Similar magnitude of post-exercise hyperglycemia despite manipulating resistance exercise intensity in type 1 diabetes individuals

Tailoring Exercise Prescription for Effective Diabetes Glucose Management

CONTEXT

Physical activity, exercise, or both are a staple of lifestyle management approaches both for type 1 diabetes mellitus (T1DM) and type 2 diabetes (T2DM). While the current literature supports both physical activity and exercise for improving glycemic control, reducing cardiovascular risk, maintaining proper weight, and enhancing overall well-being, the optimal prescription regimen remains debated.

EVIDENCE ACQUISITION

We searched PubMed and Google Scholar databases for relevant studies on exercise, insulin sensitivity, and glycemic control in people with T1DM and T2DM.

EVIDENCE SYNTHESIS

In patients with T1DM, exercise generally improves cardiovascular fitness, muscle strength, and glucose levels. However, limited work has evaluated the effect of aerobic plus resistance exercise compared to either exercise type alone on glycemic outcomes. Moreover, less research has evaluated breaks in sedentary behavior with physical activity. When considering the factors that may cause hypoglycemic effects during exercise in T1DM, we found that insulin therapy, meal timing, and neuroendocrine regulation of glucose homeostasis are all important. In T2DM, physical activity is a recommended therapy independent of weight loss. Contemporary consideration of timing of exercise relative to meals and time of day, potential medication interactions, and breaks in sedentary behavior have gained recognition as potentially novel approaches that enhance glucose management.

CONCLUSION

Physical activity or exercise is, overall, an effective treatment for glycemia in people with diabetes independent of weight loss. However, additional research surrounding exercise is needed to maximize the health benefit, particularly in "free-living" settings.

Effect of exercise on plasma insulin levels in individuals with type 1 diabetes: A systematic review and meta-analysis

AIMS

Current evidence of the impact of acute exercise on insulin levels in individuals with type 1 diabetes remains controversial. Therefore, we conducted a systematic review and meta-analysis to explore exercise-induced changes in insulin levels.

MATERIALS AND METHODS

We conducted a systematic review (until 05 November 2023) and meta-analysis exploring the effect of exercise on insulin concentration in individuals with type 1 diabetes. We included randomised cross-over studies for rapid-acting insulin and pre- and post-studies for long-acting insulin in individuals with type 1 diabetes performing any type of acute exercise and had a control condition. The exercise-induced change in insulin levels was the outcome of interest. When possible, the mean differences (MDs) in insulin levels were pooled using the DerSimonian and Laird random effect method. Risk of bias was assessed for each included study.

RESULTS

Seventeen trials, encompassing 186 participants with type 1 diabetes, were included in the systematic review. Twelve out of 17 studies included participants on rapid-acting insulin regimens and used a cross-over design, whereas five out of 17 single-arm studies included participants on (ultra)long-acting insulin. Seven out of 12 studies on rapid-acting insulins and all the single-arm studies were at high risk of bias. Results suggest a statistically significant, small-to-moderate increase of rapid-acting insulin after 30 min of exercise (MD of 18.44 [95% CI 0.02; 36.86; I2 0%] pmol/L); meanwhile, findings on (ultra)long-acting insulin were inconclusive.

CONCLUSIONS

A small-to-moderate increase of insulin levels in studies including rapid-acting insulin was found after a bout of physical exercise in individuals with type 1 diabetes. However, current gaps in high-quality evidence challenge our understanding of insulin kinetics around exercise.

Factors Affecting Reproducibility of Change in Glucose During Exercise: Results From the Type 1 Diabetes and EXercise Initiative

AIMS

To evaluate factors affecting within-participant reproducibility in glycemic response to different forms of exercise.

METHODS

Structured exercise sessions ~30 minutes in length from the Type 1 Diabetes Exercise Initiative (T1DEXI) study were used to assess within-participant glycemic variability during and after exercise. The effect of several pre-exercise factors on the within-participant glycemic variability was evaluated.

