Muscle glycogen and metabolic regulation

Aerobic mechanochemical reversible-deactivation radical polymerization

Polymer materials suffer mechano-oxidative deterioration or degradation in the presence of molecular oxygen and mechanical forces. In contrast, aerobic biological activities combined with mechanical stimulus promote tissue regeneration and repair in various organs. A synthetic approach in which molecular oxygen and mechanical energy synergistically initiate polymerization will afford similar robustness in polymeric materials. Herein, aerobic mechanochemical reversible-deactivation radical polymerization was developed by the design of an organic mechano-labile initiator which converts oxygen into activators in response to ball milling, enabling the reaction to proceed in the air with low-energy input, operative simplicity, and the avoidance of potentially harmful organic solvents. In addition, this approach not only complements the existing methods to access well-defined polymers but also has been successfully employed for the controlled polymerization of (meth)acrylates, styrenic monomers and solid acrylamides as well as the synthesis of polymer/perovskite hybrids without solvent at room temperature which are inaccessible by other means.

A non-antibiotic erythromycin derivative improves muscle endurance by regulating endogenous anti-fatigue protein orosomucoid in mice

At present, there are no official approved drugs for improving muscle endurance. Our previous research found acute phase protein orosomucoid (ORM) is an endogenous anti-fatigue protein, and macrolides antibiotics erythromycin can elevate ORM level to increase muscle bioenergetics and endurance parameters. Here, we further designed, synthesized and screened a new erythromycin derivative named HMS-01, which lost its antibacterial activity in vitro and in vivo. Data showed that HMS-01 could time- and dose-dependently prolong mice forced-swimming time and running time, and improve fatigue index in isolated soleus muscle. Moreover, HMS-01 treatment could increase the glycogen content, mitochondria number and function in liver and skeletal muscle, as well as ORM level in these tissues and sera. In Orm-deficient mice, the anti-fatigue and glycogen-elevation activity of HMS-01 disappeared. Therefore, HMS-01 might act as a promising small molecule drug targeting ORM to enhance muscle endurance.

Age-Dependent Changes in the Production of Mitochondrial Reactive Oxygen Species in Human Skeletal Muscle

A decrease in muscle mass and its functionality (strength, endurance, and insulin sensitivity) is one of the integral signs of aging. One of the triggers of aging is an increase in the production of mitochondrial reactive oxygen species. Our study was the first to examine age-dependent changes in the production of mitochondrial reactive oxygen species related to a decrease in the proportion of mitochondria-associated hexokinase-2 in human skeletal muscle. For this purpose, a biopsy was taken from m. vastus lateralis in 10 young healthy volunteers and 70 patients (26-85 years old) with long-term primary arthrosis of the knee/hip joint. It turned out that aging (comparing different groups of patients), in contrast to inactivity/chronic inflammation (comparing young healthy people and young patients), causes a pronounced increase in peroxide production by isolated mitochondria. This correlated with the age-dependent distribution of hexokinase-2 between mitochondrial and cytosolic fractions, a decrease in the rate of coupled respiration of isolated mitochondria and respiration when stimulated with glucose (a hexokinase substrate). It is discussed that these changes may be caused by an age-dependent decrease in the content of cardiolipin, a potential regulator of the mitochondrial microcompartment containing hexokinase. The results obtained contribute to a deeper understanding of age-related pathogenetic processes in skeletal muscles and open prospects for the search for pharmacological/physiological approaches to the correction of these pathologies.

Effects of short-term graded dietary carbohydrate intake on intramuscular and whole body metabolism during moderate-intensity exercise

Altering dietary carbohydrate (CHO) intake modulates fuel utilization during exercise. However, there has been no systematic evaluation of metabolic responses to graded changes in short-term (< 1 wk) dietary CHO intake. Thirteen active men performed interval running exercise combined with isocaloric diets over 3 days before evaluation of metabolic responses to 60-min running at 65% V̇O_2max on three occasions. Diets contained lower [LOW, 2.40 ± 0.66 g CHO·kg^-1·day^-1, 21.3 ± 0.5% of energy intake (EI)], moderate (MOD, 4.98 ± 1.31 g CHO·kg^-1·day^-1, 46.3 ± 0.7% EI), or higher (HIGH, 6.48 ± 1.56 g CHO·kg^-1·day^-1, 60.5 ± 1.6% EI) CHO. Preexercise muscle glycogen content was lower in LOW [54.3 ± 26.4 mmol·kg^-1 wet weight (ww)] compared with MOD (82.6 ± 18.8 mmol·kg ^-1 ww) and HIGH (80.4 ± 26.0 mmol·kg^-1 ww, P < 0.001; MOD vs. HIGH, P = 0.85). Whole body substrate oxidation, systemic responses, and muscle substrate utilization during exercise indicated increased fat and decreased CHO metabolism in LOW [respiratory exchange ratio (RER): 0.81 ± 0.01] compared with MOD (RER 0.86 ± 0.01, P = 0.0005) and HIGH (RER: 0.88 ± 0.01, P < 0.0001; MOD vs. HIGH, P = 0.14). Higher basal muscle expression of genes encoding proteins implicated in fat utilization was observed in LOW. In conclusion, muscle glycogen availability and subsequent metabolic responses to exercise were resistant to increases in dietary CHO intake from ∼5.0 to ∼6.5 g CHO·kg^-1·day^-1 (46% to 61% EI), while muscle glycogen, gene expression, and metabolic responses were sensitive to more marked reductions in CHO intake (∼2.4 g CHO·kg^-1·day^-1, ∼21% EI).NEW & NOTEWORTHY The data presented here suggest that metabolic responses to steady-state aerobic exercise are somewhat resistant to short-term changes in dietary carbohydrate (CHO) intake within the 5-6.5 g CHO·kg^-1·day^-1 [46-61% energy intake (EI)] range. In contrast, reduction in short-term dietary CHO intake to ∼2.4 g CHO·kg^-1·day^-1 (21% EI) evoked clear changes indicative of increased fat and decreased CHO metabolism during exercise.

