Skeletal muscle insulin resistance: roles of fatty acid metabolism and exercise

Insulin, IGF-I, and muscle MAPK pathway responses after sustained exercise and their contribution to growth and lipid metabolism regulation in gilthead sea bream

Herein, we studied whether sustained exercise positively affects growth of gilthead sea bream by alterations in a) plasma concentrations of insulin and IGF-I, b) signaling pathways in muscle, or c) regulation of lipid metabolism. Specifically, we evaluated the effects of moderated swimming (1.5 body lengths per second; BL/s) on the circulating concentrations of insulin and IGF-I, morphometric parameters, and expression of genes related to lipid metabolism in gilthead sea bream (80-90 g BW). Exercise increased the specific growth rate (P < 0.05) and reduced the hepatosomatic index (P = 0.006). Plasma IGF-I concentrations increased in exercised fish (P = 0.037), suggesting a role for this endocrine factor in the control of muscular growth and metabolic homeostasis during swimming. The observed decrease in plasma insulin concentrations (P = 0.016) could favor the mobilization of tissue reserves in exercised fish. In this sense, the increase in liver fatty acid content (P = 0.041) and the changes in expression of peroxisome proliferator-activated receptors PPARα (P = 0.017) and PPARγ (P = 0.033) indicated a hepatic lipid mobilization. Concentration of glycogen in both white and red muscles was decreased (P = 0.021 and P = 0.017, respectively) in exercised (n = 12) relative to control (n = 12) gilthead sea bream, whereas concentrations of glucose (P = 0.016) and lactate (P = 0.0007) were decreased only in red muscle, indicating the use of these substrates. No changes in the glucose transporter and in lipoprotein lipase mRNA expression were found in any of the tissues studied. Exercised sea bream had decreased content of PPARβ mRNA in white and red muscle relative to control sea bream expression (P = 0.001 and P = 0.049, respectively). Mitogen-activated protein kinase phosphorylation was significantly down-regulated in both white and red muscles of exercised sea bream (P = 0.0374 and P = 0.0371, respectively). Tumor necrosis factor-α expression of white muscle was down-regulated in exercised gilthead sea bream (P = 0.045). Collectively, these results contribute to the knowledge base about hormonal regulation of growth and lipid metabolism in exercised gilthead sea bream.

Modified minimal model for effect of physical exercise on insulin sensitivity and glucose effectiveness in type 2 diabetes and healthy human

The Bergman's minimal model of glucose and insulin plasma levels is commonly used to analyse the results of glucose tolerance tests in humans. In this paper, we present the modified minimal model with plasma insulin compartment under the assumption that if the plasma glucose compartment drops below the basal glucose levels, the rate of insulin entering the plasma glucose compartment is zero. Insulin is cleared from the plasma insulin compartment at a rate proportional to the amount of insulin in the plasma insulin compartment. The modified minimal model was used to study the effect of physical exercise via parameters of a mathematical model to qualitative the magnitude of changes in insulin sensitivity (S(I)) and glucose effectiveness (S(G)) in response to exercise in type 2 diabetes and healthy human. The short-term effects of physical exercise in type 2 diabetes did not improve S(G), but markedly improved the low S(I) values found in type 2 diabetes, indicating that the effects of exercise on S(I) are quantitatively important in the interpretation of training-related S(I) changes and may even be therapeutically useful in type 2 diabetes patients. Physical exercise is indicated either to prevent or delay the onset of type 2 diabetes or to assure a good control of type 2 diabetes by increasing insulin sensitivity.

Botulinum toxin effects on gasatrocnemius strength and plantar pressure in diabetics with peripheral neuropathy and forefoot ulceration

BACKGROUND

High forefoot plantar pressure is associated with plantar ulcers in people with diabetes and peripheral neuropathy. The purpose of this pilot study was to determine the safety and efficacy of botulinum toxin A injected into the gastrocnemius-soleus muscles to reduce muscle strength and plantar pressure.

METHODS

This double blind, randomized clinical trial studied 17 people with diabetes mellitus, peripheral neuropathy and a forefoot plantar ulcer. Subjects were randomized into one of three groups receiving gastrocnemius-soleus muscle injections on the involved side with; 1) Saline (n = 5, weight =99± 21 kg), 2) 200-units of Botox® (n = 7, weight = 101± 5 kg), or 3) 300-units of Botox® (n = 5, weight = 129± 22 kg). Botox® dose was converted to units/kg, the majority received between 1.9 and 2.4 units/kg (n = 11) and one 3.2 units/kg. Plantarflexor peak torque and forefoot peak plantar pressure were quantified prior and 2 weeks post-injection.