RESULTS

Data from 476 adults with type 1 diabetes were analyzed. A participant's change in glucose during exercise was reproducible within 15 mg/dL of the participant's other exercise sessions only 32% of the time. Participants who exercised with lower and more consistent glucose level, insulin on board (IOB), and carbohydrate intake at exercise start had less variability in glycemic change during exercise. Participants with lower mean glucose (P < .001), lower glucose coefficient of variation (CV) (P < .001), and lower % time <70 mg/dL (P = .005) on sedentary days had less variable 24-hour post-exercise mean glucose.

CONCLUSIONS

Reproducibility of change in glucose during exercise was low in this cohort of adults with T1D, but more consistency in pre-exercise glucose levels, IOB, and carbohydrates may increase this reproducibility. Mean glucose variability in the 24 hours after exercise is influenced more by the participant's overall glycemic control than other modifiable factors.

Physical Activity Management for Youth With Type 1 Diabetes: Supporting Active and Inactive Children

Regular physical activity and exercise are important for youth and essential components of a healthy lifestyle. For youth with type 1 diabetes, regular physical activity can promote cardiovascular fitness, bone health, insulin sensitivity, and glucose management. However, the number of youth with type 1 diabetes who regularly meet minimum physical activity guidelines is low, and many encounter barriers to regular physical activity. Additionally, some health care professionals (HCPs) may be unsure how to approach the topic of exercise with youth and families in a busy clinic setting. This article provides an overview of current physical activity research in youth with type 1 diabetes, a basic description of exercise physiology in type 1 diabetes, and practical strategies for HCPs to conduct effective and individualized exercise consultations for youth with type 1 diabetes.

Reassessing the evidence: prandial state dictates glycaemic responses to exercise in individuals with type 1 diabetes to a greater extent than intensity

Recent guidelines suggest that adding anaerobic (high intensity or resistance) activity to an exercise session can prevent blood glucose declines that occur during aerobic exercise in individuals with type 1 diabetes. This theory evolved from earlier study data showing that sustained, anaerobic activity (high intensity cycling) increases blood glucose levels in these participants. However, studies involving protocols where anaerobic (high intensity interval) and aerobic exercise are combined have extremely variable glycaemic outcomes, as do resistance exercise studies. Scrutinising earlier studies will reveal that, in addition to high intensity activity (intervals or weight lifting), these protocols had another common feature: participants were performing exercise after an overnight fast. Based on these findings, and data from recent exercise studies, it can be argued that participant prandial state may be a more dominant factor than exercise intensity where glycaemic changes in individuals with type 1 diabetes are concerned. As such, a reassessment of study outcomes and an update to exercise recommendations for those with type 1 diabetes may be warranted.

Continuous Glucose Monitoring and Physical Activity

Continuous glucose monitoring (CGM) use has several potential positive effects on diabetes management. These benefits are, e.g., increased time in range (TIR), optimized therapy, and developed documentation. Physical activity is a recommended intervention tool in diabetes management, especially for people with type 2 diabetes (T2D). The benefits of physical activity for people with diabetes can be seen as an improvement of glycemic control, glycemic variability, and the reduction of insulin resistance. In relation to the physical activity of people with T2D, the benefits of CGM use can even be increased, and CGM can be a helpful tool to prevent adverse events due to physical activity of people with diabetes, such as hypoglycemic events and nocturnal hypoglycemia after sports. This narrative review aims to provide solid recommendations for the use of CGM in everyday life physical activities based on the noted benefits and to give a general overview of the guidelines on physical activity and CGM use for people with diabetes.

The complex relationship between physical activity and diabetes: an overview

Diabetes mellitus (DM) is a widespread condition, representing a challenging disease to manage. Exercise is being increasingly recommended as part of the therapeutic regimen for DM but the management of different forms of physical activity is difficult for individuals with diabetes, trainers, and physicians. Regular exercise can improve health and well-being, helping individuals to achieve their target lipid profile, body composition, cardio-respiratory fitness, and glycemic goals. People with diabetes tend to be as inactive as the general population, with a large percentage of individuals not achieving the minimum amount of recommended physical activity levels. Indeed, several barriers to exercise exist for persons with diabetes, including sports eligibility, multi-modality management of diabetic athletes, and inadequate knowledge about adequate type and intensity of exercise. The aim of the present review is to provide the current understanding of mechanisms, recommendations, and beneficial effects of different modalities of exercise for the treatment of DM.