Anti-Fatigue Effect of a Dietary Supplement from the Fermented By-Products of Taiwan Tilapia Aquatic Waste and Monostroma nitidum Oligosaccharide Complex

The Taiwan Tilapia is an important aquaculture product in Taiwan. The aquatic by-products generated during Tilapia processing, such as fish bones and skin, are rich in minerals and protein. We aimed to explore the effect of a dietary supplement, comprising a mixture of fermented Tilapia by-products and Monostroma nitidum oligosaccharides as the raw materials, combined with physical training on exercise performance and fatigue. We used a mouse model that displays a phenotype of accelerated aging. Male senescence-accelerated mouse prone-8 (SAMP8) mice were divided into two control groups-with or without physical training-and supplemented with different doses (0.5 times: 412 mg/kg body weight (BW)/day; 1 time: 824 mg/kg BW/day; 2 times: 1648 mg/kg BW/day) of fermented Tilapia by-products and Monostroma nitidum oligosaccharide-containing mixture and combined with exercise training groups. Exercise performance was determined by testing forelimb grip strength and with a weight-bearing exhaustive swimming test. Animals were sacrificed to collect physical fatigue-related biomarkers. Mice dosed at 824 or 1648 mg/kg BW/day showed improvement in their exercise performance (p < 0.05). In terms of biochemical fatigue indicators, supplementation of 824 or 1648 mg/kg BW/day doses of test substances could effectively reduce blood urea nitrogen concentration and lactate concentration and increase the lactate ratio (p < 0.05) and liver glycogen content post-exercise (p < 0.05). Based on the above results, the combination of physical training and consumption of a dietary supplementation mixture of fermented Tilapia by-products and Monostroma nitidum oligosaccharides could improve the exercise performance of mice and help achieve an anti-fatigue effect.

Regulation of Energy Substrate Metabolism in Endurance Exercise

The human body requires energy to function. Adenosine triphosphate (ATP) is the cellular currency for energy-requiring processes including mechanical work (i.e., exercise). ATP used by the cells is ultimately derived from the catabolism of energy substrate molecules—carbohydrates, fat, and protein. In prolonged moderate to high-intensity exercise, there is a delicate interplay between carbohydrate and fat metabolism, and this bioenergetic process is tightly regulated by numerous physiological, nutritional, and environmental factors such as exercise intensity and duration, body mass and feeding state. Carbohydrate metabolism is of critical importance during prolonged endurance-type exercise, reflecting the physiological need to regulate glucose homeostasis, assuring optimal glycogen storage, proper muscle fuelling, and delaying the onset of fatigue. Fat metabolism represents a sustainable source of energy to meet energy demands and preserve the ‘limited’ carbohydrate stores. Coordinated neural, hormonal and circulatory events occur during prolonged endurance-type exercise, facilitating the delivery of fatty acids from adipose tissue to the working muscle for oxidation. However, with increasing exercise intensity, fat oxidation declines and is unable to supply ATP at the rate of the exercise demand. Protein is considered a subsidiary source of energy supporting carbohydrates and fat metabolism, contributing to approximately 10% of total ATP turnover during prolonged endurance-type exercise. In this review we present an overview of substrate metabolism during prolonged endurance-type exercise and the regulatory mechanisms involved in ATP turnover to meet the energetic demands of exercise.

Muscle Glycogen Metabolism and High-Intensity Exercise Performance: A Narrative Review

Muscle glycogen is the main substrate during high-intensity exercise and large reductions can occur after relatively short durations. Moreover, muscle glycogen is stored heterogeneously and similarly displays a heterogeneous and fiber-type specific depletion pattern with utilization in both fast- and slow-twitch fibers during high-intensity exercise, with a higher degradation rate in the former. Thus, depletion of individual fast- and slow-twitch fibers has been demonstrated despite muscle glycogen at the whole-muscle level only being moderately lowered. In addition, muscle glycogen is stored in specific subcellular compartments, which have been demonstrated to be important for muscle function and should be considered as well as global muscle glycogen availability. In the present review, we discuss the importance of glycogen metabolism for single and intermittent bouts of high-intensity exercise and outline possible underlying mechanisms for a relationship between muscle glycogen and fatigue during these types of exercise. Traditionally this relationship has been attributed to a decreased ATP resynthesis rate due to inadequate substrate availability at the whole-muscle level, but emerging evidence points to a direct coupling between muscle glycogen and steps in the excitation-contraction coupling including altered muscle excitability and calcium kinetics.

Applicability of the masseter muscle as a nutritional biomarker

Nutritional assessment is feasible with computed tomography anthropometry. The abdominal muscle at the L3 vertebra is a well-known nutritional biomarker for predicting the prognosis of various diseases, especially sarcopenia. However, studies on nutritional assessment of the brain using computed tomography are still scarce. This study aimed to investigate the applicability of the masseter muscle as a nutritional biomarker.Patients who underwent simultaneous brain and abdominopelvic computed tomography in the emergency department was retrospectively analyzed. We assessed their masseter muscle 2 cm below the zygomatic arch and abdominal muscle at L3 via computed tomography anthropometry. The skeletal muscle index, prognostic nutritional index, and other nutritional biomarkers were assessed for sarcopenia using the receiver operating characteristic curve analysis.A total of 314 patients (240 men and 72 women) were analyzed (mean age, 50.24 years; mean areas of the masseter and abdominal muscles, 1039.6 and 13478.3 mm, respectively). Masseter muscle areas significantly differed in sarcopenic, obese, and geriatric patients (P < .001). The areas under the curve of the masseter muscle in sarcopenic, geriatric, and obese patients were 0.663, 0.686, and 0.602, respectively. Multivariable linear regression analysis showed a correlation with the abdominal muscle area, weight, and age.The masseter muscle, analyzed via computed tomography anthropometry, showed a statistically significant association with systemic nutritional biomarkers, and its use as a nutritional biomarker would be feasible.

Benefits of dietary supplements on the physical fitness of German Shepherd dogs during a drug detection training course

A high standard of physical fitness is an essential characteristic of drug detection dogs because it affects not only their ability to sustain high activity levels but also their attention and olfaction efficiency. Nutritional supplements could improve physical fitness by modulating energy metabolism, oxidative processes, and perceived fatigue. The aim of this study was to investigate the physiological and biochemical changes induced by submaximal exercise on drug detection dogs (German Shepherd breed) and to assess whether a dietary supplement improves their physical fitness. During a drug detection dog training course, seven dogs were fed with a basal diet (Control Group) for three-month period, while a further seven dogs were fed with a basal diet as well as a daily nutritional supplement containing branched-chain and limiting amino acids, carnitine, vitamins, and octacosanol (Treatment Group). At the end of this period, individual physical fitness was assessed by making each subject take a graded treadmill exercise test. A human heart rate monitor system was used to record the dog's heart rate (HR) during the treadmill exercise and the subsequent recovery period. The parameters related to HR were analysed using nonparametric statistics. Blood samples were collected before starting the nutritional supplement treatment, before and after the treadmill exercise and following recovery. Linear mixed models were used. The dietary supplements accelerated HR recovery, as demonstrated by the lower HR after recovery (P<0.05) and Time constants of HR decay (P<0.05), and by the higher Absolute HR Recovered (P<0.05) recorded in the Treatment group compared with the Control dogs. The supplemented dogs showed the lowest concentrations of creatine kinase (CK; P<0.001), aspartate aminotransferase (AST, P<0.05) and non-esterified fatty acids (NEFA; P<0.01) suggesting a reduction in muscle damage and improvement of energy metabolism. These data suggest that this combined supplement can significantly enhance the physical fitness of drug detection dogs.

