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A time for exercise: The exercise window

DOI: 10.1152/japplphysiol.00685.2016
Authors:
Elsamma Chacko at Connecticut Valley Hospital, CT, USA (retired)
Elsamma Chacko
  • Connecticut Valley Hospital, CT, USA (retired)
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Abstract

How blood glucose responds to exercise depends on the timing of the physical activity with respect to the proximate meal. Although study after study has confirmed this, many researchers still report results without specifying exercise timing. This laxity could be the source of some of the uncertainties and inconsistencies found in the field. In place of the current practice of using the binary categorization of the feeding cycle into pre-meal and post-meal periods, we look at it as consisting of four time intervals: the pre-meal period plus the early, mid- and late postprandial periods. Two of these intervals stand out. Pre-meal exercise uses endogenous glucose and muscle glycogen as the main fuels offering varying effects on glycemia. Exercise during the mid-postprandial period uses exogenous glucose as the main fuel. Exogenous glucose is abundant in the blood during the 30 to 90 min post-meal period, rendering this interval a unique opportunity to use up the excess glucose as fuel for moderate aerobic exercise, thereby blunting the glucose surge. Hypoglycemia risk is minimal during this exercise window. The continuing arrival of glucose from the gut in copious amounts minimizes the risk for hypoglycemia. The role of different modes of exercise and combinations during the mid-postprandial period on metabolic markers remains to be explored.
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A time for exercise: the exercise window
Elsamma Chacko
Principal Physician, Connecticut Valley Hospital
1000 Silver Street
Middletown, CT 06457
(860) 262 5000
E-mail
elsammac@msn.com
Financial disclosure: None
Word count: 1672
Abstract
How blood glucose responds to exercise depends on the timing of the physical activity with
respect to the proximate meal. Although study after study has confirmed this, many researchers
still report results without specifying exercise timing. This laxity could be the source of some of
the uncertainties and inconsistencies found in the field. In place of the current practice of using
the binary categorization of the feeding cycle into pre-meal and post-meal periods, we look at it
as consisting of four time intervals: the pre-meal period plus the early, mid- and late postprandial
periods. Two of these intervals stand out. Pre-meal exercise uses endogenous glucose and
muscle glycogen as the main fuels offering varying effects on glycemia. Exercise during the
mid-postprandial period uses exogenous glucose as the main fuel. Exogenous glucose is
abundant in the blood during the 30 to 90 min post-meal period, rendering this interval a unique
opportunity to use up the excess glucose as fuel for moderate aerobic exercise, thereby blunting
the glucose surge. Hypoglycemia risk is minimal within the bounds of this exercise window.
The continuing arrival of glucose from the gut in copious amounts minimizes the risk for
hypoglycemia. The role of different modes of exercise and combinations during the mid-
postprandial period on metabolic markers remains to be explored.
What is new?
The pre-meal/post-meal binary categorization of the feeding cycle can be profitably
modified using the quartet: pre-meal, early, mid- and late postprandial periods. The pre-
meal (counterregulation, steady glucose) and mid-postprandial (insulin action, surging
glucose) intervals stand out. The mid-postprandial period offers a window of opportunity
to diabetes patients to exercise and blunt the glucose surge without fear of hypoglycemia.
The early and late postprandial periods are “grey” segments, constantly vulnerable to
intrusion by hepatic glucose.
A time for exercise: the exercise window
Introduction
In 1982, a team of Canadian scientists reported in the American Journal of Physiology how
exercise affected blood glucose levels (20). The exercise was a moderately paced treadmill walk
that started 30 min post-meal and lasted for 45 min. Although the focus of the study lay
elsewhere, the graphical results presented in the paper pointed to an intriguing possibility: could
physical activity be used to drain off – in real time -- the exogenous glucose entering the
bloodstream from the food being digested along the alimentary canal? The authors noted that
“with exercise, glycemia returned rapidly to fasting levels . . .” in healthy people and in those
with type 1 diabetes. Since then, a large number of studies have come out featuring exercise
timings that vary widely: pre-meal, 15 min post-meal, 30 min post-meal, 45 min post-meal and
one hour to several hours post-meal (2, 7). Many others, however, have been inexplicably silent
on the timing of the exercise in relation to meal. These studies have also used various exercise
intensities, durations, frequencies and combinations thereof. Now, 34 years later, it is still not
clear what exercise conditions would best improve the key metabolic parameters, HbA1c and
lipids. Translational efforts are exceedingly slow in this critical area. This report suggests a
somewhat more refined framework than the binary pre-meal – post-meal categorization of the
feeding cycle to help account for how meals and exercise influence blood glucose levels and
other metabolic measures. Although high-intensity/resistance exercise (25, 8) offers many health
benefits this paper will be focussing on moderate aerobic exercise. The remainder of this paper
reviews existing studies that point to the utility and rationale of this approach.
