Effects of exercise training on oxygen uptake kinetic responses in women with type 2 diabetes

Research into the effect Of SGLT2 inhibition on left ventricular remodelling in patients with heart failure and diabetes mellitus (REFORM) trial rationale and design

Background

Heart failure (HF) and diabetes (DM) are a lethal combination. The current armamentarium of anti-diabetic agents has been shown to be less efficacious and sometimes even harmful in diabetic patients with concomitant cardiovascular disease, especially HF. Sodium glucose linked co-transporter type 2 (SGLT2) inhibitors are a new class of anti-diabetic agent that has shown potentially beneficial cardiovascular effects such as pre-load and after load reduction through osmotic diuresis, blood pressure reduction, reduced arterial stiffness and weight loss. This has been supported by the recently published EMPA-REG trial which showed a striking 38 and 35 % reduction in cardiovascular death and HF hospitalisation respectively.

Methods

The REFORM trial is a novel, phase IV randomised, double blind, placebo controlled clinical trial that has been ongoing since March 2015. It is designed specifically to test the safety and efficacy of the SLGT2 inhibitor, dapagliflozin, on diabetic patients with known HF. We utilise cardiac-MRI, cardio-pulmonary exercise testing, body composition analysis and other tests to quantify the cardiovascular and systemic effects of dapagliflozin 10 mg once daily against standard of care over a 1 year observation period. The primary outcome is to detect the change in left ventricular (LV) end systolic and LV end diastolic volumes. The secondary outcome measures include LV ejection fraction, LV mass index, exercise tolerance, fluid status, quality of life measures and others.

Conclusions

This trial will be able to determine if SGLT2 inhibitor therapy produces potentially beneficial effects in patients with DM and HF, thereby replacing current medications as the drug of choice when treating patients with both DM and HF.

Trial registration Clinical Trials.gov: NCT02397421. Registered 12th March 2015

Clinical Update: Cardiovascular Disease in Diabetes Mellitus: Atherosclerotic Cardiovascular Disease and Heart Failure in Type 2 Diabetes Mellitus - Mechanisms, Management, and Clinical Considerations

Cardiovascular disease remains the principal cause of death and disability among patients with diabetes mellitus. Diabetes mellitus exacerbates mechanisms underlying atherosclerosis and heart failure. Unfortunately, these mechanisms are not adequately modulated by therapeutic strategies focusing solely on optimal glycemic control with currently available drugs or approaches. In the setting of multifactorial risk reduction with statins and other lipid-lowering agents, antihypertensive therapies, and antihyperglycemic treatment strategies, cardiovascular complication rates are falling, yet remain higher for patients with diabetes mellitus than for those without. This review considers the mechanisms, history, controversies, new pharmacological agents, and recent evidence for current guidelines for cardiovascular management in the patient with diabetes mellitus to support evidence-based care in the patient with diabetes mellitus and heart disease outside of the acute care setting.

Aerobic exercise training promotes additional cardiac benefits better than resistance exercise training in postmenopausal rats with diabetes

OBJECTIVE

The aim of this study was to evaluate the effects of aerobic exercise training or resistance exercise training on cardiac morphometric, functional, and oxidative stress parameters in rats with ovarian hormone deprivation and diabetes.

METHODS

Female Wistar rats (200-220 g) were divided into a sham-operated group (euglycemic sham-operated sedentary [ES]; n = 8) and three ovariectomized (bilateral removal of ovaries) and diabetic (streptozotocin 50 mg/kg IV) groups as follows: diabetic ovariectomized sedentary (DOS; n = 8), diabetic ovariectomized undergoing aerobic exercise training (DOTA; n = 8), and diabetic ovariectomized undergoing resistance exercise training (DOTR; n = 8). After 8 weeks of resistance (ladder) or aerobic (treadmill) exercise training, left ventricle function and morphometry were evaluated by echocardiography, whereas oxidative stress was evaluated at the left ventricle.

RESULTS

The DOS group presented with increased left ventricle cavity in diastole and relative wall thickness (RWT), and these changes were attenuated in both DOTA and DOTR groups. Systolic and diastolic function was impaired in the DOS group compared with the ES group, and only the DOTA group was able to reverse this dysfunction. Lipoperoxidation and glutathione redox balance were improved in both trained groups compared with the DOS group. Glutathione peroxidase and superoxide dismutase were higher in the DOTA group than in the other studied groups. Correlations were observed between lipoperoxidation and left ventricle cavity in diastole (r = 0.55), between redox balance and RWT (r = 0.62), and between lipoperoxidation and RWT (r = -0.60).

CONCLUSIONS

Aerobic exercise training and resistance exercise training promote attenuation of cardiac morphometric dysfunction associated with a reduction in oxidative stress in an experimental model of diabetes and menopause. However, only dynamic aerobic exercise training is able to attenuate systolic and diastolic dysfunction under this condition.

Long-Term Outcomes of Cardiac Rehabilitation in Diabetic and Non-diabetic Patients With Myocardial Infarction

OBJECTIVE

To investigate the long-term outcomes of cardiac rehabilitation (CR) on exercise capacity in diabetic (DM) and non-diabetic (non-DM) patients with myocardial infarction (MI).

METHODS

Of the MI patients who received hospital-based CR from February 2012 to January 2014, we retrospectively reviewed the medical records of the patients who continued follow-up through the outpatient clinic and community-based self-exercise after CR. A total of 37 patients (12 with DM and 25 without DM) were included in this study. Exercise capacity was measured by symptom-limited exercise tests before and after hospital-based CR and 1 year after the onset of MI.

RESULTS

Before the CR, the DM group had significantly lower exercise capacity in exercise times, peak oxygen consumption (VO2peak), and metabolic equivalent tasks (METs) than did the non-DM group. After the CR, both groups showed significantly improved exercise capacity, but the DM group had significantly lower exercise capacity in exercise times, submaximal rate pressure products (RPPsubmax), VO2peak, and METs. One year after the onset of the MI, the DM group had significantly lower exercise capacity in exercise times, RPPsubmax, and VO2peak than did the non-DM group, and neither group showed a significant difference in exercise capacity between before and after the CR.

CONCLUSION

As a result of continued follow-up through an outpatient clinic and community-based self-exercise after hospital-based CR in patients with MI, the DM group still had lower exercise capacity than did the non-DM group 1 year after the onset of MI, but both groups maintained their improved exercise capacity following hospital-based CR.

Targeting mitochondria to restore failed adaptation to exercise in diabetes

Our translational research group focuses on addressing the problem of exercise defects in diabetes with basic research efforts in cell and rodent models and clinical research efforts in subjects with diabetes mellitus. CREB (cAMP-response-element-binding protein) regulates cellular differentiation of neurons, β-cells, adipocytes and smooth muscle cells; it is also a potent survival factor and an upstream regulator of mitochondrial biogenesis. In diabetes and cardiovascular disease, CREB protein content is decreased in the vascular media, and its regulation in aberrant in β-cells, neurons and cardiomyocytes. Loss of CREB content and function leads to decreased vascular target tissue resilience when exposed to stressors such as metabolic, oxidative or sheer stress. This basic research programme set the stage for our central hypothesis that diabetes-mediated CREB dysfunction predisposes the diabetes disease progression and cardiovascular complications. Our clinical research programme revealed that diabetes mellitus leads to defects in functional exercise capacity. Our group has determined that the defects in exercise correlate with insulin resistance, endothelial dysfunction, decreased cardiac perfusion and diastolic dysfunction, slowed muscle perfusion kinetics, decreased muscle perfusion and slowed oxidative phosphorylation. Combined basic and clinical research has defined the relationship between exercise and vascular function with particular emphasis on how the signalling to CREB and eNOS [endothelial NOS (nitric oxide synthase)] regulates tissue perfusion, mitochondrial dynamics, vascular function and exercise capacity. The present review summarizes our current working hypothesis that restoration of eNOS/NOS dysfunction will restore cellular homoeostasis and permit an optimal tissue response to an exercise training intervention.