4-Phenyl butyric acid increases particulate hexokinase activity and protects against ROS injury in L6 myotubes

Hexokinase (HK) is the first enzyme in the glycolytic pathway and is responsible for glucose phosphorylation and fixation into the cell. HK (HK-II) is expressed in skeletal muscle and can be found in the cytosol or bound mitochondria, where it can protect cells against insults such as oxidative stress. 4-Phenyl butyric acid (4-PBA) is a chemical chaperone that inhibits endoplasmic reticulum stress and contributes to the restoring of glucose homeostasis.

AIMS

Here, we decided to investigate whether HK activity and its interaction with mitochondria could be a target of 4-PBA action.

MAIN METHODS

L6 myotubes were treated with 1mM 4-PBA for 24, 48 or 72h. We evaluated HK activity, glucose and oxygen consumption, gene and protein expression.

KEY FINDINGS

We found that L6 myotubes treated with 4-PBA presented more HK activity in the particulate fraction, increased glucose consumption and augmented Glut4, Hk2 and Vdac1 mRNA expression. Moreover, 4-PBA prevented the deleterious effect of antimycin-A on HK particulate activity.

SIGNIFICANCE

Together, these results suggest a new role of 4-PBA in glucose metabolism that includes HK as a potential target of beneficial effect of 4-PBA.

Short and Long Term Effects of High-Intensity Interval Training on Hormones, Metabolites, Antioxidant System, Glycogen Concentration, and Aerobic Performance Adaptations in Rats

The purpose of the study was to investigate the effects of short and long term High-Intensity Interval Training (HIIT) on anaerobic and aerobic performance, creatinine, uric acid, urea, creatine kinase, lactate dehydrogenase, catalase, superoxide dismutase, testosterone, corticosterone, and glycogen concentration (liver, soleus, and gastrocnemius). The Wistar rats were separated in two groups: HIIT and sedentary/control (CT). The lactate minimum (LM) was used to evaluate the aerobic and anaerobic performance (AP) (baseline, 6, and 12 weeks). The lactate peak determination consisted of two swim bouts at 13% of body weight (bw): (1) 30 s of effort; (2) 30 s of passive recovery; (3) exercise until exhaustion (AP). Tethered loads equivalent to 3.5, 4.0, 4.5, 5.0, 5.5, and 6.5% bw were performed in incremental phase. The aerobic capacity in HIIT group increased after 12 weeks (5.2 ± 0.2% bw) in relation to baseline (4.4 ± 0.2% bw), but not after 6 weeks (4.5 ± 0.3% bw). The exhaustion time in HIIT group showed higher values than CT after 6 (HIIT = 58 ± 5 s; CT = 40 ± 7 s) and 12 weeks (HIIT = 62 ± 7 s; CT = 49 ± 3 s). Glycogen (mg/100 mg) increased in gastrocnemius for HIIT group after 6 weeks (0.757 ± 0.076) and 12 weeks (1.014 ± 0.157) in comparison to baseline (0.358 ± 0.024). In soleus, the HIIT increased glycogen after 6 weeks (0.738 ± 0.057) and 12 weeks (0.709 ± 0.085) in comparison to baseline (0.417 ± 0.035). The glycogen in liver increased after HIIT 12 weeks (4.079 ± 0.319) in relation to baseline (2.400 ± 0.416). The corticosterone (ng/mL) in HIIT increased after 6 weeks (529.0 ± 30.5) and reduced after 12 weeks (153.6 ± 14.5) in comparison to baseline (370.0 ± 18.3). In conclusion, long term HIIT enhanced the aerobic capacity, but short term was not enough to cause aerobic adaptations. The anaerobic performance increased in HIIT short and long term compared with CT, without differences between HIIT short and long term. Furthermore, the glycogen super-compensation increased after short and long term HIIT in comparison to baseline and CT group. The corticosterone increased after 6 weeks, but reduces after 12 weeks. No significant alterations were observed in urea, uric acid, testosterone, catalase, superoxide dismutase, sulfhydryl groups, and creatine kinase in HIIT group in relation to baseline and CT.

Exercise Inducible Lactate Dehydrogenase B Regulates Mitochondrial Function in Skeletal Muscle

Lactate dehydrogenase (LDH) catalyzes the interconversion of pyruvate and lactate, which are critical fuel metabolites of skeletal muscle particularly during exercise. However, the physiological relevance of LDH remains poorly understood. Here we show that Ldhb expression is induced by exercise in human muscle and negatively correlated with changes in intramuscular pH levels, a marker of lactate production, during isometric exercise. We found that the expression of Ldhb is regulated by exercise-induced peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). Ldhb gene promoter reporter studies demonstrated that PGC-1α activates Ldhb gene expression through multiple conserved estrogen-related receptor (ERR) and myocyte enhancer factor 2 (MEF2) binding sites. Transgenic mice overexpressing Ldhb in muscle (muscle creatine kinase (MCK)-Ldhb) exhibited increased exercise performance and enhanced oxygen consumption during exercise. MCK-Ldhb muscle was shown to have enhanced mitochondrial enzyme activity and increased mitochondrial gene expression, suggesting an adaptive oxidative muscle transformation. In addition, mitochondrial respiration capacity was increased and lactate production decreased in MCK-Ldhb skeletal myotubes in culture. Together, these results identified a previously unrecognized Ldhb-driven alteration in muscle mitochondrial function and suggested a mechanism for the adaptive metabolic response induced by exercise training.

Comparison of different cryotherapy recovery methods in elite junior cyclists

Background/objective

Cold water immersion (CWI) and active recovery treatment (ACT) are commonly used recovery treatments for athletes between exercise bouts, but they are sometimes limited by space and availability of equipment in training and competition venues. Therefore, the purpose of this study was to determine whether cold compression therapy (CCT) would provide the same effect as CWI and ACT as an alternative option in a hot environment.

Methods

Eight elite male junior cyclists (age, 15.5 ± 1.2 years; height, 167.7 ± 3.3 cm; body mass, 57.3 ± 3.5 kg; peak oxygen uptake, 64.7 ± 4.3 mL/kg/min) completed a maximal cycling test to determine their peak power output (PPO) and oxygen uptake. Then they completed three tests using randomised recovery protocol of CWI, CCT and ACT for 15 minutes. Each test consisted of two 35-minute exercise bouts, with 5 minutes of warm-up, 15 minutes of cycling at 75% PPO and 15 minutes maximal trial. The two exercise bouts were separated by 60 minutes (5 minutes cool-down, 10 minutes preparation for recovery treatment, 15 minutes recovery treatment, and 30 minutes passive recovery).

