensity physical activity using a pedal desk (PD) compared with a standard desk (STD) in a pilot study on postprandial metabolic responses and work skills.

METHODS

Twelve overweight/obese full-time sedentary office workers (six men and six women; body mass index, 28.7 ± 3.6 kg·m) were tested in two conditions: 1) PD, pedaling at self-selected light-intensity pace for 2 h and 2) STD, remaining seated for 2 h in a conventional workstation setup while performing scripted computer-based work tasks. Blood samples were analyzed for plasma glucose, insulin, and free-fatty acids in response to a standardized meal and work skills were evaluated. Paired samples t-tests were used to examine the differences in metabolic responses and work performance tasks between the conditions.

RESULTS

Pedal desk use required significantly less insulin to maintain glucose concentrations compared with STD condition (peak insulin concentration, 42.1 μU·mL vs 66.9 μU·mL; P = 0.03; and area under the curve, 302.6 vs 441.8 μU·min·mL; P < 0.001). No significant changes in plasma glucose and free-fatty acid concentrations were observed at any timepoints (all P > 0.05). In addition, pedaling at a self-paced rate caused no adverse effects on work skills (P > 0.05).

CONCLUSIONS

The PD resulted in lower postmeal insulin concentrations without an overall negative impact on work skills. Thus, the PD could have the potential to achieve public and occupational health goals in sedentary work environments.

Managing free-living hyperglycemia with exercise or interrupted sitting in type 2 diabetes

Breaking up sitting with light physical activity (PA) is effective in reducing hyperglycemia in the laboratory. Whether the same effects are observed in the free-living environment remains unknown. We evaluated how daily and postprandial glycemia is impacted by 20, 40, or 60 min of activity performed as either breaks from sitting after each meal (BR) or as one continuous walk after breakfast (WALK). Thirty individuals with type 2 diabetes completed three experimental conditions [BR, WALK, and control (CON)] in a randomized crossover design. Conditions were performed in a free-living environment with strict dietary control over 7 days. Participants increased PA in BR and WALK by 20, 40, or 60 min ( n = 10 in each group) and maintained habitual levels of PA during CON. A continuous glucose monitor (iPro2) and activPAL activity monitor were worn to quantify glycemic control and PA. Using linear mixed models with repeated measures, we 1) compared postprandial glucose (PPG) across conditions and 2) assessed the relationship between activity volume and glucose responses. Whereas WALK tended to shorten the daily duration of hyperglycemia compared with CON ( P = 0.0875), BR was not different from CON. BR and WALK significantly attenuated the breakfast PPG versus CON ( P ≤ 0.05), but lunch and dinner PPG were unaffected by BR and WALK. In conclusion, continuous walking was more effective than breaks from sitting in lowering daily hyperglycemia for the group, but both conditions lowered breakfast PPG. In contrast to tightly controlled laboratory studies, breaks from sitting did not lower hyperglycemia in the free-living environment.

NEW & NOTEWORTHY Our “ecolabical” approach is new and noteworthy. This approach combines the external validity of the free-living environment (ecological) with the control of key confounding variables in the laboratory and allows for highly translatable findings by minimizing confounding variables. We found that both postmeal continuous walking and short breaks from sitting similarly attenuated the postprandial glucose (PPG) response to breakfast. Unlike previous laboratory studies, neither condition (walk after breakfast or postmeal breaks) significantly impacted PPG at lunch or dinner.

Effect of exercise on acute postprandial glucose concentrations and interleukin-6 responses in sedentary and overweight males

This study examined the effect of 2 forms of exercise on glucose tolerance and the concurrent changes in markers associated with the interleukin (IL)-6 pathways. Fifteen sedentary, overweight males (29.0 ± 3.1 kg/m2) completed 2 separate, 3-day trials in randomised and counterbalanced order. An oral glucose tolerance test (OGTT; 75 g) was performed at the same time on each day of the trial. Day 2 of each trial consisted of a single 30-min workload-matched bout of either high-intensity intermittent exercise (HIIE; alternating 100% and 50% of peak oxygen uptake) or continuous moderate-intensity exercise (CME; 60 % of peak oxygen uptake) completed 1 h prior to the OGTT. Venous blood samples were collected before, immediately after, 1 h after, and 25 h after exercise for measurement of insulin, C-peptide, IL-6, and the soluble IL-6 receptors (sIL-6R; soluble glycoprotein 130 (sgp130)). Glucose area under the curve (AUC) was calculated from capillary blood samples collected throughout the OGTT. Exercise resulted in a modest (4.4%; p = 0.003) decrease in the glucose AUC when compared with the pre-exercise AUC; however, no differences were observed between exercise conditions (p = 0.65). IL-6 was elevated immediately after and 1 h after exercise, whilst sgp130 and sIL-6R concentrations were reduced immediately after exercise. In summary, exercise was effective in reducing glucose AUC, which was attributed to improvements that took place between 60 and 120 min into the OGTT, and was in parallel with an increased ratio of IL-6 to sIL-6R, which accords with an increased activation via the "classical" IL-6 signalling pathway. Our findings suggest that acute HIIE did not improve glycaemic response when compared with CME.