Independent effect of type 2 diabetes beyond characteristic comorbidities and medications on immediate but not continued knee extensor exercise hyperemia

We tested the hypothesis that type 2 diabetes (T2D), when present in the characteristic constellation of comorbidities (obesity, hypertension, dyslipidemia) and medications, slows the dynamic adjustment of exercising muscle perfusion and blunts the steady state relative to that of controls matched for age, body mass index, fitness, comorbidities, and non-T2D medications. Thirteen persons with T2D and 11 who served as controls performed rhythmic single-leg isometric quadriceps exercise (rest-to-6 kg and 6-to-12 kg transitions, 5 min at each intensity). Measurements included leg blood flow (LBF, femoral artery ultrasound), mean arterial pressure (MAP, finger photoplethysmography), and leg vascular conductance (LVK, calculated). Dynamics were quantified using mean response time (MRT). Measures of amplitude were also used to compare response adjustment: the change from baseline to 1) the peak initial response (greatest 1-s average in the first 10 s; ΔLBFPIR, ΔLVKPIR) and 2) the on-transient (average from curve fit at 15, 45, and 75 s; ΔLBFON, ΔLVKON). ΔLBFPIR was significantly blunted in T2D vs. control individuals (P = 0.037); this was due to a tendency for reduced ΔLVKPIR (P = 0.063). In contrast, the overall response speed was not different between groups (MRT P = 0.856, ΔLBFON P = 0.150) nor was the change from baseline to steady state (P = 0.204). ΔLBFPIR, ΔLBFON, and LBF MRT did not differ between rest-to-6 kg and 6-to-12 kg workload transitions (all P > 0.05). Despite a transient amplitude impairment at the onset of exercise, there is no robust or consistent effect of T2D on top of the comorbidities and medications typical of this population on the overall dynamic adjustment of LBF, or the steady-state levels achieved during low- or moderate-intensity exercise.

Cardiorespiratory fitness and incident diabetes: the FIT (Henry Ford ExercIse Testing) project

OBJECTIVE

Prior evidence has linked higher cardiorespiratory fitness with a lower risk of diabetes in ambulatory populations. Using a demographically diverse study sample, we examined the association of fitness with incident diabetes in 46,979 patients from The Henry Ford ExercIse Testing (FIT) Project without diabetes at baseline.

RESEARCH DESIGN AND METHODS

Fitness was measured during a clinician-referred treadmill stress test performed between 1991 and 2009. Incident diabetes was defined as a new diagnosis of diabetes on three separate consecutive encounters derived from electronic medical records or administrative claims files. Analyses were performed with Cox proportional hazards models and were adjusted for diabetes risk factors.

RESULTS

The mean age was 53 years with 48% women and 27% black patients. Mean metabolic equivalents (METs) achieved was 9.5 (SD 3.0). During a median follow-up period of 5.2 years (interquartile range 2.6-8.3 years), there were 6,851 new diabetes cases (14.6%). After adjustment, patients achieving ≥12 METs had a 54% lower risk of incident diabetes compared with patients achieving <6 METs (hazard ratio 0.46 [95% CI 0.41, 0.51]; P-trend < 0.001). This relationship was preserved across strata of age, sex, race, obesity, hypertension, and hyperlipidemia.

CONCLUSIONS

These data demonstrate that higher fitness is associated with a lower risk of incident diabetes regardless of demographic characteristics and baseline risk factors. Future studies should examine the association between change in fitness over time and incident diabetes.

Diabetes and stem cell function

Diabetes mellitus is one of the most common serious metabolic diseases that results in hyperglycemia due to defects of insulin secretion or insulin action or both. The present review focuses on the alterations to the diabetic neuronal tissues and skeletal muscle, including stem cells in both tissues, and the preventive effects of physical activity on diabetes. Diabetes is associated with various nervous disorders, such as cognitive deficits, depression, and Alzheimer's disease, and that may be caused by neural stem cell dysfunction. Additionally, diabetes induces skeletal muscle atrophy, the impairment of energy metabolism, and muscle weakness. Similar to neural stem cells, the proliferation and differentiation are attenuated in skeletal muscle stem cells, termed satellite cells. However, physical activity is very useful for preventing the diabetic alteration to the neuronal tissues and skeletal muscle. Physical activity improves neurogenic capacity of neural stem cells and the proliferative and differentiative abilities of satellite cells. The present review proposes physical activity as a useful measure for the patients in diabetes to improve the physiological functions and to maintain their quality of life. It further discusses the use of stem cell-based approaches in the context of diabetes treatment.

Effects of Endurance and Endurance Strength Training on Body Composition and Physical Capacity in Women with Abdominal Obesity

AIMS

To compare the effects of endurance training with endurance strength training on the anthropometric, body composition, physical capacity, and circulatory parameters in obese women.

METHODS

44 women with abdominal obesity were randomized into groups A and B, and asked to perform endurance (A) and endurance strength training (B) for 3 months, 3 times/week, for 60 min. Dual-energy X-ray absorptiometry and Graded Exercise Test were performed before and after training.

RESULTS

Significant decreases in body mass, BMI, total body fat, total body fat mass, and waist and hip circumference were observed after both types of intervention. Marked increases in total body lean and total body fat-free mass were documented in group B. In both groups, significant increases in peak oxygen uptake, time to exhaustion, maximal work rate, and work rate at ventilatory threshold were accompanied by noticeably decreased resting heart rate, resting systolic blood pressure, and resting and exercise diastolic blood pressure. No significant differences were noticed between groups for the investigated parameters.

CONCLUSION

Our findings demonstrate evidence for a favorable and comparable effect of 3-month endurance and endurance strength training on anthropometric parameters, body composition, physical capacity, and circulatory system function in women with abdominal obesity.

Differential effects of age and type 2 diabetes on dynamic vs. peak response of pulmonary oxygen uptake during exercise

We investigated if the magnitude of the type 2 diabetes (T2D)-induced impairments in peak oxygen uptake (V̇o2) and V̇o2 kinetics was affected by age. Thirty-three men with T2D (15 middle-aged, 18 older), and 21 nondiabetic (ND) men (11 middle-aged, 10 older) matched by age were recruited. Participants completed four 6-min bouts of constant-load cycling at 80% ventilatory threshold for the determination of V̇o2 kinetics. Cardiac output (inert-gas rebreathing) was recorded at rest and 30 and 240 s during two additional bouts. Peak V̇o2 (determined from a separate graded test) was significantly (P < 0.05) reduced in middle-aged and older men with T2D compared with their respective ND counterparts (middle-aged, 3.2 ± 0.5 vs. 2.5 ± 0.5 l/min; older, 2.7 ± 0.4 vs. 2.4 ± 0.4 l/min), and the magnitude of these impairments was not affected by age. However, the time constant of phase II of the V̇o2 response was only slowed (P < 0.05) in middle-aged men with T2D compared with healthy counterparts, whereas it was similar among older men with and without T2D (middle-aged, 26.8 ± 9.3 vs. 41.6 ± 12.1 s; older, 40.5 ± 7.8 vs. 41.1 ± 8.5 s). Similarly, the "gains" in systemic vascular conductance (estimated from the slope between cardiac output and mean arterial pressure responses) were lower (P < 0.05) in middle-aged men with T2D than ND controls, but similar between the older groups. The results suggest that the mechanisms by which T2D induces significant reductions in peak exercise performance are linked to a slower dynamic response of V̇o2 and reduced systemic vascular conductance responses in middle-aged men, whereas this is not the case in older men.

