Abnormal glucoregulation during exercise in type II (non-insulin-dependent) diabetes

Effect of Chronic Exercise Training on Blood Lactate Metabolism Among Patients With Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis

Purpose: To assess the effect of chronic exercise training on blood lactate metabolism at rest (i.e., basal lactate concentrations) and during exercise (i.e., blood lactate concentration at a fixed load, load at a fixed blood lactate concentration, and load at the individual blood lactate threshold) among patients with type 2 diabetes mellitus (T2DM). Methods: PubMed (MedLine), Embase, Web of Science, and Scopus were searched. Randomized controlled trials, non-randomized controlled trials, and case-control studies using chronic exercise training (i.e., 4 weeks) and that assessed blood lactate concentrations at rest and during exercise in T2DM patients were included. Results: Thirteen studies were eligible for the systematic review, while 12 studies with 312 participants were included into the meta-analysis. In the pre-to-post intervention meta-analysis, chronic exercise training had no significant effect on changes in basal blood lactate concentrations (standardized mean difference (SMD) = -0.20; 95% CI, -0.55 to 0.16; p = 0.28), and the results were similar when comparing the effect of intervention and control groups. Furthermore, blood lactate concentration at a fixed load significantly decreased (SMD = -0.73; 95% CI, -1.17 to -0.29; p = 0.001), while load at a fixed blood lactate concentration increased (SMD = 0.40; 95% CI, 0.07 to 0.72; p = 0.02) after chronic exercise training. No change was observed in load at the individual blood lactate threshold (SMD = 0.28; 95% CI, -0.14 to 0.71; p = 0.20). Conclusion: Chronic exercise training does not statistically affect basal blood lactate concentrations; however, it may decrease the blood lactate concentrations during exercise, indicating improvements of physical performance capacity which is beneficial for T2DM patients' health in general. Why chronic exercise training did not affect basal blood lactate concentrations needs further investigation.

Cardiovagal modulation and efficacy of aerobic exercise training in obese individuals

Type 2 diabetes (T2D) is associated with poor exercise tolerance and peak aerobic capacity (V˙O2peak) even when compared to obese nondiabetic peers. Exercise training studies have demonstrated improvements in V˙O2peak among patients with T2D, yet there is a large amount of variability in this response. Recent evidence suggests that cardiac autonomic modulation may be an important factor when considering improvements in aerobic capacity.

PURPOSE

This study aimed to determine the effects of a 16-wk aerobic exercise program on V˙O2peak in obese individuals, with and without T2D, who were classified as having either high or low cardiovagal modulation (HCVM or LCVM) at baseline.

METHODS

Obese individuals (38 women and 19 men; body mass index = 36.1 kg·m(-2)) were studied in the fasted state. ECG recordings were obtained while seated for 3 min, before and after 4 months of exercise training (4 d·wk(-1), 65% V˙O(2peak)). The ECG recording was analyzed for HR variability in the spectral domain. Groups were split on a marker of CVM (normalized high frequency (HFnu)) at the 50th percentile, as either HCVM or LCVM.

RESULTS

V˙O(2peak) only increased with exercise training among those classified as having HCVM, regardless of diabetes status (T2D: HCVM = 20.3-22.5 mL·kg(-1)min(-1), LCVM = 24.3-25.0 mL·kg(-1)min(-1); obese nondiabetics: HCVM = 24.5-26.3 mL·kg(-1)min(-1), LCVM = 23.1-23.7 mL·kg(-1)min(-1)) (P < 0.05). No change in V˙O(2peak) was observed for the LCVM group. Changes in weight do not explain the change in V˙O(2peak) among the HCVM group. Glucose tolerance only improved among the LCVM group with T2D.

CONCLUSIONS

Obese individuals, with or without T2D, when classified as having relatively HCVM before exercise training, have a greater propensity to improve V˙O(2peak) after a 16-wk aerobic training program.

