The Flexibility of Ectopic Lipids

Effects of free weight and body mass-based resistance training on thigh muscle size, strength and intramuscular fat in healthy young and middle-aged individuals

NEW FINDINGS

What is the central question of this study? How do free weight resistance training (RT) and body mass-based RT for 8 weeks compare for isometric muscular strength, muscle size and intramuscular fat (IMF) content in the quadriceps femoris? What is the main finding and its importance? Free weight and body mass-based RTs could induce muscle hypertrophy; however, decreased IMF content was observed following the body mass-based RT alone.

ABSTRACT

The objective of this study was to investigate the effects of free weight and body mass-based resistance training (RT) on muscle size and thigh intramuscular fat (IMF) in young and middle-aged individuals. Healthy individuals (aged 30-64 years) were assigned to either a free weight RT group (n = 21) or a body mass-based RT group (n = 16). Both groups performed whole-body resistance exercise twice a week for 8 weeks. Free weight resistance exercises (squats, bench press, deadlift, dumbbell rows and back range) involved 70% one repetition maximum, with three sets of 8-12 repetitions per exercise. The nine body mass-based resistance exercises (leg raise, squats, rear raise, overhead shoulder mobility exercise, rowing, dips, lunge, single-leg Romanian deadlifts and push-ups) included the maximum possible repetitions per session, which were performed in one or two sets. Mid-thigh magnetic resonance images using the two-point Dixon method were taken pre- and post-training. The muscle cross-sectional area (CSA) and IMF content in the quadriceps femoris were measured from the images. Both the groups showed significantly increased muscle CSA post-training (free weight RT group, P = 0.001; body mass-based RT group, P = 0.002). IMF content in the body mass-based RT group significantly decreased (P = 0.036) but did not significantly change in the free weight RT group (P = 0.076). These results suggest that the free weight and body mass-based RTs could induce muscle hypertrophy; however, in healthy young and middle-aged individuals, decreased IMF content was induced following the body mass-based RT alone.

Effect of electromyostimulation training on intramuscular fat accumulation determined by ultrasonography in older adults

PURPOSE

Electromyostimulation (EMS) induces a short-term change in muscle metabolism, and EMS training induces long-term improvements of muscle atrophy and function. However, the effects of EMS training on intramuscular fat in older adults are still poorly known. The purpose of this study was to examine whether the intramuscular fat index and biochemical parameters change with EMS training of the quadriceps femoris muscles in older adults.

METHODS

Nineteen non-obese older men and women performed EMS training of the quadriceps femoris for 12 weeks (3 times/week; single session for 30 min). The intramuscular fat content index was estimated by echo intensity of the vastus lateralis and rectus femoris muscles on ultrasonography, and muscle thickness was also measured. Muscle strength was assessed as the maximal voluntary contraction during isometric knee extension. Echo intensity, muscle thickness, and muscle strength were measured before and after EMS training. A rested/fasting blood samples were collected before and after EMS training for measuring plasma glucose, insulin, free fatty acid, triglyceride, and interleukin-6 concentrations. To examine the acute effect of a single-EMS session on biochemical parameters, blood samples were taken before and after the EMS session.

RESULTS

EMS training did not significantly change echo intensity in muscles, muscle thickness, muscle strength, or biochemical parameters. Regarding the acute effect on blood lipid concentrations, a single-EMS session increased free fatty acid and glucose concentrations.

CONCLUSION

EMS sessions had an acute effect of increasing free fatty acid and glucose concentrations, but EMS training intervention did not improve intramuscular fat content.