Multiple Short Bouts of Walking Activity Attenuate Glucose Response in Obese Women

BACKGROUND

We sought to determine the effect of multiple walking breaks from sedentary behavior (SED) on glucose responses in sedentary obese women.

MATERIALS AND METHODS

Ten women [aged = 36 (5) y, body mass index = 38.0 (1.6) kg/m², body fat = 49.6 (1.4)%] completed 3 conditions (48-h "washout" in-between conditions) following a standardized meal in random order: 4-hour SED, 4-hour SED with 2 minutes of moderate-intensity walking every 30 minutes (SED + 2 min), and 4-hour SED with 5 minutes of moderate-intensity walking every 30 minutes (SED + 5 min). Measurements included continuous interstitial glucose concentration monitoring immediately before and during standardized conditions and accelerometry for physical activity patterns during and in-between the standardized conditions. Repeated-measures 1-way analyses of variance (α = .05) with Bonferroni correction for post hoc comparisons were performed. Effect sizes (d [95% confidence interval]) were calculated as mean difference from SED/pooled standard deviation.

RESULTS

Sedentary time was similar in the 48 hours preceding each condition (P > .05). By design, sedentary time was different between conditions (P < .001). Compared with SED, 2-hour postprandial glucose positive incremental area under the curve was lower for SED + 5 minutes (P = .005; d = - 0.57 [-1.48, 0.40]), but not for SED + 2 minutes (P = .086; d = - 0.71 [-1.63, 0.27]). Four-hour postprandial glucose area under the curve was similar between conditions (P > .05).

CONCLUSION

In sedentary obese women, 5 minutes of moderate-intensity walking breaks from SED each 30 minutes attenuate 2-hour postprandial glucose excursions.

An Interactive Simulation to Change Outcome Expectancies and Intentions in Adults With Type 2 Diabetes: Within-Subjects Experiment

Background

Computerized simulations are underutilized to educate or motivate patients with chronic disease.

Objective

The aim of this study was to test the efficacy of an interactive, personalized simulation that demonstrates the acute effect of physical activity on blood glucose. Our goal was to test its effects on physical activity-related outcome expectancies and behavioral intentions among adults with type 2 diabetes mellitus (T2DM).

Methods

In this within-subjects experiment, potential participants were emailed a link to the study website and directed through 7 tasks: (1) consent; (2) demographics, baseline intentions, and self-reported walking; (3) orientation to the diurnal glucose curve; (4) baseline outcome expectancy, measured by a novel drawing task in which participants use their mouse to draw the expected difference in the diurnal glucose curve if they had walked; (5) interactive simulation; (6) postsimulation outcome expectancy measured by a second drawing task; and (7) final measures of intentions and impressions of the website. To test our primary hypothesis that participants’ outcome expectancies regarding walking would shift toward the outcome presented in the interactive simulation, we used a paired t test to compare the difference of differences between the change in area under the curve in the simulation and participants’ two drawings. To test whether intentions to walk increased, we used paired t tests. To assess the intervention’s usability, we collected both quantitative and qualitative data on participants’ perceptions of the drawing tasks and simulation.

Results

A total of 2019 individuals visited the website and 1335 (566 males, 765 females, and 4 others) provided complete data. Participants were largely late middle-aged (mean=59.8 years; standard deviation=10.5), female 56.55% (755/1335), Caucasian 77.45% (1034/1335), lower income 64.04% (855/1335) t₁₃₃₄=3.4, P ≤.001). Our second hypothesis, that participants’ intentions to walk in the coming week would increase, was also supported; general intention (mean difference=0.31/7, t₁₀₀₁=10.8, P<.001) and minutes of walking last week versus planned for coming week (mean difference=33.5 min, t₁₃₃₄=13.2, P<.001) both increased. Finally, an examination of qualitative feedback and drawing task data suggested that some participants had difficulty understanding the website. This led to a post-hoc subset analysis. In this analysis, effects for our hypothesis regarding outcome expectancies were markedly stronger, suggesting that further work is needed to determine moderators of the efficacy of this simulation.