Type 2 diabetes exaggerates exercise effort and impairs exercise performance in older women

OBJECTIVE

Type 2 diabetes mellitus (T2DM) is associated with high levels of disability and mortality. Regular exercise prevents premature disability and mortality, but people with T2DM are generally sedentary for reasons that are not fully established. We previously observed that premenopausal women with T2DM report greater effort during exercise than their counterparts without diabetes, as measured by the Rating of Perceived Exertion (RPE) scale. We hypothesized that RPE is greater in older women with T2DM versus no T2DM.

RESEARCH DESIGN AND METHODS

We enrolled overweight, sedentary women aged 50-75 years with (n=26) or without T2DM (n=28). Participants performed submaximal cycle ergometer exercise at 30 W and 35% of individually-measured peak oxygen consumption (35% VO2peak). We assessed exercise effort by RPE (self-report) and plasma lactate concentration.

RESULTS

VO2peak was lower in T2DM versus controls (p=0.003). RPE was not significantly greater in T2DM versus controls (30 W: Control, 10.4±3.2, T2DM, 11.7±2.3, p=0.08; 35% VO2peak: Control, 11.1±0.5, T2DM, 12.1±0.5, p=0.21). However, lactate was greater in T2DM versus controls (p=0.004 at 30 W; p<0.05 at 35% VO2peak). Greater RPE was associated with higher lactate, higher heart rate, and a hypertension diagnosis (p<0.05 at 30 W and 35% VO2peak).

CONCLUSIONS

Taken together, physiological measures of exercise effort were greater in older women with T2DM than controls. Exercise effort is a modifiable and thereby targetable end point. In order to facilitate regular exercise, methods to reduce exercise effort in T2DM should be sought.

TRIAL NUMBER

NCT00785005.

Cardiovascular control during exercise in type 2 diabetes mellitus

Controlled studies of male and female subjects with type 2 diabetes mellitus (DM) of short duration (~3-5 years) show that DM reduces peak VO2 (L·min(-1) and mL·kg(-1)·min(-1)) by an average of 12-15% and induces a greater slowing of the dynamic response of pulmonary VO2 during submaximal exercise. These effects occur in individuals less than 60 years of age but are reduced or absent in older males and are consistently associated with significant increases in the exercise pressor response despite normal resting blood pressure. This exaggerated pressor response, evidence of exertional hypertension in DM, is manifest during moderate submaximal exercise and coincides with a more constrained vasodilation in contracting muscles. Maximum vasodilation during contractions involving single muscle groups is reduced by DM, and the dynamic response of vasodilation during submaximal contractions is slowed. Such vascular constraint most likely contributes to exertional hypertension, impairs dynamic and peak VO2 responses, and reduces exercise tolerance. There is a need to establish the effect of DM on dynamic aspects of vascular control in skeletal muscle during whole-body exercise and to clarify contributions of altered cardiovascular control and increased arterial stiffness to exertional hypertension.

Hemodynamic responses during graded and constant-load plantar flexion exercise in middle-aged men and women with type 2 diabetes

We tested the hypotheses that type 2 diabetes (T2D) impairs the 1) leg hemodynamic responses to an incremental intermittent plantar-flexion exercise and 2) dynamic responses of leg vascular conductance (LVC) during low-intensity (30% maximal voluntary contraction, MVC) and high-intensity (70% MVC) constant-load plantar-flexion exercise in the supine posture. Forty-four middle-aged individuals with T2D (14 women), and 35 healthy nondiabetic (ND) individuals (18 women) were tested. Leg blood flow (LBF) was measured between each contraction using venous occlusion plethysmography. During the incremental test peak force (Fpeak) relative to MVC was significantly reduced ( P < 0.05) in men and women with T2D compared with their respective nondiabetic counterparts. Peak LBF and the slope of LBF relative to percentage Fpeak were also reduced ( P < 0.05) in women with T2D compared with healthy women (peak blood flow, 460.6 ± 126.8 vs. 628.3 ± 347.7 ml/min; slope, 3.78 ± 1.74 vs. 5.85 ± 3.14 ml·min−1·%Fpeak−1) and in men with T2D compared with nondiabetic men (peak blood flow, 621.7 ± 241.3 vs. 721.2 ± 359.7 ml/min; slope, 5.75 ± 2.66 vs. 6.33 ± 3.63 ml·min−1·%Fpeak−1). During constant-load contractions at 30% MVC T2D did not affect the dynamic responses of LVC (LBF/MAP). However, at 70% MVC [completed by a subgroup of participants (20 with T2D, 6 women; 13 ND, 6 women)] the time constant of the second growth phase of LVC was longer and the amplitude of the first growth phase was lower ( P < 0.05 for both) in men and women with T2D. The results suggest that the T2D-induced impairments in performance of the leg muscles are related to reductions in blood flow in both men and women.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

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.

Similar level of impairment in exercise performance and oxygen uptake kinetics in middle-aged men and women with type 2 diabetes

The present study tested the hypothesis that the magnitude of the type 2 diabetes-induced impairments in peak oxygen uptake (V̇o2) and V̇o2 kinetics would be greater in females than males in middle-aged participants. Thirty-two individuals with type 2 diabetes (16 male, 16 female), and 32 age- and body mass index (BMI)-matched healthy individuals (16 male, 16 female) were recruited. Initially, the ventilatory threshold (VT) and peak V̇o2 were determined. On a separate day, subjects completed four 6-min bouts of constant-load cycling at 80% VT for the determination of V̇o2 kinetics using standard procedures. Cardiac output (CO) (inert gas rebreathing) was recorded at rest, 30, and 240 s during two additional bouts. Peak V̇o2 (ml·kg−1·min−1) was significantly reduced in men and women with type 2 diabetes compared with their respective nondiabetic counterparts (men, 27.8 ± 4.4 vs. 31.1 ± 6.2 ml·kg−1·min−1; women, 19.4 ± 4.1 vs. 21.4 ± 2.9 ml·kg−1·min−1). The time constant (s) of phase 2 (τ2) and mean response time (s) of the V̇o2 response (MRT) were slowed in women with type 2 diabetes compared with healthy women (τ2, 43.3 ± 9.8 vs. 33.6 ± 10.0 s; MRT, 51.7 ± 9.4 vs. 43.5 ± 11.4s) and in men with type 2 diabetes compared with nondiabetic men (τ2, 43.8 ± 12.0 vs. 35.3 ± 9.5 s; MRT, 57.6 ± 8.3 vs. 47.3 ± 9.3 s). The magnitude of these impairments was not different between males and females. The steady-state CO responses or the dynamic responses of CO were not affected by type 2 diabetes among men or women. The results suggest that the type 2 diabetes-induced impairments in peak V̇o2 and V̇o2 kinetics are not affected by sex in middle aged participants.

Speeding of pulmonary VO2 on-kinetics by light-to-moderate-intensity aerobic exercise training in chronic heart failure: clinical and pathophysiological correlates

BACKGROUND

Pulmonary VO2 on-kinetics during light-to-moderate-intensity constant-work-rate exercise, an experimental model mirroring energetic transitions during daily activities, has been shown to speed up with aerobic exercise training (AET) in normal subjects, but scant data are available in chronic heart failure (CHF).

