Muscle triglyceride and glycogen in endurance exercise: implications for performance

The role of GPR81-cAMP-PKA pathway in endurance training-induced intramuscular triglyceride accumulation and mitochondrial content changes in rats

The athlete's paradox phenomenon involves the accumulation of intramuscular triglycerides (IMTG) in both insulin-resistant and insulin-sensitive endurance athletes. Nevertheless, a complete understanding of this phenomenon is yet to be achieved. Recent research indicates that lactate, a common byproduct of physical activity, may increase the accumulation of IMTG in skeletal muscle. This is achieved through the activation of G protein-coupled receptor 81 (GPR81) leads to the suppression of the cyclic adenosine monophosphate-protein kinase A (cAMP-PKA) pathway. The mechanism accountable for the increase in mitochondrial content in skeletal muscle triggered by lactate remains incomprehensible. Based on current research, our objective is to explore the role of the GPR81-inhibited cAMP-PKA pathway in the aggregation of IMTG and the increase in mitochondrial content as a result of prolonged exercise. The GPR81-cAMP-PKA-signaling pathway regulates the buildup of IMTG caused by extended periods of endurance training (ET). This is likely due to a decrease in proteins related to fat breakdown and an increase in proteins responsible for fat production. It is possible that the GPR81-cAMP-PKA pathway does not contribute to the long-term increase in mitochondrial biogenesis and content, which is induced by chronic ET. Additional investigation is required to explore the possible hindrance of the mitochondrial biogenesis and content process during physical activity by the GPR81-cAMP-PKA signal.

From Incremental Test to Continuous Running at Fixed Lactate Thresholds: Individual Responses on %VO2max, %HRmax, Lactate Accumulation, and RPE

With Norway's successes in middle and long-distance running, lactate-guided threshold training has regained importance in recent years. Therefore, the aim of the present study was to investigate the individual responses on common monitoring parameters based on a lactate-guided conventional training method. In total, 15 trained runners (10 males, 5 females; 18.6 ± 3.3 years; VO2max: 59.3 ± 5.9 mL kg-1 min-1) completed a 40-min continuous running session at a fixed lactate threshold load of 2 mmol L-1. Lactate (La), oxygen uptake (VO2), heart rate (HR), and rating of perceived exertion (RPE) were recorded. The chosen workload led to lactate values of 2.85 ± 0.56 mmol L-1 (range: 1.90-3.80), a percentage of VO2max utilization (%VO2max) of 79.2 ± 2.5% (range: 74.9-83.8), a percentage of HRmax utilization (%HRmax) of 92.2 ± 2.5% (range: 88.1-95.3), and an RPE of 6.1 ± 1.9 (range: 3-10) at the end of the running session. Thereby, the individual responses differed considerably. These results indicate that a conventional continuous training method based on a fixed lactate threshold can lead to different individual responses, potentially resulting in various physiological impacts. Moreover, correlation analyses suggest that athletes with higher lactate threshold performance levels must choose their intensity in continuous training methods more conservatively (lower percentage intensity based on a fixed threshold) to avoid eliciting excessively strong metabolic responses.

Hydrocortisone-Containing Animal-Derived Food Intake Affects Lipid Nutrients Utilization

SCOPE

As the tremendous increases in consumption of animal-derived food, endogenous hydrocortisone migrating along the food chain to organism arouses extensive attention. This study aims to investigate the cumulative impacts of dietary hydrocortisone intake and mechanistic understanding on metabolism of lipid nutrients.

METHODS AND RESULTS

A total of 120 porcine muscles samples with different concentrations of hydrocortisone are collected at three time points. An operational food chain simulation framework is constructed and 175 lipid molecules are identified by UHPLC-Q-Orbitrap HRMS. Compared to the control group, 66 lipid molecules are significantly different, including 17 triglycerides and 31 glycerophospholipids. Integrated analyses of lipidomics and proteomics indicate that hydrocortisone promotes adipose triglyceride lipase and hormone sensitive lipase activity to precondition for triglycerides hydrolysis. Quantitative lipidomics analysis shows the presence of hydrocortisone decreases the concentration of docosahexaenoic acid (3.66 ± 0.15-3.09 ± 0.12 mg kg^-1 ) and eicosapentanoic acid (0.54 ± 0.09-0.48 ± 0.06 mg kg^-1 ). A noteworthy increase of most saturated triglycerides concentration with the prolonging of time is observed.

CONCLUSIONS

Hydrocortisone originating from animal-derived food induces glycerophospholipids degradation and triglycerides hydrolysis through promoting adipose triglyceride lipase, hormone sensitive lipase, and phosphoglycerate kinase activity and further intervenes lipid nutrients utilization.