Acute changes in glucose induced by continuous or intermittent exercise in children and adolescents with type 1 diabetes

Objective

To estimate the rate of change during exercise and during recovery in moderate-continuous exercise (MCE) and high-intensity intermittent exercise (HIIE) in children and adolescents with type 1 diabetes (T1D).

Methods

Participants performed 2 sessions of exercise: thirty minutes of continuous activity on a cycle ergometer (60% of VO_2max) and thirty minutes (60% VO_2max) interspersed with five bouts of maximum intensity lasting ten seconds every five minutes. Capillary blood glucose was measured before and after each test. The glucose rate of change in exercise (RoC_E) was calculated (final blood glucose - onset blood glucose/exercise time), and the glucose rate of change in recovery (RoC_R) (blood glucose 30 minutes after exercise - end of exercise blood glucose/recovery time).

Results

The study included thirty-one participants (aged 13 ± 1.88 years). A lower blood glucose reduction was observed in the HIIE group, as well as better recovery values before, after, and thirty minutes after the test, respectively (333.14 ± 69.53, 226.19 ± 68.05 and 201.77 ± 66.84 versus 211.36 ± 91.03, 155.98 ± 82,68 and 165.76 ± 72.94). Covariance analyses showed a significant difference in glycemic variation between continuous and intermittent protocols immediately after exercise (-2.90 versus -2.08) and during the recovery period (-0.677 versus -0.389).

Conclusion

HIIE led to a lower glucose reduction rate per minute during exercise and better recovery in the first 30 minutes after exercise compared to MCE in children and adolescents with T1D.

American Medical Society for Sports Medicine Position Statement on the Care of the Athlete and Athletic Person With Diabetes

ABSTRACT

The American Medical Society for Sports Medicine (AMSSM) developed this position statement to assist physicians and other health professionals in managing athletes and active people with diabetes. The AMSSM selected the author panel through an application process to identify members with clinical and academic expertise in the care of active patients with diabetes. This article reviews the current knowledge and gaps regarding the benefits and risks of various types of exercise and management issues for athletes and physically active people with diabetes, including nutrition and rehabilitation issues. Resistance exercises seem to be beneficial for patients with type 1 diabetes, and the new medications for patients with type 2 diabetes generally do not need adjustment with exercise. In preparing this statement, the authors conducted an evidence review and received open comment from the AMSSM Board of Directors before finalizing the recommendations.

Exercise, type 1 diabetes mellitus and blood glucose: The implications of exercise timing

The scientific literature shows that exercise has many benefits for individuals with type 1 diabetes. Yet, several barriers to exercise in this population exist, such as post-exercise hypoglycaemia or hyperglycaemia. Several studies suggest that the timing of exercise may be an important factor in preventing exercise-induced hypoglycaemia or hyperglycaemia. However, there is a paucity of evidence solely focused on summarising findings regarding exercise timing and the impact it has on glucose metabolism in type 1 diabetes. This report suggests that resistance or high-intensity interval exercise/training (often known as HIIT) may be best commenced at the time of day when an individual is most likely to experience a hypoglycaemic event (i.e., afternoon/evening) due to the superior blood glucose stability resistance and HIIT exercise provides. Continuous aerobic-based exercise is advised to be performed in the morning due to circadian elevations in blood glucose at this time, thereby providing added protection against a hypoglycaemic episode. Ultimately, the evidence concerning exercise timing and glycaemic control remains at an embryonic stage. Carefully designed investigations of this nexus are required, which could be harnessed to determine the most effective, and possibly safest, time to exercise for those with type 1 diabetes.