Research over several decades now has shown that blood glucose levels are sensitive to various
exercise conditions: timing, intensity, duration, frequency and sequencing of exercise (2, 7).
Light to moderate exercise pre-meal raised postprandial glucose, but a similar walk post-meal
lowered glucose levels (4, 5). Remarkably, an hour-long, energy-intensive interval exercise gave
the opposite results: it was the pre-meal exercise that improved glycemia (25).
Exercising in the late postprandial period could lead to hypoglycemia (7). In people with type 1
diabetes, delayed nocturnal hypoglycemia, which usually follows high-intensity or resistance
exercise, is a problem as well (17, 30). For many with type 1 diabetes, fear of hypoglycemia has
been a potent deterrent against partaking in exercise activities. This and extra carbohydrate
intake, meant to prop up falling blood glucose levels, lead to weight gain. Insulin pumps and
continuous glucose monitoring have made the task of regulating the insulin dose much simpler
(although these gadgets and associated procedures remain beyond the reach of the vast majority
of diabetes patients worldwide.)
Published accounts where no information on exercise timing is forthcoming show inconsistent
results for the effects of exercise on HbA1c (9, 10, 15). The reviews and meta-analyses reporting
on HbA1c have generally yielded only small improvements except in a few cases where the
improvements have been quite impressive (9, 10, 15). What is common to virtually all of these
studies is the absence of information on the timing of the exercise bout with respect to meals.
The physiology
The complex exercise – glycemia connection can be best understood by considering exercise
timing, the sources of glucose and the hormones involved. The post-meal period is far from
monolithic and, in fact, consists of three segments defined by the rise and fall of the glucose flux:
early (0-30 min), mid- (30-90 min) and late (> 90 min) postprandial periods. Categorization of
the feeding cycle in this manner is reasonable and warranted because, unlike the relatively
tranquil pre-meal period, the post-meal period is quite eventful, especially in people with
diabetes, what with the ebb and flow of the blood-glucose concentration (3). The dome of the
glucose peak, where exogenous glucose is abundant in the blood, is pegged as the 30-90 min
post-meal interval.
In this formulation two intervals stand out: pre-breakfast (where counterregulation is active) and
mid-postprandial (where insulin action prevails). The other two intervals are in grey areas where
the potential for intrusion by hepatic glucose is constantly present. It is, however, in the late
postprandial period that hypoglycemia mostly lurks. Fortuitously, the new framework comes
with a built-in antidote for the fear of hypoglycemia harbored by many diabetes patients. Start
and finish the daily exercise session within the bounds of the mid-postprandial period, and
patients are assured of plentiful supplies of blood glucose.
The dominant source of endogenous glucose, the liver plays a crucial role in glucose dynamics.
The hormones controlling blood glucose levels during exercise are insulin, glucagon and
catecholamines. The pre-breakfast period is characterized by low insulin-to-glucagon ratios.
Levels of catecholamines go up with high-intensity exercise (18). Moderate exercise during
insulin action lowers glucose levels while moderate exercise during counterregulation stabilizes
it (2, 22). As for high intensity pre-meal exercise, markedly elevated hepatic glucose production
leads to substantial post-exercise hyperglycemia (2, 7, 12, 13) before any glucose lowering effect
sets in (2, 6, 12, 21). In this scenario, the extent of hepatic glucose production holds the key to
glycemia. In the mid-postprandial period, hepatic glucose production is suppressed, free fatty
acids remain low and meal-derived glucose is pouring in, making the 30-90 min interval the right
time to drain off any excess glucose using moderate physical activity (1, 20, 24). What is
apparent here is the improvement of insulin sensitivity through insulin-mediated and contraction-
mediated glucose transport, nipping the post-meal surge in the bud – in real time at that. The
goal of timely exercise is to deny meal-derived glucose the chance to build up in the blood. This
denial not only avoids the serious long term consequences of repeated microvascular damage but
may reduce abnormal fat distribution.
Exercise timing
A 2013 review on exercise timing concluded that post-meal exercise of moderate intensity is
superior to pre-meal exercise for dealing with hyperglycemia (7). Moderate exercise during the
mid-postprandial period improved glucose consistently (1, 2, 4, 5, 11, 14 20, 22, 24, 26, 29).
Glucose lowering has been less efficient during the early (23) and late (5) postprandial periods
presumably because of the involvement of hepatic glucose. In the mid-postprandial period,
exercise starting at 30 min after the first bite into the meal showed the most effective blunting of
the glucose surge (1, 20, 24) (Table 1). As Nelson and colleagues demonstrated decades ago, by
intervening at the right time with an exercise bout of the right intensity, it is possible to keep the
post-meal glucose peak from forming altogether (1, 20, 24). This tactic also minimizes the
hypoglycemia risk because the continued arrival of glucose from the gut serves as a protective
measure.