Exploring the "Athlete's Paradox": Division I Cross-Country Runners Demonstrate Similar Muscle Characteristics to Recreationally Trained Young Adults

ABSTRACT

Cabre, HE, Greenwalt, CE, Gould, LM, Hirsch, KR, Blue, MNM, and Smith-Ryan, AE. Exploring the "Athlete's Paradox": Division I cross-country runners demonstrate similar muscle characteristics to recreationally trained young adults. J Strength Cond Res XX(X): 000-000, 2021-Endurance training can influence body composition and muscle characteristics. Endurance athletes have demonstrated elevated intramuscular fat (IMF), yet individuals with greater body fat also demonstrate elevated IMF. The purpose of this study was to examine differences in muscle characteristics (echo intensity [EI] and muscle cross-sectional area [mCSA]) and body composition between Division I collegiate athletes and college-age adults matched for percent fat (%fat). Thirty cross-country athletes (XC) and 30 normal-weight (NW) recreationally active college students (male athletes: n = 30; female athletes: n = 30; mean ± SD: age: 19.2 ± 1.1 years; body mass: 61.7 ± 8.7 kg; %fat: 18.0 ± 5.2%) underwent a panoramic ultrasound scan of the vastus lateralis to evaluate EI and mCSA. A full-body dual-energy x-ray absorptiometry scan was used to assess fat mass (FM), lean mass (LM), and %fat. Independent t-tests were used to evaluate mCSA, EI, and body composition. Significance level was set at ≤ 0.05. There were no significant differences between the XC and NW cohorts in mCSA (mean difference [MD; XC - NW], -1.30 ± -0.40 cm3; p = 0.340) or EI (MD: 3.97 ± 2.66 a.u.; p = 0.478). Body composition was not different between the groups: FM (MD: -0.14 ± -0.54 kg; p = 0.848), LM (-3.07 ± 1.25 kg; p = 0.268), or bone mineral content (-0.21 ± 0.03 kg; p = 0.120). There were also no significant differences for any outcome variables when stratified by male athletes (p = 0.097-0.468) or female athletes (p = 0.055-0.700). These results suggest that XC athletes may have similar muscle characteristics to NW individuals when matched for %fat. Understanding and tracking muscle characteristics in XC athletes may be important for performance, injury prevention, and the transition to retirement.

Metabolomics study on the intervention effect of Radix Salviae Miltiorrhizae extract in exercise-induced exhaustion rat using gas chromatography coupled to mass spectrometry

The metabolomics approach based on the gas chromatography coupled to mass spectrometry (GC-MS) was adopted to explore the underlying mechanism of the anti-fatigue effect of Radix Salviae Miltiorrhizae (RSM), a famous herbal medicine in China used for multiple biological functions, in load-weighted swimming test in rat, combined with biochemical parameters evaluations. As a result, the metabolomics study followed by orthogonal partial least-square (OPLS) analysis could differentiate metabolic profiling between the control and exhaustive exercise group, showing the rats underwent an obvious metabolic perturbation, whereas RSM treatment restored scores plot close to normal and showed regulatory effects on the muscle metabolic profiles. The changed metabolic pathways of the potential biomarkers in response to the effect of RSM treatment for exhaustive exercise rats included in glucose metabolism (glucose, lactic acid, alanine), glutathione metabolism (glycine, glutamate, 5-oxo-proline), TCA cycle (succinic acid), arginine biosynthesis (glutamine, ornithine, urea), glyoxylate and dicarboxylate metabolism (serine, glycine), oxidative stress (taurine) and purine metabolism (inosine). In addition, intervention of RSM increased hepatic glycogen, muscle glycogen and serum glucose, and decreased triglyceride and blood urea nitrogen levels, indicating RSM treatment may regulate energy metabolism by increasing the rate of fat utilization, decrease the protein and carbohydrate utilization. Furthermore, RSM reduced exhaustive exercise-induced accumulation of the lipid peroxidation byproduct malonaldehyde and elevated antioxidants' levels, including reduced glutathione and superoxide dismutase, which might be a positive reflection of improved oxidant-antioxidant balance. Moreover, RSM could protect against exercise-induced muscle damage by attenuating creatine kinase release. In summary, RSM provided a good anti-fatigue effect by regulating energy metabolism, oxidant-antioxidant balance, and the endogenous metabolites in the exercising muscle. This study demonstrates that metabolomics is an effective tool for the estimation of the potential anti-fatigue effect of RSM and for the illustration of its pharmacological mechanism.

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.

A genome-wide case-control association study of dark cutting in beef cattle

The genetic architecture of dark cutting was investigated with a case-control genome-wide association study on two groups of beef cattle analyzed separately and together (combined group). Groups I (n = 64) and II (n = 150) were genotyped using the 70K GeneSeek Genomic Profiler for Beef Cattle-HD and the 50K Illumina BovineSNP50v2 BeadChip, respectively. Dark cutting was analyzed as a binary trait (case versus control) using logistic regression in an additive model implemented in PLINK version 1.9. Significant loci were not identified when correcting for multiple testing (false discovery rate), suggesting that the trait is not controlled by genes with big effects, or the sample size was not large enough to detect these major genes. Regions harbouring single-nucleotide polymorphisms (SNPs) with a raw p < 0.01 using 1 MB window were analyzed for gene function using the ingenuity pathway analysis. For groups I, II, and the combined group, 449, 301, and 191 SNPs were identified, respectively. Genes identified were involved in pyruvic acid modification and release, 2-deoxyglucose clearance and disposal, sucrose recognition, energy production, and metabolism of carbohydrate. Although detected SNP associations require validation in a large population, results suggested the possibility for marker-assisted or genomic selection of beef cattle to reduce dark cutting.