RESULTS

There were no complications from the injections. Plantarflexor peak torque on the involved side increased in the placebo and 300 groups (3± 4 Nm and 6± 10 Nm, respectively) and decreased -8± 11 Nm in the 200 group. There was no relationship between units/kg of Botox® for each subject and change in plantarflexor peak torque. Forefoot peak plantar pressure did not change in the placebo and 300 groups (0± 11 and 0± 5 N/cm(2), respectively) and decreased -4± 16 N/cm2 (4%) for the 200 group.

CONCLUSION

There were no adverse events associated with the Botox® injections. This study was unable to determine the dose to consistently reduce plantarflexor strength and forefoot plantar pressure. Additional research is needed to investigate diabetes mellitus specific physiological changes and their impact of BoNT-A effectiveness in order to guide appropriate dosing.

Electrical pulse stimulation of cultured human skeletal muscle cells as an in vitro model of exercise

Background and Aims

Physical exercise leads to substantial adaptive responses in skeletal muscles and plays a central role in a healthy life style. Since exercise induces major systemic responses, underlying cellular mechanisms are difficult to study in vivo. It was therefore desirable to develop an in vitro model that would resemble training in cultured human myotubes.

Methods

Electrical pulse stimulation (EPS) was applied to adherent human myotubes. Cellular contents of ATP, phosphocreatine (PCr) and lactate were determined. Glucose and oleic acid metabolism were studied using radio-labeled substrates, and gene expression was analyzed using real-time RT-PCR. Mitochondrial content and function were measured by live imaging and determination of citrate synthase activity, respectively. Protein expression was assessed by electrophoresis and immunoblotting.

Results

High-frequency, acute EPS increased deoxyglucose uptake and lactate production, while cell contents of both ATP and PCr decreased. Chronic, low-frequency EPS increased oxidative capacity of cultured myotubes by increasing glucose metabolism (uptake and oxidation) and complete fatty acid oxidation. mRNA expression level of pyruvate dehydrogenase complex 4 (PDK4) was significantly increased in EPS-treated cells, while mRNA expressions of interleukin 6 (IL-6), cytochrome C and carnitin palmitoyl transferase b (CPT1b) also tended to increase. Intensity of MitoTracker®Red FM was doubled after 48 h of chronic, low-frequency EPS. Protein expression of a slow fiber type marker (MHCI) was increased in EPS-treated cells.

Conclusions

Our results imply that in vitro EPS (acute, high-frequent as well as chronic, low-frequent) of human myotubes may be used to study effects of exercise.

Repeated Application of Low-Frequency Electroacupuncture Improves High-Fructose Diet-Induced Insulin Resistance in Rats

Background

Insulin resistance is frequently present in obesity and during the development of type 2 diabetes mellitus.

Objective

The purpose of the present study was to investigate the effect of electroacupuncture (EA) on high-fructose diet (HFD)-induced insulin resistance.

Methods

Male Wistar rats were fed HFD for 4 weeks and developed insulin resistance. Insulin sensitivity was assessed by clamp. The number of animals was seven, eight and seven in the control, HFD and HFD+EA groups, respectively. AMP-activated protein kinase (AMPK) and glucose transporter 4 (GLUT4) in skeletal muscle were measured by Western blotting analysis (n=7 in each group). EA stimulation was carried out 12 times over 4 weeks at an intensity of 1–3 mA and a frequency of 2/15 Hz in a conscious state without restraint.

Results

There was no significant difference in mean body weight and fasting blood glucose concentration between groups at the end of the experiment. The mean glucose infusion rate during the clamp was significantly lower in the HFD group than in controls (p<0.05). There was no significant difference in expression of GLUT4 in skeletal muscle in the control and each group. Phosphorylated AMPKα (Thr172) in skeletal muscle showed a significant increase immediately after the final EA stimulation when compared with the control group (p<0.05).

Conclusion

Repeated application of EA is capable of improving diet-induced insulin resistance, probably through activation of AMPK signalling pathways in skeletal muscle. These results suggest that repeated application of EA may have beneficial effects on diet-induced insulin resistance.

Enhanced exercise-induced muscle damage and muscle protein degradation in streptozotocin-induced type 2 diabetic rats

Aims/Introduction:  The effects of 5-day voluntary exercise on muscle damage and muscle protein degradation were investigated in a streptozotocin-induced rat model of moderately glycemic, uncontrolled, type 2 diabetes.

MATERIALS AND METHODS

  In the preliminary experiment, an oral glucose tolerance (1.0 g/kg) test was carried out to confirm the development of diabetes 3 days after streptozotocin treatment (30 mg/kg). In the genuine experiment, rats were divided into four groups: (i) non-diabetic rats without exercise (controls); (ii) non-diabetic rats with exercise; (iii) diabetic rats without exercise; and (iv) diabetic rats with exercise. After 5 days of voluntary wheel running exercise, blood and 24-h urine were collected, and levels of serum creatine kinase, a marker of muscle damage, and 24-h urinary excretion of muscle degradation products were determined.