More Time in Glucose Range During Exercise Days than Sedentary Days in Adults Living with Type 1 Diabetes

Objective: This study analysis was designed to examine the 24-h effects of exercise on glycemic control as measured by continuous glucose monitoring (CGM). Methods: Individuals with type 1 diabetes (ages: 15-68 years; hemoglobin A1c: 7.5% ± 1.5% [mean ± standard deviation (SD)]) were randomly assigned to complete twice-weekly aerobic, high-intensity interval, or resistance-based exercise sessions in addition to their personal exercise sessions for a period of 4 weeks. Exercise was tracked with wearables and glucose concentrations assessed using CGM. An exercise day was defined as a 24-h period after the end of exercise, while a sedentary day was defined as any 24-h period with no recorded exercise ≥10 min long. Sedentary days start at least 24 h after the end of exercise. Results: Mean glucose was lower (150 ± 45 vs. 166 ± 49 mg/dL, P = 0.01), % time in range [70-180 mg/dL] higher (62% ± 23% vs. 56% ± 25%, P = 0.03), % time >180 mg/dL lower (28% ± 23% vs. 37% ± 26%, P = 0.01), and % time <70 mg/dL higher (9.3% ± 11.0% vs. 7.1% ± 9.1%, P = 0.04) on exercise days compared with sedentary days. Glucose variability and % time <54 mg/dL did not differ significantly between exercise and sedentary days. No significant differences in glucose control by exercise type were observed. Conclusion: Participants had lower 24-h mean glucose levels and a greater time in range on exercise days compared with sedentary days, with mode of exercise affecting glycemia similarly. In summary, this study offers data supporting frequency of exercise as a method of facilitating glucose control but does not suggest an effect for mode of exercise.

The Effect of Physical Activity on Glycemic Variability in Patients With Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

PURPOSE

The effect of physical activity on glycemic variability remains controversial. This meta-analysis aimed to assess the overall effect of physical activity treatment on glycemic variability in patients with diabetes.

METHODS

PubMed/MEDLINE, Embase, and Cochrane databases were searched for clinical trials that conducted in patients with type 1 diabetes mellitus and type 2 diabetes mellitus with reports of the mean amplitude of glycemic excursion (MAGE), time in range (TIR), time above range (TAR), or time below range (TBR). Eligible trials were analyzed by fixed-effect model, random effect model, and meta-regression analysis accordingly.

RESULTS

In total, thirteen trials were included. Compared with the control group, physical activity intervention was significantly associated with increased TIR (WMDs, 4.17%; 95% CI, 1.11 to 7.23%, P<0.01), decreased MAGE (WMDs, -0.68 mmol/L; 95% CI, -1.01 to -0.36 mmol/L, P<0.01) and decreased TAR (WMDs, -3.54%; 95% CI, -5.21 to -1.88%, P<0.01) in patients with diabetes, but showed insignificant effects on TBR. Patients with higher baseline BMI levels was associated with a greater decrease in MAGE (β=-0.392, 95% CI: -0.710, -0.074), and patients with lower baseline HbA1c levels was associated with a greater increase in TBR during physical activities (β=-0.903, 95% CI: -1.550, -0.255).

CONCLUSION

Physical activity was associated with significantly decreased glycemic variability in patients with diabetes. Patients with higher BMI might benefit more from physical activity therapy in terms of a lower MAGE. Hypoglycemia associated with physical activity treatment still warranted caution, especially in patients with intensive glycemic control.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO [CRD42021259807].

Glucose management for exercise using continuous glucose monitoring (CGM) and intermittently scanned CGM (isCGM) systems in type 1 diabetes: position statement of the European Association for the Study of Diabetes (EASD) and of the International Society for Pediatric and Adolescent Diabetes (ISPAD) endorsed by JDRF and supported by the American Diabetes Association (ADA)

Physical exercise is an important component in the management of type 1 diabetes across the lifespan. Yet, acute exercise increases the risk of dysglycaemia, and the direction of glycaemic excursions depends, to some extent, on the intensity and duration of the type of exercise. Understandably, fear of hypoglycaemia is one of the strongest barriers to incorporating exercise into daily life. Risk of hypoglycaemia during and after exercise can be lowered when insulin-dose adjustments are made and/or additional carbohydrates are consumed. Glycaemic management during exercise has been made easier with continuous glucose monitoring (CGM) and intermittently scanned continuous glucose monitoring (isCGM) systems; however, because of the complexity of CGM and isCGM systems, both individuals with type 1 diabetes and their healthcare professionals may struggle with the interpretation of given information to maximise the technological potential for effective use around exercise (i.e. before, during and after). This position statement highlights the recent advancements in CGM and isCGM technology, with a focus on the evidence base for their efficacy to sense glucose around exercise and adaptations in the use of these emerging tools, and updates the guidance for exercise in adults, children and adolescents with type 1 diabetes. Graphical abstract.