The Effect of Consuming Carbohydrate With and Without Protein on the Rate of Muscle Glycogen Re-synthesis During Short-Term Post-exercise Recovery: a Systematic Review and Meta-analysis

Background

Rapid restoration of muscle glycogen stores is imperative for athletes undertaking consecutive strenuous exercise sessions with limited recovery time (e.g. ≤ 8 h). Strategies to optimise muscle glycogen re-synthesis in this situation are essential. This two-part systematic review and meta-analysis investigated the effect of consuming carbohydrate (CHO) with and without protein (PRO) on the rate of muscle glycogen re-synthesis during short-term post-exercise recovery (≤ 8 h).

Methods

Studies were identified via the online databases Web of Science and Scopus. Investigations that measured muscle glycogen via needle biopsy during recovery (with the first measurement taken ≤ 30 min post-exercise and at least one additional measure taken ≤ 8 h post-exercise) following a standardised exercise bout (any type) under the following control vs. intervention conditions were included in the meta-analysis: part 1, water (or non-nutrient beverage) vs. CHO, and part 2, CHO vs. CHO+PRO. Publications were examined for methodological quality using the Rosendal scale. Random-effects meta-analyses and meta-regression analyses were conducted to evaluate intervention efficacy.

Results

Overall, 29 trials (n = 246 participants) derived from 21 publications were included in this review. The quality assessment yielded a Rosendal score of 61 ± 8% (mean ± standard deviation). Part 1: 10 trials (n = 86) were reviewed. Ingesting CHO during recovery (1.02 ± 0.4 g·kg body mass (BM)⁻¹ h⁻¹) improved the rate of muscle glycogen re-synthesis compared with water; change in muscle glycogen (MG_Δ) re-synthesis rate = 23.5 mmol·kg dm⁻¹ h⁻¹, 95% CI 19.0–27.9, p < 0.001; I² = 66.8%. A significant positive correlation (R² = 0.44, p = 0.027) was observed between interval of CHO administration (≤ hourly vs. > hourly) and the mean difference in rate of re-synthesis between treatments. Part 2: 19 trials (n = 160) were reviewed. Ingesting CHO+PRO (CHO: 0.86 ± 0.2 g·kg BM⁻¹ h⁻¹; PRO: 0.27 ± 0.1 g·kg BM⁻¹ h⁻¹) did not improve the rate of muscle glycogen re-synthesis compared to CHO alone (0.95 ± 0.3 g·kg BM⁻¹ h⁻¹); MG_Δ re-synthesis rate = 0.4 mmol·kg  dm⁻¹ h⁻¹, 95% CI −2.7 to 3.4, p = 0.805; I² = 56.4%.

Conclusions

Athletes with limited time for recovery between consecutive exercise sessions should prioritise regular intake of CHO, while co-ingesting PRO with CHO appears unlikely to enhance (or impede) the rate of muscle glycogen re-synthesis.

Trial Registration

Registered at the International Prospective Register of Systematic Reviews (PROSPERO) (identification code CRD42020156841).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40798-020-00297-0.

The effects of Jilin sika Deer's (Cervus dybowski) tendon liquid supplementation on endurance drop jumps performance, biochemistry profile of free boxing players

ETHNOPHARMACOLOGICAL RELEVANCE

Risk of anterior cruciate ligament is a persistent and severe problem in athletes owing to strenuous exercise-induced lower-body injury. Tendon of deer liquid (TD) a familiar traditional Chinese medicine, has been used for strengthening the bones and muscles.

AIM OF THE STUDY

In this study, we seek to demonstrate the application of TD in improving endurance exercise performance and reducing the risk of endurance training injury for free boxing players.

MATERIALS AND METHODS

Sixteen male free boxing players were randomly assigned to the TD and placebo groups. Body composition, clinical biochemistry profiles, kinematic and physiology exercise tests were evaluated at 2 time points - pre-supplementation (pre-) and after 6 weeks post-supplementation (post-).

RESULTS

TD group exhibited significant increase in levels of serum total protein (TP) compared to the placebo group after a 6-week supplementation. Following the treadmill test, serum glucose and maximal oxygen consumption (VO₂ max) levels were increased in the TD group. In the endurance test consisting of 200 counts of drop vertical jumps (DVJs), subjects in the TD group also showed an increase in vertical jump height and reduced risk of musculoskeletal system injuries.

CONCLUSIONS

TD supplementation leads to better physiological adaptation in free boxing players and has the potential for use as a nutrient supplement toward a variety of benefits for endurance athletes.