Conclusions

A novel interactive simulation is efficacious in changing the outcome expectancies and behavioral intentions of adults with T2DM. We discuss applications of our results to the design of mobile health (mHealth) interventions.

Glucose response to exercise in the post-prandial period is independent of exercise intensity

This study investigated the acute glucose response to low-intensity, moderate-intensity, and high-intensity interval exercise compared to no-exercise in healthy insufficiently active males using a four-arm, randomized, crossover design. Ten males (age: 37.3 ± 7.3 years, BMI: 29.3 ± 6.5 kg·m^-2 ) completed four 30-minute interventions at weekly intervals comprising low-intensity exercise (LIE) at ~35% V˙O₂ R, moderate-intensity exercise (MIE) at ~50% V˙O₂ R, high-intensity interval exercise (HIIE) at ~80% V˙O₂ R, and a no-exercise control. Participants performed cycle ergometer exercise 30 minutes after finishing breakfast. Glucose response was assessed using a continuous glucose monitor under free-living conditions with dietary intake replicated. A significant effect for intensity on energy expenditure was identified (P < .001) with similar energy cost in MIE (mean ± SD: 869 ± 148 kJ) and HIIE (806 ± 145 kJ), which were both greater than LIE (633 ± 129 kJ). The pattern of glucose response between the interventions over time was different (P = .02). Glucose was lower 25 minutes into each of the HIIE, MIE and LIE trials respectively (mean difference ± SD: -0.7 ± 1.1; -0.9 ± 1.1; -0.6 ± 0.9 mmol·L^-1 ; P < .05) than in the no-exercise trial. Glucose response was not different between exercise intensities (P > .05). Twenty-four-hour AUC was not affected by exercise intensity (P = .75). There was a significant effect for exercise enjoyment (P = .02), with LIE (69 ± 4) preferred less than HIIE (mean ± SD: 84 ± 14; P = .02), MIE (73 ± 5; P = .03), and no-exercise (75 ± 4; P = .03). Exercise at any intensity 30 minutes after a meal affects glycemic regulation equally in insufficiently active males. Moderate to vigorous exercise intensities were preferred, and therefore, the exercise guidelines appear appropriate for the prevention of cardiometabolic disease.

Postmeal exercise blunts postprandial glucose excursions in people on metformin monotherapy

Metformin is used clinically to reduce fasting glucose with minimal effects on postprandial glucose. Postmeal exercise reduces postprandial glucose and may offer additional glucose-lowering benefit beyond that of metformin alone, yet controversy exists surrounding exercise and metformin interactions. It is currently unknown how postmeal exercise and metformin monotherapy in combination will affect postprandial glucose. Thus, we examined the independent and combined effects of postmeal exercise and metformin monotherapy on postprandial glucose. A randomized crossover design was used to assess the influence of postmeal exercise on postprandial glucose excursions in 10 people treated with metformin monotherapy (57 ± 10 yr, HbA1C = 6.3 ± 0.6%). Each participant completed the following four conditions: sedentary and postmeal exercise (5 × 10-min bouts of treadmill walking at 60% V̇o2max) with metformin and sedentary and postmeal exercise without metformin. Peak postprandial glucose within a 2-h time window and 2-h total area under the curve was assessed after a standardized breakfast meal, using continuous glucose monitoring. Postmeal exercise significantly blunted 2-h peak ( P = 0.001) and 2-h area under the curve ( P = 0.006), with the lowest peak postprandial glucose excursion observed with postmeal exercise and metformin combined ( P < 0.05 vs. all other conditions: metformin/sedentary: 12 ± 3.4, metformin/exercise: 9.7 ± 2.3, washout/sedentary: 13.3 ± 3.2, washout/exercise: 11.1 ± 3.4 mmol/l). Postmeal exercise and metformin in combination resulted in the lowest peak postprandial glucose excursion compared with either treatment modality alone. Exercise timed to the postprandial phase may be important for optimizing glucose control during metformin monotherapy.