Table 1 summarizes representative studies (4, 14, 20, 21, 23, 27, 28) done during the four
segments of the feeding cycle. A few cautionary observations are in order here. The glucose
responses shown use different measures: the quoted area-under-the-curve (AUC) values may
refer to the “total,” “incremental” or unspecified variety. Also, hyperglycemia reduction can be
just for the meal or for the whole day. But the overall trend is apparent: intervention starting
closer to the 30 min mark in the mid-postprandial period with exercise of moderate intensity
yields better glycemic control. Tellingly, these studies were not done for the purpose for which
they are being cited here and as such whatever support they offer to the considerations laid out in
this paper may be deemed independently proffered.
Same timing, different intensities
In two studies healthy people exercised at 30 min post-meal for 60 min at different intensities,
50% VO2max and 71% VO2max (24, 19). The lower intensity exercise normalized the glucose
level in 15 min and kept it at that level throughout the exercise, thereby blunting the peak well
(24). At the higher intensity, after the initial drop, glucose started going up 20-min into the
exercise bout and hyperglycemia persisted until the exercise ended (19). When Manders and
colleagues compared two intensities, 35% VO2max for 60 min and 70% VO2max for 30 min, at 60
min post-meal in people with type 2 diabetes, the lower intensity exercise offered the better
glycemic outcome (16). At higher intensitiesthe high end of the moderate intensity range, shorter
duration of exercise may be needed to keep hepatic glucose at bay.
Coordinating meals and exercise
A practical approach to moderating the 24-h glucose profile is to have one big meal, preferably
breakfast, as the designated “exercise meal” and two smaller meals plus two or three snacks.
This meal plan, along with mid-postprandial exercise would lower hyperglycemia after breakfast,
lunch and dinner (29). This lifestyle also minimizes the risk for hypoglycemia. The alternative,
of course, is to exercise three times a day. Light exercise for 15 min after every meal showed
some blunting of the peaks, but the energy expenditure was not enough to produce a significant
effect (5, 29). Taken together, the studies shown in Table 1 hold the promise of an even better
glycemic response to moderate activity starting 30 min post-meal (1, 2, 20, 24). Moderate post-
meal exercise can be done every day, the effects on glycemia are additive (28).
There's work to do
Although there is good evidence that the right time to start the moderate exercise session for
maximum benefit is some 30 min after the start of the meal (20, 24), data on HbA1c and lipids are
scarce. Immediate (real time), short term (48-72hours) and long term (3 months) effects of
moderate aerobic exercise on metabolic measures (HbA1c, levels of lipids, liver fat, and markers
of oxidative stress) in the mid-postprandial period remain to be explored.
Focusing research efforts on the mid-post-meal period is critical for accelerated translation:
physical activity is the one means available to vast populations living with diabetes in the
impoverished corners of the world. Moreover, if diabetes patients follow the current guidelines
and exercise moderately before breakfast or work out intensely any time other than in the mid-
postprandial period, chances are that glucose levels go up right after the physical activity (4, 5,
12, 13).
Conclusion
Although many studies extant inexplicably do not specify the timing of the exercise in relation to
the meal, enough data exist to suggest the rationale and utility of looking at the feeding cycle as
consisting of four segments: the pre-meal, early postprandial, mid-postprandial and late
postprandial periods. The mid-postprandial period (30 – 90 min post-meal) offers a unique
opportunity to diabetes patients to manage hyperglycemia, with minimal risk of hypoglycemia,
using a moderate aerobic activity. When exercise timing and intensity are taken into account
blood glucose levels respond to the physical activity in a predictable and consistent manner.
Funding: This work received no specific funding.
Duality of interest: The author declares that there is no duality of interest associated with this
manuscript.
Author's contribution: The author is the sole contributor to this paper.
Table 1. Glucose response to moderate aerobic exercise at different timing
Exercise
Mode
Population Timing Intensity & duration Favorable Glycemic
Response
Pre-meal (21) T2D “before breakfast” 60-75% HRmax for 60
min
Hyperglycemia/day
reduced by 12-15%
(delayed effect)
Early
postprandial
(23)
T1D 15 min post-meal 65% VO2max for 30 min Hyper glycemia for the
meal reduced by one
third
Mid-
postprandial
(20)
T1D and
Healthy
30 min post-meal 55% VO2max for 45 min “. . . glycemia returned
rapidly to fasting
levels.”