Transcriptional programming of lipid and amino acid metabolism by the skeletal muscle circadian clock

Circadian clocks are fundamental physiological regulators of energy homeostasis, but direct transcriptional targets of the muscle clock machinery are unknown. To understand how the muscle clock directs rhythmic metabolism, we determined genome-wide binding of the master clock regulators brain and muscle ARNT-like protein 1 (BMAL1) and REV-ERBα in murine muscles. Integrating occupancy with 24-hr gene expression and metabolomics after muscle-specific loss of BMAL1 and REV-ERBα, here we unravel novel molecular mechanisms connecting muscle clock function to daily cycles of lipid and protein metabolism. Validating BMAL1 and REV-ERBα targets using luciferase assays and in vivo rescue, we demonstrate how a major role of the muscle clock is to promote diurnal cycles of neutral lipid storage while coordinately inhibiting lipid and protein catabolism prior to awakening. This occurs by BMAL1-dependent activation of Dgat2 and REV-ERBα-dependent repression of major targets involved in lipid metabolism and protein turnover (MuRF-1, Atrogin-1). Accordingly, muscle-specific loss of BMAL1 is associated with metabolic inefficiency, impaired muscle triglyceride biosynthesis, and accumulation of bioactive lipids and amino acids. Taken together, our data provide a comprehensive overview of how genomic binding of BMAL1 and REV-ERBα is related to temporal changes in gene expression and metabolite fluctuations.

Intensity- and Duration-Based Options to Regulate Endurance Training

The regulation of endurance training is usually based on the prescription of exercise intensity. Exercise duration, another important variable of training load, is rarely prescribed by individual measures and mostly set from experience. As the specific exercise duration for any intensity plays a substantial role regarding the different kind of cellular stressors, degree, and kind of fatigue as well as training effects, concepts integrating the prescription of both intensity and duration within one model are needed. An according recent approach was the critical power concept which seems to have a physiological basis; however, the mathematical approach of this concept does not allow applying the three zones/two threshold model of metabolism and its different physiological consequences. Here we show the combination of exercise intensity and duration prescription on an individual basis applying the power/speed to distance/time relationship. The concept is based on both the differentiation of intensities by two lactate or gas exchange variables derived turn points, and on the relationship between power (or velocity) and duration (or distance). The turn points define three zones of intensities with distinct acute metabolic, hormonal, and cardio-respiratory responses for endurance exercise. A maximal duration exists for any single power or velocity such as described in the power-duration relationship. Using percentages of the maximal duration allows regulating fatigue, recovery time, and adaptation for any single endurance training session. Four domains of duration with respect to induced fatigue can be derived from maximal duration obtained by the power-duration curve. For any micro-cycle, target intensities and durations may be chosen on an individual basis. The model described here is the first conceptual framework of integrating physiologically defined intensities and fatigue related durations to optimize high-performance exercise training.

Black ginger extract increases physical fitness performance and muscular endurance by improving inflammation and energy metabolism

We previously reported that polymethoxyflavones (PMFs) in black ginger (Kaempferia parviflora) extract (KPE) increased energy production by activating AMP-activated protein kinase (AMPK) in C2C12 myoblasts. We herein evaluated the effects of KPE on physical fitness performance and muscular endurance in mice. Male mice were orally administered KPE for 4 weeks, and then forced swimming test, open-field test, inclined plane test, and wire hanging test were performed. KPE significantly increased the swimming time, motility after swimming, and grip strength. IL-6 and TNF-α mRNA expression levels were decreased in the soleus muscle, whereas peroxisome proliferator-activated receptor γ coactivator (PGC)-1α and glycogen synthase mRNA expression levels, mitochondrial number, and glycogen content were increased. These results were in agreement with those obtained for KPE and PMFs in C2C12. Therefore, the activation of AMPK by PMFs may be one of the mechanisms by which KPE improves physical fitness performance and muscular endurance.

Hepatocellular carcinoma and lifestyles

The majority of hepatocellular carcinoma occurs over pre-existing chronic liver diseases that share cirrhosis as an endpoint. In the last decade, a strong association between lifestyle and hepatocellular carcinoma has become evident. Abundance of energy-rich food and sedentary lifestyles have caused metabolic conditions such as obesity and diabetes mellitus to become global epidemics. Obesity and diabetes mellitus are both tightly linked to non-alcoholic fatty liver disease and also increase hepatocellular carcinoma risk independent of cirrhosis. Emerging data suggest that physical activity not only counteracts obesity, diabetes mellitus and non-alcoholic fatty liver disease, but also reduces cancer risk. Physical activity exerts significant anticancer effects in the absence of metabolic disorders. Here, we present a systematic review on lifestyles and hepatocellular carcinoma.

Pacing in a self-paced world record attempt in 24-h road cycling

Background

Pacing strategy plays a major role in sport performance. However, there is a dearth of knowledge concerning pacing during ultra-endurance sport events. The present case study investigated the pacing of an ultra-cyclist in a self-paced attempt to break the world record in 24-h road cycling and, with all the caveats and the limitations affecting a case report, could be useful in generating hypotheses and further studies about pacing dynamics during prolonged sport performances.

Case description

A well experienced ultra-cyclist completed laps of 11.731 km during 24 h and the support crew recorded for each lap time and power output in Watt. The trend in cycling speed and power output across laps was investigated using regression analyses. A mixed-effects regression model including lap, ambient air temperature, air pressure, air humidity and wind speed as fixed variables was used to investigate a relationship of environmental factors with cycling speed.