NEW & NOTEWORTHY The interactive effects of metformin and exercise on key physiological outcomes remain an area of controversy. Findings from this study show that the combination of metformin monotherapy and moderate-intensity postmeal exercise led to beneficial reductions in postprandial glucose excursions. Postmeal exercise may be a useful strategy for the management of postprandial glucose in people on metformin.

Effects of postmeal exercise on postprandial glucose excursions in people with type 2 diabetes treated with add-on hypoglycemic agents

AIMS

Type 2 diabetes treatment primarily focuses on reducing hyperglycemia, including postprandial glucose excursions. Hypoglycemic agents are used clinically to lower fasting and postprandial glucose. Metformin is the first-line therapy; however, if metformin is inadequate then 'add-on' hypoglycemic agents are implemented. Postmeal exercise has been shown to lower postprandial glucose. The aim of this study was to assess if postmeal exercise provides additional glucose-lowering benefit, beyond medication alone, in those on add-on hypoglycemic agents.

METHODS

Postprandial glucose excursions in eight participants with type 2 diabetes (Age: 60±10.7, HbA_1C: 7.9±2.3) being treated with add-on hypoglycemic agents were assessed during both drug-treated sedentary and drug-treated postmeal exercise conditions. Continuous glucose monitoring was used to assess peak and area under the glucose curve (AUC) during exercise, as well as peak within a 2-h time window, 2-h total and 2-h incremental AUC after a standardized breakfast meal. Postmeal exercise consisted of 3×10-min intervals of treadmill walking at 50% maximal oxygen uptake.

RESULTS

Glucose peak (drug only: 13.8±3.7, drug/exercise: 9.9±2.7mmol/L; p=0.02) and AUC (drug only: 500±136, drug/exercise: 357±89mmol/L×40min; p=0.03) were reduced during postmeal exercise. Breakfast 2-h incremental AUC was also reduced (drug only: 585±291, drug/exercise: 330±294; p=0.047).

DISCUSSION

Post-breakfast exercise lowered glucose during the exercise bout, although this effect was not sustained on later meals.

Acute high-intensity interval exercise reduces human monocyte Toll-like receptor 2 expression in type 2 diabetes

Type 2 diabetes (T2D) is characterized by chronic low-grade inflammation that contributes to disease pathophysiology. Exercise has anti-inflammatory effects, but the impact of high-intensity interval training (HIIT) is not known. The purpose of this study was to determine the impact of a single session of HIIT on cellular, molecular, and circulating markers of inflammation in individuals with T2D. Participants with T2D (n = 10) and healthy age-matched controls (HC; n = 9) completed an acute bout of HIIT (7 × 1 min at ~85% maximal aerobic power output, separated by 1 min of recovery) on a cycle ergometer with blood samples obtained before (Pre), immediately after (Post), and at 1 h of recovery (1-h Post). Inflammatory markers on leukocytes were measured by flow cytometry, and TNF-α was assessed in both LPS-stimulated whole blood cultures and plasma. A single session of HIIT had an overall anti-inflammatory effect, as evidenced by 1) significantly lower levels of Toll-like receptor (TLR) 2 surface protein expression on both classical and CD16+ monocytes assessed at Post and 1-h Post compared with Pre (P < 0.05 for all); 2) significantly lower LPS-stimulated TNF-α release in whole blood cultures at 1-h Post (P < 0.05 vs. Pre); and 3) significantly lower levels of plasma TNF-α at 1-h Post (P < 0.05 vs. Pre). There were no differences between T2D and HC, except for a larger decrease in plasma TNF-α in HC vs. T2D (group × time interaction, P < 0.05). One session of low-volume HIIT has immunomodulatory effects and provides potential anti-inflammatory benefits to people with, and without, T2D.