Mid-
postprandial
(14)
T2D 45 min post-meal 53% VO2max for 45 min 4 h glucose-AUC for
the meal reduced by
50%
Mid-
postprandial
(4)
People with
metabolic
syndrome
60 min post-meal 60% VO2max for 45
min
3 h glucoseAUC for
breakfast reduced by
22%
Mid-
postprandial
(27)
T2D 90 min post-meal 50% Wmax for 30 min Hyperglycemia/day
reduced by 24%
Late
postprandial
(28)
T2D with and
w/o insulin
150 min post-meal 50% Wmax for 45 min Hyperglycemia/day
reduced by 33%
T2D- type 2 diabetes; T1D- type 1 diabetes; AUC-area under the curve
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... For decades, nutrient-exercise interactions have been studied in the field of sport and exercise science. Of interest, the importance of timing of acute exercise relative to the timing of meals has been associated with glycemic control in patients with type 2 diabetes mellitus (10)(11)(12). Changes at different tissue levels (e.g., skeletal muscle and adipose tissue) can potentially be clinically relevant to the optimization of therapeutic benefits of physical activity in type 2 diabetes (13), as exercise timing relative to meal ingestion is rarely considered in designing exercise training studies, especially in type 2 diabetes patients. Of interest, the responses to acute exercise in the fed or fasted state in type 2 diabetes revealed that postprandial exercise more consistently led to reductions in glycemia than prior-meal exercise (in particular when exercise was commenced 30-90 min postprandial). ...
... The role of feeding status on different aspects of glycemic control is currently under intense but relevant debate, especially in terms of optimizing prevention and treatment strategies for metabolic diseases (15). Acute exercise of moderate intensity in the fed state has been described to more consistently ameliorate glucose concentrations compared with fasted-state exercise in patients with type 2 diabetes (10,19,20). Of interest, the most optimal timing to perform exercise was suggested to be midpostprandial (i.e., 30-90 min postmeal) (10,14). ...
... Acute exercise of moderate intensity in the fed state has been described to more consistently ameliorate glucose concentrations compared with fasted-state exercise in patients with type 2 diabetes (10,19,20). Of interest, the most optimal timing to perform exercise was suggested to be midpostprandial (i.e., 30-90 min postmeal) (10,14). ...
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Introduction: This study examines the role of nutritional status during exercise training in patients with type 2 diabetes mellitus by investigating the effect of endurance-type exercise training in the fasted versus the fed state on clinical outcome measures, glycemic control, and skeletal muscle characteristics in male type 2 diabetes patients. Methods: Twenty-five male patients (glycated hemoglobin (HbA1c), 57 ± 3 mmol·mol (7.4% ± 0.3%)) participated in a randomized 12-wk supervised endurance-type exercise intervention, with exercise being performed in an overnight-fasted state (n = 13) or after consuming breakfast (n = 12). Patients were evaluated for glycemic control, blood lipid profiles, body composition and physical fitness, and skeletal muscle gene expression. Results: Exercise training was well tolerated without any incident of hypoglycemia. Exercise training significantly decreased whole-body fat mass (-1.6 kg) and increased high-density lipoprotein concentrations (+2 mg·dL), physical fitness (+1.7 mL·min·kg), and fat oxidation during exercise in both groups (PTIME < 0.05), with no between-group differences (PTIME × GROUP > 0.05). HbA1c concentrations significantly decreased after exercise training (PTIME < 0.001), with a significant greater reduction after consuming breakfast (-0.30% ± 0.06%) compared with fasted state (-0.08% ± 0.06%; mean difference, 0.21%; PTIME × GROUP = 0.016). No interaction effects were observed for skeletal muscle genes related to lipid metabolism or oxidative capacity. Conclusions: Endurance-type exercise training in the fasted or fed state do not differ in their efficacy to reduce fat mass, increase fat oxidation capacity, and increase cardiorespiratory fitness and high-density lipoprotein concentrations or their risk of hypoglycemia in male patients with type 2 diabetes. HbA1c seems to be improved more with exercise performed in the postprandial compared with the postabsorptive state.
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... For decades, nutrient-exercise interactions have been studied in the field of sport and exercise science. Of interest, the importance of timing of acute exercise relative to the timing of meals has been associated with glycemic control in patients with type 2 diabetes mellitus (10)(11)(12). Changes at different tissue levels (e.g., skeletal muscle and adipose tissue) can potentially be clinically relevant to the optimization of therapeutic benefits of physical activity in type 2 diabetes (13), as exercise timing relative to meal ingestion is rarely considered in designing exercise training studies, especially in type 2 diabetes patients. Of interest, the responses to acute exercise in the fed or fasted state in type 2 diabetes revealed that postprandial exercise more consistently led to reductions in glycemia than prior-meal exercise (in particular when exercise was commenced 30-90 min postprandial). ...
... The role of feeding status on different aspects of glycemic control is currently under intense but relevant debate, especially in terms of optimizing prevention and treatment strategies for metabolic diseases (15). Acute exercise of moderate intensity in the fed state has been described to more consistently ameliorate glucose concentrations compared with fasted-state exercise in patients with type 2 diabetes (10,19,20). Of interest, the most optimal timing to perform exercise was suggested to be midpostprandial (i.e., 30-90 min postmeal) (10,14). ...
... Acute exercise of moderate intensity in the fed state has been described to more consistently ameliorate glucose concentrations compared with fasted-state exercise in patients with type 2 diabetes (10,19,20). Of interest, the most optimal timing to perform exercise was suggested to be midpostprandial (i.e., 30-90 min postmeal) (10,14). ...