The Pathological Links between Adiposity and the Carpal Tunnel Syndrome

An association between obesity and carpal tunnel syndrome is found in many epidemiological studies. Therefore, there is a need to evaluate the physiopathological links that could explain the association between these two entities. Ectopic adipose tissue is responsible for metabolic syndrome and inflammation, and is a major risk factor for diabetes and cardiovascular diseases. Taking these elements into consideration, we conducted an extensive literature revision of the subject, considering as ectopic fat-related mechanisms the following: (a) the direct compression and the association with the metabolic syndrome of the fat deposition around the wrist, (b) the insulin resistance, dyslipidemia, inflammatory, and oxidative mechanisms related to the central deposition of the fat, (c) the impaired muscle contraction and metabolism related to myosteatosis. Each section presents the cellular pathways which are modified by the ectopic deposition of the adipose tissue and the impact in the pathogeny of the carpal tunnel syndrome. In conclusion, the experimental and clinical data support the epidemiological findings. Efforts to reduce the obesity epidemics will improve not only cardio-metabolic health but will reduce the burden of the disability-free life expectancy due to the carpal tunnel syndrome.

Unsupervised Exercise Training Was Not Found to Improve the Metabolic Health or Phenotype over a 6-Month Dietary Intervention: A Randomised Controlled Trial with an Embedded Economic Analysis

Ectopic fat leads to metabolic health problems. This research aimed to assess the effectiveness of a hypocaloric diet intervention together with an unsupervised exercise training program in comparison with a hypocaloric diet alone to reduce ectopic fat deposition. Sixty-one premenopausal women with overweight or obesity participated in this controlled trial and were each randomised into either a usual care group (hypocaloric diet) or intervention group (hypocaloric diet + unsupervised exercise training). Ectopic fat deposition, metabolic parameters, incremental costs from a societal perspective and incremental quality-adjusted life years (QALYs) were assessed before, during and after the six-month intervention period. In the total sample, there was a significant decrease in visceral adipose tissue (VAT: -18.88 cm², 95% CI -11.82 to -25.95), subcutaneous abdominal adipose tissue (SAT: -46.74 cm², 95% CI -29.76 to -63.18), epicardial fat (ECF: -14.50 cm³, 95% CI -10.9 to -18.98) and intrahepatic lipid content (IHL: -3.53%, 95% CI -1.72 to -5.32). Consequently, an "adapted" economic analysis revealed a non-significant decrease in costs and an increase in QALYs after the intervention. No significant differences were found between groups. A multidisciplinary lifestyle approach seems successful in reducing ectopic fat deposition and improving the metabolic risk profile in women with overweight and obesity. The addition of unsupervised exercise training did not further improve the metabolic health or phenotype over the six months.

Plasma Free Fatty Acid Concentration as a Modifiable Risk Factor for Metabolic Disease

Plasma free fatty acid (FFA) concentration is elevated in obesity, insulin resistance (IR), non-alcoholic fatty liver disease (NAFLD), type 2 diabetes (T2D), and related comorbidities such as cardiovascular disease (CVD). Furthermore, experimentally manipulating plasma FFA in the laboratory setting modulates metabolic markers of these disease processes. In this article, evidence is presented indicating that plasma FFA is a disease risk factor. Elevations of plasma FFA can promote ectopic lipid deposition, IR, as well as vascular and cardiac dysfunction. Typically, elevated plasma FFA results from accelerated adipose tissue lipolysis, caused by a high adipose tissue mass, adrenal hormones, or other physiological stressors. Reducing an individual’s postabsorptive and postprandial plasma FFA concentration is expected to improve health. Lifestyle change could provide a significant opportunity for plasma FFA reduction. Various factors can impact plasma FFA concentration, such as chronic restriction of dietary energy intake and weight loss, as well as exercise, sleep quality and quantity, and cigarette smoking. In this review, consideration is given to multiple factors which lead to plasma FFA elevation and subsequent disruption of metabolic health. From considering a variety of medical conditions and lifestyle factors, it becomes clear that plasma FFA concentration is a modifiable risk factor for metabolic disease.

Effect of electromyostimulation on intramyocellular lipids of the vastus lateralis in older adults: a randomized controlled trial

BACKGROUND

Excessive intramyocellular lipid (IMCL) accumulation is a primary cause of skeletal muscle insulin resistance, especially in older adults, and interventions that reduce IMCL contents are important to improve insulin sensitivity. Electromyostimulation (EMS)-induced changes in IMCL content in older adults remain unknown. The purpose of this study was to clarify the effects of a single bout of EMS on the IMCL content of the vastus lateralis muscle in older adults.