The Acute Effects of Interval-Type Exercise on Glycemic Control in Type 2 Diabetes Subjects: Importance of Interval Length. A Controlled, Counterbalanced, Crossover Study

Interval-type exercise is effective for improving glycemic control, but the optimal approach is unknown. The purpose of this study was to determine the importance of the interval length on changes in postprandial glycemic control following a single exercise bout. Twelve subjects with type 2 diabetes completed a cross-over study with three 1-hour interventions performed in a non-randomized but counter-balanced order: 1) Interval walking consisting of repeated cycles of 3 min slow (aiming for 54% of Peak oxygen consumption rate [VO2peak]) and 3 min fast (aiming for 89% of VO2peak) walking (IW3); 2) Interval walking consisting of repeated cycles of 1 min slow and 1 min fast walking (IW1) and 3) No walking (CON). The exercise interventions were matched with regards to walking speed, and VO2 and heart rate was assessed throughout all interventions. A 4-hour liquid mixed meal tolerance test commenced 30 min after each intervention, with blood samples taken regularly. IW3 and IW1 resulted in comparable mean VO2 and heart rates. Overall mean postprandial blood glucose levels were lower after IW3 compared to CON (10.3±3.0 vs. 11.1±3.3 mmol/L; P < 0.05), with no significant differences between IW1 (10.5±2.8 mmol/L) and CON or IW3 and IW1 (P > 0.05 for both). Conversely blood glucose levels at specific time points during the MMTT differed significantly following both IW3 and IW1 as compared to CON. Our findings support the previously found blood glucose lowering effect of IW3 and suggest that reducing the interval length, while keeping the walking speed and time spend on fast and slow walking constant, does not result in additional improvements.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02257190.

Targeting specific interstitial glycemic parameters with high-intensity interval exercise and fasted-state exercise in type 2 diabetes

AIMS

To compare the acute glycemic responses to a bout of high-intensity interval exercise (HIIE) and energy-matched moderate-intensity continuous exercise (MICE) performed under fasted and postprandial conditions.

METHODS

A randomized, controlled, crossover design was used. Ten individuals with type 2 diabetes were each tested in five experimental conditions after an overnight fast: 1) fasted-state HIIE (HIIEfast); 2) post-breakfast HIIE (HIIEfed); 3) fasted-state MICE (MICEfast); 4) post-breakfast MICE (MICEfed); and 5) no exercise (control). MICE was performed at workload corresponding to 55% of V.V̇O2peak, whereas HIIE was composed of repetitions of three minutes at workload corresponding to 40% followed by one minute at workload corresponding to 100% V.V̇̇O2peak. Interstitial glucose was monitored by continuous glucose monitoring over 24h under standardized diet and medication.

RESULTS

Fasted-state exercise attenuated postprandial glycemic increments (p<0.05) to a greater extent than post-breakfast exercise did. HIIE reduced nocturnal and fasting glycemia on the day following exercise more than MICE did (main effect: both p<0.05). Compared to the control condition, HIIEfast lowered most interstitial glycemic parameters, i.e., 24-h mean glucose (-1.5mmol·l(-1); p<0.05), fasting glucose (-1.0mmol·l(-1); p<0.05), overall postprandial glycemic increment (-257mmol·360min·l(-1); p<0.05), glycemic variability (-1.79mmol·l(-1); p<0.05), and time spent in hyperglycemia (-283min; p<0.05).

CONCLUSION

This study showed that HIIE is more effective than MICE in lowering nocturnal/fasting glycemia. Exercise performed in the fasted state reduces postprandial glycemic increments to a greater extent than post-breakfast exercise does. Performing HIIE under fasted condition may be most advantageous as it lowered most aspects of glycemia.

Exercising Tactically for Taming Postmeal Glucose Surges

This review seeks to synthesize data on the timing, intensity, and duration of exercise found scattered over some 39 studies spanning 3+ decades into optimal exercise conditions for controlling postmeal glucose surges. The results show that a light aerobic exercise for 60 min or moderate activity for 20-30 min starting 30 min after meal can efficiently blunt the glucose surge, with minimal risk of hypoglycemia. Exercising at other times could lead to glucose elevation caused by counterregulation. Adding a short bout of resistance exercise of moderate intensity (60%-80%  VO2max) to the aerobic activity, 2 or 3 times a week as recommended by the current guidelines, may also help with the lowering of glucose surges. On the other hand, high-intensity exercise (>80%  VO2max) causes wide glucose fluctuations and its feasibility and efficacy for glucose regulation remain to be ascertained. Promoting the kind of physical activity that best counters postmeal hyperglycemia is crucial because hundreds of millions of diabetes patients living in developing countries and in the pockets of poverty in the West must do without medicines, supplies, and special diets. Physical activity is the one tool they may readily utilize to tame postmeal glucose surges. Exercising in this manner does not violate any of the current guidelines, which encourage exercise any time.