RESULTS

  Type 2 diabetic rats with insulin deficiency that exercised had higher serum creatine kinase and greater urinary excretions of creatinine, urea nitrogen and 3-methylhistidine compared with both type 2 diabetic rats with insulin deficiency and non-diabetic rats that did not exercise. However, there were no differences in serum creatine kinase and urinary excretions of creatinine, urea nitrogen and 3-methylhistidine between non-diabetic rats that did and did not exercise.

CONCLUSIONS

  These findings suggest that muscle damage is induced and muscle protein degradation are enhanced by chronic moderate exercise in moderately glycemic uncontrolled type 2 diabetic rats with insulin deficiency at an intensity level of exercise that does not affect muscle damage and muscle protein degradation in non-diabetic rats. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00130.x, 2011).

Transcriptional metabolic inflexibility in skeletal muscle among individuals with increasing insulin resistance

Disturbances in skeletal muscle lipid metabolism may play an important role in development of insulin resistance (IR). The aim was to investigate transcriptional control of skeletal muscle fatty acid (FA) metabolism in individuals with the metabolic syndrome (MetS) with varying degrees of insulin sensitivity (S(I)). 122 individuals with MetS (NCEP-ATP III criteria) at age 35-70 years, BMI 27-38 kg/m(2) were studied (subgroup EU-LIPGENE study). Individuals were divided into quartiles of S(I) measured during a frequently sampled insulin modified intravenous glucose tolerance test. Skeletal muscle normalized mRNA expression levels of genes important in skeletal muscle FA handling were analyzed with quantitative real-time PCR. The expression of sterol regulatory element binding protein 1c (SREBP1c), acetyl-CoA carboxylase 2 (ACC2), diacylglycerol acyltransferase (DGAT1), and nuclear respiration factor (NRF) was higher in the lowest two quartiles of S(I) (<50th) compared with the highest two quartiles of S(I) (>50th). Interestingly, peroxisome proliferator-activated receptor coactivator 1α (PGC1α), peroxisome proliferator-activated receptor α (PPARα), and muscle carnitine palmitoyl transferase 1b (mCPT1), important for oxidative metabolism, showed a complex mRNA expression profile; levels were lower in both the most "insulin sensitive" (IS) as well as the most "IR" individuals. Lipoprotein lipase (LPL) mRNA was reduced in the lowest quartile of S(I). Enhanced gene expression of SREBP1c and ACC2 in the IR state suggests a tendency towards FA storage rather than oxidation. From the lower expression of PGC1α, PPARα, and mCPT1 in both the most "IS" as well as the most "IR" individuals, it may be speculated that "IS" subjects do not need to upregulate these genes to have a normal FA oxidation, whereas the most "IR" individuals are inflexible in upregulating these genes.

Exercise training improves sleep pattern and metabolic profile in elderly people in a time-dependent manner

Aging and physical inactivity are two factors that favors the development of cardiovascular disease, metabolic syndrome, obesity, diabetes, and sleep dysfunction. In contrast, the adoption a habitual of moderate exercise may present a non-pharmacological treatment alternative for sleep and metabolic disorders. We aimed to assess the effects of moderate exercise training on sleep quality and on the metabolic profile of elderly people with a sedentary lifestyle. Fourteen male sedentary, healthy, elderly volunteers performed moderate training for 60 minutes/day, 3 days/week for 24 wk at a work rate equivalent to the ventilatory aerobic threshold. The environment was kept at a temperature of 23 ± 2°C, with an air humidity 60 ± 5%. Blood and polysomnographs analysis were collected 3 times: at baseline (1 week before training began), 3 and 6 months (after 3 and 6 months of training). Training promoted increasing aerobic capacity (relative VO₂, time and velocity to VO_2max; p < 0.05), and reduced serum NEFA, and insulin concentrations as well as improved HOMA index (p < 0.05), and increased adiponectin levels (p < 0.05), after 3 months of training when compared with baseline data. The sleep parameters, awake time and REM sleep latency were decreased after 6 months exercise training (p < 0.05) in relation baseline values. Our results demonstrate that the moderate exercise training protocol improves the sleep profile in older people, but the metabolism adaptation does not persist. Suggesting that this population requires training strategy modifications as to ensure consistent alterations regarding metabolism.

Improving glucose metabolism with resveratrol in a swine model of metabolic syndrome through alteration of signaling pathways in the liver and skeletal muscle

HYPOTHESIS

We hypothesized that supplemental resveratrol would affect glucose metabolism in the skeletal muscle and liver to improve blood glucose control.