METHODS AND RESULTS

Thirty CHF patients were randomized to 3 months of light-to-moderate-intensity AET (CHF-AET) or control (CHF-C). Baseline and end-protocol evaluations included i) one incremental cardiopulmonary exercise test with near infrared spectroscopy analysis of peak deoxygenated hemoglobin+myoglobin concentration changes (Δ[deoxy(Hb+Mb)]) in vastus lateralis muscle, ii) 8 light-to-moderate-intensity constant-work-rate exercise tests for VO2 on-kinetics phase I duration, phase II τ, and mean response time (MRT) assessment, and iii) circulating endothelial progenitor cell (EPC) measurement. Reference values were obtained in 7 age-matched normals (N). At end-protocol, phase I duration, phase II τ, and MRT were significantly reduced (-12%, -22%, and -19%, respectively) and peak VO2, peak Δ[deoxy(Hb+Mb)], and EPCs increased (9%, 20%, and 98%, respectively) in CHF-AET, but not in CHF-C. Peak Δ[deoxy(Hb+Mb)] and EPCs relative increase correlated significantly to that of peak VO2 (r=0.61 and 0.64, respectively, p<0.05).

CONCLUSIONS

Light-to-moderate-intensity AET determined a near-normalization of pulmonary VO2 on-kinetics in CHF patients. Such a marked plasticity has important implications for AET intensity prescription, especially in patients more functionally limited and with high exercise-related risk. The AET-induced simultaneous improvement of phase I and phase II, associated with an increase of peak peripheral oxygen extraction and EPCs, supports microcirculatory O2 delivery impairment as a key factor determining exercise intolerance in CHF.

Gymnasium-based unsupervised exercise maintains benefits in oxygen uptake kinetics obtained following supervised training in type 2 diabetes

Supervised exercise (SE) in patients with type 2 diabetes improves oxygen uptake kinetics at the onset of exercise. Maintenance of these improvements, however, has not been examined when supervision is removed. We explored if potential improvements in oxygen uptake kinetics following a 12-week SE that combined aerobic and resistance training were maintained after a subsequent 12-week unsupervised exercise (UE). The involvement of cardiac output (CO) in these improvements was also tested. Nineteen volunteers with type 2 diabetes were recruited. Oxygen uptake kinetics and CO (inert gas rebreathing) responses to constant-load cycling at 50% ventilatory threshold (V(T)), 80% V(T), and mid-point between V(T) and peak workload (50% Δ) were examined at baseline (on 2 occasions) and following each 12-week training period. Participants decided to exercise at a local gymnasium during the UE. Thirteen subjects completed all the interventions. The time constant of phase 2 of oxygen uptake was significantly faster (p < 0.05) post-SE and post-UE compared with baseline at 50% V(T) (17.3 ± 10.7 s and 17.5 ± 5.9 s vs. 29.9 ± 10.7 s), 80% V(T) (18.9 ± 4.7 and 20.9 ± 8.4 vs. 34.3 ± 12.7s), and 50% Δ (20.4 ± 8.2 s and 20.2 ± 6.0 s vs. 27.6 ± 3.7 s). SE also induced faster heart rate kinetics at all 3 intensities and a larger increase in CO at 30 s in relation to 240 s at 80% V(T); and these responses were maintained post-UE. Unsupervised exercise maintained benefits in oxygen uptake kinetics obtained during a supervised exercise in subjects with diabetes, and these benefits were associated with a faster dynamic response of heart rate after training.

Plasticity of microvascular oxygenation control in rat fast-twitch muscle: effects of experimental creatine depletion

Aging, heart failure and diabetes each compromise the matching of O2 delivery (Q˙O2)-to-metabolic requirements (O2 uptake, V˙O2) in skeletal muscle such that the O2 pressure driving blood-myocyte O2 flux (microvascular PO2, PmvO2) is reduced and contractile function impaired. In contrast, β-guanidinopropionic acid (β-GPA) treatment improves muscle contractile function, primarily in fast-twitch muscle (Moerland and Kushmerick, 1994). We tested the hypothesis that β-GPA (2% wt/BW in rat chow, 8 weeks; n=14) would improve Q˙O2-to-V˙O2 matching (elevated PmvO2) during contractions (4.5V @ 1Hz) in mixed (MG) and white (WG) portions of the gastrocnemius, both predominantly fast-twitch). Compared with control (CON), during contractions PmvO2 fell less following β-GPA (MG -54%, WG -26%, P<0.05), elevating steady-state PmvO2 (CON, MG: 10±2, WG: 9±1; β-GPA, MG 16±2, WG 18±2 mmHg, P<0.05). This reflected an increased Q˙O2/V˙O2 ratio due primarily to a reduced V˙O2 in β-GPA muscles. It is likely that this adaptation helps facilitate the β-GPA-induced enhancement of contractile function in fast-twitch muscles.

Cardiac output is not related to the slowed O2 uptake kinetics in type 2 diabetes

PURPOSE

This study aimed to investigate whether cardiac output (CO) responses were related to VO2 kinetics during cycling in type 2 diabetes.

METHODS

A total of 9 middle-aged women with uncomplicated type 2 diabetes, 9 nondiabetic overweight women, and 11 nondiabetic lean women were recruited. Initially, the ventilatory threshold (VT) and peak VO2 were determined during a maximal graded test. Then, on two separate days, subjects completed three 7-min bouts of constant-load cycling at each of three intensities: 50% VT, 80% VT, and midpoint between VT and peak VO2 (50% Δ). CO (inert gas rebreathing) was recorded at 30 and 240 s of an additional bout at each intensity. VO2 kinetic parameters were determined by fitting a biexponential (50% VT and 80% VT) or triexponential (50% Δ) function to the VO2 data.

RESULTS

Peak VO2 was significantly lower in type 2 diabetes compared with the two nondiabetic groups (P < 0.05). The time constant of phase 2 was significantly greater (P < 0.05) in type 2 diabetes compared with the nondiabetic heavy and lean groups at 50% VT (34.2 ± 15.7 vs 15.4 ± 7.3 and 20.2 ± 9.7 s) and 80% VT (39.1 ± 9.0 vs 24.8 ± 8.8 and 36.8 ± 7.9 s), but none of the VO2 kinetic parameters were different at 50% Δ. CO responses during exercise were not different among the three groups, and at 80% VT, the change in CO from 30 to 240 s was significantly larger in type 2 diabetes compared with the two nondiabetic groups.

CONCLUSIONS

The results confirm that type 2 diabetes slows the dynamic response of VO2 during light and moderate relative intensity exercise in females but that this occurs in the absence of any slowing of the CO response during the initial period of exercise.

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.

Older Type 2 diabetic males do not exhibit abnormal pulmonary oxygen uptake and muscle oxygen utilization dynamics during submaximal cycling exercise

There are reports of abnormal pulmonary oxygen uptake (V̇o2) and deoxygenated hemoglobin ([HHb]) kinetics in individuals with Type 2 diabetes (T2D) below 50 yr of age with disease durations of <5 yr. We examined the V̇o2 and muscle [HHb] kinetics in 12 older T2D patients with extended disease durations (age: 65 ± 5 years; disease duration 9.3 ± 3.8 years) and 12 healthy age-matched control participants (CON; age: 62 ± 6 years). Maximal oxygen uptake (V̇o2max) was determined via a ramp incremental cycle test and V̇o2 and [HHb] kinetics were determined during subsequent submaximal step exercise. The V̇o2max was significantly reduced ( P < 0.05) in individuals with T2D compared with CON (1.98 ± 0.43 vs. 2.72 ± 0.40 l/min, respectively) but, surprisingly, V̇o2 kinetics was not different in T2D compared with CON (phase II time constant: 43 ± 17 vs. 41 ± 12 s, respectively). The Δ[HHb]/ΔV̇o2 was significantly higher in T2D compared with CON (235 ± 99 vs. 135 ± 33 AU·l−1·min−1; P < 0.05). Despite a lower V̇o2max, V̇o2 kinetics is not different in older T2D compared with healthy age-matched control participants. The elevated Δ[HHb]/ΔV̇o2 in T2D individuals possibly indicates a compromised muscle blood flow that mandates a greater O2 extraction during exercise. Longer disease duration may result in adaptations in the O2 extraction capabilities of individuals with T2D, thereby mitigating the expected age-related slowing of V̇o2 kinetics.