Type 2 diabetes mellitus and exercise impairment

Limitations in physical fitness, a consistent finding in individuals with both type I and type 2 diabetes mellitus, correlate strongly with cardiovascular and all-cause mortality. These limitations may significantly contribute to the persistent excess cardiovascular mortality affecting this group. Exercise impairments in VO2 peak and VO2 kinetics manifest early on in diabetes, even with good glycemic control and in the absence of clinically apparent complications. Subclinical cardiac dysfunction is often present but does not fully explain the observed defect in exercise capacity in persons with diabetes. In part, the cardiac limitations are secondary to decreased perfusion with exercise challenge. This is a reversible defect. Similarly, in the skeletal muscle, impairments in nutritive blood flow correlate with slowed (or inefficient) exercise kinetics and decreased exercise capacity. Several correlations highlight the likelihood of endothelial-specific impairments as mediators of exercise dysfunction in diabetes, including insulin resistance, endothelial dysfunction, decreased myocardial perfusion, slowed tissue hemoglobin oxygen saturation, and impairment in mitochondrial function. Both exercise training and therapies targeted at improving insulin sensitivity and endothelial function improve physical fitness in subjects with type 2 diabetes. Optimization of exercise functions in people with diabetes has implications for diabetes prevention and reductions in mortality risk. Understanding the molecular details of endothelial dysfunction in diabetes may provide specific therapeutic targets for the remediation of this defect. Rat models to test this hypothesis are under study.

Exercise attenuates the premature cardiovascular aging effects of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2D) is an example of a disease process that results in decrements in function additional to those imposed by the inexorable 'primary aging' process. These decrements due to disease, rather than primary aging, can be termed 'secondary aging', and include the premature development (as early as adolescence) of asymptomatic preclinical cardiovascular abnormalities (e.g. endothelial dysfunction, arterial stiffness, diastolic dysfunction), as well as impaired exercise performance. These abnormalities are important, as they are associated with greater cardiovascular morbidity and mortality in people with and without T2D. A better understanding of the pathophysiology of secondary cardiovascular aging in people with T2D is warranted, and an evaluation of the benefits of existing treatments for these abnormalities is useful (e.g. exercise training). The focus of this review is to discuss the data relevant to the following key postulates: (a) T2D causes premature cardiovascular aging; (b) in contrast to primary cardiovascular aging, the premature cardiovascular aging of T2D may be modifiable with exercise. The exercise-focused perspective for this review is appropriate because impairments in exercise performance are markers of premature cardiovascular aging in T2D, and also because exercise training shows promise to attenuate some aspects of cardiovascular aging during the preclinical stage.

Comparison of aerobic exercise capacity and muscle strength in overweight women with and without polycystic ovary syndrome

OBJECTIVE

To assess maximal aerobic capacity (VO2max) and muscle strength in overweight and obese women with polycystic ovary syndrome (PCOS) and determine their relationship with metabolic and hormonal factors.

DESIGN

Cross-sectional study.

SETTING

Clinical Research Unit.

POPULATION

Overweight and obese women with PCOS (n = 10) and age-and weight-matched healthy controls (n = 16).

METHODS

VO2max was measured during an incremental treadmill test and maximal isometric (ImS) and isokinetic knee extensor strength (IkS) (120 degrees/second) were assessed by isokinetic dynamometry.

MAIN OUTCOME MEASURES

VO2max, ImS, IkS, waist circumference, blood lipids, glucose, insulin, insulin resistance (homeostatic model assessment [HOMA2]), C-reactive protein (CRP), hormonal profile.

RESULTS

PCOS women had higher levels of testosterone and free testosterone (P < or = 0.05), but there were no significant differences in any cardiovascular disease (CVD) risk markers between the groups. VO2max was similar in women with PCOS and healthy controls (PCOS 26.0 +/- 4.1 ml/kg/minute, controls 25.7 +/- 3.8 ml/kg/minute; P = 0.90), as was ImS (PCOS 1.50 +/- 0.54 Nm/kg, controls 1.50 +/- 0.47 Nm/kg; P = 0.96) and IkS (PCOS 1.04 +/- 0.32 Nm/kg, controls 1.16 +/- 0.23 Nm/kg; P = 0.32). VO2max was inversely related to waist circumference, insulin, HOMA2 and CRP. Waist circumference was inversely associated with ImS and IkS. No significant associations between exercise parameters and hormonal variables were identified.