Acute inactivity impairs glycemic control but not blood flow to glucose ingestion

PURPOSE

Insulin-stimulated increases in skeletal muscle blood flow play a role in glucose disposal. Indeed, 7 d of aerobic exercise in patients with Type 2 diabetes increased blood flow responses to an oral glucose tolerance test (OGTT) and improved insulin sensitivity. More recent work suggests that reduced daily physical activity impairs glycemic control (GC) in healthy individuals. Herein, we sought to determine whether an acute reduction in daily activity (from >10,000 to <5000 steps per day) for 5 d (RA5) in healthy individuals reduced insulin-stimulated blood flow and GC in parallel and if a 1-d return to activity (RTA1) improved these outcomes.

METHODS

OGTT were performed as a stimulus to increase insulin in 14 healthy, recreationally active men (24 ± 1.1 yr) at baseline, RA5, and RTA1. Measures of insulin sensitivity (Matsuda index) and femoral and brachial artery blood flow were made during the OGTT. Free-living measures of GC including peak postprandial glucose (peak PPG) were also made via continuous glucose monitoring.

RESULTS

Femoral and brachial artery blood flow increased during the OGTT but neither was significantly impacted by changes in physical activity (P > 0.05). However, insulin sensitivity was decreased by RA5 (11.3 ± 1.5 to 8.0 ± 1.0, P < 0.05). Likewise, free-living GC measures of peak PPG (113 ± 3 to 123 ± 5 mg·dL(-1), P < 0.05) was significantly increased at RA5. Interestingly, insulin sensitivity and GC as assessed by peak PPG were not restored after RTA1 (P > 0.05).

CONCLUSIONS

Thus, acute reductions in physical activity impaired GC and insulin sensitivity; however, blood flow responses to an OGTT were not affected. Further, a 1-d return to activity was not sufficient to normalize GC after 5 d of reduced daily physical activity.

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.

Acute effect of fast walking on postprandial blood glucose control in type 2 diabetes

Purpose

Several guidelines have recently recommended exercise for prevention and treatment of type 2 diabetes. However, determining the optimum exercise conditions, e.g., the intensity, amount, frequency, and type of exercise, is difficult, particularly by patients themselves. We have investigated the acute effect of fast walking on postprandial blood glucose levels among patients with type 2 diabetes.

Methods

Fourteen patients diagnosed with type 2 diabetes at least 1 year previously were eligible for inclusion in this study during educational hospitalization. Three walking programs, natural walking (walking at a natural speed), 10 % fast walking, and 20 % fast walking, were performed 1 h after lunch in a randomized sequence with a washout period of 1 day. Walking time was 30 min in all the programs. Primary outcome was determined by self-monitoring of blood glucose. Blood glucose levels were measured before walking, after walking for 15 min, and at the end of walking. Heart rate and systolic and diastolic pressure were also measured for safety reasons.

Results

All the participants completed the study with no adverse effects. Compared with natural walking, fast walking markedly improved postprandial glucose excursion in an intensity-dependent manner without any adverse effects.

Conclusion

Fast walking acutely reduced postprandial blood glucose levels among patients with type 2 diabetes. Our method has major implications for the practice of diabetes education in clinical rehabilitation.

A pilot study examining the effects of consuming a high-protein vs normal-protein breakfast on free-living glycemic control in overweight/obese 'breakfast skipping' adolescents

To examine whether the daily consumption of normal-protein (NP) vs higher-protein (HP) breakfasts improve free-living glycemic control in overweight/obese, 'breakfast skipping' adolescents. Twenty-eight healthy, but overweight, teens (age: 19±1 year; BMI: 29.9±0.8 kg m(-2)) completed a 12-week randomized parallel-arm study in which the adolescents consumed either a 350 kcal NP breakfast (13 g protein) or HP breakfast (35 g protein). Pre- and post-study 24-h blood glucose measures were assessed using continuous glucose monitoring. Although no main effects of time or group were detected, time by group interactions were observed. Post hoc pairwise comparisons assessing the post-pre changes revealed that the daily consumption of the HP breakfasts tended to reduce the 24-h glucose variability (s.d.) vs NP (-0.17±0.09 vs +0.09±0.10 s.d.; P=0.06) and tended to reduce the time spent above the high glucose limit (-292±118 vs -24±80 min; P=0.09). The consumption of the HP breakfasts also reduced the 24-h maximal (peak) glucose response (-0.94±0.36 vs +0.30±0.18 mmol l(-1); P<0.01) and reduced postprandial glucose fluctuations (-0.88±0.44 vs +0.49±0.34 mmol l(-1); P<0.03) vs NP. These data suggest that the daily addition of a HP breakfast, containing 35 g of high-quality protein, has better efficacy at improving free-living glycemic control compared with a NP breakfast in overweight/obese, but otherwise healthy, 'breakfast skipping' adolescents.