Effect of exercise training on physical fitness in type II diabetes mellitus

Few studies have compared changes in cardiorespiratory fitness between aerobic training only or in combination with resistance training. In addition, no study to date has compared strength gains between resistance training and combined exercise training in type II diabetes mellitus (T2DM).

PURPOSE

We evaluated the effects of aerobic exercise training (A group), resistance exercise training (R group), combined aerobic and resistance training (A + R group), and sedentary lifestyle (C group) on cardiorespiratory fitness and muscular strength in individuals with T2DM.

METHODS

Two hundred and fifty-one participants in the Diabetes Aerobic and Resistance Exercise trial were randomly allocated to A, R, A + R, or C. Peak oxygen consumption (V O(2peak)), workload, and treadmill time were determined after maximal exercise testing at 0 and 6 months. Muscular strength was measured as the eight-repetition maximum on the leg press, bench press, and seated row. Responses were compared between younger (aged 39-54 yr) and older (aged 55-70 yr) adults and between sexes.

RESULTS

VO(2peak) improved by 1.73 and 1.93 mL O(2)*kg(-1)*min(-1) with A and A + R, respectively, compared with C (P < 0.05). Strength improvements were significant after A + R and R on the leg press (A + R: 48%, R: 65%), bench press (A + R: 38%, R: 57%), and seated row (A + R: 33%, R: 41%; P < 0.05). There was no main effect of age or sex on training performance outcomes. There was, however, a tendency for older participants to increase VO(2peak) more with A + R (+1.5 mL O(2)*kg(-1)*min(-1)) than with A only (+0.7 mL O(2)*kg(-1)*min(-1)).

CONCLUSIONS

Combined training did not provide additional benefits nor did it mitigate improvements in fitness in younger subjects compared with aerobic and resistance training alone. In older subjects, there was a trend to greater aerobic fitness gains with A + R versus A alone.

Impact of exercise intensity and duration on insulin sensitivity in women with T2D

BACKGROUND

Clinical guidelines seldom provide in depth information about the most suitable type and intensity of exercise to obtain optimal benefit in different subgroups of T2D individuals. The aim of this study was to examine the effect of group exercise training on exercise capacity, insulin sensitivity and HbA1c in women with diabetes.

METHODS

Twenty-two women with T2D participated in a supervised group exercise program for six months. The program combined endurance and resistance exercise. The duration and intensity of exercise for each subject was recorded. The volume of exercise was calculated as the product of exercise duration and intensity. Exercise capacity, insulin sensitivity and HbA1c were measured at baseline and after six months of training. The subjects were dichotomized with respect to training volume in a high training volume group and a low training volume group.

RESULTS

Exercise capacity did not change significantly during the training period. Insulin sensitivity increased significantly and HbA1c decreased significantly from baseline in the high volume group but not in the low volume group. The increase in insulin sensitivity was explained with the intensity of exercise by 30%. The reduction in HbA1c was explained with exercise by 25%.

CONCLUSION

Improvement in insulin sensitivity after six months combined supervised group training in female diabetic subjects is related to exercise intensity, whereas the reduction in HbA1c is related mainly to training volume. Metabolic effects of training may be seen in the absence of improved exercise capacity.

Exploratory study on oxygen consumption on-kinetics during treadmill walking in women with systemic lupus erythematosus

OBJECTIVE

To determine whether oxygen consumption (V o(2)) on-kinetics differed between groups of women with systemic lupus erythematosus (SLE) and sedentary but otherwise healthy controls.

DESIGN

Exploratory case-control study.

SETTING

Medical school exercise physiology laboratory.

PARTICIPANTS

Convenience samples of women with SLE (n=12) and sedentary but otherwise healthy controls (n=10).

INTERVENTION

None.

MAIN OUTCOME MEASURES

V o(2) on-kinetics indices including time to steady state, rate constant, mean response time (MRT), transition constant, and oxygen deficit measured during bouts of treadmill walking at intensities of 3 and 5 metabolic equivalents (METs).

RESULTS

Time to steady state and oxygen deficit were increased and rate constant was decreased in the women with SLE compared with controls. At the 5-MET energy demand, the transition constant was lower and MRT was longer in the women with SLE than in controls. For a similar relative energy expenditure that was slightly lower than the anaerobic threshold, the transition constant was higher in controls than in women with SLE.

CONCLUSION

V o(2) on-kinetics was prolonged in women with SLE. The prolongation was concomitant with an increase in oxygen deficit and may underlie performance fatigability in women with SLE.

Heart rate prescribed walking training improves cardiorespiratory fitness but not glycaemic control in people with type 2 diabetes

In this study, we examined the effects of a supervised, heart rate intensity prescribed walking training programme on cardiorespiratory fitness and glycaemic control in people with type 2 diabetes mellitus. After receiving local ethics approval, 27 individuals (21 males, 6 females) with type 2 diabetes were randomly assigned to an experimental ("walking") or control group. Participants completed a Balke-Ware test to determine peak heart rate, peak oxygen consumption (VO(2peak)), and peak gradient. The walking group then completed a 7-week (four sessions a week) supervised, heart rate prescribed walking training programme, whereas the control group continued daily life. After training, participants completed another Balke-Ware test. Fasting blood glucose and glycosylated haemoglobin were measured at rest. The results showed that walking training elicited 80% (s = 2) of peak heart rate and a rating of perceived exertion of 11 (s = 1). Peak heart rate and VO(2peak) were higher in the walking than in the control group after training (P < 0.05). Based on the peak gradient before training, the respiratory exchange ratio was significantly lower (P < 0.05) and there was a strong trend for VO(2) (P = 0.09) and heart rate (P = 0.09) to be lower after training at the same gradient in the walking compared with the control group. These improvements increased walking peak gradient by 5 min (s = 4 min) compared with the control (P < 0.05). There was no change in fasting blood glucose or glycosylated haemoglobin after training. Despite no change in glycaemic control, heart rate prescribed walking improved peak and sub-maximal cardiorespiratory responses. The beneficial adaptations support the use of heart rate monitoring during walking in people with type 2 diabetes mellitus.

Walking: a matter of quantity and quality physical activity for type 2 diabetes management

Walking is often prescribed as a mode of physical activity for people with type 2 diabetes (T2D). We and others have found that although people with T2D may increase the amount that they walk (e.g., more steps per day), improvements in key health outcomes are rarely achieved. We agree that walking is an acceptable approach for people with T2D to meet current clinical practice guidelines, but consideration of both the total number of daily steps and the walking speed of a portion of those total daily steps are necessary to gain health benefit.

Increased levels of apoptosis in gastrocnemius skeletal muscle in patients with peripheral arterial disease

Intermittent claudication (IC) is the major clinical manifestation of peripheral arterial disease (PAD). Apoptosis has been linked to skeletal muscle pathophysiology in other chronic diseases such as congestive heart failure. This study tested the hypothesis that there would be increased levels of apoptosis in the skeletal muscle of patients with PAD compared with control individuals. In total, 26 individuals with PAD and 28 age-appropriate controls underwent studies of peak oxygen consumption (peak VO2) and a gastrocnemius muscle biopsy in the most symptomatic leg. Muscle biopsies were analyzed for apoptosis and caspase-3 activity. Patients with PAD had a reduced peak VO2 compared with controls. Apoptosis was increased in those with PAD compared with age-appropriate controls (3.83% +/- 2.6 vs 1.53% +/- 0.96; p < 0.001). In conclusion, PAD is associated with increased levels of apoptosis in the peripheral skeletal muscle. Further study is required to ascertain whether apoptosis plays a role in decreased functional capacity.

