A critical examination of sport discipline typology: identifying inherent limitations and deficiencies in contemporary classification systems.

Exercise scientists (especially in the field of biomolecular research) frequently classify athletic cohorts into categories such as endurance, strength, or mixed, and create a practical framework for studying diverse athletic populations between seemingly similar groups. It is crucial to recognize the limitations and complexities of these classifications, as they may oversimplify the multidimensional characteristics of each sport. If so, the validity of studies dealing with such approaches may become compromised and the comparability across different studies challenging or impossible. This perspective critically examines and highlights the issues associated with current sports typologies, critiques existing sports classification systems, and emphasizes the imperative for a universally accepted classification model to enhance the quality of biomolecular research of sports in the future.

An open-source automated magnetic optical density meter for analysis of suspensions of magnetic cells and particles.

We present a spectrophotometer (optical density meter) combined with electromagnets dedicated to the analysis of suspensions of magnetotactic bacteria. The instrument can also be applied to suspensions of other magnetic cells and magnetic particles. We have ensured that our system, called MagOD, can be easily reproduced by providing the source of the 3D prints for the housing, electronic designs, circuit board layouts, and microcontroller software. We compare the performance of our system to existing adapted commercial spectrophotometers. In addition, we demonstrate its use by analyzing the absorbance of magnetotactic bacteria as a function of their orientation with respect to the light path and their speed of reorientation after the field has been rotated by 90°. We continuously monitored the development of a culture of magnetotactic bacteria over a period of 5 days and measured the development of their velocity distribution over a period of one hour. Even though this dedicated spectrophotometer is relatively simple to construct and cost-effective, a range of magnetic field-dependent parameters can be extracted from suspensions of magnetotactic bacteria. Therefore, this instrument will help the magnetotactic research community to understand and apply this intriguing micro-organism.

Sex, Drugs, and Impulse Regulation: A Perspective on Reducing Transmission Risk Behavior and Improving Mental Health Among MSM Living With HIV.

Unprotected sexual contact continues to be a main cause of HIV transmission and poses certain key populations at increased risk for HIV infection. One of the populations at high risk are men who have sex with men. A subset of MSM engages in chemsex, whereby consumption of illicit drugs is used to facilitate or enhance sexual activity. This practice can have several negative consequences, such as sexually transmitted infections (including HIV) and mental health problems (including compulsive sexual behavior, addiction, and mood disorders). In this article, we provide our perspective on the current situation that medical professionals dealing with MSM living with HIV often feel empty-handed in how to deal with these behavioral and psychological issues. Close collaboration between somatic and mental health professionals is key to address treatment needs of people living with HIV, regarding the negative consequences of chemsex and their overall quality of life. In this article, we discuss possibilities for psychological treatment, including behavioral skills training to improve impulse control and reduce compulsive sexual behaviors among MSM living with HIV who persistently engage in sexual transmission risk behavior, based on our experience with implementing such an intervention. Important barriers and facilitators for further implementation of behavioral interventions will be discussed. Reduction of HIV transmission risk behavior is needed to achieve the WHO aim to end HIV as a public health threat by 2030. We propose that close collaboration between somatic and mental health professionals and implementation of behavioral interventions for risk populations are key to achieve this goal.

Skeletal muscle transcriptome profiles related to different training intensities and detraining in Standardbred horses: a search for overtraining biomarkers.

Training horses improves athletic capabilities by inducing skeletal muscle-specific and systemic adaptations. However, rest is required to recover from exercise or else overtraining may occur and affect performance and welfare. Biomarkers would be useful to identify early chronic overtraining in animals. The objective of the current study was to investigate skeletal muscle gene expression patterns and underlying biological mechanisms related to training of different intensities and detraining. Untrained 20 month-old Standardbred geldings were exercised at varying intensities (endurance and sprint) followed by detraining (n=5 per phase). The results indicated that training mainly affected skeletal muscle-specific protein metabolism and increased CO2 export from the tissues. Intensive training increased energy metabolism and affected heart and adipose tissues, while having an adverse effect on stress, apoptosis and immune capacity. The intensity of the training could be related to decreased expression of extra cellular matrix proteins (ECM), cell-cell contacts and intracellular signalling pathways. During detraining, most mechanisms were reversed, but heart tissue-related changes and increased expression of skeletal muscle-specific proteins were still evident. The study suggested that changes to ECM expression and cell-cell contact mechanisms may be long-lasting and related to multifactorial aspects of training and detraining. These biomarkers may be useful to identify horses in the early stages of chronic overloading or early overtraining.