Postdinner resistance exercise improves postprandial risk factors more effectively than predinner resistance exercise in patients with type 2 diabetes

Abnormally elevated postprandial glucose and triacylglycerol (TAG) concentrations are risk factors for cardiovascular disease in type 2 diabetes. The most effective time to exercise to lower postprandial glucose and TAG concentrations is unknown. Thus the aim of this study was to determine what time is more effective, either pre- or postdinner resistance exercise (RE), at improving postprandial risk factors in patients with type 2 diabetes. Thirteen obese patients with type 2 diabetes completed three trials in a random order in which they consumed a dinner meal with 1) no RE (NoRE), 2) predinner RE (RE → M), and 3) postdinner RE beginning 45 min after dinner (M → RE). Clinical outcome measures included postprandial glucose and TAG concentrations. In addition, postprandial acetaminophen (gastric emptying), endocrine responses, free fatty acids, and β-cell function (mathematical modeling) were measured to determine whether these factors were related to changes in glucose and TAG. The TAG incremental area under the curve (iAUC) was ∼92% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M, an effect due in part to lower very-low-density lipoprotein-1 TAG concentrations. The glucose iAUC was reduced (P = 0.02) by ∼18 and 30% during the RE → M and M → RE trials, respectively, compared with NoRE, with no difference between RE trials. RE → M and M → RE reduced the insulin iAUC by 35 and 48%, respectively, compared with NoRE (P < 0.01). The glucagon-like peptide-1 iAUC was ∼50% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M. Given that predinner RE only improves postprandial glucose concentrations, whereas postdinner RE improves both postprandial glucose and TAG concentrations, postdinner RE may lower the risk of cardiovascular disease more effectively.

Postdinner resistance exercise improves postprandial risk factors more effectively than predinner resistance exercise in patients with type 2 diabetes

Abnormally elevated postprandial glucose and triacylglycerol (TAG) concentrations are risk factors for cardiovascular disease in type 2 diabetes. The most effective time to exercise to lower postprandial glucose and TAG concentrations is unknown. Thus the aim of this study was to determine what time is more effective, either pre- or postdinner resistance exercise (RE), at improving postprandial risk factors in patients with type 2 diabetes. Thirteen obese patients with type 2 diabetes completed three trials in a random order in which they consumed a dinner meal with 1) no RE (NoRE), 2) predinner RE (RE → M), and 3) postdinner RE beginning 45 min after dinner (M → RE). Clinical outcome measures included postprandial glucose and TAG concentrations. In addition, postprandial acetaminophen (gastric emptying), endocrine responses, free fatty acids, and β-cell function (mathematical modeling) were measured to determine whether these factors were related to changes in glucose and TAG. The TAG incremental area under the curve (iAUC) was ∼92% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M, an effect due in part to lower very-low-density lipoprotein-1 TAG concentrations. The glucose iAUC was reduced (P = 0.02) by ∼18 and 30% during the RE → M and M → RE trials, respectively, compared with NoRE, with no difference between RE trials. RE → M and M → RE reduced the insulin iAUC by 35 and 48%, respectively, compared with NoRE (P < 0.01). The glucagon-like peptide-1 iAUC was ∼50% lower (P ≤ 0.02) during M → RE compared with NoRE and RE → M. Given that predinner RE only improves postprandial glucose concentrations, whereas postdinner RE improves both postprandial glucose and TAG concentrations, postdinner RE may lower the risk of cardiovascular disease more effectively.

High-intensity interval training for improving postprandial hyperglycemia

High-intensity interval training (HIIT) has garnered attention in recent years as a time-efficient exercise option for improving cardiovascular and metabolic health. New research demonstrates that HIIT may be particularly effective for improving postprandial hyperglycemia in individuals with, or at risk for, type 2 diabetes (T2D). These findings have clinical relevance because elevated postprandial hyperglycemia is a significant risk factor for cardiovascular morbidity and mortality. This article summarizes the latest evidence demonstrating that HIIT can improve postprandial glucose control to highlight the potential application of HIIT in the prevention and management of T2D and associated cardiovascular complications.