Modeling and analysis of the effect of training on V O2 kinetics and anaerobic capacity

In this paper, we present an application of a number of tools and concepts for modeling and analyzing raw, unaveraged, and unedited breath-by-breath oxygen uptake data. A method for calculating anaerobic capacity is used together with a model, in the form of a set of coupled nonlinear ordinary differential equations to make predictions of the VO(2) kinetics, the time to achieve a percentage of a certain constant oxygen demand, and the time limit to exhaustion at intensities other than those in which we have data. Speeded oxygen kinetics and increased time limit to exhaustion are also investigated using the eigenvalues of the fixed points of our model. We also use a way of analyzing the oxygen uptake kinetics using a plot of V O(2)(t) vs V O(2)(t) which allows one to observe both the fixed point solutions and also the presence of speeded oxygen kinetics following training. A method of plotting the eigenvalue versus oxygen demand is also used which allows one to observe where the maximum amplitude of the so-called slow component will be and also how training has changed the oxygen uptake kinetics by changing the strength of the attracting fixed point for a particular demand.

Aerobic exercise training improves the role of high-density lipoprotein antioxidant and reduces plasma lipid peroxidation in type 2 diabetes mellitus

In this study, we analyzed the effect of aerobic exercise training (AET) and of a single bout of exercise on plasma oxidative stress and on antioxidant defenses in type 2 diabetes mellitus (DM) and in healthy control subjects (C). DM and C did not differ regarding triglycerides, high-density lipoprotein cholesterol (HDL-c), insulin, and HOMA index at baseline and after AET. To measure the lag time for low-density lipoprotein (LDL) oxidation (LAG) and the maximal rate of conjugated diene formation (MCD), participants' plasma HDL(2) and HDL(3) were incubated with LDL from pooled healthy donors' plasma. In the presence of HDL(3), both LAG and MCD were similar in C and DM, but only in DM did AET improve LAG and reduce MCD. In the presence of HDL(2), the lower baseline LAG in DM equaled C after AET. MCD was unchanged in DM after AET, but was lower than C only after AET. Furthermore, after AET plasma thiobarbituric acid-reactive substances were reduced only in DM subjects. Despite not modifying the total plasma antioxidant status and serum paraoxonase-1 activity in both groups, AET lowered the plasma lipid peroxides, corrected the HDL(2), and improved the HDL(3) antioxidant efficiency in DM independent of the changes in blood glucose, insulin, and plasma HDL concentration and composition.

Skeletal muscle deoxygenation after the onset of moderate exercise suggests slowed microvascular blood flow kinetics in type 2 diabetes

OBJECTIVE

People with type 2 diabetes have impaired exercise responses even in the absence of cardiovascular complications. One key factor associated with the exercise intolerance is abnormally slowed oxygen uptake (VO2) kinetics during submaximal exercise. The mechanisms of this delayed adaptation during exercise are unclear but probably relate to impairments in skeletal muscle blood flow. This study was conducted to compare skeletal muscle deoxygenation (deoxygenated hemoglobin/myoglobin [HHb]) responses and estimated microvascular blood flow (Qm) kinetics in type 2 diabetic and healthy subjects after the onset of moderate exercise.

RESEARCH DESIGN AND METHODS

Pulmonary VO2 kinetics and [HHb] (using near-infrared spectroscopy) were measured in 11 type 2 diabetic and 11 healthy subjects during exercise transitions from unloaded to moderate cycling exercise. Qm responses were calculated using VO2 kinetics and [HHb] responses via rearrangement of the Fick principle.

RESULTS

VO2 kinetics were slowed in type 2 diabetic compared with control subjects (43.8 +/- 9.6 vs. 34.2 +/- 8.2 s, P < 0.05), and the initial [HHb] response after the onset of exercise exceeded the steady-state level of oxygen extraction in type 2 diabetic compared with control subjects. The mean response time of the estimated Qm increase was prolonged in type 2 diabetic compared with healthy subjects (47.7 +/- 14.3 vs. 35.8 +/- 10.7 s, P < 0.05).

CONCLUSIONS

Type 2 diabetic skeletal muscle demonstrates a transient imbalance of muscle O2 delivery relative to O2 uptake after onset of exercise, suggesting a slowed Qm increase in type 2 diabetic muscle. Impaired vasodilatation due to vascular dysfunction in type 2 diabetes during exercise may contribute to this observation. Further study of the mechanisms leading to impaired muscle oxygen delivery may help explain the abnormal exercise responses in type 2 diabetes.

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.

Physical activity in individuals at risk for diabetes: Diabetes Prevention Program

PURPOSE AND METHODS

Leisure physical activity was assessed using questionnaires with different time frames in the Diabetes Prevention Program (DPP) cohort of 3234 overweight individuals aged > 25 yr with impaired glucose tolerance (IGT) from 27 centers across the United States. The three questionnaires were the Modifiable Activity Questionnaire (MAQ; past year), the Low-Level Physical Activity Recall (LOPAR; past 7 d), and the Third National Health and Nutrition Examination Survey (NHANES III; past month). This provided the opportunity to examine the relationship between the three activity measures and to compare activity levels of the DPP sample with that of a national sample with IGT.

RESULTS

Leisure activity determined by the three questionnaires significantly correlated with each other, although the correlations between MAQ and NHANES III were stronger (men: rho = 0.52; women: rho = 0.49; P < 0.01) than between LOPAR and either measure (men: rho = 0.20 for MAQ, 0.24 for NHANES; women: rho = 0.10 for MAQ, 0.13 for NHANES). In the DPP, measures of obesity and glucose tolerance were significantly correlated with activity levels determined by MAQ and NHANES, but not LOPAR. Activity levels in DPP participants determined by the NHANES III questionnaire were generally higher than those reported by individuals meeting DPP eligibility criteria who were part of the NHANES cohort for similar age, body mass index, and race or ethnicity.

CONCLUSION

If the DPP participants were more active than a national sample of individuals with IGT, this would have implications for translation when using the DPP lifestyle intervention in less active or less motivated populations. Finally, the weak relationship between activity levels obtained with MAQ and LOPAR may result from the fact that they encompass different time frames and different components of leisure activity.

Rosiglitazone improves exercise capacity in individuals with type 2 diabetes

OBJECTIVE

Although exercise is recommended as a cornerstone of treatment for type 2 diabetes, it is often poorly adopted by patients. We have noted that even in the absence of apparent cardiovascular disease, persons with type 2 diabetes have an impaired ability to carry out maximal exercise, and the impairment is correlated with insulin resistance and endothelial dysfunction. We hypothesized that administration of a thiazolidinedione (TZD) agent would improve exercise capacity in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twenty participants with uncomplicated type 2 diabetes were randomly assigned in a double-blind study to receive either 4 mg/day of rosiglitazone or matching placebo after baseline measurements to assess endothelial function (brachial artery diameter by brachial ultrasound), maximal oxygen consumption (VO(2max)), oxygen uptake (VO(2)) kinetics, and insulin sensitivity by hyperinsulinemic-euglycemic clamp. Measurements were reassessed after 4 months of treatment.