METHODS

Twenty-two physically active, non-obese older men and women were randomly assigned to an EMS intervention group (69.0 ± 5.2 years, n = 12) or a control group (68.4 ± 3.5 years, n = 10). EMS was applied to the vastus lateralis (7 s on and 7 s off) for 30 min; control participants sat quietly for 30 min. IMCL content within the vastus lateralis was quantified with ¹H-magnetic resonance spectroscopy (n = 7 per group). Fasting plasma glucose and insulin values were determined from blood samples collected before and after the EMS intervention.

RESULTS

EMS induced a significant reduction in plasma glucose (93.1 ± 9.6 to 89.5 ± 9.1 mg/dL, p < 0.01), but not IMCL content (15.7 ± 15.7 to 15.8 ± 13.1 mmol/kg wet weight, p = 0.49) or insulin (5.4 ± 2.4 to 4.7 ± 2.7 μIU/mL, p = 0.18). In the control group, no changes in IMCL content in the vastus lateralis was observed after prolonged quiet sitting.

CONCLUSION

EMS intervention for 30 min induces changes in plasma glucose, but no changes in IMCL content in older adults.

TRIAL REGISTRATION

University hospital Medical Information Network (UMIN) Center ID: UMIN000020126 . Retrospectively registered on December 222,015. https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000023242.

CORP: quantification of human skeletal muscle carnosine concentration by proton magnetic resonance spectroscopy

Noninvasive techniques to quantify metabolites in skeletal muscle provide unique insight into human physiology and enable the translation of research into practice. Proton magnetic resonance spectroscopy (¹H-MRS) permits the assessment of several abundant muscle metabolites in vivo, including carnosine, a dipeptide composed of the amino acids histidine and beta-alanine. Muscle carnosine loading, accomplished by chronic oral beta-alanine supplementation, improves muscle function and exercise capacity and has pathophysiological relevance in multiple diseases. Moreover, the marked difference in carnosine content between fast-twitch and slow-twitch muscle fibers has rendered carnosine an attractive candidate to estimate human muscle fiber type composition. However, the quantification of carnosine with ¹H-MRS requires technical expertise to obtain accurate and reproducible data. In this review, we describe the technical and physiological factors that impact the detection, analysis, and quantification of carnosine in muscle with ¹H-MRS. We discuss potential sources of error during the acquisition and preprocessing of the ¹H-MRS spectra and present best practices to enable the accurate, reliable, and reproducible application of this technique.

Proton magnetic resonance spectroscopy in skeletal muscle: Experts' consensus recommendations

1 H-MR spectroscopy of skeletal muscle provides insight into metabolism that is not available noninvasively by other methods. The recommendations given in this article are intended to guide those who have basic experience in general MRS to the special application of 1 H-MRS in skeletal muscle. The highly organized structure of skeletal muscle leads to effects that change spectral features far beyond simple peak heights, depending on the type and orientation of the muscle. Specific recommendations are given for the acquisition of three particular metabolites (intramyocellular lipids, carnosine and acetylcarnitine) and for preconditioning of experiments and instructions to study volunteers.

Transient elevation of triacylglycerol content in the liver: a fundamental component of the acute response to exercise

Exercise is well appreciated as a therapeutic approach to improve health. Although chronic exercise training can change metabolism, even a single exercise session can have significant effects upon metabolism. Responses of adipose tissue lipolysis and skeletal muscle triacylglycerol (TAG) utilization have been well appreciated as components of the acute exercise response. However, there are other central components of the physiological response to be considered, as well. A robust and growing body of literature depicts a rapid responsiveness of hepatic TAG content to single bouts of exercise, and there is a remaining need to incorporate this information into our overall understanding of how exercise affects the liver. TAG content in the liver increases during an exercise session and can continue to rise for a few hours afterwards, followed by a fairly rapid return to baseline. Here, we summarize evidence that rapid responsiveness of hepatic TAG content to metabolic stress is a fundamental component of the exercise response. Adipose tissue lipolysis and plasma free fatty acid concentration are likely the major metabolic controllers of enhanced lipid storage in the liver after each exercise bout, and we discuss nutritional impacts as well as health implications. Although traditionally clinicians would be merely concerned with hepatic lipids in overnight-fasted, rested individuals, it is now apparent that the content of hepatic TAG fluctuates in response to metabolic challenges such as exercise, and these responses likely exert significant impacts on health and cellular homeostasis.

