Interaction of exercise and meal timing on blood glucose concentrations.

PURPOSE OF REVIEW: Exercise and diet are among the most studied behaviors that can affect blood glucose concentrations. Despite multiple studies examining these interventions in different populations and contexts, inconsistencies across studies have led to variable expectations. The purpose of this review is to more specifically examine how the timing of when exercise is performed in relation to meals can modify changes in glucose concentrations or insulin sensitivity. When possible, studies in type 2 diabetes are emphasized, but recent research in type 1 diabetes, obesity, and athletes is also considered. RECENT FINDINGS: The effect of a single bout of exercise performed after an overnight fast is often comparable to that of postprandial exercise on 24 h mean glucose concentrations. However, there is recent evidence to suggest that in some situations, but not all, longer term metabolic adaptations can be more favorable when exercise is regularly performed in the fasted state. SUMMARY: Exercise after an overnight fast can have different effects on glucose metabolism compared with postprandial exercise. The shorter term and longer term changes following fasting exercise can be relevant to those who are seeking greater glucoregulatory benefit from their exercise sessions, such as people with diabetes.

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.

Steady-state cerebral blood flow regulation at altitude: interaction between oxygen and carbon dioxide.

High-altitude ascent imposes a unique cerebrovascular challenge due to two opposing blood gas chemostimuli. Specifically, hypoxia causes cerebral vasodilation, whereas respiratory-induced hypocapnia causes vasoconstriction. The conflicting nature of these two superimposed chemostimuli presents a challenge in quantifying cerebrovascular reactivity (CVR) in chronic hypoxia. During incremental ascent to 4240 m over 7 days in the Nepal Himalaya, we aimed to (a) characterize the relationship between arterial blood gas stimuli and anterior, posterior and global (g)CBF, (b) develop a novel index to quantify cerebral blood flow (CBF) in relation to conflicting steady-state chemostimuli, and (c) assess these relationships with cerebral oxygenation (rSO2). On rest days during ascent, participants underwent supine resting measures at 1045 m (baseline), 3440 m (day 3) and 4240 m (day 7). These measures included pressure of arterial (Pa)CO2, PaO2, arterial O2 saturation (SaO2; arterial blood draws), unilateral anterior, posterior and gCBF (duplex ultrasound; internal carotid artery [ICA] and vertebral artery [VA], gCBF [{ICA + VA} × 2], respectively) and rSO2 (near-infrared spectroscopy). We developed a novel stimulus index (SI), taking into account both chemostimuli (PaCO2/SaO2). Subsequently, CBF was indexed against the SI to assess steady-state cerebrovascular responsiveness (SS-CVR). When both competing chemostimuli are taken into account, (a) SS-CVR was significantly higher in ICA, VA and gCBF at 4240 m compared to lower altitudes, (b) delta SS-CVR with ascent (1045 m vs. 4240 m) was higher in ICA vs. VA, suggesting regional differences in CBF regulation, and (c) ICA SS-CVR was strongly and positively correlated (r = 0.79) with rSO2 at 4240 m.

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.

Effects of Moderate Cycling Exercise on Blood Glucose Regulation Following Successful Clinical Islet Transplantation.

Context: Islet transplantation is effective in preventing hypoglycemia in patients with type 1 diabetes (T1D). However, it is unknown whether transplanted islets regulate plasma glucose concentrations appropriately during and after exercise in human islet transplant recipient (ITxs). Objective: To determine the effect of exercise on plasma glucose, insulin, and glucagon concentrations in ITxs compared with control subjects (CONs) without diabetes. Intervention: Participants completed two conditions in random order: 45 minutes of aerobic exercise (60% VO2peak) and 45 minutes of seated rest. Blood samples were drawn at baseline, immediately after exercise or rest, and every 15 minutes throughout a 60-minute recovery period. Postexercise (24 hours) interstitial glucose was monitored with continuous glucose monitoring (CGM). Results: Twenty-four participants (12 ITxs, 12 CONs) completed the protocol. Plasma glucose decreased more over time with exercise in ITxs compared with CONs [main effects of treatment (P = 0.019), time (P = 0.001), and group (P = 0.012)]. Plasma glucose was lower during exercise vs rest in ITxs but not CONs [treatment by group interaction (P = 0.028)]. Plasma glucose decreased more during exercise than during rest [treatment by time interaction (P = 0.001)]. One ITx and one CON experienced plasma glucose concentrations <3.5 mmol/L at the end of exercise, both of whom returned above that threshold within 15 minutes. Nocturnal CGM glucose <3.5 mmol/L was detected in two CONs but no ITxs. Conclusion: Despite a greater plasma glucose decline during exercise in ITxs, hypoglycemia risk was similar during and after exercise in ITxs compared with CONs.

Spleen reactivity during incremental ascent to altitude.