Results

There was no significant difference between average power output, blood lactate, rating of perceived exertion, and heart rate for two time-trial bouts for all recovery treatments. A significant decrease in core temperature was noted prior to the start of the second exercise bout for CWI.

Conclusion

CCT, CWI and ACT are all useful recovery treatments between exercise bouts.

Interval Versus Continuous Training With Identical Workload: Physiological and Aerobic Capacity Adaptations

The interval model training has been more recommended to promote aerobic adaptations due to recovery period that enables the execution of elevated intensity and as consequence, higher workload in relation to continuous training. However, the physiological and aerobic capacity adaptations in interval training with identical workload to continuous are still uncertain. The purpose was to characterize the effects of chronic and acute biomarkers adaptations and aerobic capacity in interval and continuous protocols with equivalent load. Fifty Wistar rats were divided in three groups: Continuous training (GTC), interval training (GTI) and control (CG). The running training lasted 8 weeks (wk) and was based at Anaerobic Threshold (AT) velocity. GTI showed glycogen super-compensation (mg/100 mg) 48 h after training session in relation to CG and GTC (GTI red gastrocnemius (RG)=1.41±0.16; GTI white gastrocnemius (WG)=1.78±0.20; GTI soleus (S)=0.26±0.01; GTI liver (L)=2.72±0.36; GTC RG=0.42±0.17; GTC WG=0.54±0.22; GTC S=0.100±0.01; GTC L=1.12±0.24; CG RG=0.32±0.05; CG WG=0.65±0.17; CG S=0.14±0.01; CG L=2.28±0.33). The volume performed by GTI was higher than GTC. The aerobic capacity reduced 11 % after experimental period in GTC when compared to GTI, but this change was insignificant (19.6±5.4 m/min; 17.7±2.5 m/min, effect size = 0.59). Free fatty acids and glucose concentration did not show statistical differences among the groups. Corticosterone concentration increased in acute condition for GTI and GTC. Testosterone concentration reduced 71 % in GTC immediately after the exercise in comparison to CG. The GTI allowed positive adaptations when compared to GTC in relation to: glycogen super-compensation, training volume performed and anabolic condition. However, the GTI not improved the aerobic performance.

Myocyte enhancer factor 2C function in skeletal muscle is required for normal growth and glucose metabolism in mice

BACKGROUND

Skeletal muscle is the most abundant tissue in the body and is a major source of total energy expenditure in mammals. Skeletal muscle consists of fast and slow fiber types, which differ in their energy usage, contractile speed, and force generation. Although skeletal muscle plays a major role in whole body metabolism, the transcription factors controlling metabolic function in muscle remain incompletely understood. Members of the myocyte enhancer factor 2 (MEF2) family of transcription factors play crucial roles in skeletal muscle development and function. MEF2C is expressed in skeletal muscle during development and postnatally and is known to play roles in sarcomeric gene expression, fiber type control, and regulation of metabolic genes.

METHODS

We generated mice lacking Mef2c exclusively in skeletal muscle using a conditional knockout approach and conducted a detailed phenotypic analysis.

RESULTS

Mice lacking Mef2c in skeletal muscle on an outbred background are viable and grow to adulthood, but they are significantly smaller in overall body size compared to control mice and have significantly fewer slow fibers. When exercised in a voluntary wheel running assay, Mef2c skeletal muscle knockout mice aberrantly accumulate glycogen in their muscle, suggesting an impairment in normal glucose homeostasis. Consistent with this notion, Mef2c skeletal muscle knockout mice exhibit accelerated blood glucose clearance compared to control mice.

CONCLUSIONS

These findings demonstrate that MEF2C function in skeletal muscle is important for metabolic homeostasis and control of overall body size.

Disuse induced by the spine rectification vest: experimental study

The spine is the main support and movement axis of the locomotor system, and numberless clinical conditions may require that this structure be submitted to functional restriction. Among the non-invasive treatments used in spinal or appendicular skeleton injuries, the immobilization of the spine is used as a rehabilitation strategy. Because of the functional restrictions generated by restraining devices used on the spine, the proposal of this study was to adapt a spinal orthosis on rats, thus mimicking the immobilization of corrective vests and assessing the energetic conditions of thoracic muscles after 12 weeks of application. Wistar rats that were 42 days old were used in this study (post-weaning period), followed-up for 12 weeks in 2 groups called control (C) and rectification vests (R), which were made of PVC to immobilize the spine. The following concentrations were evaluated: glycogen (GLY) of the paravertebral muscle and the thorax; total proteins and DNA (TP/DNA) and interleukin-6 (IL-6). The normality Kolmogorov-Smirnov test was used for statistical analysis, followed by the Tukey test. A 5% level was established for all of the calculations. It was observed that group R presented 12% less body mass and GLY stores 21% lower; the ratio between TP/DNA was in average 6.6% lower; IL-6 concentrations were in average 25% higher. The study shows that the movement restriction in the spine leads to energetic crisis and compromised muscular development. More studies should be conducted with this model to generate physical therapy strategies that could reduce muscle compromise after spine immobilization.

Nuclear receptors and epigenetic signaling: novel regulators of glycogen metabolism in skeletal muscle

Glycogen is an energy storage depot for the mammalian species. This review focuses on recent developments that have identified the role of nuclear hormone receptor (NR) signaling and epigenomic control in the regulation of important genes that modulate glycogen metabolism. Specifically, new studies have revealed that the NR4A subgroup (of the NR superfamily) are strikingly sensitive to beta-adrenergic stimulation in skeletal muscle, and transgenic studies in mice have revealed the expression of these NRs affects endurance and glycogen levels in muscle. Furthermore, other studies have demonstrated that one of the NR coregulator class of enzymes that mediate chromatin remodeling, the histone methyltransferases (for example, protein arginine methyltransferase 4) regulates the expression of several genes involved in glycogen metabolism and glycogen storage diseases in skeletal muscle. Importantly, NRs and histone methyltransferases, have the potential to be pharmacologically exploited and may provide novel targets in the quest to treat disorders of glycogen storage.