View
... Better meal composition improves PPG after breakfast (from 184 to 159 mg/dL) and after lunch (from 160 to141 mg/dL); TIR (from 99 to 100%), and mean glucose (from 127 to 117 mg/dL). (12,(27)(28)(29)(30)(31). If the goal is to blunt the post-meal glucose surge, an appropriate amount of glucose needs to be expended. ...
... Exogenous glucose being the main fuel for moderate post-meal activity, the resulting glucose tolerance is short-lived (32) and may not improve FBG (20). Post-meal exercise performed at the right time and of the right intensity is still quite valuable for day-to-day diabetes management (27)(28)(29)(30)(31). ...
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... There is general agreement among researchers that timely postmeal exercise lowers blood glucose levels in a variety of populations (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68)(69). However, postmeal exercise with a high energy expenditure may cause hyperglycemia (25,26) or hypoglycemia (36,37). ...
... Furthermore, with regard to exercise sequencing, resistance exercise followed by aerobic exercise is preferable to aerobic exercise followed by resistance exercise (79). The main benefit of starting postmeal exercise 30-60 minutes after meals is to blunt postmeal glucose surges (50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68). The risk of delayed hypoglycemia is minimal with moderate postmeal physical activities. ...
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... People with diabetes have poor glucose tolerance in the morning and evening (78). A morning walk, followed by a morning snack (15)(16)(17), every other day and combined short-duration RE and AE after bigger meals (65,(86)(87)(88)(89) would be ideal for diabetes self-management. I have been practicing these two exercise modalities, along with a healthy eating pattern, for >3 years with excellent results. ...
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... For people with or without type 2 diabetes, the glycaemic response to a single meal can be attenuated to a greater extent with post-versus pre-meal exercise, partly through a greater oxidation of the ingested carbohydrates (Poirier et al., 2000;Poirier et al., 2001). As such, it has been proposed that moderate-intensity physical activity could be undertaken between 30-to 120-min after carbohydrate-rich meals are consumed, to lower blood glucose excursions from that particular meal (Haxhi et al., 2012;Chacko, 2016). ...
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Full-text available
  • Jan 2021
Nutrition and exercise metabolism are vibrant physiological fields, yet at times it feels as if greater progress could be made by better integrating these disciplines. Exercise is advocated for improving metabolic health, in part by increasing peripheral insulin sensitivity and glycaemic control. However, when a modest-to-high carbohydrate load is consumed before and/or during each exercise bout within a training programme, increases in oral glucose insulin sensitivity can be blunted in both men of a healthy weight and those with overweight/obesity. Exercise training-induced adaptation in the energy sensing AMP-activated protein kinase (AMPK) and the insulin-sensitive glucose transporter GLUT4 protein levels are sensitive to pre-exercise feeding status in both healthy individuals and individuals classified as overweight or obese. Increased lipid oxidation may, in part, explain the enhanced adaptive responses to exercise training performed before (i.e. fasted-state exercise) versus after nutrient ingestion. Evidence in individuals with type 2 diabetes currently shows no effect of altering nutrient-exercise timing for measured markers of metabolic health, or greater reductions in glycated haemoglobin (HbA1c) concentrations with exercise performed after versus before nutrient provision. Since the metabolic inflexibility associated with type 2 diabetes diminishes differences in lipid oxidation between the fasted and fed states, it is plausible that pre-exercise feeding status does not alter adaptations to exercise when metabolic flexibility is already compromised. Current evidence suggests restricting carbohydrate intake before and during exercise can enhance some health benefits of exercise, but in order to establish clinical guidelines, further research is needed with hard outcomes and different populations.
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... Because exercise stimulates glucose uptake independently from insulin, it was recently proposed that the timing of the exercise bout in relation to a meal may be an important factor for exercise's optimal blood glucose lowering effect (32). In support of this, Colberg et al showed that postprandial walking was better for lowering the glycemic effect of dinner than pre-dinner exercise in individuals with T2D (33). ...
Current advances in our understanding of exercise as medicine in metabolic disease
Article
  • Apr 2019
Exercise is a powerful means to maintain health, prevent disease, and even act as medicine for a wide range of non-communicable diseases. The key effects by which exercise benefits our metabolic health include (i) events that occur during exercise and in the hours to days following exercise, and (ii) the adaptations that occur following long-term repeated exercise training. Here, we provide a contemporary overview of recent significant advances in our knowledge of exercise as medicine in metabolic disease with a focus on muscle glucose metabolism.
