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

Triceps-surae musculotendinous stiffness: relative differences between obese and non-obese postmenopausal women

BACKGROUND

There is a lack of research into the relationship between obesity and muscle-tendon unit stiffness in postmenopausal women. Muscle-tendon unit stiffness appears to affect human motion performance and excessive and insufficient stiffness can increase the risk of bone and soft tissue injuries, respectively. The aim of this study was to investigate the relationship between muscle-tendon unit stiffness and obesity in postmenopausal women.

METHODS

105 postmenopausal women (58 [SD 5.5] years) participated. Four groups (normal weight, pre-obese, obesity class I and obesity class II) were defined according World Health Organization classification of body mass index. The ankle muscle-tendon unit stiffness was assessed in vivo with a free oscillation technique using a load of 30% of maximal voluntary isometric contraction.

FINDINGS

ANOVA shows significant difference in muscle-tendon unit stiffness among the groups defined (P<0.001). Post hoc analysis reveals significant differences between the following groups: normal weight-pre-obese; normal weight-obesity class I and normal weight-obesity class II. The normal weight group had stiffness of 15789 (SD 2969) N/m, pre-obese of 19971 (SD 3678) N/m, obesity class I of 21435 (SD 4295) N/m, and obesity class II of 23497 (SD 1776) N/m.

INTERPRETATION

Obese subjects may have increased muscle-tendon unit stiffness because of fat infiltration in leg skeletal muscles, range of motion restrictions and stability/posture reasons and might be more predisposed to develop musculoskeletal injuries. Normal weight group had identical stiffness values to those reported in studies where subjects were not yet menopausal, suggesting that stiffness might not be influenced by menopause.

The origin of intermuscular adipose tissue and its pathophysiological implications

The intermuscular adipose tissue (IMAT) is a depot of adipocytes located between muscle bundles. Several investigations have recently been carried out to define the phenotype, the functional characteristics, and the origin of the adipocytes present in this depot. Among the different mechanisms that could be responsible for the accumulation of fat in this site, the dysdifferentiation of muscle-derived stem cells or other mesenchymal progenitors has been postulated, turning them into cells with an adipocyte phenotype. In particular, muscle satellite cells (SCs), a heterogeneous stem cell population characterized by plasticity and self-renewal that allow muscular growth and regeneration, can acquire features of adipocytes, including the abilities to express adipocyte-specific genes and accumulate lipids. Failure to express the transcription factors that direct mesenchymal precursors into fully differentiated functionally specialized cells may be responsible for their phenotypic switch into the adipogenic lineage. We proved that human SCs also possess a clear adipogenic potential that could explain the presence of mature adipocytes within skeletal muscle. This occurs under some pathological conditions (i.e., primary myodystrophies, obesity, hyperglycemia, high plasma free fatty acids, hypoxia, etc.) or as a consequence of thiazolidinedione treatment or simply because of a sedentary lifestyle or during aging. Several pathways and factors (PPARs, WNT growth factors, myokines, GEF-GAP-Rho, p66(shc), mitochondrial ROS production, PKCβ) could be implicated in the adipogenic conversion of SCs. The understanding of the molecular pathways that regulate muscle-to-fat conversion and SC behavior could explain the increase in IMAT depots that characterize many metabolic diseases and age-related sarcopenia.

Statin therapy, muscle function and falls risk in community-dwelling older adults

BACKGROUND

Statin therapy can cause myopathy, however it is unclear whether this exacerbates age-related muscle function declines.

AIM

To describe differences between statin users and non-users in muscle mass, muscle function and falls risk in a group of community-dwelling older adults.

DESIGN

A prospective, population-based cohort study with a mean follow-up of 2.6 years.

METHODS

Total 774 older adults [48% female; mean (standard deviation) age = 62 (7) years] were examined at baseline and follow-up. Differences in percentage appendicular lean mass (%ALM), leg strength, leg muscle quality (LMQ; specific force) and falls risk were compared for statin users and non-users.