Computed tomography-based skeletal muscle and adipose tissue attenuation: Variations by age, sex, and muscle

OBJECTIVE

This study aimed to investigate how skeletal muscle attenuation and adipose tissue (AT) attenuation of the quadriceps, hamstrings, paraspinal muscle groups and the psoas muscle vary according to the targeted muscles, sex, and age.

DESIGN

Population-based cross-sectional study.

SETTING

Community-dwelling old population in Reykjavik, Iceland.

SUBJECTS

A total of 5331 older adults (42.8% women), aged 66-96 years from the Age, Gene/Environment Susceptibility (AGES)- Reykjavik Study, who participated in the baseline visit (between 2002 and 2006) and had valid thigh and abdominal computed tomography (CT) scans were studied.

METHODS

Muscle attenuation and AT attenuation of the quadriceps, hamstrings, paraspinal muscle groups and the psoas muscle were determined using CT. Linear mixed model analysis of variance was performed for each sex, with skeletal muscle or AT attenuation as the dependent variable.

RESULTS

Muscle attenuation decreased, and AT attenuation increased with age in both sexes, and these differences were specific for each muscle, although not in all age groups. Age-related differences in muscle and AT attenuation varied with specific muscle. In general, for both sexes, skeletal muscle attenuation of the hamstrings declined more than average with age. Men and women displayed a different pattern in the age differences in AT attenuation for each muscle.

CONCLUSIONS

Our data support the hypotheses that skeletal muscle attenuation decreases, and AT attenuation increases with aging. In addition, our data add new evidence, supporting that age-related differences in skeletal muscle and AT attenuation vary between muscles.

Impact of diets rich in olive oil, palm oil or lard on myokine expression in rats

It has recently emerged that myokines may be an important skeletal muscle adaptive response to obesogenic diets in sedentary subjects (who do not exercise). This study aimed to assess the influence of various high fat (HF) diets rich in either crude palm oil (cPO), refined palm oil (rPO), olive oil (OO) or lard on the modulation of myokine gene expression in the gastrocnemius. Five groups of 8 rats were each fed HF or control diet for 12 weeks. Systemic parameters concerning glucose, insulin, inflammation, cholesterol, triglycerides (TG) and transaminases were assessed by routine methods or ELISA. Akt and ACC phosphorylation were analyzed by WB in the soleus. Mitochondrial density, inflammation, and the gene expression of 17 myokines and the apelin receptor (Apj) were assessed by qPCR in the gastrocnemius. We found that HF diet-fed rats were insulin resistant and Akt phosphorylation decreased in the soleus muscle, but without any change in Glut4 gene expression. Systemic (IL-6) and muscle inflammation (NFκB and IκB) were not affected by the HF diets as well as TBARS, and ASAT level was enhanced with OO diet. Soleus pACC phosphorylation and gastrocnemius mitochondrial density were not significantly altered. The gene expression of some myokines was respectively increased (myostatin and Il-15) and decreased (Fndc5 and apelin) with the HF diets, whatever the type of fat used. The gene expression of two myokines with anti-inflammatory properties, Il-10 and myonectin, was dependent on the type of fat used and was most increased respectively with cPO or both rPO and OO diets. In conclusion, high-fat diets can differentially modulate the expression of some myokines, either in a dependent manner or independently of their composition.

Acute exercise in mice transiently remodels the hepatic lipidome in an intensity-dependent manner

Background

The content of triacylglycerol (TAG) in the liver is known to rapidly increase after a single bout of exercise followed by recovery to sedentary levels. The response of other hepatic lipids, and acyl chain composition of lipid classes, would provide a deeper understanding of the response of hepatic lipid metabolism to acute exercise.