CONCLUSIONS

Compared to age- and weight-matched healthy overweight and obese women with similar insulin resistance and CVD risk profiles, women with PCOS had similar aerobic capacity and muscle strength. This suggests PCOS, at least in the absence of an adverse metabolic profile is unlikely to limit physical function. Larger studies examining the effects of PCOS on exercise tolerance in a diverse range of PCOS phenotypes is required.

Cardiovascular, metabolic and hormonal responses to the progressive exercise performed to exhaustion in patients with type 2 diabetes treated with metformin or glyburide

OBJECTIVES

To evaluate the effects of Metformin and Glyburide on cardiovascular, metabolic and hormonal parameters during progressive exercise performed to exhaustion in the post-prandial state in women with type 2 diabetes (T2DM).

DESIGN AND METHODS

Ten T2DM patients treated with Metformin (M group), 10 with Glyburide (G group) and 10 age-paired healthy subjects exercised on a bicycle ergometer up to exercise peak. Cardiovascular and blood metabolic and hormonal parameters were measured at times -60 min, 0 min, exercise end, and at 10 and 20 minutes of recovery phase. Thirty minutes before the exercise, a standard breakfast was provided to all participants. The diabetic patients took Metformin or Glyburide before or with meal.

RESULTS

Peak oxygen uptake (VO(2)) was lower in patients with diabetes. Plasma glucose levels remained unchanged, but were higher in both diabetic groups. Patients with diabetes also presented lower insulin levels after meals and higher glucagon levels at exercise peak than C group. Serum cortisol levels were higher in G than M group at exercise end and recovery phase. Lactate levels were higher in M than G group at fasting and in C group at exercise peak. Nor epinephrine, GH and FFA responses were similar in all 3 groups.

CONCLUSION

Progressive exercise performed to exhaustion, in the post-prandial state did not worsen glucose control during and after exercise. The administration of the usual dose of Glyburide or Metformin to T2DM patients did not influence the cardiovascular, metabolic and hormonal response to exercise.

The effects of metformin and glibenclamide on glucose metabolism, counter-regulatory hormones and cardiovascular responses in women with Type 2 diabetes during exercise of moderate intensity

AIMS

To compare the effects of metformin and glibenclamide on cardiovascular, metabolic and hormonal parameters during exercise of moderate intensity performed in the postprandial state, in women with Type 2 diabetes.

METHODS

Ten patients treated with metformin, 10 with glibenclamide and 10 control subjects (C) exercised on a bicycle ergometer at 50% of oxygen uptake (VO(2)) peak for 45 min. Cardiovascular, blood metabolic and hormonal parameters were determined at times -60 min (fasting), 0, +15, +30, +45 min (exercise) and at +60, +90 min (recovery). Thirty minutes prior to exercise, participants consumed a standard breakfast. Patients with diabetes took metformin or glibenclamide before the meal.

RESULTS

Systolic and diastolic blood pressure and plasma glucose were higher in both diabetic groups, for the whole experiment. Blood glucose did not change during exercise in the three groups and increased at recovery only in the control group. Plasma glucagon concentrations at the end of exercise and recovery, and plasma lactate concentrations at recovery were higher in the metformin group. Insulin, noradrenaline, growth hormone, cortisol and free fatty acid responses were similar in all three groups.

CONCLUSIONS

Our results suggest that the usual dose of glibenclamide and metformin can be taken safely before postprandial exercise of moderate intensity without affecting cardiovascular, metabolic and hormonal responses. However, after exercise, glibenclamide and metformin prevent the normal rise in blood glucose and metformin delays the fall in plasma lactate concentrations.