DESIGN

Case-control study.

SETTING

Hospital laboratory.

SUBJECTS

Yorkshire miniswine.

INTERVENTION

The swine developed metabolic syndrome by consuming a high-calorie, high–fat/cholesterol diet for 11 weeks. Pigs were fed either a normal diet (control) (n = 7), a hypercholesterolemic diet (HCC) (n = 7), or a hypercholesterolemic diet with supplemental resveratrol (100 mg/kg/d) (HCRV) (n = 7). Animals underwent dextrose challenge prior to euthanasia and tissue collection.

MAIN OUTCOME MEASURES

Measurements of glucose and insulin levels, skeletal muscle and liver protein expression, and liver function test results.

RESULTS

The HCC group had significantly increased blood glucose levels at 30 minutes as compared with the control and HCRV groups. The HCC group demonstrated increased fasting serum insulin levels and levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. Oil red O staining demonstrated increased lipid deposition in the livers of the HCC animals. Immunoblotting in the liver showed increased levels of mammalian target of rapamycin, insulin receptor substrate 1, and phosphorylated AKT in the HCRV group. Immunoblotting in skeletal muscle tissue demonstrated increased glucose transporter type 4 (Glut 4), peroxisome proliferating activation receptor coactivator 1α, peroxisome proliferator-activated receptor α, peroxisome proliferator-activated receptor , and phosphorylated AKT at threonine 308 expression as well as decreased retinol binding protein 4 in the HCRV group. Immunofluorescence staining for Glut 4 in the skeletal muscle demonstrated increased Glut 4 staining in the HCRV group compared with the HCC or control groups.

CONCLUSION

Supplemental resveratrol positively influences glucose metabolism pathways in the liver and skeletal muscle and leads to improved glucose control in a swine model of metabolic syndrome.

Resistance Exercise Did Not Alter Intramuscular Adipose Tissue but Reduced Retinol-binding Protein-4 Concentration in Individuals with Type 2 Diabetes Mellitus

Lipid accumulation in muscle is associated with diminished insulin sensitivity. It was hypothesized that resistance exercise decreases muscular adipose tissue and reduces the level of retinol-binding protein-4 (RBP4), which is linked to adipose tissue and insulin sensitivity in diabetics. Forty-four women with type 2 diabetes were randomly assigned to three groups for a period of 12 weeks: control (asked to maintain a sedentary lifestyle); resistance exercise (elastic band exercise at moderate intensity five times per week); and aerobic exercise (walking for 60 min at moderate intensity five times per week). Subcutaneous (SCAT), subfascial (SFAT) and intramuscular (IMAT) adipose tissues at mid-thigh level were assessed using computed tomography, and RBP4 level and insulin sensitivity (fractional disappearance rate of insulin, kITT) were assessed before and after intervention. Changes in SCAT, SFAT, IMAT, RBP4 and kITT were similar among the three groups. Within-group analysis revealed that body mass index and waist circumference decreased significantly in both exercise groups, but RBP4 decreased significantly only with resistance exercise. Resistance exercise did not alter muscular adipose tissue or improve insulin sensitivity.

Differential regulation of PGC-1alpha expression in rat liver and skeletal muscle in response to voluntary running

BACKGROUND

The beneficial actions of exercise training on lipid, glucose and energy metabolism and insulin sensitivity appear to be in part mediated by PGC-1alpha. Previous studies have shown that spontaneously exercised rats show at rest enhanced responsiveness to exogenous insulin, lower plasma insulin levels and increased skeletal muscle insulin sensitivity. This study was initiated to examine the functional interaction between exercise-induced modulation of skeletal muscle and liver PGC-1alpha protein expression, whole body insulin sensitivity, and circulating FFA levels as a measure of whole body fatty acid (lipid) metabolism.

METHODS

Two groups of male Wistar rats (2 Mo of age, 188.82 +/- 2.77 g BW) were used in this study. One group consisted of control rats placed in standard laboratory cages. Exercising rats were housed individually in cages equipped with running wheels and allowed to run at their own pace for 5 weeks. At the end of exercise training, insulin sensitivity was evaluated by comparing steady-state plasma glucose (SSPG) concentrations at constant plasma insulin levels attained during the continuous infusion of glucose and insulin to each experimental group. Subsequently, soleus and plantaris muscle and liver samples were collected and quantified for PGC-1alpha protein expression by Western blotting. Collected blood samples were analyzed for glucose, insulin and FFA concentrations.