Discussion and evaluation

The athlete achieved 896.173 km within the 24 h. He set a new world record by breaking the old record (Jure Robic, 2004, 834.77 km) by 61.403 km. He cycled at an average speed of 37.34 km/h with an average power output of 250.2 W. The decrease in cycling speed and power output across laps could be modelled linearly. Temperature and wind speed were related to cycling speed during the whole event. There was a significant interaction air temperature × relative humidity for the whole event.

Conclusions

The athlete adopted a positive pacing (i.e. speed gradually declined throughout the event) and environmental factors (i.e. temperature and wind speed) influenced cycling speed during the event.

Anti-Fatigue and Antioxidant Activity of the Polysaccharides Isolated from Millettiae speciosae Champ. Leguminosae

Millettiae speciosae Champ. Leguminosae (MSC), is a well-known Chinese herb traditionally used as food material and medicine for enhancing physical strength. Our preliminary study found that the aqueous extract of this herb (MSE) had an anti-fatigue effect. In this paper, we further separated MSE into total polysaccharides (MSP) and supernatant (MSS) by alcohol precipitation, and explored which fraction was active for its anti-fatigue effect. Mice were orally administered with MSP or MSS at the doses of 200, 400, and 800 mg/kg for 20 days and the anti-fatigue effect was assessed by exhaustive swimming exercise (ESE). The biochemical parameters related to fatigue after ESE and the in vitro antioxidant activity of active fraction were determined. Our results showed that MSP, instead of MSS, significantly extended the swimming time to exhaustion (p < 0.05), indicating that MSP is responsible for the anti-fatigue effect of MSE. In addition, MSP treatment increased the levels of glucose (Glu) and muscle glycogen, whereas it decreased the accumulations of blood urea nitrogen (BUN) and lactic acid (Lac). Moreover, ESE increased the levels of creatine phosphokinase (CK), lactic dehydrogenase (LDH), and malondialdehyde (MDA) but reduced superoxide dismutase (SOD) and glutathione (GSH) in plasma. In contrast, MSP inhibited all the above changes relating to fatigue. Furthermore, an in vitro antioxidant test revealed that MSP dose-dependently scavenged ·OH and DPPH free radicals. Taken together, these findings strongly suggested that MSP was able to alleviate physical fatigue by increasing energy resources and decreasing accumulation of detrimental metabolites. The antioxidant activity may crucially contribute to the observed anti-fatigue effect of MSP.

Volume-dependent effect of supervised exercise training on fatty liver and visceral adiposity index in subjects with type 2 diabetes The Italian Diabetes Exercise Study (IDES)

AIMS

This study evaluated the effect of supervised exercise training on liver enzymes and two surrogate measures of non-alcoholic fatty liver disease (NAFLD) in subjects with type 2 diabetes.

METHODS

Sedentary patients from 22 outpatient diabetes clinics were randomized by center, age and treatment to twice-a-week supervised aerobic and resistance training plus structured exercise counseling (exercise group, EXE; n=303) versus counseling alone (control group, CON; n=303) for 12 months. EXE participants were further randomized to low-to-moderate (n=142) or moderate-to-high (n=161) intensity training of equal energy cost. Baseline and end-of-study levels of liver enzymes, fatty liver index (FLI) and visceral adiposity index (VAI) were obtained.

RESULTS

Enzyme levels did not change, whereas FLI and VAI decreased significantly in EXE, but not CON participants. Physical activity (PA) volume was an independent predictor of both FLI and VAI reductions, the extent of which increased from the 1st to the 4th quintile of PA volume and baseline to end-of-study changes in fitness parameters. Differences in the effect of LI versus HI training were negligible.

CONCLUSIONS

Data from this large cohort of subjects with type 2 diabetes indicate that FLI and VAI decrease with supervised training in a volume-dependent manner.

Television viewing and fatty liver in early midlife. The Cardiovascular Risk in Young Finns Study

INTRODUCTION

Both sedentary behaviour and fatty liver are associated with increased risk of obesity and non-communicable diseases, but their relationship remains unknown. We investigated the relationship of television (TV) viewing time with serum gamma-glutamyltransferase (GGT) and Fatty Liver Index (FLI), and ultrasonographically assessed liver fat.

METHODS

A total of 1,367 adults of the population-based Cardiovascular Risk in Young Finns study (748 women, 619 men, aged 34-49 years) had fasting serum GGT, triglycerides, weight, height, and waist circumference, and self-reported TV time data from 2001, 2007, and 2011. Changes in GGT and FLI, and liver ultrasound images in 2011 were studied in groups with constantly low (≤ 1 h/d), moderate (1-3 h/d), or high (≥ 3 h/d) daily TV time, and in groups with ≥ 1 hour increase/decrease in daily TV time between 2001 and 2011.

RESULTS

Constantly high TV time was associated with higher GGT and FLI (P < 0.02 in both), and 2.3-fold (95% CI 1.2-4.5) increased risk of fatty liver regardless of age, sex, leisure-time and occupational physical activity, energy intake, diet composition, alcohol use, sleep duration, socioeconomic status, and smoking. Adjustment for BMI partly attenuated the associations.

CONCLUSIONS

High TV viewing increases fatty liver risk. It may be one mechanism linking sedentary behaviour with increased cardiometabolic disease risks.