Influence of glycemic control on pulmonary function and heart rate in response to exercise in subjects with type 2 diabetes mellitus

Conflicting results exist regarding the impact of glycemic control on peak oxygen uptake (VO2peak) in subjects with type 2 diabetes mellitus. The influence of glycemic control on submaximal oxygen uptake (VO2) in these subjects is unknown. The aim of this study was to evaluate the impact of fasting blood glucose (FBG) (short-term glycemic control) and glycated hemoglobin (HbA1c) (long-term glycemic control) on submaximal VO2 and VO2peak during exercise in subjects with type 2 diabetes mellitus without cardiovascular disease. FBG and HbA1c levels and exercise tolerance in 30 sedentary men with type 2 diabetes mellitus treated with oral hypoglycemic agents and/or diet were evaluated. VO2, carbon dioxide production (VCO2), heart rate, pulmonary ventilation (VE), and the respiratory exchange ratio (RER) were measured throughout the exercise protocol. Subjects were separated into 2 groups of the same age, weight, and body mass index according to median FBG and HbA1c levels (6.5 mmol/L and 6.1%, respectively). Per protocol design, there was a significant difference in FBG and HbA1c levels (P < .001), but not for age, weight, or body mass index. There was no significant difference in peak exercise parameters between the 2 groups according to median FBG or median HbA1c levels. However, the subjects with elevated HbA1c level had lower submaximal V e throughout the exercise protocol (P < .03), and the subjects with elevated FBG concentration had a blunted heart rate pattern during submaximal exercise (P < .03). Although relatively small abnormalities in the control of glycemia do not affect VO2peak in subjects with type 2 diabetes mellitus without cardiovascular disease, they may influence pulmonary function and the chronotropic response during submaximal exercise in these subjects.

The effect of exercise on regional adipose tissue and splanchnic lipid metabolism in overweight type 2 diabetic subjects

AIMS/HYPOTHESIS

To test the hypothesis that adipose tissue lipolysis is enhanced in patients with Type 2 diabetes mellitus, we examined the effect of exercise on regional adipose tissue lipolysis and fatty acid mobilisation and measured the acute effects of exercise on the co-ordination of adipose tissue and splanchnic lipid metabolism.

METHODS

Abdominal, subcutaneous adipose tissue and splanchnic lipid metabolism were studied by conducting measurements of arterio-venous concentrations and regional blood flow in six overweight Type 2 diabetic subjects before, during and after exercise.

RESULTS

Exercise induced an increase in adipose tissue lipolysis and fatty acid release. However, the increase in adipose tissue blood flow was small, limiting fatty acid mobilisation from this tissue. Some of the fatty acids were released in excess in the post-exercise phase. The splanchnic fatty acid uptake was unchanged during the experiment but splanchnic ketogenesis increased in the post-exercise phase. The arterial glucose concentration decreased during exercise and continued to decrease afterwards, indicating an imbalance between splanchnic glucose production and whole-body glucose utilisation.

CONCLUSIONS/INTERPRETATION

Regional subcutaneous, abdominal adipose tissue lipolysis is no higher in patients with Type 2 diabetes than in young, healthy subjects. Exercise stimulates adipose tissue lipolysis, but due to an insufficient increase in blood flow, a high fraction of the fatty acids liberated by lipolysis cannot be released to the blood. Splanchnic glucose release is smaller than whole-body glucose utilisation during exercise and post-exercise recovery.