Glucose management for exercise using continuous glucose monitoring (CGM) and intermittently scanned CGM (isCGM) systems in type 1 diabetes: position statement of the European Association for the Study of Diabetes (EASD) and of the International Society for Pediatric and Adolescent Diabetes (ISPAD) endorsed by JDRF and supported by the American Diabetes Association (ADA)

Physical exercise is an important component in the management of type 1 diabetes across the lifespan. Yet, acute exercise increases the risk of dysglycaemia, and the direction of glycaemic excursions depends, to some extent, on the intensity and duration of the type of exercise. Understandably, fear of hypoglycaemia is one of the strongest barriers to incorporating exercise into daily life. Risk of hypoglycaemia during and after exercise can be lowered when insulin-dose adjustments are made and/or additional carbohydrates are consumed. Glycaemic management during exercise has been made easier with continuous glucose monitoring (CGM) and intermittently scanned continuous glucose monitoring (isCGM) systems; however, because of the complexity of CGM and isCGM systems, both individuals with type 1 diabetes and their healthcare professionals may struggle with the interpretation of given information to maximise the technological potential for effective use around exercise (ie, before, during and after). This position statement highlights the recent advancements in CGM and isCGM technology, with a focus on the evidence base for their efficacy to sense glucose around exercise and adaptations in the use of these emerging tools, and updates the guidance for exercise in adults, children and adolescents with type 1 diabetes.

Accuracy of the Dexcom G6 Glucose Sensor during Aerobic, Resistance, and Interval Exercise in Adults with Type 1 Diabetes

The accuracy of continuous glucose monitoring (CGM) sensors may be significantly impacted by exercise. We evaluated the impact of three different types of exercise on the accuracy of the Dexcom G6 sensor. Twenty-four adults with type 1 diabetes on multiple daily injections wore a G6 sensor. Participants were randomized to aerobic, resistance, or high intensity interval training (HIIT) exercise. Each participant completed two in-clinic 30-min exercise sessions. The sensors were applied on average 5.3 days prior to the in-clinic visits (range 0.6–9.9). Capillary blood glucose (CBG) measurements with a Contour Next meter were performed before and after exercise as well as every 10 min during exercise. No CGM calibrations were performed. The median absolute relative difference (MARD) and median relative difference (MRD) of the CGM as compared with the reference CBG did not differ significantly from the start of exercise to the end exercise across all exercise types (ranges for aerobic MARD: 8.9 to 13.9% and MRD: −6.4 to 0.5%, resistance MARD: 7.7 to 14.5% and MRD: −8.3 to −2.9%, HIIT MARD: 12.1 to 16.8% and MRD: −14.3 to −9.1%). The accuracy of the no-calibration Dexcom G6 CGM was not significantly impacted by aerobic, resistance, or HIIT exercise.

Effects of acute aerobic, resistance and combined exercises on 24-h glucose variability and skeletal muscle signalling responses in type 1 diabetics

PURPOSE

To compare the effect of high-intensity aerobic (AER), resistance (RES), and combined (COMB: RES + AER) exercise, on interstitial glucose (IG) variability and skeletal muscle signalling pathways in type 1 diabetes (T1D).

METHODS

T1D participants (6 M/6F) wore a flash glucose monitoring system in four randomized sessions: one control (CONT), and one AER, RES and COMB (40 min each). Mean amplitude of glycemic excursions (MAGE), standard deviation (SD) and coefficient variation (CV) of IG were used to compare the 24 h post-exercise IG variability. Blood and muscle samples were collected to compare exercise-induced systemic and muscle signalling responses related to metabolic, growth and inflammatory adaptations.