Energy balance of triathletes during an ultra-endurance event

The nutritional strategy during an ultra-endurance triathlon (UET) is one of the main concerns of athletes competing in such events. The purpose of this study is to provide a proper characterization of the energy and fluid intake during real competition in male triathletes during a complete UET and to estimate the energy expenditure (EE) and the fluid balance through the race.

METHODS

Eleven triathletes performed a UET. All food and drinks ingested during the race were weighed and recorded in order to assess the energy intake (EI) during the race. The EE was estimated from heart rate (HR) recordings during the race, using the individual HR-oxygen uptake (Vo2) regressions developed from three incremental tests on the 50-m swimming pool, cycle ergometer, and running treadmill. Additionally, body mass (BM), total body water (TBW) and intracellular (ICW) and extracellular water (ECW) were assessed before and after the race using a multifrequency bioimpedance device (BIA).

RESULTS

Mean competition time and HR was 755 ± 69 min and 137 ± 6 beats/min, respectively. Mean EI was 3643 ± 1219 kcal and the estimated EE was 11,009 ± 664 kcal. Consequently, athletes showed an energy deficit of 7365 ± 1286 kcal (66.9% ± 11.7%). BM decreased significantly after the race and significant losses of TBW were found. Such losses were more related to a reduction of extracellular fluids than intracellular fluids.

CONCLUSIONS

Our results confirm the high energy demands of UET races, which are not compensated by nutrient and fluid intake, resulting in a large energy deficit.

Exploring mechanisms of fatigue during repeated exercise and the dose dependent effects of carbohydrate and protein ingestion: study protocol for a randomised controlled trial

Background

Muscle glycogen has been well established as the primary metabolic energy substrate during physical exercise of moderate- to high-intensity and has accordingly been implicated as a limiting factor when such activity is sustained for a prolonged duration. However, the role of this substrate during repeated exercise after limited recovery is less clear, with ongoing debate regarding how recovery processes can best be supported via nutritional intervention. The aim of this project is to examine the causes of fatigue during repeated exercise bouts via manipulation of glycogen availability through nutritional intervention, thus simultaneously informing aspects of the optimal feeding strategy for recovery from prolonged exercise.

Methods/Design

The project involves two phases with each involving two treatment arms administered in a repeated measures design. For each treatment, participants will be required to exercise to the point of volitional exhaustion on a motorised treadmill at 70% of previously determined maximal oxygen uptake, before a four hour recovery period in which participants will be prescribed solutions providing 1.2 grams of sucrose per kilogram of body mass per hour of recovery (g.kg^-1.h^-1) relative to either a lower rate of sucrose ingestion (that is, 0.3 g.kg^-1. h^-1; Phase I) or a moderate dose (that is, 0.8 g.kg^-1.h^-1) rendered isocaloric via the addition of 0.4 g.kg^-1.h^-1 whey protein hydrolysate (Phase II); the latter administered in a double blind manner as part of a randomised and counterbalanced design. Muscle biopsies will be sampled at the beginning and end of recovery for determination of muscle glycogen resynthesis rates, with further biopsies taken following a second bout of exhaustive exercise to determine differences in substrate availability relative to the initial sample taken following the first exercise bout.

Discussion

Phase I will inform whether a dose–response relationship exists between carbohydrate ingestion rate and muscle glycogen availability and/or the subsequent capacity for physical exercise. Phase II will determine whether such effects are dependent on glycogen availability per se or energy intake, potentially via protein mediated mechanisms.

Trial registration

ISRCTN87937960.

Carbohydrate supplementation increases intramyocellular lipid stores in elite runners

The objective was to determine the effects of carbohydrate (CHO) supplementation on exercise-induced hormone responses and post-training intramyocellular lipid stores (IMCL). Twenty-four elite male athletes (28.0±1.2 years) were randomized to receive CHO (maltodextrin solution) or zero energy placebo solution (control group). The high-intensity running protocol consisted of 10×800 m at 100% of the best 3000-m speed (Vm3 km) and 2×1000 m maximal bouts in the morning and a submaximal 10-km continuous easy running in the afternoon of day 9. IMCL concentrations were assessed by (1)H-MRS before (-day 9) and after training (day 9) in soleus (SO) and tibialis anterior (TA) muscles. Blood hormones were also measured before, during, and post-exercise. The percent change (Δ%) in TA-IMCL was higher in the CHO group (47.9±24.5 IMCL/Cr) than in the control group (-1.7±13.1, respectively) (P=.04). Insulin concentrations were higher in the CHO group post-intermittent running compared to control (P=.02). Circulating levels of free fatty acids and GH were lower in the CHO group (P>.01). The decline in performance in the 2nd 1000-m bout was also attenuated in this group compared to control (P<.001 and P=.0035, respectively). The hormonal milieu (higher insulin and lower GH levels) in the CHO group, together with unchanged free fatty acid levels, probably contributed to the increased IMCL stores. This greater energy storage capacity may have improved post-exercise recovery and thus prevented performance deterioration.