Methods

Female mice performed a single bout of continuous exercise (CE), high-intensity interval exercise (HIIE), or no exercise (CON). The total content of various lipids in the liver, and fatty acids within lipid classes, were measured in tissues collected 3 h after exercise (Day 1) and the day following exercise (Day 2).

Results

The total concentration of TAG rose on Day 1 after exercise (P < 0.05), with a greater elevation in HIIE than CE (P < 0.05), followed by a decline toward CON levels on Day 2. The total concentration of other measured lipid classes was not significantly altered by exercise. However, n-6 polyunsaturated fatty acid relative abundance in diacylglycerol (DAG) was increased by HIIE (P < 0.05). In CON liver, TAG content was positively correlated with DAG and phosphatidylethanolamine (P < 0.05), while these statistical associations were disrupted in exercised mice on Day 1.

Conclusions

The response of lipid metabolism to exercise involves the coordination of metabolism between various tissues, and the lipid metabolism response to acute exercise places a metabolic burden upon the liver. The present findings describe how the liver copes with this metabolic challenge. The flexibility of the TAG pool size in the liver, and other remodeling of the hepatic lipidome, may be fundamental components of the physiological response to intense exercise.

Marathon running transiently depletes the myocardial lipid pool

Lipids, stored as intracellular triacylglycerol droplets within the myocardium, serve as an important source of energy, particularly in times of prolonged increased energy expenditure. In only a few studies, the acute effects of exercise on such ectopic myocardial lipid storage were investigated. We studied the dynamic behavior of the myocardial lipid pool in response to completing the 2017 Amsterdam Marathon using proton magnetic resonance (MR) spectroscopy (1 H-MRS). We hypothesized that the prolonged increased myocardial energy demand of running a marathon could shift the balance of myocardial triacylglycerol turnover from triacylglycerol synthesis toward lipolysis and mitochondrial fatty acid β-oxidation, and decrease the myocardial lipid pool. We employed two 3 Tesla MR systems in parallel to noninvasively examine endurance-trained healthy men (n = 8; age 50.7 [50.1-52.7] y) at 1 week prior (baseline), <6 hr after finishing the marathon (post-marathon), and 2 weeks thereafter (recovery). Exercise intensity was 89 ± 6% of the age-predicted maximal heart rate, with a finish time of 3:56 [3:37-4:42] h:min. Myocardial lipid content was 0.66 [0.58-0.87]% of the total myocardial water signal at baseline, was lower post-marathon (0.47 [0.41-0.63]% of the total myocardial water signal), and had restored to 0.55 [0.49-0.83]% of the total myocardial water signal at recovery, representing a transient marathon running-induced depletion of 29 ± 24% (p = .04). The magnitude of this myocardial lipid pool depletion did not correlate with exercise intensity (r = -0.39; p = .39), nor with marathon finishing time (ρ = 0.57; p = .15). Our data show that prolonged high-intensity exercise can induce a transient depletion of the myocardial lipid pool, reinforcing the dynamic nature of ectopic triacylglycerol storage under real-life conditions of extreme endurance exercise.

Significance of single and multi-voxel 1H magnetic resonance spectroscopy in the quantification of myocellular lipid in young non-obese Asian Indian males

To prospectively assess intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) using single voxel spectroscopy (SVS) and multi voxel magnetic resonance spectroscopy (MVS) in soleus muscle and correlate results with metabolic variables in non-obese (BMI < 23 kg/m²) Asian Indian males. Thirty one patients with diabetes (cases) and twelve normoglycaemic subjects (controls) underwent point resolved spectroscopy sequence (PRESS) of soleus muscle using SVS and MVS in a 3 T MRI scanner. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) were measured from MRI images and body composition was measured from dual-energy x-ray absorptiometry (DXA). The mean IMCL from SVS and MVS were 1.6% and 2.6% in cases and 2.3% and 3.4% in controls respectively. The mean EMCL from SVS and MVS were 1.8% and 3% in cases and 1.5% and 3% respectively in controls. A significant correlation between IMCL and total fat mass (rho = 0.42, p < 0.01) and total body fat (rho = 0.46; p < 0.01) were observed in cases while using the SVS technique and no correlations were found in the MVS technique. The SVS showed significant correlations between total myocellular lipids with VAT and SAT in cases alone. Total myocellular lipids acquired using both techniques showed a significant correlation with BMI, waist circumference, total fat mass, total body fat and truncal fat in cases alone. Quantification of IMCL of soleus muscle using the SVS technique is useful in studying the relationship with metabolic markers in non-obese Asian Indians with diabetes.