RESULTS

Rats housed in the exercise wheel cages demonstrated almost linear increases in running activity with advancing time reaching to maximum value around 4 weeks. On an average, the rats ran a mean (Mean +/- SE) of 4.102 +/- 0.747 km/day and consumed significantly more food as compared to sedentary controls (P < 0.001) in order to meet their increased caloric requirement. Mean plasma insulin (P < 0.001) and FFA (P < 0.006) concentrations were lower in the exercise-trained rats as compared to sedentary controls. Mean steady state plasma insulin (SSPI) and glucose (SSPG) concentrations were not significantly different in sedentary control rats as compared to exercise-trained animals. Plantaris PGC-1alpha protein expression increased significantly from a 1.11 +/- 0.12 in the sedentary rats to 1.74 +/- 0.09 in exercising rats (P < 0.001). However, exercise had no effect on PGC-1alpha protein content in either soleus muscle or liver tissue. These results indicate that exercise training selectively up regulates the PGC-1alpha protein expression in high-oxidative fast skeletal muscle type such as plantaris muscle.

CONCLUSION

These data suggest that PGC-1alpha most likely plays a restricted role in exercise-mediated improvements in insulin resistance (sensitivity) and lowering of circulating FFA levels.

Vasopressin V1a receptor polymorphism and interval walking training effects in middle-aged and older people

We assessed whether single nucleotide polymorphism rs1042615 of the vasopressin V1a receptor altered the indices of lifestyle-related diseases in middle-aged and older people (mean+/-SD: 64+/-7 years), and, if so, whether it also altered the effects of interval walking training (IWT). CC, CT, and TT carriers of rs1042615 (42, 118, and 64 men, respectively; 113, 263, and 154 women, respectively) performed IWT. We included 5 sets of 3-minute fast walking at > or =70% peak aerobic capacity for walking and 3-minute slow walking at 40% peak aerobic capacity per day for > or =4 days per week for 5 months. Before IWT, the body mass index and diastolic blood pressure (DBP) for men were 25.1+/-0.3 kg/m(2) (mean+/-SE) and 84+/-1 mm Hg in TT, higher than the 23.6+/-0.4 kg/m(2) and 78+/-1 mm Hg in CC, respectively (P<0.01), differences that disappeared after IWT despite similar training achievement between groups (P>0.6). After IWT, body mass index and DBP decreased in TT (-0.9+/-0.1 kg/m(2) and -5+/-1 mm Hg, respectively), more than in CC (-0.5+/-0.1 kg/m(2) and 1+/-1 mm Hg, respectively; P<0.05), with a greater decrease in low-density lipoprotein cholesterol in TT than CC carriers (P<0.01). The decreases in DBP and low-density lipoprotein cholesterol were still greater in TT carriers even after adjustment for their pretraining values. On the other hand, for women, these parameters before IWT and their changes after IWT were similar among CC, CT, and TT carriers. Thus, polymorphism rs1042615 of the V1a receptor altered body mass index and DBP in middle-aged and older men and the training-induced responses of DBP and low-density lipoprotein cholesterol, whereas women did not show any of these responses.

Astragalus polysaccharide improves insulin sensitivity in KKAy mice: regulation of PKB/GLUT4 signaling in skeletal muscle

ETHNOPHARMACOLOGICAL RELEVANCE

Astragalus polysaccharide (APS) is an important bioactive component of Astragalus membranaceus Bunge (Leguminosae) that has been used in traditional Chinese medicine for treating diabetes.

AIM OF THE STUDY

To study the mechanisms by which APS ameliorates diabetes, we examined whether treatment with APS improves insulin sensitivity in insulin-resistant mice and whether this is associated with an improvement of dysregulated protein kinase B and glucose transporter 4 expressions in skeletal muscle.

METHODS

APS (700 mg kg(-1)day(-1)) or vehicle was administered to 12-week-old diabetic KKAy and nondiabetic C57BL/6J mice for 8 weeks. Changes in body weight, blood glucose level, insulin resistance index, and oral glucose tolerance were routinely evaluated. The expressions of protein kinase B and glucose transporter 4 in skeletal muscle tissues were determined with Western blot.

RESULTS

KKAy mice developed persistent hyperglycemia, impaired glucose tolerance and insulin resistance. Insulin-stimulated protein kinase B phosphorylation and glucose transporter 4 translocation were significantly decreased in KKAy compared to age-matched C57BL/6J mice. APS treatment ameliorated hyperglycemia and insulin resistance. Although the content of protein kinase B and glucose transporter 4 in KKAy skeletal muscle were not affected by APS, insulin-induced protein kinase B Ser-473 phosphorylation and glucose transporter 4 translocation in skeletal muscle were partially restored by APS treatment. In contrast, APS did not have any effect on C57BL/6J mice.

CONCLUSIONS

These results indicate that APS can regulate part of the insulin signaling in insulin-resistant skeletal muscle, and that APS could be a potential insulin sensitizer for the treatment of type 2 diabetes.