RESULTS

Both RES and COMB decreased the 24 h MAGE compared to CONT; additionally, COMB decreased the 24 h SD and CV. In the 6-12 h post-exercise, all exercise modalities reduced the IG CV while SD decreased only after COMB. Both AER and COMB stimulated the PGC-1α mRNA expression and promoted the splicing of IGF-1Ea variant, while Akt and p38MAPK phosphorylation increased only after RES and COMB. Additionally, COMB enhanced eEF2 activation and RES increased myogenin and MRF4 mRNA expression. Blood lactate and glycerol levels and muscle IL-6, TNF-α, and MCP-1 mRNAs increased after all exercise sessions, while serum CK and LDH level did not change.

CONCLUSION

COMB is more effective in reducing IG fluctuations compared to single-mode AER or RES exercise. Moreover, COMB simultaneously activates muscle signalling pathways involved in substrate metabolism and anabolic adaptations, which can help to improve glycaemic control and maintain muscle health in T1D.

Endocrine Mechanisms Connecting Exercise to Brown Adipose Tissue Metabolism: a Human Perspective

PURPOSE OF REVIEW

To summarize the state-of-the-art regarding the exercise-regulated endocrine signals that might modulate brown adipose tissue (BAT) activity and/or white adipose tissue (WAT) browning, or through which BAT communicates with other tissues, in humans.

RECENT FINDINGS

Exercise induces WAT browning in rodents by means of a variety of physiological mechanism. However, whether exercise induces WAT browning in humans is still unknown. Nonetheless, a number of protein hormones and metabolites, whose signaling can influence thermogenic adipocyte's metabolism, are secreted during and/or after exercise in humans from a variety of tissues and organs, such as the skeletal muscle, the adipose tissue, the liver, the adrenal glands, or the cardiac muscle. Overall, it seems plausible to hypothesize that, in humans, exercise secretes an endocrine cocktail that is likely to induce WAT browning, as it does in rodents. However, even if exercise elicits a pro-browning endocrine response, this might result in a negligible effect if blood flow is restricted in thermogenic adipocyte-rich areas during exercise, which is still to be determined. Future studies are needed to fully characterize the exercise-induced secretion (i.e., to determine the effect of the different exercise frequency, intensity, type, time, and volume) of endocrine signaling molecules that might modulate BAT activity and/or WAT browning or through which BAT communicates with other tissues, during exercise. The exercise effect on BAT metabolism and/or WAT browning could be one of the still unknown mechanisms by which exercise exerts beneficial health effects, and it might be pharmacologically mimicked.

Effect of Acute Bouts of Volume-Matched High-Intensity Resistance Training Protocols on Blood Glucose Levels

Monroe, JC, Naugle, KM, and Naugle, KE. Effect of acute bouts of volume-matched high-intensity resistance training protocols on blood glucose levels. J Strength Cond Res 34(2): 445-450, 2020-Resistance exercise has the capability to alter glucose metabolism in healthy adults; however, to what extent single sessions of varying intensities of resistance exercise affect capillary glucose levels is not completely understood. The purpose of this study was to compare the effect of different resistance training intensities on capillary blood glucose levels in healthy adults. Thirteen resistance-trained men (age 24.4 ± 2.7 years) participated in an evaluation and 2 separate experimental resistance training sessions. The experimental sessions were a high-intensity resistance training session (HT) consisting of 7 sets of 3 repetitions at 90% of the participant's estimated 1 repetition maximum (e1RM), and a moderate-/high-intensity resistance training session (MT) consisting of 3 sets of 9 repetitions at 70% of the participant's e1RM. At least 7 days separated the completion of each session. Four glucose readings during each session were recorded using a capillary glucometer: G1 (baseline); G2 (pre-exercise); G3 (after exercise); and G4 (10 minutes after exercise). Results were analyzed using repeated-measures analysis of variances. Analysis revealed a significant decrease in blood glucose levels between G2 and G3, and G2 and G4 in both the HT and MT experimental sessions (p = 0.045). In addition, there was a significant difference in the magnitude of change in glucose levels from G2 to G3 between HT and MT (HT = -38.2 ± 5.3% SE, p = 0.042, MT = -22.2 ± 5.9% SE). Although both of the acute resistance exercise protocols decreased blood glucose levels in healthy men, a greater decrease in blood glucose levels from pre-exercise to post-exercise was observed in HT group compared with MT group.