Protein supplementation during resistance-type exercise training in the elderly.

INTRODUCTION: Resistance training has been well established as an effective treatment strategy to increase skeletal muscle mass and strength in the elderly. We assessed whether dietary protein supplementation can further augment the adaptive response to prolonged resistance-type exercise training in healthy elderly men and women. METHODS: Healthy elderly men (n = 31, 70 ± 1 yr) and women (n = 29, 70 ± 1 yr) were randomly assigned to a progressive, 24-wk resistance-type exercise training program with or without additional protein supplementation (15 g·d-1). Muscle hypertrophy was assessed on a whole-body Dual-energy X-ray absorptiometry (DXA), limb (computed tomography), and muscle fiber (biopsy) level. Strength was assessed regularly by 1-repetition maximum (RM) strength testing. Functional capacity was assessed with a sit-to-stand and handgrip test. RESULTS: One-RM strength increased by 45% ± 6% versus 40% ± 3% (women) and 41% ± 4% versus 44% ± 3% (men) in the placebo versus protein group, respectively (P < 0.001), with no differences between groups. Leg muscle mass (women, 4% ± 1% vs 3% ± 1%; men, 3% ± 1% vs 3% ± 1%) and quadriceps cross-sectional area (women, 9% ± 1% vs 9% ± 1%; men, 9% ± 1% vs 10% ± 1%) increased similarly in the placebo versus protein groups (P < 0.001). Type II muscle fiber size increased over time in both placebo and protein groups (25% ± 13% vs 30% ± 9% and 23% ± 12% vs 22% ± 10% in the women and men, respectively). Sit-to-stand improved by 18% ± 2% and 19% ± 2% in women and men, respectively (P < 0.001). CONCLUSION: Prolonged resistance-type exercise training increases skeletal muscle mass and strength, augments functional capacity, improves glycemia and lipidemia, and reduces blood pressure in healthy elderly men and women. Additional protein supplementation (15 g·d-1) does not further increase muscle mass, strength, and/or functional capacity.

Effects of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in Standardbreds.

OBJECTIVE: To determine the influence of intensified training and subsequent reduced training on glucose metabolism rate and peripheral insulin sensitivity in horses and identify potential markers indicative of early overtraining. ANIMALS: 12 Standardbred geldings. PROCEDURES: Horses underwent 4 phases of treadmill-based training. In phase 1, horses were habituated to the treadmill. In phase 2, endurance training was alternated with high-intensity exercise training. In phase 3, horses were divided into control and intensified training groups. In the intensified training group, training intensity, duration, and frequency were further increased via a protocol to induce overtraining; in the control group, these factors remained unaltered. In phase 4, training intensity was reduced. Standardized exercise tests were performed after each phase and hyperinsulinemic euglycemic clamp (HEC) tests were performed after phases 2, 3, and 4. RESULTS: 10 of 12 horses completed the study. Dissociation between mean glucose metabolism rate and mean glucose metabolism rate-to-plasma insulin concentration ratio (M:I) was evident in the intensified training group during steady state of HEC testing after phases 3 and 4. After phase 4, mean glucose metabolism rate was significantly decreased (from 31.1 ± 6.8 µmol/kg/min to 18.1 ± 3.4 µmol/kg/min), as was M:I (from 1.05 ± 0.31 to 0.62 ± 0.17) during steady state in the intensified training group, compared with phase 3 values for the same horses. CONCLUSIONS AND CLINICAL RELEVANCE: Dissociation between the glucose metabolism rate and M:I in horses that underwent intensified training may reflect non-insulin-dependent increases in glucose metabolism.

Assessment of endogenous growth hormone pulsatility in gelded yearling horses using deconvolution analysis.