Novel actions of thiazolidinediones on vascular function and exercise capacity

The endothelium is the first line of defense for maintaining normal vascular function in the vessel wall; however, the endothelium is sensitive to metabolic stress. In patients with insulin resistance or type 2 diabetes mellitus, a set of metabolic insults--namely high plasma levels of glucose and free fatty acids, increased inflammation, dyslipidemia, and hypertension--cause endothelial dysfunction and a transition from an antiatherogenic endothelium to a proatherogenic endothelium. Disruption of endothelial function leads to activation of platelets and macrophages, increased thrombotic potential, transition of macrophages to foam cells, stimulation of cytokine secretion, and proliferation of vascular smooth muscle cells. Insulin-sensitizing agents, such as the thiazolidinediones (TZDs), improve flow-mediated vasodilation, decrease macrophage and smooth muscle cell activation, proliferation, and migration, and decrease plaque formation. The TZDs exert multifaceted effects on the vasculature by regulating the expression of transcription factors and orchestrating whole-gene programs that restore vascular physiology to the healthy state. Exercise training and increased levels of habitual physical activity have therapeutic benefit in terms of both preventing and treating insulin resistance and diabetes. However, this benefit of exercise training and increased physical activity is complicated by the fact that individuals with insulin resistance or type 2 diabetes have decreased maximal exercise capacity or maximal oxygen consumption and have slower oxygen uptake kinetics at the beginning of exercise. Both of these abnormalities contribute to the decreased levels of habitual physical activity observed in patients with diabetes. Preliminary data suggest that TZDs improve measures of cardiac function and exercise capacity, and investigators are assessing the impact of treatment with rosiglitazone on exercise capacity in an ongoing clinical trial.

Prior meal enhances the plasma glucose lowering effect of exercise in type 2 diabetes

PURPOSE

To compare the changes in plasma glucose and insulin levels in response to 1 h of exercise performed at 60% of VO(2peak) either in the fasted state or 2 h after a standardized breakfast in subjects with type 2 diabetes.

METHODS

Ten sedentary men with type 2 diabetes treated with oral agents and not under strict metabolic control were tested on two occasions (fasted and fed state) in a random order at a 1-wk interval.

RESULTS

Plasma glucose was slightly but not significantly higher at the beginning of exercise performed in the fed state versus the fasted state (12.4 +/- 1.3 vs 11.1 +/- 1.1 mmol x L(-1) respectively; mean +/- SE, P = 0.06). However, after exercise, plasma glucose levels were much lower in the fed state (7.6 +/- 1.1 mmol x L(-1)) compared with the fasted state (10.0 +/- 1.0 mmol x L(-1); P = 0.009). Insulin levels were higher at the beginning of the exercise bout performed in the fed state (177 +/- 26 vs 108 +/- 19 pmol x L(-1); P < 0.05) and during exercise. Similar respiratory exchange ratio at identical workload indicated that the difference in glycemic response was not due to differences in whole body substrate utilization. Plasma concentrations of free fatty acids, glucagon, epinephrine, and norepinephrine were also similar during both experiments.

CONCLUSIONS

One hour of aerobic exercise has a minimal impact on plasma glucose level when performed in fasted moderately hyperglycemic men with type 2 diabetes but induces an important decrease in plasma glucose level when performed 2 h after breakfast. Because glucose utilization increased similarly during exercise in both conditions, the higher insulin levels after the meal might have blunted glucose production, creating an imbalance between total glucose production and total peripheral utilization in the fed state in contrast to the fasted state.

The acute versus the chronic response to exercise

PURPOSE

There is strong and consistent evidence that a single exercise session can acutely reduce triglycerides and increase high-density lipoprotein (HDL) cholesterol (HDL-C), reduce blood pressure, and improve insulin sensitivity and glucose homeostasis. Such observations suggest that at least some of the effects on atherosclerotic cardiovascular disease (ASCVD) risk factors attributed to exercise training may be the result of recent exercise.

RESULTS

These acute and chronic exercise effects cannot be considered in isolation. Exercise training increases the capacity for exercise, thereby permitting more vigorous and/or more prolonged individual exercise sessions and a more significant acute effect. The intensity, duration, and energy expenditure required to produce these acute exercise effects are not clearly defined. The acute effect of exercise on triglycerides and HDL-C appears to increase with overall energy expenditure possibly because the effect maybe mediated by reductions in intramuscular triglycerides. Prolonged exercise appears necessary for an acute effect of exercise on low-density lipoprotein (LDL) cholesterol (LDL-C) levels. The acute effect of exercise on blood pressure is a low threshold phenomenon and has been observed after energy expenditures requiring only 40% maximal capacity. The acute effect of exercise on glucose metabolism appears to require exercise near 70% maximal, but this issue has not been carefully examined.