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Precision Exercise and Physical Activity for Diabetes
Chapter
  • Jan 2022
Exercise and physical activity are important tools in the management of both type 1 and type 2 diabetes due, in part, to their ability to decrease risk factors associated with diabetes-related complications and improve overall health. Like any other treatment, however, a great deal of interindividual and intraindividual variation exists in responses to different activity doses (type, timing, intensity, frequency, and duration). This chapter provides an overview of the factors that may influence both short- and long-term adaptation to exercise and physical activity in individuals with both type 1 and type 2 diabetes so that the right treatment, for the right person, at the right time can be combined in developing an appropriate exercise/physical activity prescription.KeywordsAerobic exerciseResistance exerciseHigh-intensity intermittent exerciseBlood glucoseInsulinA1c
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Modulation of Interloukin-1β (IL-1β ) , Tumor necrosis factor –α (TNF-α) and Interloukin-10 (IL-10 ) Genes Expression following Concurrent Training in Women with Type2 Diabetes
Article
Full-text available
  • Aug 2020
Abstract Background&Purpose: The purpose of this study was to investigate the effect of concurrent training on pre-inflammatory (IL-1β, TNF-α) and anti-inflammatory (IL-10) cytokines gene expression in women with type2 diabetes. Methodology: 18-patients (age30-38, >130 glycemic index) were selected, randomly, and divided into control (n=6) the concurrent training(diabetes, n=6) and the concurrent training (healthy, n=6) groups. The concurrent training protocol consisted of 3 sessions resistance training per week, 8sets with 80% one maximum repetition(3 80/8) and the endurance training preformed with 30- minutes running (3sets×10 minutes) on treadmill with 70-80 maximum heart rate(70-80 MHR), immediately. The leukocyte ,s IL-1β,TNF-α and IL-10genes expression determined by Real time-PCR technique. Quantitative expression of the cytokines gene was calculated using 2-ΔΔ CT method. The between groups differences in variables were determined by independent t-test (permutation test) through REST software and independent one-way anova. Results: The results showed that IL-1β,TNF-α mRNA genes expression reduced significantly after the concurrent training in both the training groups in comparison to control group (P<0/05). In addition, the results also showed that IL-10 mRNA gene expression was not expressed in leukocytes after the concurrent training in both training groups in comparison to the control group (P>0/05). Conclusion: In conclusion , the results suggest that the concurrent training modulate IL-1β and TNF-α mRNA genes expression significantly in diabetic women but could not change IL-10 genes expression. This type of exercise training seems to be more effective in reducing the expression of pro-inflammatory cytokines than in enhancing anti-inflammatory cytokines. Keywords: Type2 Diabetes; Concurrent Training; IL-1β; TNF-α ; IL-10
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Exercising Tactically for Taming Postmeal Glucose Surges
Article
Full-text available
  • Mar 2016
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% V O 2 m a x ) 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% V O 2 m a x ) 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.
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Targeting specific interstitial glycemic parameters with high-intensity interval exercise and fasted-state exercise in type 2 diabetes
Article
Full-text available
  • Jan 2016
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.
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The effects of high-intensity interval training on glucose regulation and insulin resistance: A meta-analysis
Article
Full-text available
The aim of this meta-analysis was to quantify the effects of high-intensity interval training (HIIT) on markers of glucose regulation and insulin resistance compared to control conditions (CON) or continuous training (CT). Databases were searched for HIIT interventions based on the inclusion criteria: training ≥2 weeks, adult participants, and outcome measurements that included insulin resistance, fasting glucose, HbA1c or fasting insulin. Dual interventions and participants with type 1 diabetes were excluded. Fifty studies were included. There was a reduction in insulin resistance following HIIT compared to both CON & CT, (HIIT vs. CON: standardised mean difference (SMD)=-0.49, confidence intervals (CI) -0.87 to -0.12, p=0.009; CT: SMD=-0.35, -0.68 to -0.02, p=0.036). Compared to CON, HbA1c decreased by 0.19% (-0.36 to -0.03, p=0.021) and body weight decreased by 1.3kg (-1.9 to -0.7, p<0.001). There were no statistically significant differences between groups in other outcomes overall. However, participants with or at risk of Type 2 diabetes experienced reductions in fasting glucose (-0.92mmol.L-1, -1.22 to -0.62, p<0.001) compared to CON. HIIT appears effective at improving metabolic health, particularly in those at risk of or with Type 2 diabetes. Larger randomised controlled trials of longer duration than those included in this meta-analysis are required to confirm these results.
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Effects of a Pre-Exercise Meal on Plasma Growth Hormone Response and Fat Oxidation during Walking
Article
Full-text available
  • Sep 2013
The purpose of this study was to determine the effects of a pre-exercise meal on the plasma human growth hormone (hGH) response and fat oxidation during walking. Subjects (n=8) were randomly provided with either 1 g/kg body weight of glucose in 200 mL water (CHO) or 200 mL water alone (CON) 30 min prior to exercise and subsequently walked on a treadmill at 50% of VO2max for 60 min. Plasma hGH concentrations were significantly higher in subjects who received CHO compared to those who received CON at 15 and 30 min. The fat oxidation rate in the CHO was significantly lower than the CON while walking for 5~15, 25~35 and 45~55 min. Plasma FFA levels were also significantly lower in the CHO compared to the CON at 30, 45 and 60 min. Plasma glucose levels in the CHO were significantly lower while plasma insulin levels were significantly higher than in the CON at 15 and 30 min. Therefore, the results of this study suggest that the elevation of plasma hGH levels due to the intake of a pre-exercise meal may not be strongly related to fat oxidation and plasma free fatty acid (FFA) levels during low-intensity exercise.