Intramuscular triacylglycerol and insulin resistance: guilty as charged or wrongly accused?

The term lipotoxicity elicits visions of steatotic liver, fat laden skeletal muscles and engorged lipid droplets that spawn a number of potentially harmful intermediates that can wreak havoc on signal transduction and organ function. Prominent among these so-called lipotoxic mediators are signaling molecules such as long chain acyl-CoAs, ceramides and diacyglycerols; each of which is thought to engage serine kinases that disrupt the insulin signaling cascade, thereby causing insulin resistance. Defects in skeletal muscle fat oxidation have been implicated as a driving factor contributing to systemic lipid imbalance, whereas exercise-induced enhancement of oxidative potential is considered protective. The past decade of diabetes research has focused heavily on the foregoing scenario, and indeed the model is grounded in strong experimental evidence, albeit largely correlative. This review centers on mechanisms that connect lipid surplus to insulin resistance in skeletal muscle, as well as those that underlie the antilipotoxic actions of exercise. Emphasis is placed on recent studies that challenge accepted paradigms.

Clinical measures of physical fitness predict insulin resistance in people at risk for diabetes

BACKGROUND AND PURPOSE

Physical inactivity has been well documented as a risk factor for type 2 diabetes. Previous studies measured the level of physical activity either with questionnaires or with direct measurements of maximum oxygen uptake. However, questionnaires are patient-report measures, and methods for obtaining direct maximum oxygen uptake measurements often are not available clinically. The purpose of this study was to investigate whether clinical measurement of health-related physical fitness with a simple test battery can predict insulin resistance, a precursor of type 2 diabetes, in people at risk for diabetes.

SUBJECTS AND METHODS

A total of 151 volunteers with at least one diabetes risk factor (overweight, hypertension, dyslipidemia, family history, impaired glucose tolerance, gestational diabetes, or delivering a baby weighing more than 4.0 kg) were recruited. Insulin resistance (as determined with the homeostasis model assessment of insulin resistance [HOMA-IR]), physical fitness (including body composition, as determined with the body mass index and waist circumference), muscle strength (handgrip strength [force-generating capacity]), muscle endurance (sit-up test), flexibility (sit-and-reach test), and cardiorespiratory endurance (step test) were measured, and a physical activity questionnaire was administered. Backward regression analysis was used to build the prediction models for insulin resistance from components of physical fitness and physical activity.

RESULTS

Body mass index, muscle strength, and cardiorespiratory fitness predicted HOMA-IR in men (adjusted R(2)=.264). In women, age, waist circumference, and cardiorespiratory fitness were the predictors of HOMA-IR (adjusted R(2)=.438).

DISCUSSION AND CONCLUSION

Clinical measures of physical fitness can predict insulin resistance in people at risk for diabetes. The findings support the validity of clinical measures of physical fitness for predicting insulin resistance in people at risk for diabetes.

Epidemiology of diabetes and diabetes-related complications

In 2005, it was estimated that more than 20 million people in the United States had diabetes. Approximately 30% of these people had undiagnosed cases. Increased risk for diabetes is primarily associated with age, ethnicity, family history of diabetes, smoking, obesity, and physical inactivity. Diabetes-related complications--including cardiovascular disease, kidney disease, neuropathy, blindness, and lower-extremity amputation--are a significant cause of increased morbidity and mortality among people with diabetes, and result in a heavy economic burden on the US health care system. With advances in treatment for diabetes and its associated complications, people with diabetes are living longer with their condition. This longer life span will contribute to further increases in the morbidity associated with diabetes, primarily in elderly people and in minority racial or ethnic groups. In 2050, the number of people in the United States with diagnosed diabetes is estimated to grow to 48.3 million.

RESULTS

from randomized controlled trials provide evidence that intensive lifestyle interventions can prevent or delay the onset of diabetes in high-risk individuals. In addition, adequate and sustained control of blood sugar levels, blood pressure, and blood lipid levels can prevent or delay the onset of diabetes-related complications in people with diabetes. Effective interventions, at both the individual and population levels, are desperately needed to slow the diabetes epidemic and reduce diabetes-related complications in the United States. This report describes the current diabetes epidemic and the health and economic impact of diabetes complications on individuals and on the health care system. The report also provides suggestions by which the epidemic can be curbed.

Comparison of combined aerobic and high-force eccentric resistance exercise with aerobic exercise only for people with type 2 diabetes mellitus

BACKGROUND AND PURPOSE

The purpose of this study was to compare the outcomes between a diabetes exercise training program using combined aerobic and high-force eccentric resistance exercise and a program of aerobic exercise only.