CONCLUSIONS

Exercise has definite acute effects on blood lipids, blood pressure, and glucose homeostasis. Exercise also has acute effects on other factors related to atherosclerosis such as immunological function, vascular reactivity, and hemostasis. Considerable additional research is required to define the threshold of exercise required to produce these putatively beneficial effects.

Substrate utilization and glucose turnover during exercise of varying intensities in individuals with NIDDM

PURPOSE

This investigation was undertaken to examine substrate utilization and glucose turnover during exercise of varying intensities in NIDDM patients.

METHODS

Six male NIDDM patients (N) and six male controls (C) of similar age, body weight, % body fat, and VO2peak were studied in two experimental sessions administered in a randomized counterbalanced order. During each session the subjects cycled at a power output corresponding to 50% of VO2peak or 70% of VO2peak. Duration of exercise was adjusted so that energy expenditure (EE) was equal in both the 50% and 70% trials. Isotope infusion technique and indirect calorimetry were used to assess substrate utilization and glucose turnover during exercise.

RESULTS

Rates of carbohydrate (CHO) and lipid oxidation increased (P < 0.05) during both the 50% and 70% trials. Rates of CHO oxidation were greater (P < 0.05) during the 70% than during the 50% trial. However, rates of lipid oxidation were similar in the two trials. No differences in rates of CHO and lipid oxidation were observed in N and C. Rates of hepatic glucose production (Ra) and plasma glucose utilization (Rd) increased (P < 0.05) during exercise, and the increases were similar in the 50% and 70% trials. Ra did not differ between N and C. However, Rd was greater (P < 0.05) in N than in C. Plasma glucose concentration decreased (P < 0.05) in N, with the decrease being similar in the 50% and 70% trials. In contrast, plasma glucose concentration remained unchanged during both the 50% and 70% trials in C.

CONCLUSIONS

Exercise results in a greater increase in plasma glucose utilization in patients with NIDDM compared with that in normal individuals, and this increase mediates the decline in plasma glucose concentrations in patients with NIDDM. Under isocaloric conditions, the changes in plasma glucose utilization and plasma glucose concentrations are similar during exercise of varying intensities. Despite a greater glucose utilization, carbohydrate and fat oxidation are similar in the two groups and their relations to exercise intensity are not altered by NIDDM.

Lifestyle modifications for diabetes management

Nutrition therapy and physical activity can assist persons with diabetes to achieve metabolic goals. Several lifestyle strategies can be used. Monitoring metabolic parameters, including blood glucose, glycated hemoglobin, lipids, blood pressure, and body weight, as well as assessing for quality of life are essential to determine whether treatment goals are being achieved by lifestyle changes. If not, adjustments in the overall management plan need to be made.

Utilization of glycogen but not plasma glucose is reduced in individuals with NIDDM during mild-intensity exercise

To test the hypothesis that substrate utilization during mild-intensity exercise differs in non-insulin-dependent diabetes mellitus (NIDDM) compared with nondiabetic subjects, seven lean healthy subjects (L), seven obese healthy subjects (O), and seven individuals with NIDDM were studied during 40 min of mild-intensity cycling (40% of peak O2 uptake). Systemic utilization of plasma glucose (Glc Rd) was determined by using isotope dilution methods. Gas exchange was measured to determine rates of carbohydrate (CHO) and lipid oxidation. During exercise, when CHO oxidation was greater than Glc Rd, the net oxidation of glycogen was calculated as the difference: CHO oxidation - Glc Rd. During mild-intensity cycling, the respiratory exchange ratio was similar across groups (0.87 +/- 0.02, 0.85 +/- 0.02, and 0.86 +/- 0.01 in L, O, and NIDDM subjects, respectively), and CHO oxidation accounted for one-half of total energy expenditure during exercise. Glc Rd increased during exercise and was greatest in subjects with NIDDM (3.0 +/- 0.2, 2.9 +/- 0.2, and 4.5 +/- 0.4 ml.kg-1.min-1 in L, O, and NIDDM subjects, respectively, P < 0.05), yet Glc Rd was less than CHO oxidation during exercise, indicating net oxidation of glycogen. Glycogen oxidation was greater in L and O than in NIDDM subjects (3.4 +/- 1.0, 2.5 +/- 0.9, and 1.7 +/- 0.8 ml.kg-1.min-1; P < 0.05). In summary, during mild-intensity exercise, NIDDM subjects have an increased Glc Rd and a decreased oxidation of muscle glycogen.