RESULTS

There were 147 (19%) statin users at baseline and 179 (23%) at follow-up. Longitudinal analyses revealed statin use at baseline predicted increased falls risk scores over 2.6 years (0.14, 95% CI 0.01 to 0.27) and a trend towards increased %ALM (0.45%, 95% CI -0.01 to 0.92). Statin users at both time points demonstrated decreased leg strength (-5.02 kg, 95% CI -9.65 to -0.40) and LMQ (-0.30 kg/kg, 95% CI -0.59 to -0.01), and trended towards increased falls risk (0.13, 95% CI -0.01 to 0.26) compared to controls. Finally, statin users at both baseline and follow-up demonstrated decreased leg strength (-16.17 kg, 95% CI -30.19 to -2.15) and LMQ (-1.13 kg/kg, 95% CI -2.02 to -0.24) compared to those who had ceased statin use at follow-up.

CONCLUSION

Statin use may exacerbate muscle performance declines and falls risk associated with aging without a concomitant decrease in muscle mass, and this effect may be reversible with cessation.

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

The purpose of this review is to provide information about the role of exercise in the prevention of skeletal muscle insulin resistance, that is, the inability of insulin to properly cause glucose uptake into skeletal muscle. Insulin resistance is associated with high levels of stored lipids in skeletal muscle cells. Aerobic exercise training decreases the amounts of these lipid products and increases the lipid oxidative capacity of muscle cells. Thus, aerobic exercise training may prevent insulin resistance by correcting a mismatch between fatty acid uptake and fatty acid oxidation in skeletal muscle. Additionally, a single session of aerobic exercise increases glucose uptake by muscle during exercise, increases the ability of insulin to promote glucose uptake, and increases glycogen accumulation after exercise, all of which are important to blood glucose control. There also is some indication that resistance exercise may be effective in preventing insulin resistance. The information provided is intended to help clinicians understand and explain the roles of exercise in reducing insulin resistance.

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.

Plantar stresses on the neuropathic foot during barefoot walking

BACKGROUND AND PURPOSE

Patients with diabetes mellitus and peripheral neuropathy are at high risk for plantar skin breakdown due to unnoticed plantar stresses during walking. The purpose of this study was to determine differences in stress variables (peak plantar pressure, peak pressure gradient, peak maximal subsurface shear stress, and depth of peak maximal subsurface shear stress) between the forefoot (where most ulcers occur) and the rear foot in subjects with and without diabetes mellitus, peripheral neuropathy, and a plantar ulcer measured during barefoot walking.

SUBJECTS

Twenty-four subjects participated: 12 with diabetes mellitus, peripheral neuropathy, and a plantar ulcer (DM+PN group) and 12 with no history of diabetes mellitus or peripheral neuropathy (control group). The subjects (11 men, 13 women) had a mean age (+/-SD) of 54+/-8 years.

METHODS

Plantar pressures were measured during barefoot walking using a pressure platform. Stress variables were estimated at the forefoot and the rear foot for all subjects.

RESULTS

All stress variables were higher (127%-871%) in the forefoot than in the rear foot, and the peak pressure gradient showed the greatest difference (538%-871%). All stress variables were higher in the forefoot in the DM+PN group compared with the control group (34%-85%), and the peak pressure gradient showed the greatest difference (85%). The depth (X+/-SD) of peak maximum subsurface shear stress in the forefoot in the DM+PN group was half that in the control group (3.8+/-2.0 versus 8.0+/-4.3 mm, respectively).

DISCUSSION AND CONCLUSION

: These results indicate that stresses are relatively higher and located closer to the skin surface in locations where skin breakdown is most likely to occur. These stress variables may have additional value in predicting skin injury over the traditionally measured peak plantar pressure, but prospective studies using these variables to predict ulcer risk are needed to test this hypothesis.

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.