Interaction of physical trainings and coffee intakes in fuel utilization during exercise in rats

This study investigates the impact of exercises, coffee intakes, and physical trainings on fuel utilization in rats. Ninety-six rats were fed a control diet with either water (C) or coffee (CF; 0.12 g freeze-dried instant coffee/100 g body weight/d). Additionally, the animals go through physical training (TC and TCF) or no training (NTC and NTCF) for 4 weeks. For physical training, animals have to exercise on treadmills for 30 minutes (5 d per week, 15° incline, 0.5-0.8 km/h). At the end of week 4, the animals in each group were subdivided into three exercise groups: before exercise (BE), during exercise (DE), and after exercise (AE). The DE rats exercised on treadmills for 1 hour immediately before being sacrificed. Hemoglobin, hematocrit, glucose, glycogen, protein, triglyceride (TG), and free fatty acid (FFA) levels in the plasma, liver, and skeletal muscle of the rats were compared accordingly. Organ weights were also measured. Coffee-training interaction had a significant impact on heart weight, visceral fat, hemoglobin, hematocrit, liver glycogen in DE and AE, and liver triglyceride in DE and AE. Exercise (meaning exercised on a treadmill for 1 hour immediately before being sacrificed) training interaction was significant in liver glycogen, muscle glycogen in control diet and control diet with coffee, FFA and muscle TG levels at control diet with coffee group. Exercise-coffee interactions significantly influenced the FFA with no training groups. Exercise-coffee-training interaction significantly effects on FFA, Liver TG and Muscle TG. Coffee intakes can increase lipolysis during exercising but coffee consumptions delay the recovery of liver glycogen levels in trained rats after exercising. Coffee intakes can increase lipolysis during exercising but coffee consumptions delay the recovery of liver glycogen levels in trained rats after exercising. Coffee can be an effective ergogenic aid during exercise for physically trained rats.

Monitoring chronic physical stress using biomarkers, performance protocols and mathematical functions to identify physiological adaptations in rats

This study was undertaken to characterize the effects of monotonous training at lactate minimum (LM) intensity on aerobic and anaerobic performances; glycogen concentrations in the soleus muscle, the gastrocnemius muscle and the liver; and creatine kinase (CK), free fatty acids and glucose concentrations in rats. The rats were separated into trained ( n = 10), baseline ( n = 10) and sedentary ( n = 10) groups. The trained group was submitted to the following: 60 min/day, 6 day/week and intensity equivalent to LM during the 12-week training period. The training volume was reduced after four weeks according to a sigmoid function. The total CK (U/L) increased in the trained group after 12 weeks (742.0 ± 158.5) in comparison with the baseline (319.6 ± 40.2) and the sedentary (261.6 ± 42.2) groups. Free fatty acids and glycogen stores (liver, soleus muscle and gastrocnemius muscle) increased after 12 weeks of monotonous training but aerobic and anaerobic performances were unchanged in relation to the sedentary group. The monotonous training at LM increased the level of energy substrates, unchanged aerobic performance, reduced anaerobic capacity and increased the serum CK concentration; however, the rats did not achieve the predicted training volume.

Thr649Ala-AS160 knock-in mutation does not impair contraction/AICAR-induced glucose transport in mouse muscle

AS160 and its closely related protein TBC1D1 have emerged as key mediators for both insulin- and contraction-stimulated muscle glucose uptake through regulating GLUT4 trafficking. Insulin increases AS160 phosphorylation at multiple Akt/PKB consensus sites, including Thr(649), and promotes its binding to 14-3-3 proteins through phospho-Thr(649). We recently provided genetic evidence that AS160-Thr(649) phosphorylation/14-3-3 binding plays a key role in mediating insulin-stimulated glucose uptake in muscle. Contraction has also been proposed to increase phosphorylation of AS160 and TBC1D1 via AMPK, which could be detected by a generic phospho-Akt substrate (PAS) antibody. Here, analysis of AS160 immunoprecipitates from muscle extracts with site-specific phospho-antibodies revealed that contraction and AICAR caused no increase but rather a slight decrease in phosphorylation of the major PAS recognition site AS160-Thr(649). In line with this, contraction failed to enhance 14-3-3 binding to AS160. Consistent with previous reports, we also observed that in situ contraction stimulated the signal intensity of PAS antibody immunoreactive protein of ∼150-160 kDa in muscle extracts. Using a TBC1D1 deletion mutant mouse, we showed that TBC1D1 protein accounted for the majority of the PAS antibody immunoreactive signals of ∼150-160 kDa in extracts of contracted muscles. Consistent with the proposed role of AS160-Thr(649) phosphorylation/14-3-3 binding in mediating glucose uptake, AS160-Thr(649)Ala knock-in mice displayed normal glucose uptake upon contraction and AICAR in isolated muscles. We conclude that the previously reported PAS antibody immunoreactive band ∼150-160 kDa, which were increased upon contraction, does not represent AS160 but TBC1D1, and that AS160-Thr(649)Ala substitution impairs insulin- but neither contraction- nor AICAR-stimulated glucose uptake in mouse skeletal muscle.

The effects of carbohydrate intake and muscle glycogen content on self-paced intermittent-sprint exercise despite no knowledge of carbohydrate manipulation

The aim of this study was to determine the effects of carbohydrate (CHO) ingestion and muscle glycogen content, without the influence of knowledge of CHO consumption, on intermittent-sprint performance. Ten males completed two conditions on two consecutive days. Day 1 involved 2 × 40 min of leg cycling separated by 15 min of arm cycling, followed by an overnight diet consuming either a high [HCHO; 7 g/kg body weight (bw)] or low (LCHO; 2 g/kg bw) CHO diet. Participants were blinded to the knowledge CHO was being examined or manipulated. Day 2 included a 60-min intermittent-sprint exercise (ISE) protocol that included 15-m maximal sprints every minute and self-paced efforts of varying intensities. Pre and post-ISE muscle biopsies were obtained on Day 2. Pre- and post-exercise maximal voluntary torque (MVT), voluntary activation (VA) and twitch contractile properties were assessed during 15 maximal isometric contractions. Blood glucose and lactate, heart rate (HR) and rating of perceived exertion (RPE) were also recorded. Pre-ISE muscle glycogen was greater in HCHO compared with LCHO (597 ± 115 vs. 318 ± 72 mmol kg dry weight; P = 0.001). Total distance and hard running distance were 4.9 and 8.1% greater in HCHO, respectively (P = 0.02-0.04). Peak MVT, VA, HR and RPE were not different between conditions (P > 0.05). Blood glucose was higher pre-ISE for LCHO but lower post-ISE compared with HCHO (P < 0.05). These results indicate HCHO improved self-paced exercise intensities during the ISE protocol despite no knowledge of dietary manipulation. Due to the blinded study design, exercise intensities seem manipulated due to peripheral perturbations associated with CHO content rather than a conscious manipulation of exercise intensities.