Effects of carbohydrate, branched-chain amino acids, and arginine in recovery period on the subsequent performance in wrestlers

Many athletes need to participate in multiple events in a single day. The efficient post-exercise glycogen recovery may be critical for the performance in subsequent exercise. This study examined whether post-exercise carbohydrate supplementation could restore the performance in the subsequent simulated wrestling match. The effect of branched-chain amino acids and arginine on glucose disposal and performance was also investigated. Nine well-trained male wrestlers participated in 3 trials in a random order. Each trial contained 3 matches with a 1-hr rest between match 1 and 2, and a 2-hr rest between match 2 and 3. Each match contained 3 exercise periods interspersed with 1-min rests. The subjects alternated 10-s all-out sprints and 20-s rests in each exercise period. At the end of match 2, 3 different supplementations were consumed: 1.2 g/kg glucose (CHO trial), 1 g/kg glucose + 0.1 g/kg Arg + 0.1 g/kg BCAA (CHO+AA trial), or water (placebo trial). The peak and average power in the 3 matches was similar in the 3 trials. After the supplementation, CHO and CHO+AA trial showed significantly higher glucose and insulin, and lower glycerol and non-esterified fatty acid concentrations than the placebo trial. There was no significant difference in these biochemical parameters between the CHO and CHO+AA trials. Supplementation of carbohydrate with or without BCAA and arginine during the post-match period had no effect on the performance in the following simulated match in wrestlers. In addition, BCAA and arginine did not provide additional insulinemic effect.

Organelle dysfunction in hepatitis C virus-associated steatosis: anything to learn from nonalcoholic steatohepatitis?

Nonalcoholic fatty liver disease (NAFLD) spans a pathological spectrum from nonalcoholic steatosis to steatohepatitis. The pathophysiology of this disorder is complex, but includes insulin resistance and disrupted lipid and carbohydrate homeostasis, which at a subcellular level results in oxidative stress, free fatty acid-mediated lipotoxicity, defects in mitochondrial function, endoplasmic reticulum stress and cytokine-mediated toxicity. In chronic hepatitis C (CHC), systemic metabolic derangements similar to NAFLD may be operative, but in addition, virus-specific factors contribute to steatosis. The mechanisms for steatosis in CHC appear to share common pathways with those observed in NAFLD. This article outlines our current understanding of the subcellular mechanisms of steatosis in NAFLD and CHC, including their similarities and differences.

Significant lowering of plasma ghrelin but not des-acyl ghrelin in response to acute exercise in men

Ghrelin, an acylated peptide produced predominantly in the stomach, stimulates feeding and growth hormone (GH) secretion via interaction with the GH secretagogue receptor. Ghrelin molecules are present in two major endogenous forms, an acylated form (ghrelin) and a des-acylated form (des-acyl ghrelin). Recent studies indicated that aerobic exercise did not change plasma total ghrelin levels, however, dynamics of circulating ghrelin and des-acyl ghrelin during aerobic exercise remains unclear. The purpose of this study is to examine the effects of moderate intensity exercise on plasma ghrelin and des-acyl ghrelin concentrations, and to investigate the relationship between ghrelin molecules and other hormonal and metabolic parameters during exercise. Nine healthy males (25.2 ± 0.5 years) exercised for 60 min at 50% of their maximal oxygen consumptions. We measured the plasma concentrations of ghrelin, des-acyl ghrelin, GH, norepinephrine (NE), epinephrine (E), dopamine (DA), insulin, and glucose. Plasma ghrelin level significantly decreased during exercise, whereas plasma des-acyl ghrelin and total ghrelin levels did not change. Plasma NE, E, DA and GH levels were significantly increased during exercise. Plasma insulin level significantly decreased during exercise, and plasma glucose levels remained steady during exercise. NE, E, DA, and GH were correlated negatively with plasma ghrelin levels. These findings suggest that acute moderate exercise may suppress ghrelin release from the stomach, decrease ghrelin O-acyltransferase activity, and/or activate ghrelin utilization in peripheral tissues and that exercise-induced ghrelin suppression may be mediated by activated adrenergic system.

Fitness versus fatness: moving beyond weight loss in nonalcoholic fatty liver disease

The rapid emergence of nonalcoholic fatty liver disease (NAFLD) as a cause of both liver-related morbidity and mortality and cardiometabolic risk has led to the search for effective lifestyle strategies to reduce liver fat. Lifestyle intervention comprising dietary restriction in conjunction with increased physical activity has shown clear hepatic benefits when weight loss approximating 3%-10% of body weight is achieved. Yet, the poor sustainability of weight loss challenges the current therapeutic focus on body weight and highlights the need for alternative strategies for NAFLD management. Epidemiologic data show an independent relationship between liver fat, physical activity, and fitness, and a growing body of longitudinal research demonstrates that increased physical activity participation per se significantly reduces hepatic steatosis and serum aminotransferases in individuals with NAFLD, independent of weight loss. Mechanistic insights to explain this interaction are outlined, and recommendations for the implementation of lifestyle intervention involving physical activity are discussed. In light of the often poor sustainability of weight loss strategies, and the viability of physical activity therapy, clinicians should assess physical fitness and physical activity habits, educate patients on the benefits of fitness outside of weight loss, and focus on behavior change which promotes physical activity adoption.