Carbohydrate Intake in the Context of Exercise in People with Type 1 Diabetes

Although the benefits of regular exercise on cardiovascular risk factors are well established for people with type 1 diabetes (T1D), glycemic control remains a challenge during exercise. Carbohydrate consumption to fuel the exercise bout and/or for hypoglycemia prevention is an important cornerstone to maintain performance and avoid hypoglycemia. The main strategies pertinent to carbohydrate supplementation in the context of exercise cover three aspects: the amount of carbohydrates ingested (i.e., quantity in relation to demands to fuel exercise and avoid hypoglycemia), the timing of the intake (before, during and after the exercise, as well as circadian factors), and the quality of the carbohydrates (encompassing differing carbohydrate types, as well as the context within a meal and the associated macronutrients). The aim of this review is to comprehensively summarize the literature on carbohydrate intake in the context of exercise in people with T1D.

Morning (Fasting) vs Afternoon Resistance Exercise in Individuals With Type 1 Diabetes: A Randomized Crossover Study

OBJECTIVE

To determine the effect of morning exercise in the fasting condition vs afternoon exercise on blood glucose responses to resistance exercise (RE).

RESEARCH DESIGN AND METHODS

For this randomized crossover design, 12 participants with type 1 diabetes mellitus [nine females; aged 31 ± 8.9 years; diabetes duration, 19.1 ± 8.3 years; HbA1c, 7.4% ± 0.8% (57.4 ± 8.5 mmol/mol)] performed ∼40 minutes of RE (three sets of eight repetitions, seven exercises, at the individual's predetermined eight repetition maximum) at either 7 am (fasting) or 5 pm. Sessions were performed at least 48 hours apart. Venous blood samples were collected immediately preexercise, immediately postexercise, and 60 minutes postexercise. Interstitial glucose was monitored overnight postexercise by continuous glucose monitoring (CGM).

RESULTS

Data are presented as mean ± SD. Blood glucose rose during fasting morning exercise (9.5 ± 3.0 to 10.4 ± 3.0 mmol/L), whereas it declined with afternoon exercise (8.2 ± 2.5 to 7.4 ± 2.6 mmol/L; P = 0.031 for time-by-treatment interaction). Sixty minutes postexercise, blood glucose concentration was significantly higher after fasting morning exercise than after afternoon exercise (10.9 ± 3.2 vs 7.9 ± 2.9 mmol/L; P = 0.019). CGM data indicated more glucose variability (2.7 ± 1.1 vs 2.0 ± 0.7 mmol/L; P = 0.019) and more frequent hyperglycemia (12 events vs five events; P = 0.025) after morning RE than after afternoon RE.

CONCLUSIONS

Compared with afternoon RE, morning (fasting) RE was associated with distinctly different blood glucose responses and postexercise profiles.

Resistance Isn't Futile: The Physiological Basis of the Health Effects of Resistance Exercise in Individuals With Type 1 Diabetes

The importance of regular exercise for glucose management in individuals with type 1 diabetes is magnified by its acknowledgment as a key adjunct to insulin therapy by several governmental, charitable, and healthcare organisations. However, although actively encouraged, exercise participation rates remain low, with glycaemic disturbances and poor cardiorespiratory fitness cited as barriers to long-term involvement. These fears are perhaps exacerbated by uncertainty in how different forms of exercise can considerably alter several acute and chronic physiological outcomes in those with type 1 diabetes. Thus, understanding the bodily responses to specific forms of exercise is important for the provision of practical guidelines that aim to overcome these exercise barriers. Currently, the majority of existing exercise research in type 1 diabetes has focused on moderate intensity continuous protocols with less work exploring predominately non-oxidative exercise modalities like resistance exercise. This is surprising, considering the known neuro-muscular, osteopathic, metabolic, and vascular benefits associated with resistance exercise in the wider population. Considering that individuals with type 1 diabetes have an elevated susceptibility for complications within these physiological systems, the wider health benefits associated with resistance exercise may help alleviate the prevalence and/or magnitude of pathological manifestation in this population group. This review outlines the health benefits of resistance exercise with reference to evidence in aiding some of the common complications associated with individuals with type 1 diabetes.