HYPOTHESIS/OBJECTIVES: Defining normal Growth Hormone (GH) secretory dynamics in the horse is necessary to understand altered GH dynamics related to issues like welfare and disease. ANIMALS AND METHODS: Twelve healthy yearlings and two mature Standardbreds were used to quantify GH secretion. Endogenous GH half-life was determined after administration of 1.0 µg/kg BW GH releasing hormone (GHRH). Exogenous GH half-life was determined after administration of 20 µg/kg BW recombinant equine GH (reGH) with and without suppression of endogenous GH secretion by somatostatin infusion (50 µg/m(2)/h). Pulse detection algorithm (Cluster) as well as deconvolution analysis was used to quantify GH secretory dynamics based on GH concentration-time series sampled every 5 min from 22:00 till 06:00 h. In addition, reproducibility, impact of sampling frequency and influence of altering initial GH half-life on parameter estimates were studied. RESULTS: Mean endogenous GH half-life of 17.7 ± 4.4 (SD) min and mean exogenous half-life of 26.0 ± 2.9 min were found. The mean number of GH secretion peaks in 8 h was 12 ± 3.2. Ninety-nine percent of the total amount of GH secreted occurred in pulses, basal secretion was 0.012 ± 0.014 µg/L/min and half-life was 8.9 ± 2.6 min. Compared with a 5-min sampling frequency, 20- and 30-min sampling underestimated the number of secretory events by 45% and 100%, respectively. CONCLUSIONS: The deconvolution model used was valid to GH time series in Standardbreds. As in man, the equine pituitary gland secretes GH in volleys consisting of multiple secretory bursts, without measurable intervening tonic secretion. The required GH sampling frequency for the horse should be around 3 min. CLINICAL RELEVANCE: Defining normal GH secretory dynamics in the horse will make it possible to detect alterations in the GH axis due to pathophysiologic mechanisms as well as abuse of reGH.

Plasma acylcarnitine and fatty acid profiles during exercise and training in Standardbreds.

OBJECTIVE: To evaluate alterations in skeletal muscle carnitine metabolism during exercise and training by measuring changes in plasma acylcarnitine concentrations in Standardbreds. ANIMALS: 10 Standardbred geldings with a mean +/- SD age of 20 +/- 2 months and weight of 384 +/- 42 kg. PROCEDURES: In a 32-week longitudinal study, training on a treadmill was divided into 4 phases as follows: phase 1, acclimatization for 4 weeks; phase 2, 18 weeks with alternating endurance and high-intensity exercise training; phase 3, increased training volume and intensity for another 6 weeks; and phase 4, deconditioning for 4 weeks. In phase 3, horses were randomly assigned to 2 groups as follows: control horses (which continued training at the same level as in phase 2) and high-intensity exercise trained horses. At the end of each phase, a standardized exercise test (SET) was performed. Plasma acylcarnitine, fatty acids, and lactic acid and serum beta-hydroxybutyric acid (BHBA) concentrations were assessed before and at different time points after each SET. RESULTS: Plasma lactic acid, total nonesterified fatty acids, 3-hydroxyisobutyric acid, and acetylcarnitine (C2-carnitine) concentrations significantly increased during SETs, whereas serum BHBA, plasma propionylcarnitine (C3-carnitine), and plasma butyryl- and isobutyrylcarnitine (C4-carnitine) concentrations decreased significantly, compared with those before SETs. CONCLUSIONS AND CLINICAL RELEVANCE: Our findings indicated that the plasma acylcarnitine profile in horses likely reflects skeletal muscle carnitine metabolism following exercise, thereby providing a possible practical method to investigate potential disorders in carnitine metabolism in horses with myopathy.

(Over)training effects on quantitative electromyography and muscle enzyme activities in standardbred horses.

Too intensive training may lead to overreaching or overtraining. To study whether quantitative needle electromyography (QEMG) is more sensitive to detect training (mal)adaptation than muscle enzyme activities, 12 standardbred geldings trained for 32 wk in age-, breed-, and sex-matched fixed pairs. After a habituation and normal training (NT) phase (phases 1 and 2, 4 and 18 wk, respectively), with increasing intensity and duration and frequency of training sessions, an intensified training (IT) group (phase 3, 6 wk) and a control group (which continued training as in the last week of phase 2) were formed. Thereafter, all horses entered a reduced training phase (phase 4, 4 wk). One hour before a standardized exercise test (SET; treadmill), QEMG analysis and biochemical enzyme activity were performed in muscle or in biopsies from vastus lateralis and pectoralis descendens muscle in order to identify causes of changes in exercise performance and eventual (mal)adaptation in skeletal muscle. NT resulted in a significant adaptation of QEMG parameters, whereas in muscle biopsies hexokinase activity was significantly decreased. Compared with NT controls, IT induced a stronger adaptation (e.g., higher amplitude, shorter duration, and fewer turns) in QEMG variables resembling potentially synchronization of individual motor unit fiber action potentials. Despite a 19% decrease in performance of the SET after IT, enzyme activities of 3-hydroxyacyl dehydrogenase and citrate synthase displayed similar increases in control and IT animals. We conclude that 1) QEMG analysis is a more sensitive tool to monitor training adaptation than muscle enzyme activities but does not discriminate between overreaching and normal training adaptations at this training level and 2) the decreased performance as noted in this study after IT originates most likely from a central (brain) rather than peripheral level.