Splanchnic and muscle metabolism during exercise in NIDDM patients

To characterize splanchnic and muscle metabolism during exercise in non-insulin-dependent diabetes mellitus (NIDDM), eight male nonobese patients and seven healthy control subjects (CON) were studied during 40 min of bicycle exercise at 60% of maximal oxygen uptake. Biopsies were obtained from the quadriceps femoris muscle at rest and immediately after exercise. Arterial glucose concentration in NIDDM had declined by 10% (P < 0.01) at the end of exercise, whereas in CON it had risen by 21% (P < 0.05). Leg glucose uptake rose from 0.19 +/- 0.06 mmol/min at rest to 2.25 +/- 0.61 mmol/min at the end of exercise in NIDDM and from 0.13 +/- 0.05 to 1.17 +/- 0.34 mmol/min in CON. Splanchnic glucose output increased from 0.52 +/- 0.06 to 2.37 +/- 0.26 mmol/min in NIDDM and from 0.79 +/- 0.12 to 2.44 +/- 0.38 mmol/min in CON. Leg lactate output during exercise was twofold higher in NIDDM. Muscle contents of lactate and glycogen were similar in both groups at rest, whereas after exercise lactate tended to be higher (19.5 +/- 1.7 vs. 12.7 +/- 5.9 mmol/kg dry wt) and glycogen lower (154 +/- 35 vs. 251 +/- 41 mmol glucosyl units/kg dry wt) in NIDDM. Whole body respiratory exchange ratio during exercise was higher in NIDDM (0.84 +/- 0.02 vs. 0.78 +/- 0.02, P < 0.05). Exercise-induced changes in other muscle metabolites were similar in NIDDM and CON. These data indicate that the decline in blood glucose during exercise in nonobese NIDDM is due to enhanced peripheral glucose utilization rather than to an attenuated increase in splanchnic glucose output.

Exercise for patients with diabetes. Benefits, risks, precautions

Exercise is beneficial in both prevention and control of non-insulin-dependent (type II) diabetes. Whether a patient has insulin-dependent or type II diabetes, a regular exercise program can produce positive changes in the lipid profile, reduce blood pressure and weight, and improve other cardiovascular risk factors. The risks of an exercise program include precipitation of cardiovascular events, damage to the soft tissue and joints of the feet, visual loss, early and delayed hypoglycemia, and hyperglycemia and ketosis. Consequently, a comprehensive clinical assessment to identify potentially harmful diabetic complications and to determine the patient's fitness level is needed before a suitable exercise program can be prescribed. With careful manipulation of insulin doses and home monitoring of blood glucose levels, exercise need not adversely affect glycemic control. Moreover, the metabolic and cardiovascular benefits that result from a sensible exercise program can greatly improve the quality of life for most diabetic patients.

Impaired adrenergic response to prolonged exercise in type I diabetes

Patients with type I diabetes mellitus commonly experience hypoglycemia related to physical activity. We investigated the metabolic and hormonal response to exercise in type I diabetics, normal controls, and controls exercising under hypoglycemic conditions. All subjects exercise for 60 minutes at 60% to 65% of their VO2max while insulin concentrations were clamped at basal or hyperinsulinemic levels. With low-dose insulin infusion, despite similar free insulin levels, diabetics had a greater decrease in plasma glucose concentrations during exercise than controls. Nevertheless, the increments of epinephrine (E) and norepinephrine (NE) during exercise tended to be less in the diabetic subjects. Circulating levels of free fatty acids (FFA) were lower in diabetics, especially during early recovery from exercise. To better compare responses, a group of normal controls exercised during an infusion of insulin, which resulted in a similar decrease in plasma glucose to that of exercising diabetics. While exercising during a similar degree of hypoglycemia, diabetics had a significantly smaller increment of E and NE compared with controls. Increments of glucagon (GL) and growth hormone (GH) were not different. These studies suggest that there is a subnormal catecholamine response to exercise under hypoglycemic conditions in some patients with type I diabetes. The hypoglycemia during and after exercise in these individuals is probably the result of multiple factors, including relative hyperinsulinemia, decreased increment in catecholamines, and decreased availability of FFA.