The spleen contains a reservoir of red blood cells that are mobilized into circulation when under physiological stress. Despite the spleen having an established role in compensation to acute hypoxia, no previous work has assessed the role of the spleen during ascent to high altitude. Twelve participants completed 2 min of handgrip exercise at 30% of maximal voluntary contraction at 1,045, 3,440, and 4,240 m. In a subset of eight participants, an infusion of phenylephrine hydrochloride was administered at a dosage of 30 µg/l of predicted blood volume at each altitude. The spleen was imaged by ultrasound via a 2- to 5.5-MHz curvilinear probe. Spleen volume was calculated by the prolate ellipsoid formula. Finger capillary blood samples were taken to measure hematocrit. Spleen images and hematocrit were taken both before and at the end of both handgrip and phenylephrine infusion. No changes in resting spleen volume were observed between altitudes. At low altitude, the spleen contracted in response to handgrip [272.8 ml (SD 102.3) vs. 249.6 ml (SD 105.7), P = 0.009], leading to an increase in hematocrit (42.6% (SD 3.3) vs. 44.3% (SD 3.3), P = 0.023] but did not contract or increase hematocrit at the high-altitude locations. Infusion of phenylephrine led to spleen contraction at all altitudes, but only lead to an increase in hematocrit at low altitude. These data reveal that the human spleen may not contribute to acclimatization to chronic hypoxia, contrary to its response to acute sympathoexcitation. These results are explained by alterations in spleen reactivity to increased sympathetic activation at altitude. NEW & NOTEWORTHY The present study demonstrated that, despite the known role of the human spleen in increasing oxygen delivery to tissues during acute hypoxia scenarios, the spleen does not mobilize red blood cells during ascent to high altitude. Furthermore, the spleen's response to acute stressors at altitude depends on the nature of the stressor; the spleen's sensitivity to neurotransmitter is maintained, while its reflex response to stress is dampened.

Effect of 16 weeks of resistance exercise and detraining comparing two methods of blood flow restriction in muscle strength of healthy older women: A randomized controlled trial.

OBJECTIVE: The objective of this study was to compare the effect of 16 weeks of resistance training using different occlusion pressures, followed by 6 weeks of detraining on the muscular strength levels of older women. METHODS: This randomized-controlled trial included 56 recreationally active women (68.8 ±â€¯5.09 years), randomized into 5 groups: 1) Low-intensity with blood flow restriction "High" (LI + BFR_H): with higher occlusion pressure, 2) Low-intensity with blood flow restriction "Low" (LI + BFR_L): with lower occlusion pressure, 3) High-intensity (HI), 4) Low-intensity (LI), and 5) Control Group (CG). Participants completed 16 weeks of resistance exercise training, followed by a 6-week detraining period. Maximal isokinetic torque (N.m) of right and left knee extension (PTRE/PTLE) and flexion (PTRF/PTLF) was measured at pre-training, post-training and immediately following the detraining period. RESULTS: Increased strength was observed in the LI + BFR_H, LI + BRF_L and HI groups post-training compared to baseline in the PTRE (Δ% = 27.2, 15.75 and 13.81%, p < .05, respectively), PTLE (Δ% = 25.2, 18.95 and 30.39%, p < .05, respectively), PTRF (Δ% = 36.7, 22.79 and 34.97%, p < .05, respectively) and PTLF in the groups (Δ% = 35.8, 24.93 and 26.14%, p < .05, respectively). Following the detraining period, the LI + BFR_H, LI + BFR_L and HI groups had a decrease in strength levels, but values did not decrease below baseline level. CONCLUSION: Low intensity BFR resistance exercise increases muscle strength in older women similar to HI, with higher occlusion pressures being more effective. Muscle strength was well preserved following a 6-week detraining period, and although reductions were observed, some preservation of strength can be explained by possible neural adaptations to exercise.

Aquatic exercise for adults with type 2 diabetes: a meta-analysis.

AIMS: The purpose of this systematic review and meta-analysis was to examine the effects of aquatic exercise (AquaEx) on indicators of glycemic control (i.e., glycated hemoglobin [A1c] and fasting plasma glucose) in adults with type 2 diabetes mellitus (T2DM). It was hypothesized that AquaEx would improve glycemic control to a similar extent as land-based exercise (LandEx), but to a greater extent than non-exercise control (Ctrl). METHODS: A literature search was completed in February 2017 for studies examining AquaEx training in adults with T2DM. Assessment of glycemic control was necessary for inclusion, while secondary outcomes such as quality of life and cardiometabolic risk factors (i.e., blood pressure, triglycerides and total cholesterol) were considered, but not required for inclusion. Outcomes were measured before and after at least 8 weeks of AquaEx, and data were analyzed using weighted mean differences (WMDs) and fixed effect models, when appropriate. RESULTS: Nine trials including 222 participants were identified. Three trials compared AquaEx to LandEx, two compared AquaEx to Crtl, and four had a pre-/post-design without a comparison group. Results indicate no difference in A1c between LandEx and AquaEx (WMD = -0.02%, 95% confidence interval = [-0.71, 0.66]). Post-intervention A1c was lower in AquaEx when compared to Crtl (WMD = -0.96%, [-1.87, -0.05]). Post-AquaEx A1c was lower compared to baseline (WMD = -0.48%, [-0.66, -0.30]). CONCLUSIONS: A1c can be reduced after eight-twelve weeks of AquaEx. However, at this time few studies have examined whether changes in A1c are different from LandEx or Crtl.