The nuclear receptor PPARβ/δ programs muscle glucose metabolism in cooperation with AMPK and MEF2

To identify new gene regulatory pathways controlling skeletal muscle energy metabolism, comparative studies were conducted on muscle-specific transgenic mouse lines expressing the nuclear receptors peroxisome proliferator-activated receptor α (PPARα; muscle creatine kinase [MCK]-PPARα) or PPARβ/δ (MCK-PPARβ/δ). MCK-PPARβ/δ mice are known to have enhanced exercise performance, whereas MCK-PPARα mice perform at low levels. Transcriptional profiling revealed that the lactate dehydrogenase b (Ldhb)/Ldha gene expression ratio is increased in MCK-PPARβ/δ muscle, an isoenzyme shift that diverts pyruvate into the mitochondrion for the final steps of glucose oxidation. PPARβ/δ gain- and loss-of-function studies in skeletal myotubes demonstrated that PPARβ/δ, but not PPARα, interacts with the exercise-inducible kinase AMP-activated protein kinase (AMPK) to synergistically activate Ldhb gene transcription by cooperating with myocyte enhancer factor 2A (MEF2A) in a PPARβ/δ ligand-independent manner. MCK-PPARβ/δ muscle was shown to have high glycogen stores, increased levels of GLUT4, and augmented capacity for mitochondrial pyruvate oxidation, suggesting a broad reprogramming of glucose utilization pathways. Lastly, exercise studies demonstrated that MCK-PPARβ/δ mice persistently oxidized glucose compared with nontransgenic controls, while exhibiting supranormal performance. These results identify a transcriptional regulatory mechanism that increases capacity for muscle glucose utilization in a pattern that resembles the effects of exercise training.

Cold water immersion recovery following intermittent-sprint exercise in the heat

This study examined the effects of cold water immersion (CWI) on recovery of neuromuscular function following simulated team-sport exercise in the heat. Ten male team-sport athletes performed two sessions of a 2 × 30-min intermittent-sprint exercise (ISE) in 32°C and 52% humidity, followed by a 20-min CWI intervention or passive recovery (CONT) in a randomized, crossover design. The ISE involved a 15-m sprint every minute separated by bouts of hard running, jogging and walking. Voluntary and evoked neuromuscular function, ratings of perceived muscle soreness (MS) and blood markers for muscle damage were measured pre- and post-exercise, immediately post-recovery, 2-h and 24-h post-recovery. Measures of core temperature (Tcore), heart rate (HR), capillary blood and perceptions of exertion, thermal strain and thirst were also recorded at the aforementioned time points. Post-exercise maximal voluntary contraction (MVC) and activation (VA) were reduced in both conditions and remained below pre-exercise values for the 24-h recovery (P < 0.05). Increased blood markers of muscle damage were observed post-exercise in both conditions and remained elevated for the 24-h recovery period (P < 0.05). Comparative to CONT, the post-recovery rate of reduction in Tcore, HR and MS was enhanced with CWI whilst increasing MVC and VA (P < 0.05). In contrast, 24-h post-recovery MVC and activation were significantly higher in CONT compared to CWI (P = 0.05). Following exercise in the heat, CWI accelerated the reduction in thermal and cardiovascular load, and improved MVC alongside increased central activation immediately and 2-h post-recovery. However, despite improved acute recovery CWI resulted in an attenuated MVC 24-h post-recovery.

The effect of a carbohydrate beverage on the physiological responses during prolonged load carriage

Effects of a carbohydrate beverage on the physiological responses to load carriage were examined. Ten fit male participants (age: 28 ± 9 years, body mass: 81.5 ± 10.5 kg, VO(2max): 55.0 ± 5.5 mL kg(-1) min(-1)) completed two test conditions in random order, walking on a treadmill (6.5 km h(-1)) for 120 min, carrying a 25-kg backpack. At 0 and 60 min of exercise participants consumed 250 mL of a placebo (flavoured water) (PLA) or 6.4% carbohydrate (CHO) beverage. There were no differences in VO(2,) respiratory exchange ratio (RER), heart rate or EMG activity of m. rectus femoris, m. vastus lateralis, m. semitendinosus and m. biceps femoris between conditions at minute 5 of exercise. The increase in VO(2) between minutes 5 and 120 was less during CHO than PLA (8 ± 5 vs. 14 ± 6%, P = 0.036). RER decreased during PLA, from 0.96 ± 0.05 at minute 5 to 0.87 ± 0.04 at minute 120 (P < 0.001), but not during CHO (P = 0.056). Heart rate increased between minutes 5 and 120 during PLA (16 ± 10%, P < 0.001) and CHO (12 ± 6%, P < 0.001), with no difference between conditions (P = 0.251). EMG peak RMS did not change between minutes 7 and 107 during PLA or CHO for the leg muscles. However, individual responses in EMG were highly variable (i.e. both increases and decreases in RMS). It was concluded that carbohydrate intake during load carriage reduced the VO(2) drift, which could be partially attributed to higher carbohydrate oxidation rates. Despite muscle fatigue/damage previously being identified as a cause of VO(2) drift, it appears that carbohydrate had no effect on neuromuscular responses during load carriage.

Subcellular localization-dependent decrements in skeletal muscle glycogen and mitochondria content following short-term disuse in young and old men

Previous studies have shown that skeletal muscle glycogen and mitochondria are distributed in distinct subcellular localizations, but the role and regulation of these subcellular localizations are unclear. In the present study, we used transmission electron microscopy to investigate the effect of disuse and aging on human skeletal muscle glycogen and mitochondria content in subsarcolemmal (SS), intermyofibrillar (IMF), and intramyofibrillar (intra) localizations. Five young (∼23 yr) and five old (∼66 yr) recreationally active men had their quadriceps muscle immobilized for 2 wk by whole leg casting. Biopsies were obtained from m. vastus lateralis before and after the immobilization period. Immobilization induced a decrement of intra glycogen content by 54% (P < 0.001) in both age groups and in two ultrastructurally distinct fiber types, whereas the content of IMF and SS glycogen remained unchanged. A localization-dependent decrease (P = 0.03) in mitochondria content following immobilization was found in both age groups, where SS mitochondria decreased by 33% (P = 0.02), superficial IMF mitochondria decreased by 20% (P = 0.05), and central IMF mitochondria remained unchanged. In conclusion, our findings demonstrate a localization-dependent adaptation to immobilization in glycogen and mitochondria content of skeletal muscles of both young and old individuals. Specifically, this suggests that short-term disuse preferentially affects glycogen particles located inside the myofibrils and that mitochondria volume plasticity can be dependent on the distance to the fiber border.