Sarcopenia: etiology, clinical consequences, intervention, and assessment

The aging process is associated with loss of muscle mass and strength and decline in physical functioning. The term sarcopenia is primarily defined as low level of muscle mass resulting from age-related muscle loss, but its definition is often broadened to include the underlying cellular processes involved in skeletal muscle loss as well as their clinical manifestations. The underlying cellular changes involve weakening of factors promoting muscle anabolism and increased expression of inflammatory factors and other agents which contribute to skeletal muscle catabolism. At the cellular level, these molecular processes are manifested in a loss of muscle fiber cross-sectional area, loss of innervation, and adaptive changes in the proportions of slow and fast motor units in muscle tissue. Ultimately, these alterations translate to bulk changes in muscle mass, strength, and function which lead to reduced physical performance, disability, increased risk of fall-related injury, and, often, frailty. In this review, we summarize current understanding of the mechanisms underlying sarcopenia and age-related changes in muscle tissue morphology and function. We also discuss the resulting long-term outcomes in terms of loss of function, which causes increased risk of musculoskeletal injuries and other morbidities, leading to frailty and loss of independence.

Energy and macronutrient requirements for physical fitness in exercising subjects

Optimal nutritional intakes are critical for health- and skill-related physical fitness. This review details the effect of energy restriction and supplementation on physical fitness, discusses the optimal chronic macronutrient intakes for physical fitness in exercising subjects and finally overviews the impact of short-term intakes of carbohydrate and protein, before, during and after exercise, on physical fitness of athletes. The present standings highlight that it is essential that health care givers personalize nutritional advice to meet the specific needs of exercising individuals while applying the described recommendations. It reminds the difficulty of providing straight nutritional recommendations for physical fitness on the basis of evidence-based medicine.

Swimming performance and energetics as a function of temperature in killifish Fundulus heteroclitus

Populations of the common killifish Fundulus heteroclitus are found along a latitudinal temperature gradient in habitats with high thermal variability. The objectives of this study were to assess the effects of temperature and population of origin on killifish swimming performance (assessed as critical swimming speed, U(crit)). Acclimated fish from northern and southern killifish populations demonstrated a wide zone (from 7 degrees to 33 degrees C) over which U(crit) showed little change with temperature, with performance declining significantly only at lower temperatures. Although we observed significant differences in swimming performance between a northern and a southern population of killifish in one experiment, with northern fish having an approximately 1.5-fold-greater U(crit) than southern fish across all acclimation temperatures, we were unable to replicate this finding in other populations or collection years, and performance was consistently high across all populations and at both low (7 degrees C) and high (23 degrees C) acclimation temperatures. The poor swimming performance of southern killifish from a single collection year was correlated with low muscle [glycogen] rather than with other indicators of fuel stores or body condition. Killifish acclimated to 18 degrees C and acutely challenged at temperatures of 5 degrees , 18 degrees , 25 degrees , or 34 degrees C showed modest thermal sensitivity of U(crit) between 18 degrees and 34 degrees C, with performance declining substantially at 5 degrees C. Thus, much of the zone of relative thermal insensitivity of swimming performance is intrinsic in this species rather than acquired as a result of acclimation. These data suggest that killifish are broadly tolerant of changing temperatures, whether acute or chronic, and demonstrate little evidence of local adaptation in endurance swimming performance in populations from different thermal habitats.

Analysis of global mRNA expression in human skeletal muscle during recovery from endurance exercise

To search for novel transcriptional pathways that are activated in skeletal muscle after endurance exercise, we used cDNA microarrays to measure global mRNA expression after an exhaustive bout of high-intensity cycling (approximately 75 min). Healthy, young, sedentary males performed the cycling bout, and skeletal muscle biopsies were taken from the vastus lateralis before, and at 3 and 48 h after exercise. We examined mRNA expression in individual muscle samples from four subjects using cDNA microarrays, used repeated-measures significance analysis of microarray (SAM) to determine statistically significant expression changes, and confirmed selected results using real-time RT-PCR. In total, the expression of 118 genes significantly increased 3 h postcycling and 8 decreased. At 48 h, the expression of 29 genes significantly increased and 5 decreased. Many of these are potentially important novel genes involved in exercise recovery and adaptation, including several involved in 1) metabolism and mitochondrial biogenesis (FOXO1, PPARdelta, PPARgamma, nuclear receptor binding protein 2, IL-6 receptor, ribosomal protein L2, aminolevulinate delta-synthase 2); 2) the oxidant stress response (metalothioneins 1B, 1F, 1G, 1H, 1L, 2A, 3, interferon regulatory factor 1); and 3) electrolyte transport across membranes [Na+-K+-ATPase (beta3), SERCA3, chloride channel 4]. Others include genes involved in cell stress, proteolysis, apoptosis, growth, differentiation, and transcriptional activation, as well as all three nuclear receptor subfamily 4A family members (Nur77, Nurr1, and Nor1). This study is the first to characterize global mRNA expression during recovery from endurance exercise, and the results provide potential insight into 1) the transcriptional contributions to homeostatic recovery in human skeletal muscle after endurance exercise, and 2) the transcriptional contributions from a single bout of endurance exercise to the adaptive processes that occur after a period of endurance exercise training.