SUBJECTS AND METHODS

Fifteen participants with type 2 diabetes mellitus (T2DM) participated in a 16-week supervised exercise training program: 7 (mean age=50.7 years, SD=6.9) in a combined aerobic and eccentric resistance exercise program (AE/RE group) and 8 (mean age=58.5 years, SD=6.2) in a program of aerobic exercise only (AE group). Outcome measures included thigh lean tissue and intramuscular fat (IMF), glycosylated hemoglobin, body mass index (BMI), and 6-minute walk distance.

RESULTS

Both groups experienced decreases in mean glycosylated hemoglobin after training (AE/RE group: -0.59% [95% confidence interval (CI)=-1.5 to 0.28]; AE group: -0.31% [95% CI=-0.60 to -0.03]), with no significant between-group differences. There was an interaction between group and time with respect to change in thigh lean tissue cross-sectional area, with the AE/RE group gaining more lean tissue (AE/RE group: 15.1 cm(2) [95% CI=7.6 to 22.5]; AE group: -5.6 cm(2) [95% CI=-10.4 to 0.76]). Both groups experienced decreases in mean thigh IMF cross-sectional area (AE/RE group: -1.2 cm(2) [95% CI=-2.6 to 0.26]; AE group: -2.2 cm(2) [95% CI=-3.5 to -0.84]) and increases in 6-minute walk distance (AE/RE group: 45.5 m [95% CI=7.5 to 83.6]; AE group: 29.9 m [95% CI=-7.7 to 67.5]) after training, with no between-group differences. There was an interaction between group and time with respect to change in BMI, with the AE/RE group experiencing a greater decrease in BMI.

DISCUSSION AND CONCLUSION

Significant improvements in long-term glycemic control, thigh composition, and physical performance were demonstrated in both groups after participating in a 16-week exercise program.

SUBJECTS

in the AE/RE group demonstrated additional improvements in thigh lean tissue and BMI. Improvements in thigh lean tissue may be important in this population as a means to increase resting metabolic rate, protein reserve, exercise tolerance, and functional mobility.

Excessive adipose tissue infiltration in skeletal muscle in individuals with obesity, diabetes mellitus, and peripheral neuropathy: association with performance and function

BACKGROUND AND PURPOSE

The primary purpose of this study was to report differences in calf intermuscular adipose tissue (IMAT), muscle strength (peak torque), power, and physical function in individuals with obesity, diabetes mellitus (DM), and peripheral neuropathy (PN) compared with those without these impairments. A secondary purpose was to assess the relationship between IMAT and muscle strength, power, and physical function.

SUBJECTS AND METHODS

Six participants with obesity, DM, and PN (2 women, 4 men; mean age=58 years, SD=10; mean body mass index=36.3, SD=5; mean modified Physical Performance Test [PPT] score=22, SD=3) and 6 age- and sex-matched control subjects without these impairments were assessed and compared in muscle strength, muscle power, physical functioning, and muscle and fat volume, including IMAT in the calf muscles. Muscle, adipose tissue, and IMAT volumes of each calf were quantified by noninvasive magnetic resonance imaging. Muscle strength and power of the plantar-flexor and dorsiflexor muscles were quantified using isokinetic dynamometry. The modified PPT was used to assess physical function.

RESULTS

Leg muscle and fat volumes were similar between groups, although IMAT volumes were 2.2-fold higher in the subjects with obesity, DM, and PN (X=120 cm(3), SD=47) than in the control subjects (X=54 cm(3), SD=41). Muscle strength, muscle power, ratio of leg muscle power to leg muscle volume, and modified PPT scores were lower in subjects with obesity, DM, and PN compared with the control subjects.

DISCUSSION AND CONCLUSION

The data indicate that excess fat infiltration in leg skeletal muscles is associated with low calf muscle strength, low calf muscle power, and impaired physical function in individuals who are obese with DM and PN.

Diabetes and associated risk factors in patients referred for physical therapy in a national primary care electronic medical record database

OBJECTIVE

The prevalence of diabetes (type 2) in the general population has increased dramatically over the last decade, yet patients with diabetes are rarely referred for physical therapy management of their condition. The majority of patients referred for outpatient physical therapy have musculoskeletal-related conditions. Secondary conditions, such as diabetes, may be prevalent in this population, and physical therapists need to be aware of this to adjust interventions and treatment. The purpose of this article is to describe the prevalence of diabetes and the associated risk factors in adults referred for physical therapy in a primary care outpatient setting.

SUBJECTS AND METHODS

Patients aged 18 years or older referred for physical therapy were identified from the Centricity Electronic Medical Records database during the period of December 13, 1995, to June 30, 2007. Patients were evaluated on the basis of clinical (height, weight, blood pressure, laboratory values), treatment (prescriptions), and diagnostic (ICD-9 codes) criteria to identify the presence of diabetes or associated risk factors (eg, hypertension, elevated triglycerides, low high-density lipoprotein, body mass index, and prediabetes).