RESULTS

Participant groups did not differ at baseline in any measure. Rosiglitazone-treated participants (n = 10) had significantly improved VO(2max) (19.8 +/- 5.3 ml . kg(-1) . min(-1) before rosiglitazone vs. 21.2 +/- 5.1 ml . kg(-1) . min(-1) after rosiglitazone, P < 0.01), insulin sensitivity, and endothelial function. A change in VO(2max) correlated with improved insulin sensitivity measured by clamp (r = 0.68, P < 0.05) and with improved brachial artery diameter (r = 0.70, P < 0.05). Placebo-treated participants (n = 10) showed no changes in VO(2max) (19.4 +/- 5.2 ml . kg(-1) . min(-1) before rosiglitazone vs. 18.1 +/- 5.3 ml . kg(-1) . min(-1) after rosiglitazone, NS) or brachial artery diameter.

CONCLUSIONS

This is the first known report showing that a TZD improved exercise function in type 2 diabetes. Whether this is due to the observed improvements in insulin sensitivity and/or endothelial function or to another action of the TZD class requires further exploration.

Exercise training increases glycogen synthase activity and GLUT4 expression but not insulin signaling in overweight nondiabetic and type 2 diabetic subjects

Exercise training improves insulin sensitivity in subjects with and without type 2 diabetes. However, the mechanism by which this occurs is unclear. The present study was undertaken to determine how improved insulin signaling, GLUT4 expression, and glycogen synthase activity contribute to this improvement. Euglycemic clamps with indirect calorimetry and muscle biopsies were performed before and after 8 weeks of exercise training in 16 insulin-resistant nondiabetic subjects and 6 type 2 diabetic patients. Training increased peak aerobic capacity (Vo(2peak)) in both nondiabetic (from 34 +/- 2 to 39 +/- 2 mL O(2)/kg fat-free mass [FFM]/min, 14% +/- 2%, P <.001) and diabetic (from 26 +/- 3 to 34 +/- 3 mL O(2)/kg FFM/min, 32% +/- 4%) subjects. Training also increased insulin-stimulated glucose disposal in nondiabetic (from 6.2 +/- 0.5 to 7.1 +/- 0.7 mg/kg FFM/min) and diabetic subjects (from 4.3 +/- 0.6 to 5.5 +/- 0.6 mg/kg FFM/min). Total glycogen synthase activity was increased by 46% +/- 17% and 45% +/- 12% in nondiabetic and diabetic subjects, respectively, in response to training (P <.01 v before training). Moreover, after training, glycogen synthase fractional velocity was correlated with insulin-stimulated glucose storage (r = 0.53, P <.05) and the training-induced improvement in glucose disposal was accounted for primarily by increased insulin-stimulated glucose storage. Training also increased GLUT4 protein by 38% +/- 8% and 22% +/- 10% in nondiabetic and diabetic subjects, respectively (P <.05 v. before training). Akt protein expression, which was decreased by 29% +/- 3% (P <.05) in the diabetic subjects before training (compared to the nondiabetics), increased significantly in both groups (P <.001). In contrast, exercise training did not enhance the ability of insulin to stimulate insulin receptor substrate-1 (IRS-1)-associated phosphatidylinositol 3 (PI 3)-kinase activity. The present data are consistent with a working model whereby 8 weeks of exercise training increases insulin-stimulated glucose disposal primarily by increasing GLUT4 protein expression without enhancing insulin-stimulated PI 3-kinase signaling, and that once the glucose enters the myocyte, increased glycogen synthase activity preferentially shunts it into glycogen synthesis.

The metabolic syndrome: an emerging health epidemic in women

The metabolic syndrome is a compilation of factors characterized by insulin resistance and the identification of 3 of the 5 criteria of abdominal obesity, elevated triglycerides, decreased high-density lipoprotein (HDL) level, elevated blood pressure, and elevated fasting plasma glucose. According to census data from 2000, these criteria have lead to the diagnosis of approximately 47 million Americans with the metabolic syndrome, correlating with the 61% increase in the incidence of obesity between 1991 and 2000. Insulin resistance occurs when target tissues cannot respond properly to normal concentrations of insulin. The results are hypercoagulability, endothelial dysfunction, inflammation, and eventually coronary artery disease. Treatment involves lifestyle modification, including diet and exercise, to treat obesity and prevent the development of diabetes. Patients who meet the criteria for the metabolic syndrome may also be treated with insulin-sparing and insulin-sensitizing medications that help to improve endothelial function, vascular reactivity, and vascular inflammation. Ultimately, treatment goals are to prevent cardiovascular disease by both altering the risk factors that are components of the syndrome, and treating the lifestyle issues inherent to the disease process, such as caloric restriction and increased physical activity. There are 2 million more women than men in the United States categorized as being obese, with the trend of obesity and diabetes increasing. In the last decade there has been a 74% increase in obesity, mostly in women. This epidemic needs to be understood and managed to prevent further morbidity and mortality owing to diabetes and cardiovascular disease.

Cardiovascular adaptations to exercise training in postmenopausal women with type 2 diabetes mellitus

Background

Type 2 diabetes mellitus (DM-2) is one of the most prevalent chronic diseases of the aged and contributes to a significant amount of cardiovascular disease morbidity and mortality. Exercise training may be beneficial in attenuating the cardiovascular maladaptations associated with DM-2. The purpose of this study was to examine the effects of exercise training on left ventricular (LV) and vascular function in a sample of postmenopausal women with DM-2.

Methods

Twenty-eight postmenopausal women with DM-2 (age: 59 ± 7 yrs) were assigned to either an exercise training (ET) (n = 17) or control group (CT) (n = 7). Cardiorespiratory fitness (), LV filling dynamics and arterial compliance were assessed at baseline in all participants. The ET group performed a supervised aerobic and resistance training intervention three days per week for a period of 10 weeks, while the CT group continued normal activities of daily living.

Results

Body mass index, , age and duration of diabetes were similar between the ET and CT groups at baseline. (21.3 ± 3.3 to 24.5 ± 4.2 ml·kg^-1·min^-1, p < 0.05) and large artery compliance (1.0 ± 0.4 to 1.2 ± 0.4 mL·mmHg^-1, p < 0.05), increased significantly in the ET group following training despite no change in LV filling dynamics, blood pressure, lipid profile or insulin sensitivity. All variables remained unchanged in the CT group.

Conclusions

Exercise training improves large artery compliance and cardiorespiratory fitness in postmenopausal women with DM-2, without any appreciable changes in LV filling dynamics or conventional risk factors for cardiovascular disease.

Preventing cardiovascular events in patients with diabetes mellitus

Diabetes mellitus and obesity are becoming increasingly prevalent in the United States. Patients with diabetes are 2 to 3 times more likely to develop cardiovascular disease (CVD) than are individuals without diabetes, but proper diabetes management and metabolic control can reduce this risk. Nonpharmacologic interventions, such as diet and exercise, can help to reduce weight and control insulin resistance, blood glucose levels, and lipid abnormalities, thereby lowering the risk of adverse cardiovascular outcomes. However, diet and exercise can provide particular challenges for the patient with diabetes. Antiobesity drugs, such as sibutramine and orlistat, can help individuals with diabetes lose weight and can have some effect on metabolic control. Alcohol use and hormone replacement therapy are still controversial topics with regard to reducing the risk of CVD. Smoking is known to be particularly dangerous for those with diabetes, and it is important for health care providers to help their patients stop smoking. Early and aggressive intervention in treating risk factors can reduce the risk of developing diabetes and prevent CVD in the patient with diabetes.