Adipose Tissue Composition in Obesity and After Bariatric Surgery

The adipose tissue is a complex organ that regulates food intake and energy expenditure as well as induces low-grade inflammation. This review deals with changes in the composition and activity of the adipose organ after bariatric surgery, focusing on epicardial and ectopic fat and on relationships between white and brown adipose tissues. Postoperative improvements of ectopic fat and epicardial fat size and composition account for the metabolic recovery and the decreased cardiovascular risk. Following Roux-en-Y gastric bypass or biliopancreatic diversion, a proportional increase in the size and activity of the metabolically active brown adipose tissue was observed, most likely related to the postoperative rearrangement of the entero-hormonal pattern with an increase of GLP-1 production: this aspect would promote the postoperative weight loss and maintenance of post-surgery benefits.

Skeletal Muscle Lipid Droplets and the Athlete's Paradox

The lipid droplet (LD) is an organelle enveloped by a monolayer phospholipid membrane with a core of neutral lipids, which is conserved from bacteria to humans. The available evidence suggests that the LD is essential to maintaining lipid homeostasis in almost all organisms. As a consequence, LDs also play an important role in pathological metabolic processes involving the ectopic storage of neutral lipids, including type 2 diabetes mellitus (T2DM), atherosclerosis, steatosis, and obesity. The degree of insulin resistance in T2DM patients is positively correlated with the size of skeletal muscle LDs. Aerobic exercise can reduce the occurrence and development of various metabolic diseases. However, trained athletes accumulate lipids in their skeletal muscle, and LD size in their muscle tissue is positively correlated with insulin sensitivity. This phenomenon is called the athlete’s paradox. This review will summarize previous studies on the relationship between LDs in skeletal muscle and metabolic diseases and will discuss the paradox at the level of LDs.

Relationship between physical activity and intramyocellular lipid content is different between young and older adults

PURPOSE

Intramyocellular lipid (IMCL) is influenced by physical exercise; however, whether the habitual level of physical activity affects resting IMCL content remains unclear. The purpose of this study was to determine the relationship between physical activity levels and resting IMCL content in young and older adults.

METHODS

In total, 15 nonobese young adults (21.0 ± 0.0 years) and 15 older adults (70.7 ± 3.8 years) were recruited. Time spent performing physical activities for 10 days was assessed using a three-dimensional ambulatory accelerometer, and intensity was categorized as light [< 3.0 metabolic equivalents (METs)], moderate (3.0-6.0 METs), or vigorous (> 6.0 METs). Physical activity level was calculated as the product of METs and time spent performing physical activities (MET h) at each intensity level. The IMCL content in the vastus lateralis was determined using ¹H-magnetic resonance spectroscopy after overnight fasting.

RESULTS

No significant differences in IMCL content were observed between young and older adults. Vigorous intensity physical activity (time and MET h) was significantly lower in older than young adults (p < 0.01); this difference was not observed for light and moderate intensity physical activity. Light intensity physical activity (time and MET h) was significantly and inversely correlated with IMCL content in young adults (r = - 0.59 and r = - 0.58; both p < 0.05), but not in older adults.

CONCLUSIONS

These results suggest that daily light intensity physical activity reduces resting IMCL content in young adults, whereas no significant relationship was seen between daily physical activity and resting IMCL content in older adults.