Exercise and diabetes mellitus

As more is understood about the physiology of exercise, both in normal and in diabetic subjects, its role in the treatment of diabetes is becoming better defined. Although persons with diabetes may derive many benefits from regular physical exercise, there also are a number of hazards that make exercise difficult to manage. In insulin-treated diabetics, there are risks of hypoglycemia during or after exercise or of worsening metabolic control if insulin deficiency is present. Type II diabetics being treated with sulfonylureas also are at some increased risk of developing hypoglycemia during or following exercise, although this is less of a problem than occurs with insulin treatment. In individuals treated by diet alone, regulation of blood glucose during exercise usually results in a decrease in glucose concentration toward normal but not to hypoglycemic levels and exercise can be used safely as an adjunct to diet to achieve weight loss and improved insulin sensitivity. When obese patients with type II diabetes are treated with very low calorie diets, adequate amounts of carbohydrate must be provided to ensure maintenance of normal muscle glycogen content, particularly if individuals wish to participate in high intensity exercise that places a heavy workload on specific muscle groups. On the other hand, moderate intensity exercise such as vigorous walking can be tolerated by individuals on very low calorie, carbohydrate-restricted diets after an appropriate period of adaptation. A number of strategies can be employed to avoid hypoglycemia in patients with insulin-treated diabetes and both type I and type II diabetic subjects should be examined carefully for long term complications of their disease, which may be worsened by exercise. These considerations have led many diabetologists to consider exercise to be beneficial in the management of diabetes for some individuals but not to be recommended for everyone as a "necessary" part of diabetic treatment as was thought in the past. Instead, the goals should be to teach patients to incorporate exercise into their daily lives if they wish and to develop strategies to avoid the complications of exercise. The rationale for the use of exercise as part of the treatment program in type II diabetes is much clearer and regular exercise may be prescribed as an adjunct to caloric restriction for weight reduction and as a means of improving insulin sensitivity in the obese, insulin-resistant individual.

Impaired fibrinolytic response to exercise in type II diabetes: effects of exercise and physical training

We studied the effects of exercise and physical training on coagulation parameters and fibrinolytic activity in 16 sedentary non-insulin-dependent diabetics and nine control subjects matched for prior physical activity. Parameters were measured at rest and after 30 minutes of bicycle exercise at 70% to 75% of maximal oxygen uptake before and after 6 weeks of thrice-weekly physical training. In the untrained state, fibrinolytic activity was impaired in diabetics compared with controls (1.26 +/- 0.19 v 2.20 +/- 0.34 U; P less than .03), and resting levels of plasma fibrinogen (329 +/- 21 v 266 +/- 17 mg/dL; P less than .01) and the prothrombin time (PT) maximal velocity (Vmax) (4.9 +/- 0.5 v 2.9 +/- 0.5; P less than .05) were increased. The activated partial thromboplastin time (APTT) Vmax was also increased but this did not reach statistical significance (3.6 +/- 0.2 v 2.3 +/- 0.5; P less than 0.10). Activation of fibrinolysis occurred following exercise in both groups but the peak activity and increment were less in diabetics. Physical training for 6 weeks had no effect on plasma fibrinogen levels but significantly improved the resting and postexercise APTT Vmax and resting fibrinolytic activity in diabetics. The exercise-induced increment in fibrinolytic activity following training remained depressed compared with normal controls. The changes in APTT Vmax correlated with changes in the indices of blood glucose control. The relevance of these findings to possible antiatherogenic effects of exercise and the mechanism by which exercise produces these effects remain to be established.