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Effect of Moderate-Intensity Exercise Versus Activities of Daily Living on 24-Hour Blood Glucose Homeostasis in Male Patients With Type 2 Diabetes
Article
Full-text available
  • Sep 2013
OBJECTIVE To investigate the impact of activities of daily living (ADL) versus moderate-intensity endurance-type exercise on 24-h glycemic control in patients with type 2 diabetes.RESEARCH DESIGN AND METHODS Twenty males with type 2 diabetes participated in a randomized crossover study consisting of three experimental periods of 3 days each. Subjects were studied under sedentary control conditions, and under conditions in which prolonged sedentary time was reduced either by three 15-min bouts of ADL (postmeal strolling, ∼3 METs) or by a single 45-min bout of moderate-intensity endurance-type exercise (∼6 METs). Blood glucose concentrations were assessed by continuous glucose monitoring, and plasma insulin concentrations were determined in frequently sampled venous blood samples.RESULTSHyperglycemia (glucose >10 mmol/L) was experienced for 6 h 51 min ±1 h 4 min per day during the sedentary control condition and was significantly reduced by exercise (4 h 47 min ± 1 h 2 min; P < 0.001), but not by ADL (6 h 2 min ± 1 h 16 min; P = 0.67). The cumulative glucose incremental areas under the curve (AUCs) of breakfast, lunch, and dinner were, respectively, 35 ± 5% (P < 0.001) and 17 ± 6% (P < 0.05) lower during the exercise and ADL conditions compared with the sedentary condition. The insulin incremental AUCs were, respectively, 33 ± 4% (P < 0.001) and 17 ± 5% (P < 0.05) lower during the exercise and ADL conditions compared with the sedentary condition.CONCLUSIONS When matched for total duration, moderate-intensity endurance-type exercise represents a more effective strategy to improve daily blood glucose homeostasis than repeated bouts of ADL. Nevertheless, the introduction of repeated bouts of ADL during prolonged sedentary behavior forms a valuable strategy to improve postprandial glucose handling in patients with type 2 diabetes.
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Effect of aerobic exercise intensity on glycemic control in type 2 diabetes: a meta-analysis of head-to-head randomized trials
Article
  • Jun 2016
Aims To conduct a meta-analysis of head-to-head trials comparing aerobic exercise training of different intensities on glycemic control in type 2 diabetes. Methods Databases, including MEDLINE and EMBASE, were searched up to January 2016. Randomized trials of at least 12 weeks in duration that compared two exercise interventions of different intensities were identified. Two reviewers independently extracted data from eligible trials. Using fixed effect model, weighted mean differences (WMD) between different exercise intensities were calculated for changes in glycated hemoglobin (HbA1c) and secondary outcomes, such as fasting glucose and fasting insulin. Results Eight studies with a total of 235 participants were eligible. The exercise interventions lasted from 12 weeks to 6 months. The prescribed exercise intensities varied among studies. Four studies utilized vigorous exercise intensities for short durations by performing interval training. Overall, higher-intensity exercise resulted in a greater reduction in HbA1c compared to lower-intensity exercise (WMD = −0.22 %; 95 % confidence interval [−0.38, −0.06]; or −2.4 mmol/mol [−4.15, −0.66], I 2 = 0). Adherence to exercise and proportion of dropouts did not differ within trials. No adverse events were reported in these small trials with selected inclusion criteria. Conclusions Although our meta-analysis had a limited sample size, increasing exercise intensity safely accentuated reductions in HbA1c in some people with type 2 diabetes. Different approaches have been used to increase exercise intensity (i.e., some used interval training, whereas others used higher-intensity continuous exercise). However, at this time, it is unclear which form, if any, leads to the most favorable results.
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Postdinner resistance exercise improves postprandial risk factors more effectively than predinner resistance exercise in patients with type 2 diabetes
Article
  • Dec 2014
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 post-dinner 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) pre-dinner RE (RE→M), and 3) post-dinner 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, FFA, and beta-cell function (mathematical modeling) were measured to determine if these factors were related to changes in glucose and TAG. The TAG incremental-AUC (iAUC) was ~92% lower (P≤0.02) during M→RE compared to NoRE and RE→M, an effect due in part to lower VLDL-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 to NoRE, with no difference between RE trials. RE→M and M→RE reduced the insulin iAUC by 35% and 48%, respectively, compared to NoRE (P<0.01). The GLP-1 iAUC was ~50% lower (P≤0.02) during M→RE compared to NoRE and RE→M. Given that pre-dinner RE only improves postprandial glucose concentrations, whereas post-dinner RE improves both postprandial glucose and TAG concentrations, post-dinner RE may lower the risk of cardiovascular disease more effectively. Copyright © 2014, Journal of Applied Physiology.