The regulation of muscle glycogen: the granule and its proteins

Despite decades of studying muscle glycogen in many metabolic situations, surprisingly little is known regarding its regulation. Glycogen is a dynamic and vital metabolic fuel that has very limited energetic capacity. Thus its regulation is highly complex and multifaceted. The stores in muscle are not homogeneous and there appear to be various metabolic pools. Each granule is capable of independent regulation and fundamental aspects of the regulation appear to be associated with a complex set of proteins (some are enzymes and others serve scaffolding roles) that associate both with the granule and with each other in a dynamic fashion. The regulation includes altered phosphorylation status and often translocation as well. The understanding of the roles and the regulation of glycogenin, protein phosphatase 1, glycogen targeting proteins, laforin and malin are in their infancy. These various processes appear to be the mechanisms that give the glycogen granule precise, yet dynamic regulation.

CaMKII regulates contraction- but not insulin-induced glucose uptake in mouse skeletal muscle

Studies using chemical inhibitors have suggested that the Ca(2+)-sensitive serine/threonine kinase Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is a key regulator of both insulin- and contraction-stimulated glucose uptake in skeletal muscle. However, due to nonspecificity of these inhibitors, the specific role that CaMKII may play in the regulation of glucose uptake is not known. We sought to determine whether specific inhibition of CaMKII impairs insulin- and/or contraction-induced glucose uptake in mouse skeletal muscle. Expression vectors containing green fluorescent protein conjugated to a CaMKII inhibitory (KKALHRQEAVDCL) or control (KKALHAQERVDCL) peptide were transfected into tibialis anterior muscles by in vivo electroporation. After 1 wk, muscles were assessed for peptide expression, CaMK activity, insulin- and contraction-induced 2-[(3)H]deoxyglucose uptake, glycogen concentrations, and changes in intracellular signaling proteins. Expression of the CaMKII inhibitory peptide decreased muscle CaMK activity approximately 35% compared with control peptide. Insulin-induced glucose uptake was not changed in muscles expressing the inhibitory peptide. In contrast, expression of the inhibitory peptide significantly decreased contraction-induced muscle glucose uptake (approximately 30%). Contraction-induced decreases in muscle glycogen were not altered by the inhibitory peptide. The CaMKII inhibitory peptide did not alter expression of the glucose transporter GLUT4 and did not impair contraction-induced increases in the phosphorylation of AMP-activated protein kinase (Thr(172)) or TBC1D1/TBC1D4 on phospho-Akt substrate sites. These results demonstrate that CaMKII does not regulate insulin-stimulated glucose uptake in skeletal muscle. However, CaMKII plays a critical role in the regulation of contraction-induced glucose uptake in mouse skeletal muscle.

Glycogen: an overview of possible regulatory roles of the proteins associated with the granule

While scientists have routinely measured muscle glycogen in many metabolic situations for over 4 decades, there is surprisingly little known regarding its regulation. In the past decade, considerable evidence has illustrated that the carbohydrate stores in muscle are not homogeneous, and it is very likely that metabolic pools exist or that each granule has independent regulation. The fundamental aspects appear to be associated with a complex set of proteins that associate with both the granule and each other in a dynamic fashion. Some of the proteins are enzymes and others play scaffolding roles. A number of the proteins can translocate, depending on the metabolic stimulus. These various processes appear to be the mechanisms that give the glycogen granule precise yet dynamic regulation. This may also allow the stores to serve as an important metabolic regulator of other metabolic events.

The formation of peroxynitrite in the applied physiology of mitochondrial nitric oxide

Mitochondria require nitric oxide ((.)NO) to exert a delicate control of metabolic rate as well as to regulate life functions, cell cycle activation and arrest, and apoptosis. All activities depend on the matrical (.)NO steady state concentration as provided by mitochondrial (mtNOS) and cytosolic sources (eNOS) and reduced by forming superoxide anion and H2O2 and a low peroxynirite (ONOO(-)) yield. We review herein the biochemical pathways involved in the control of (.)NO mitochondrial level and its biological and physiological significance in hormone effects and aging. At high ()NO, the cost of this physiological regulation is that ONOO(-) excess will lead to nitrosation/nitration and oxidization of mitochondrial and cell proteins and lipids. The disruption of (.)NO modulation of mitochondrial respiration supports then, a platform for prevalent neurodegenerative and metabolic diseases.

Muscle as an endocrine organ: focus on muscle-derived interleukin-6

Skeletal muscle has recently been identified as an endocrine organ. It has, therefore, been suggested that cytokines and other peptides that are produced, expressed, and released by muscle fibers and exert paracrine, autocrine, or endocrine effects should be classified as "myokines." Recent research demonstrates that skeletal muscles can produce and express cytokines belonging to distinctly different families. However, the first identified and most studied myokine is the gp130 receptor cytokine interleukin-6 (IL-6). IL-6 was discovered as a myokine because of the observation that it increases up to 100-fold in the circulation during physical exercise. Identification of IL-6 production by skeletal muscle during physical activity generated renewed interest in the metabolic role of IL-6 because it created a paradox. On one hand, IL-6 is markedly produced and released in the postexercise period when insulin action is enhanced but, on the other hand, IL-6 has been associated with obesity and reduced insulin action. This review focuses on the myokine IL-6, its regulation by exercise, its signaling pathways in skeletal muscle, and its role in metabolism in both health and disease.

Control of muscle mitochondria by insulin entails activation of Akt2-mtNOS pathway: implications for the metabolic syndrome

Background

In the metabolic syndrome with hyperinsulinemia, mitochondrial inhibition facilitates muscle fat and glycogen accumulation and accelerates its progression. In the last decade, nitric oxide (NO) emerged as a typical mitochondrial modulator by reversibly inhibiting citochrome oxidase and oxygen utilization. We wondered whether insulin-operated signaling pathways modulate mitochondrial respiration via NO, to alternatively release complete glucose oxidation to CO₂ and H₂O or to drive glucose storage to glycogen.

Methodology/Principal Findings

We illustrate here that NO produced by translocated nNOS (mtNOS) is the insulin-signaling molecule that controls mitochondrial oxygen utilization. We evoke a hyperinsulinemic-normoglycemic non-invasive clamp by subcutaneously injecting adult male rats with long-lasting human insulin glargine that remains stable in plasma by several hours. At a precise concentration, insulin increased phospho-Akt2 that translocates to mitochondria and determines in situ phosphorylation and substantial cooperative mtNOS activation (+4–8 fold, P<.05), high NO, and a lowering of mitochondrial oxygen uptake and resting metabolic rate (−25 to −60%, P<.05). Comparing in vivo insulin metabolic effects on gastrocnemius muscles by direct electroporation of siRNA nNOS or empty vector in the two legs of the same animal, confirmed that in the silenced muscles disrupted mtNOS allows higher oxygen uptake and complete (U-¹⁴C)-glucose utilization respect to normal mtNOS in the vector-treated ones (respectively 37±3 vs 10±1 µmolO₂/h.g tissue and 13±1 vs 7.2±1 µmol ³H₂O/h.g tissue, P<.05), which reciprocally restricted glycogen-synthesis by a half.