Impaired repletion of intramyocellular lipids in patients with growth hormone deficiency after a bout of aerobic exercise

BACKGROUND

Ectopic lipids such as intramyocellular lipids (IMCL) are depleted by exercise and repleted by diet, whereas intrahepatocellular lipids (IHCL) are increased immediately after exercise. So far, it is unclear how ectopic lipids behave 24 h after exercise and whether the lack of growth hormone (GH) significantly affects ectopic lipids 24 h after exercise.

METHODS

Seven male patients with growth hormone deficiency (GHD) and seven sedentary male control subjects (CS) were included. VO_2max was assessed by spiroergometry; visceral and subcutaneous fat by whole body MRI. ¹H-MR-spectroscopy was performed in M. vastus intermedius and in the liver before and after 2 h of exercise at 50% VO_2max and 24 h thereafter, while diet and physical activity were standardized.

RESULTS

Sedentary male subjects (7 GHD, 7 CS) were recruited. Age, BMI, waist circumference, visceral and subcutaneous fat mass was not significantly different between GHD and CS. VO_2max was significantly lower in GHD vs. CS. IMCL were diminished through aerobic exercise in both groups: (-11.5 ± 21.9% in CS; -8.9% ±19.1% in GHD) and restored after 24 h in CS (-5.5 ± 26.6% compared to baseline) but not in GHD (-17.9 ± 15.3%). IHCL increased immediately after exercise and decreased to baseline within 24 h.

CONCLUSION

These findings suggest that GHD may affect repletion of IMCL 24 h after aerobic exercise.

Exercise Metabolism: Fuels for the Fire

During exercise, the supply of adenosine triphosphate (ATP) is essential for the energy-dependent processes that underpin ongoing contractile activity. These pathways involve both substrate-level phosphorylation, without any need for oxygen, and oxidative phosphorylation that is critically dependent on oxygen delivery to contracting skeletal muscle by the respiratory and cardiovascular systems and on the supply of reducing equivalents from the degradation of carbohydrate, fat, and, to a limited extent, protein fuel stores. The relative contribution of these pathways is primarily determined by exercise intensity, but also modulated by training status, preceding diet, age, gender, and environmental conditions. Optimal substrate availability and utilization before, during, and after exercise is critical for maintaining exercise performance. This review provides a brief overview of exercise metabolism, with expanded discussion of the regulation of muscle glucose uptake and fatty acid uptake and oxidation.

Type 2 diabetes: Does pancreatic fat really matter?

With the increasing prevalence of obesity, the interest of research in nonalcoholic fatty pancreas disease (NAFPD) has grown. Even though the pancreas appears more susceptible to lipid accumulation compared with the liver, NAFPD has been less investigated due to the limits in detecting techniques. Several definitions and synonyms for NAFPD are used by authors and can be misleading. This, together with differences in methodology and ethnicity, make the integration and comparison of studies on this topic challenging. NAFPD could be used as an early indicator of ectopic fat deposition, which is recognized as a key factor of obesity cardio-metabolic complications. However, evidence that NAFPD has a pathogenetic role in type 2 diabetes is also emerging. This article reviews the current state of knowledge on the clinical and pathophysiologic relevance of NAFPD in β-cell function and insulin resistance.

Molecular Regulation of Fatty Acid Oxidation in Skeletal Muscle during Aerobic Exercise

This review summarizes how fatty acid (FA) oxidation is regulated in skeletal muscle during exercise. From the available evidence it seems that acetyl-CoA availability in the mitochondrial matrix adjusts FA oxidation to exercise intensity and duration. This is executed at the step of mitochondrial fatty acyl import, as the extent of acetyl group sequestration by carnitine determines the availability of carnitine for the carnitine palmitoyltransferase 1 (CPT1) reaction. The rate of glycolysis seems therefore to be central to the amount of β-oxidation-derived acetyl-CoA that is oxidized in the tricarboxylic acid (TCA) cycle. FA oxidation during exercise is also determined by FA availability to mitochondria, dependent on trans-sarcolemmal FA uptake via cluster of differentiation 36/SR-B2 (CD36) and FAs mobilized from myocellular lipid droplets.