Time Lag and Accuracy of Continuous Glucose Monitoring During High Intensity Interval Training in Adults with Type 1 Diabetes

Background: This study investigated the accuracy of real-time continuous glucose monitoring (rtCGM) during high intensity interval training (HIIT) in patients with type 1 diabetes (T1D). Methods: Seventeen participants with T1D, using multiple daily injections (MDI) with basal insulin glargine 300 U/mL (Gla-300), completed four fasted HIIT sessions over 4 weeks while wearing a Dexcom rtCGM G4 Platinum system. Each exercise consisted of high intensity interval cycling and multimodal training over 25 min. Reference venous plasma glucose (PG) was measured at 60- and 10-min before exercise (Stage 1), every 10 min during exercise and then every 15 min until 180 min after the end of exercise (Stage 2: during exercise and 45-min early recovery; Stage 3: 45 min to 3 h after the end of exercise); and at 6-, 10-, and 13-h postexercise (Stage 4). Results: In the 64 HIIT sessions that resulted in hyperglycemia, PG increased 90.0 ± 32.4 mg/dL (mean ± standard deviation), peaking at 68.0 ± 18.4 min from the start of HIIT. Mean absolute relative difference was highest during exercise and early recovery (Stage 2) at 17.8%, versus Stage 1 (10.4%), Stage 3 (10.6%), and Stage 4 (11.5%) (P < 0.001). During Stage 2, rtCGM showed a significant negative bias of 35.3 mg/dL (P < 0.001) compared to reference glucose. Lag time to reach the half-maximal glucose rise was 35 min in rtCGM versus PG. The Surveillance Error Grid found that in Stage 2, only 65.5% of paired values were in the no-risk zone and the %15/15 was 50%, significantly lower than the other stages (P < 0.001). Conclusions: During HIIT and early recovery, there is an increase in lag time and a related decline in accuracy of Dexcom rtCGM G4, compared to pre-exercise and later recovery, in patients with T1D using MDI.

Continuous Glucose Monitoring and Exercise in Type 1 Diabetes: Past, Present and Future

Prior to the widespread use of continuous glucose monitoring (CGM), knowledge of the effects of exercise in type 1 diabetes (T1D) was limited to the exercise period, with few studies having the budget or capacity to monitor participants overnight. Recently, CGM has become a staple of many exercise studies, allowing researchers to observe the otherwise elusive late post-exercise period. We performed a strategic search using PubMed and Academic Search Complete. Studies were included if they involved adults with T1D performing exercise or physical activity, had a sample size greater than 5, and involved the use of CGM. Upon completion of the search protocol, 26 articles were reviewed for inclusion. While outcomes have been variable, CGM use in exercise studies has allowed the assessment of post-exercise (especially nocturnal) trends for different exercise modalities in individuals with T1D. Sensor accuracy is currently considered adequate for exercise, which has been crucial to developing closed-loop and artificial pancreas systems. Until these systems are perfected, CGM continues to provide information about late post-exercise responses, to assist T1D patients in managing their glucose, and to be useful as a tool for teaching individuals with T1D about exercise.

Exercise and the Development of the Artificial Pancreas: One of the More Difficult Series of Hurdles

Regular physical activity (PA) promotes numerous health benefits for people living with type 1 diabetes (T1D). However, PA also complicates blood glucose control. Factors affecting blood glucose fluctuations during PA include activity type, intensity and duration as well as the amount of insulin and food in the body at the time of the activity. To maintain equilibrium with blood glucose concentrations during PA, the rate of glucose appearance (Ra) to disappearance (Rd) in the bloodstream must be balanced. In nondiabetics, there is a rise in glucagon and a reduction in insulin release at the onset of mild to moderate aerobic PA. During intense aerobic -anaerobic work, insulin release first decreases and then rises rapidly in early recovery to offset a more dramatic increase in counterregulatory hormones and metabolites. An "exercise smart" artificial pancreas (AP) must be capable of sensing glucose and perhaps other physiological responses to various types and intensities of PA. The emergence of this new technology may benefit active persons with T1D who are prone to hypo and hyperglycemia.