The Role of Exercise in the Treatment of Cardiovascular Disease Associated with Type 2 Diabetes Mellitus

The role of exercise training in the prevention and treatment of type 2 diabetes mellitus has been studied extensively over the past two decades. Although the primary treatment aim for patients with type 2 diabetes is metabolic control, the morbidity and mortality associated with the disease is more a function of cardiovascular disease. As exercise is associated with favourable reductions in the risk for cardiovascular disease in other high-risk populations, here we explore the role of exercise in the treatment of cardiovascular maladaptations associated with type 2 diabetes. The cardiovascular adaptation to type 2 diabetes is characterised by hypertrophy, stiffening and loss of functional reserve. Clinically, the cardiovascular adaptations to the diabetic state are associated with an increased risk for cardiovascular disease. Functionally, these adaptations have been shown to contribute to a reduced exercise capacity, which may explain the reduced cardiovascular fitness observed in this population. Exercise training is associated with improved exercise capacity in various populations, including type 2 diabetes. Several structural and functional adaptations within the cardiovascular system following exercise training could explain these findings, such as reductions in ventricular and vascular structural hypertrophy and compliance coupled with increased functional reserve. Although these cardiovascular adaptations to aerobic exercise training have been well documented in older populations with similar decrements in cardiovascular fitness and function, they have yet to be examined in patients with type 2 diabetes. For this reason, we contend that exercise training may be an excellent therapeutic adjunct in the treatment of diabetic cardiovascular disease.

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.

Meta-analysis of the effect of structured exercise training on cardiorespiratory fitness in Type 2 diabetes mellitus

AIMS/HYPOTHESIS

Low cardiorespiratory fitness is a powerful and independent predictor of mortality in people with diabetes. Several studies have examined the effects of exercise on cardiorespiratory fitness in Type 2 diabetic individuals. However, these studies had relatively small sample sizes and highly variable results. Therefore the aim of this study was to systematically review and quantify the effects of exercise on cardiorespiratory fitness in Type 2 diabetic individuals.

METHODS

MEDLINE, EMBASE, and four other databases were searched up to March 2002 for randomized, controlled trials evaluating effects of structured aerobic exercise interventions of 8 weeks or more on cardiorespiratory fitness in adults with Type 2 diabetes. Cardiorespiratory fitness was defined as maximal oxygen uptake (VO(2max)) during a maximal exercise test.

RESULTS

Seven studies, presenting data for nine randomized trials comparing exercise and control groups (overall n=266), met the inclusion criteria. Mean exercise characteristics were as follows: 3.4 sessions per week, 49 min per session for 20 weeks. Exercise intensity ranged from 50% to 75% of VO(2max). There was an 11.8% increase in VO(2max) in the exercise group and a 1.0% decrease in the control group (post intervention standardized mean difference =0.53, p<0.003). Studies with higher exercise intensities tended to produce larger improvements in VO(2max). Exercise intensity predicted post-intervention weighted mean difference in HbA(1c) (r=-0.91, p=0.002) to a larger extent than did exercise volume (r=-0.46, p=0.26).

CONCLUSIONS/INTERPRETATION

Regular exercise has a statistically and clinically significant effect on VO(2max) in Type 2 diabetic individuals. Higher intensity exercise could have additional benefits on cardiorespiratory fitness and HbA(1c).

Insulin- and exercise-stimulated skeletal muscle blood flow and glucose uptake in obese men

OBJECTIVE

Insulin resistance in obese subjects results in the impaired use of glucose by insulin-sensitive tissues, e.g., skeletal muscle. In the present study, we determined whether insulin resistance in obesity is associated with an impaired ability of exercise to stimulate muscle blood flow, oxygen delivery, or glucose uptake.

RESEARCH METHODS AND PROCEDURES

Nine obese (body mass index = 36 +/- 2 kg/m(2)) and 11 age-matched nonobese men (body mass index = 22 +/- 1 kg/m(2)) performed one-legged isometric exercise during hyperinsulinemia. Rates of femoral muscle blood flow, oxygen consumption, and glucose uptake were measured simultaneously in both legs using [(15)O]H(2)O, [(15)O]O(2), [(18)F]fluoro-deoxy-glucose, and positron emission tomography.

RESULTS

The obese subjects exhibited resistance to insulin stimulation of glucose uptake in resting muscle, regardless of whether glucose uptake was expressed per kilogram of femoral muscle mass (p = 0.001) or per the total mass of quadriceps femoris muscle. At similar workloads, oxygen consumption, blood flow, and glucose uptake were lower in the obese than the nonobese subjects when expressed per kilogram of muscle, but similar when expressed per quadriceps femoris muscle mass.

DISCUSSION

We conclude that obesity is characterized by insulin resistance of glucose uptake in resting skeletal muscle regardless of how glucose uptake is expressed. When compared with nonobese individuals at similar absolute workloads and under identical hyperinsulinemic conditions, the ability of exercise to increase muscle oxygen uptake, blood flow, and glucose uptake per muscle mass is blunted in obese insulin-resistant subjects. However, these defects are compensated for by an increase in muscle mass.

Current concepts in insulin resistance, type 2 diabetes mellitus, and the metabolic syndrome

A clustering of risk factors, including elevated triglycerides, decreased high-density lipoprotein cholesterol, hyperinsulinemia, and hypertension often are observed in patients who are insulin resistant. Insulin resistance has been found to play a critical role in the development of cardiovascular disease, particularly in patients with type 2 diabetes. Patients with insulin resistance have an increase in small, dense low-density lipoprotein (LDL) cholesterol, which is more atherogenic than large, buoyant LDL cholesterol. In the context of insulin resistance, insulin has reduced effects on the phosphatidylinositol 3 kinase (PI3K) pathway, whereas mitogen-activated protein kinase activity is maintained. The result is an exaggeration of the mitogenic actions of insulin leading to vascular smooth muscle proliferation and elevated plasminogen activator inhibitor (PAI)-1. Notably, nitric oxide-mediated vasodilation also is impaired, further contributing to atherogenicity. In addition, hyperinsulinemia further contributes to cardiovascular risk by promoting thrombosis. Patients who are insulin resistant have decreased fibrinolysis, as indicated by increased levels of PAI-1. Studies have shown that enhancing insulin sensitivity with insulin sensitizers, such as thiazolidinediones, may improve insulin resistance and limit the development of adverse cardiovascular consequences.

Dynamics of microvascular oxygen pressure during rest-contraction transition in skeletal muscle of diabetic rats

Type I diabetes reduces dramatically the capacity of skeletal muscle to receive oxygen (QO(2)). In control (C; n = 6) and streptozotocin-induced diabetic (D: n = 6, plasma glucose = 25.3 +/- 3.9 mmol/l and C: 8.3 +/- 0.5 mmol/l) rats, phosphorescence quenching was used to test the hypothesis that, in D rats, the decline in microvascular PO(2) [Pm(O(2)), which reflects the dynamic balance between O(2) utilization (VO(2)) and QO(2)] of the spinotrapezius muscle after the onset of electrical stimulation (1 Hz) would be faster compared with that of C rats. Pm(O(2)) data were fit with a one or two exponential process (contingent on the presence of an undershoot) with independent time delays using least-squares regression analysis. In D rats, Pm(O(2)) at rest was lower (C: 31.2 +/- 3.2 mmHg; D: 24.3 +/- 1.3 mmHg, P < 0.05) and at the onset of contractions decreased after a shorter delay (C: 13.5 +/- 1.8 s; D: 7.6 +/- 2.1 s, P < 0.05) and with a reduced mean response time (C: 31.4 +/- 3.3 s; D: 23.9 +/- 3.1 s, P < 0.05). Pm(O(2)) exhibited a marked undershoot of the end-stimulation response in D muscles (D: 3.3 +/- 1.1 mmHg, P < 0.05), which was absent in C muscles. These results indicate an altered VO(2)-to-QO(2) matching across the rest-exercise transition in muscles of D rats.