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'Exercise snacks' before meals: A novel strategy to improve glycaemic control in individuals with insulin resistance
Article
The aim of this study was to investigate whether small doses of intense exercise before each main meal ('exercise snacks') would result in better blood glucose control than a single bout of prolonged, continuous, moderate-intensity exercise in individuals with insulin resistance. Nine individuals completed three exercise interventions in randomised order. Measures were recorded across 3 days with exercise performed on the middle day, as either: (1) traditional continuous exercise (CONT), comprising 30 min moderate-intensity (60% of maximal heart rate [HRmax]) incline walking before dinner; (2) exercise snacking (ES), consisting of 6 × 1 min intense (90% HRmax) incline walking intervals 30 min before each meal; or (3) composite exercise snacking (CES), encompassing 6 × 1 min intervals alternating between walking and resistance-based exercise, 30 min before meals. Meal timing and composition were controlled within participants for exercise interventions. ES attenuated mean 3 h postprandial glucose concentration following breakfast (by 1.4 ± 1.5 mmol/l, p = 0.02) but not lunch (0.4 ± 1.0 mmol/l, p = 0.22), and was more effective than CONT following dinner (0.7 ± 1.5 mmol/l below CONT; p = 0.04). ES also reduced 24 h mean glucose concentration by 0.7 ± 0.6 mmol/l (p = 0.01) and this reduction persisted for the subsequent 24 h (lower by 0.6 ± 0.4 mmol/l vs CONT, relative to their baselines; p = 0.01). CES was just as effective as ES (p > 0.05 for all glycaemic variables) at improving glycaemic control. Dosing exercise as brief, intense 'exercise snacks' before main meals is a time-efficient and effective approach to improve glycaemic control in individuals with insulin resistance.
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Vigorous Intensity Exercise for Glycemic Control in Patients with Type 1 Diabetes
Article
  • Dec 2013
Regular physical activity has substantial health benefits in persons with type 1 diabetes, including reduced risk of complications and cardiovascular mortality as well as improved self-rated quality of life. Despite these benefits, individuals with type 1 diabetes are often less active than their peers without diabetes. When factors such as time constraints, work pressure and environmental conditions are often cited as barriers to physical activity in the general population, 2 additional major factors may also explain the low rates of physical activity in young people with type 1 diabetes: (1) fear of hypoglycemia both during and after (particularly overnight) exercise and (2) a lack of empiric evidence for the efficacy of physical activity for achieving optimal glycemic control. A number of acute exercise trials recently showed that the inclusion of vigorous intensity physical activity in conventional moderate intensity (i.e. walking and light cycling) exercise sessions may overcome these barriers. No studies have tested the efficacy of high-intensity physical activity on glycemic control (A1C) or post-exercise hypoglycemia in a randomized controlled trial. This article summarizes the literature related to the role of physical activity for the management of blood glucose levels in individuals with type 1 diabetes and provides a rationale for the need of a randomized controlled trial examining the effects of vigorous-intensity physical activity on blood glucose control.
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One Bout of Exercise Alters Free-Living Postprandial Glycemia in Type 2 Diabetes
Article
  • Jul 2013
Elevated postprandial glycemic excursions (PPG) are significant risk factors for cardiovascular disease in type 2 diabetes patients. Here we tested if and for how many meals a single bout of exercise would reduce PPG responses to subsequent meals in type 2 diabetes (T2D) patients using continuous glucose monitors (CGMS). We recruited 9 sedentary (<30 minutes/week of exercise) individuals with T2D (BMI: 36.0 ± 1.1 kg/m; age 60.3 ± 1.0 years; HbA1c: 6.3 ± 0.2 %). The subjects consumed a eucaloric diet (51% carbohydrate, 31% fat, 18% protein) consisting of 3 meals, identical in composition, over a 2-day period while wearing CGMS in two different conditions (exercise (EX; one 60 minute bout at 60-75% of heart rate reserve performed prior to breakfast) vs. a sedentary (SED) condition). We quantified 24-h average glucose, PPG-AUC (4 h glucose AUC following meals) and PPG-2 h (2 hour post-prandial glucose). EX significantly reduced average [glucose] during the first 24 hour period (p=0.03). EX caused a reduction in PPG-AUC (p=0.02) for all of the meals over the two days (main effect between conditions). Comparison between the EX and SED conditions at each meal revealed that EX reduced PPG-AUC following the second meal of day 1 (lunch) (p=0.04). PPG-2 h was not significantly different between EX and SED. Although a single EX bout does lower 24-h average [glucose], it only significantly lowered PPG-AUC at the second meal following the bout suggesting that daily exercise may be needed to most effectively improve PPG at the advent of exercise training in T2D patients.
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