The acute effects of interval- Vs continuous-walking exercise on glycemic control in subjects with type 2 diabetes: a crossover, controlled study

CONTEXT

Glycemic control improves with physical activity, but the optimal exercise mode is unknown.

OBJECTIVE

The objective of the study was to determine whether interval-based exercise improves postprandial glucose tolerance and free-living glycemia more than oxygen consumption- and time duration-matched continuous exercise.

DESIGN

This was a crossover, controlled study with trials performed in randomized order.

SETTING

The study was conducted in hospitalized and ambulatory care.

PATIENTS

PATIENTS diagnosed with type 2 diabetes mellitus (n=10, no withdrawals) participated in the study.

INTERVENTIONS

Subjects performed three 1-hour interventions: 1) interval walking (IW; repeated cycles of 3 min of slow and fast walking); 2) continuous walking (CW); and 3) control (CON). Oxygen consumption (VO2) was measured continuously to match mean VO2 between exercise sessions (∼75% VO2peak).

MAIN OUTCOME MEASURES

A mixed-meal tolerance test (MMTT; 450 kcal, 55% carbohydrate) with stable glucose isotopic tracers was provided after each intervention, and glucose kinetics were measured during the following 4 hours. Free-living glycemic control was assessed for approximately 32 hours after the MMTT using continuous glucose monitoring.

RESULTS

VO2 was well matched between the exercise interventions. IW decreased the mean and maximal incremental plasma glucose during the MMTT when compared with the CON (mean 1.2 ± 0.4 vs 2.0 ± 0.5 mmol/L, P < .001; maximal 3.7 ± 0.6 vs 4.6 ± 0.7 mmol/L, P = .005) and mean when compared with CW (1.7 ± 0.4 mmol/L, P = .02). No differences in the mean or maximal incremental plasma glucose values were seen between the CW and CON. The metabolic clearance rate of glucose during the MMTT was increased in the IW compared with CW (P = .049) and CON (P < .001). Continuous glucose monitoring mean glucose was reduced in IW compared with CW for the rest of the intervention day (8.2 ± 0.4 vs 9.3 ± 0.7 mmol/L, P = .03), whereas no differences were found between IW and CW the following day.

CONCLUSIONS

One interval-based exercise session improves glycemic control in type 2 diabetes mellitus subjects when compared with an oxygen consumption- and time duration-matched continuous exercise session.

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.

Effects of high-intensity interval exercise versus continuous moderate-intensity exercise on postprandial glycemic control assessed by continuous glucose monitoring in obese adults

The purpose of this study was to examine the impact of acute high-intensity interval training (HIIT) compared with continuous moderate-intensity (CMI) exercise on postprandial hyperglycemia in overweight or obese adults. Ten inactive, overweight or obese adults (41 ± 11 yrs, BMI = 36 ± 7 kg/m(2)) performed an acute bout of HIIT (10 × 1 min at approximately 90% peak heart rate (HRpeak) with 1-min recovery periods) or matched work CMI (30 min at approximately 65% HRpeak) in a randomized, counterbalanced fashion. Exercise was performed 2 h after breakfast, and glucose control was assessed by continuous glucose monitoring under standardized dietary conditions over 24 h. Postprandial glucose (PPG) responses to lunch, dinner, and the following day's breakfast were analyzed and compared with a no-exercise control day. Exercise did not affect the PPG responses to lunch, but performing both HIIT and CMI in the morning significantly reduced the PPG incremental area under the curve (AUC) following dinner when compared with control (HIIT = 110 ± 35, CMI = 125 ± 34, control = 162 ± 46 mmol/L × 2 h, p < 0.05). The PPG AUC (HIIT = 125 ± 53, CMI = 186 ± 55, control = 194 ± 96 mmol/L × 2 h) and the PPG spike (HIIT = Δ2.1 ± 0.9, CMI = Δ3.0 ± 0.9, control = Δ3.0 ± 1.5 mmol/l) following breakfast on the following day were significantly lower following HIIT compared with both CMI and control (p < 0.05). Absolute AUC and absolute glucose spikes were not different between HIIT, CMI, or control for any meal (p > 0.05 for all). We conclude that a single session of HIIT has greater and more lasting effects on reducing incremental PPG when compared with CMI.