RESULTS

There were 52,667 patients referred for physical therapy, the majority of whom were referred for a musculoskeletal-related condition. Approximately 80% of the total study population had diabetes, prediabetes, or risk factors associated with diabetes. The prevalence of diabetes in the study population was 13.2%. Of the diabetes-associated risk factors evaluated, hypertension was the most prevalent (70.4%), and less than half (39.1%) of the study population had an elevated body mass index. Only 20% of the study population had values within normal limits for all clinical, treatment, and diagnostic criteria. Clinical and treatment measurements available to physical therapists identified the majority of associated risk factors.

CONCLUSIONS

Although not the primary indications for referral, diabetes and associated risk factors were identified in a high proportion of the study population. The evaluation of associated conditions in the outpatient orthopedic setting needs to be considered for treatment planning adjustments and to optimize care.

Diabetes mellitus and gait dysfunction: possible explanatory factors

BACKGROUND AND OBJECTIVE

Gait characteristics differ in individuals with diabetes compared with those without diabetes. Limited information regarding potential explanatory factors for this association exists. This study examined the association between diabetes and gait characteristics in older adults and explored potential explanatory factors.

DESIGN

A cross-sectional, observational study design was used.

METHODS

At the 1998-1999 clinic visit, 558 ambulatory older adults (mean age=79 years) from the Pittsburgh site of the Cardiovascular Health Study had an assessment of their gait characteristics, diabetes, health status, cognition, mood, lower-extremity circulation and sensation, vision, lower-extremity strength (force-producing capacity), physical activity, and body mass index (BMI). A series of linear regression models were developed to examine the association between diabetes and gait characteristics and to examine potential explanatory factors for the associations.

RESULTS

Diabetes was related to gait speed (beta=-.06 m/s); however, the association was partially explained by health status variables, cognition, mood, lower-extremity circulation and sensation, visual impairment, lower-extremity strength, physical activity, and BMI. Health status and lower-extremity strength each explained the greatest proportion of the association (beta reduced 66% by each). Diabetes was related to step width (beta=.02 m), and the association could not be explained by the examined factors.

CONCLUSIONS

Diabetes was associated with gait alterations in older adults. Slowed gait speed appears to be secondary to the peripheral effect of the disease on other body systems. The effect of diabetes on step width was not explained in the analyses and may be related to peripheral motor nerve function or central influences of the disease, which could not be assessed in this study.

Diabetes-related microvascular and macrovascular diseases in the physical therapy setting

Physical therapists commonly treat people with diabetes for a wide variety of diabetes-associated impairments, including those from diabetes-related vascular disease. Diabetes is associated with both microvascular and macrovascular diseases affecting several organs, including muscle, skin, heart, brain, and kidneys. A common etiology links the different types of diabetes-associated vascular disease. Common risk factors for vascular disease in people with diabetes, specifically type 2 diabetes, include hyperglycemia, insulin resistance, dyslipidemia, hypertension, tobacco use, and obesity. Mechanisms for vascular disease in diabetes include the pathologic effects of advanced glycation end product accumulation, impaired vasodilatory response attributable to nitric oxide inhibition, smooth muscle cell dysfunction, overproduction of endothelial growth factors, chronic inflammation, hemodynamic dysregulation, impaired fibrinolytic ability, and enhanced platelet aggregation. It is becoming increasingly important for physical therapists to be aware of diabetes-related vascular complications as more patients present with insulin resistance and diabetes. The opportunities for effective physical therapy interventions (such as exercise) are significant.

Intricacies of fat

One of the most exciting cell biology fields of study concerns the physiology and pathology of fat. The basic assumptions once held concerning the function of adipose tissue have been shown to be oversimplified or sometimes completely wrong. Fat does more than store excess energy; it is actually the largest endocrine organ in the body, and it may be one of the most active. Adipocytes release hormones and other molecules that act on nearby tissues and travel through the vasculature to distant sites, such as the brain, skeletal muscle, and liver. Under conditions of normal weight, those signals help the body to suppress hunger, utilize glucose, and decrease the risk of cardiovascular disease. However, under conditions of obesity, the hormones (or the proteins that bind the hormones) become abnormal and can result in states of chronic inflammation leading to diabetes and heart disease. In addition, excessive fat can lead to the accumulation of lipid droplets in nonfat cells, including skeletal and cardiac muscle. Although some lipid droplets are used as an immediate source of energy for cells, large numbers of stored droplets can cause cellular damage and cell death. The purposes of this article are to review the normal and deviant signals released by fat cells, to draw a link between those signals and chronic diseases such as diabetes, and to discuss the role of exercise in reversing some of the deviant signaling perpetrated by excess fat.