Conclusions/Significance

These evidences show that after energy replenishment, insulin depresses mitochondrial respiration in skeletal muscle via NO which permits substrates to be deposited as macromolecules; at discrete hyperinsulinemia, persistent mtNOS activation could contribute to mitochondrial dysfunction with insulin resistance and obesity and therefore, to the progression of the metabolic syndrome.

Metabolic transformation of rabbit skeletal muscle cells in primary culture in response to low glucose

We have investigated the mechanism of the changes in the profile of metabolic enzyme expression that occur in association with fast-to-slow transformation of rabbit skeletal muscle. The hypotheses assessed are: do 1) lowered intracellular ATP concentration or 2) reduction of the muscular glycogen stores act as triggers of metabolic transformation? We find that 3 days of decreased cytosolic ATP content have no impact on the investigated metabolic markers, whereas incubation of the cells with little or no glucose leads to decreases in glycogen in conjunction with decreases in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter activity, GAPDH mRNA and specific GAPDH enzyme activity (indicators of the anaerobic glycolytic pathway), and furthermore to increases in mitochondrial acetoacetyl-CoA thiolase (MAT, also known as ACAT) promoter activity, peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) expression and citrate synthase (CS) specific enzyme activity (all indicators of oxidative metabolic pathways). The AMP-activated protein kinase (AMPK) activity under these conditions is reduced compared to controls. In experiments with two inhibitors of glycogen degradation we show that the observed metabolic transformation caused by low glucose takes place even if intracellular glycogen content is high. These findings for the first time provide evidence that metabolic adaptation of skeletal muscle cells from rabbit in primary culture can be induced not only by elevation of intracellular calcium concentration or by a rise of AMPK activity, but also by reduction of glucose supply. Contrary to expectations, neither an increase in phospho-AMPK nor a reduction of muscular glycogen content are crucial events in the glucose-dependent induction of metabolic transformation in the muscle cell culture system studied.

Overreaching-induced oxidative stress, enhanced HSP72 expression, antioxidant and oxidative enzymes downregulation

Overreaching (OVR) is defined as the initial phase of overtraining syndrome and is known as a metabolic imbalance leading to short-term fatigue. Exercise increases reactive oxygen species production, which can oxidize intracellular structures impairing cell function and thus leads to OVR process. The aim of this work is to study the behavior of oxidative stress markers in subjects submitted to an OVR protocol. Thirty rats were divided in exercise and control group, and submitted to an 8-week-endurance training (ET) and a 3-week-OVR protocol. Thiobarbituric acid reactive substances (TBARs), reactive carbonylated derivatives (RCD), glutathione reductase (GR), catalase (CAT) and citrate synthase (CS) activities and stress protein HSP72 were measured in soleus (SO), extensor digital longus (EDL) and semitendinuous (ST) muscles. ET induced significant enhancement (P<0.05) in CS, GR, CAT, TBARs, RCD and HSP72 in SO, EDL and ST. OVR induced higher levels (P<0.05) of TBARs, RCD and HSP72 compared with ET only in SO, while in EDL and ST all measured parameters ranged at same levels reached during ET. We concluded that stress-induced OVR protocol is fiber type dependent, the SO muscle fiber type I being the most affected by this treatment.

Physical activity and health, novel concepts and new targets: report from the 12th Conference of the International Research Group on the Biochemistry of Exercise

The present paper is the introductory paper to a series of brief reviews representing the proceedings of a recent conference on ‘The biochemical basis for the health effects of exercise’ organized by the International Research Group on the Biochemistry of Exercise in conjunction with the Nutrition Society. Here the aim is to briefly review and highlight the main innovations presented during this meeting. The following topics were covered during the meeting: exercise signalling pathways controlling fuel oxidation during and after exercise; the fatty acid transporters of skeletal muscle; mechanisms involved in exercise-induced mitochondrial biogenesis in skeletal muscle; new methodologies and insights in the regulation of fat metabolism during exercise; muscle hypertrophy: the signals of insulin, amino acids and exercise; adipose tissue–liver–muscle interactions leading to insulin resistance. In these symposia state-of-the-art knowledge on how physical exercise exerts its effects on health was presented. The fast-growing number of identified pathways and processes involved in the health effects of physical exercise, which were discussed during the meeting, will help to develop tailored physical-activity regimens in the prevention of inactivity-induced deterioration of health.

The Role of Salt and Glucose Replacement Drinks in the Marathon

There is a large and growing body of scientific evidence that documents the benefits of ingesting salt and glucose (carbohydrates) during prolonged exercise. Those benefits include maintenance of cardiovascular function, enhanced carbohydrate oxidation, blunted decline in plasma sodium concentration and improved performance. The consumption of approximately 1g of carbohydrate per kilogram of bodyweight per hour appears sufficient to improve performance in prolonged exercise. Research also indicates that approximately 450mg of sodium per hour is the minimum amount required to maintain plasma volume and slow the decline in plasma sodium concentration that can accompany prolonged exercise in some runners. Adequate carbohydrate and electrolyte intake can be achieved by consuming a well formulated sports drink at regular intervals during exercise, in volumes designed to minimise dehydration. For marathon runners, this could range from approximately 400mL to >1.5L per hour, depending upon individual sweating rates.

Fiber type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise

The effect of carbohydrate intake before and during exercise on muscle glycogen content was investigated. According to a randomized crossover study design, eight young healthy volunteers (n = 8) participated in two experimental sessions with an interval of 3 wk. In each session subjects performed 2 h of constant-load bicycle exercise ( approximately 75% maximal oxygen uptake). On one occasion (CHO), they received carbohydrates before ( approximately 150 g) and during (1 g.kg body weight(-1).h(-1)) exercise. On the other occasion they exercised after an overnight fast (F). Fiber type-specific relative glycogen content was determined by periodic acid Schiff staining combined with immunofluorescence in needle biopsies from the vastus lateralis muscle before and immediately after exercise. Preexercise glycogen content was higher in type IIa fibers [9.1 +/- 1 x 10(-2) optical density (OD)/microm(2)] than in type I fibers (8.0 +/- 1 x 10(-2) OD/microm(2); P < 0.0001). Type IIa fiber glycogen content decreased during F from 9.6 +/- 1 x 10(-2) OD/microm(2) to 4.5 +/- 1 x 10(-2) OD/microm(2) (P = 0.001), but it did not significantly change during CHO (P = 0.29). Conversely, in type I fibers during CHO and F the exercise bout decreased glycogen content to the same degree. We conclude that the combination of carbohydrate intake both before and during moderate- to high-intensity endurance exercise results in glycogen sparing in type IIa muscle fibers.