Insulin resistance, physical fitness, body composition and leptin concentration in 7-8 year-old children.

The aim of this study was to investigate the association between insulin resistance and physical fitness, leptin concentration, body composition and family history for diabetes in non-selected young children. Physical fitness, fasting plasma glucose, insulin and leptin concentrations, anthropometric characteristics and medical history were available in two hundred and fifty-seven 7-year-old Dutch children. Correlations with the homeostasis model assessment (HOMA) index for insulin resistance were studied. A multiple regression model was calculated for HOMA. The differences between children with or without a family history for diabetes were not significant. Boys scored higher on glucose concentration and aerobic fitness and lower on sum of skin folds and leptin concentration (p<.05). After adjustment for sum of skin folds, HOMA was significantly associated with leptin in both genders (boys r=.184 p=.031; girls r=.430 p=.000). The association between physical fitness and HOMA was mediated by sum of skin folds. The associations were stronger in girls than in boys. In the regression model (R(2)=.205) the leptin concentration was the only significant predictor for HOMA. The influence of family history for diabetes on insulin resistance is shown as a trend at this age. Our findings suggest that plasma leptin concentration is independently associated with the development of insulin resistance in a non-selected prepubertal population. The association of physical fitness with insulin resistance seems to be mediated by the sum of skin folds.

Whole-body vibration induced adaptation in knee extensors; consequences of initial strength, vibration frequency, and joint angle.

It was hypothesized that both vibration frequency and muscle length modulate the strengthening of muscles that is assumed to result from whole-body vibration (WBV). Length of knee extensor muscles during vibration is affected by the knee joint angle; the lengths of the knee extensors increase with more flexed knee joint angles. In an intervention study 28 volunteers were randomly assigned to 1 of 4 groups. Each group received 4 weeks of WBV at 1 of 3 different frequencies (20, 27, or 34 Hz) or 1 of 2 different lengths of knee extensors. Voluntary, isometric knee extension moment-angle relationship was determined. Initially, stronger subjects reacted differently to WBV than weaker participants. In stronger subjects knee extension moment did not improve; in the weaker subjects considerable improvements were observed ranging from 10 to 50%. Neither vibration frequency nor muscle length during the intervention affected the improvements. In addition to strength, the knee joint angle at which the maximal joint moment was generated (optimal joint angle) was affected. When trained at short muscle lengths, optimal angle shifted to more extend joint position. WBV training at long muscle lengths tended to induce an opposite shift. The amount of this shift tended to be influenced by vibration frequency; the lower the vibration frequency the larger the shift. Shifts of optimal lengths occurred in both weaker and stronger subjects. This study shows that muscle length during training affects the angle of knee joint at which the maximal extension moment was generated. Moreover, in weaker subjects WBV resulted in higher maximal knee joint extension moments. Vibration frequency and muscle length during vibration did not affect this joint moment gain.

Influence of acute exercise on hyperglycemia in insulin-treated type 2 diabetes.

INTRODUCTION: The impact of exercise on blood glucose homeostasis has not been assessed in long-standing type 2 diabetes patients receiving exogenous insulin treatment. PURPOSE: To study the effects of an acute bout of exercise on the subsequent 24-h blood glucose excursions under free-living conditions in insulin-treated type 2 diabetes patients. METHODS: Eleven male type 2 diabetes patients (59 +/- 2 yr) performed an acute bout of exercise. One day before the exercise bout, a continuous glucose monitoring system (GlucoDay, A. Menarini Diagnostics) was inserted subcutaneously in the periumbilical region. The glucose sensor continuously measured glucose concentrations in the dialysate during a 48-h period. RESULTS: The prevalence of hyperglycemic glucose excursions was reduced by 39% during a 24-h period (equivalent to 3 h) after an acute bout of exercise (P < 0.05). Average glucose concentrations 24 h before and after the exercise bout did not differ (NS). Mean dialysate glucose concentrations and the prevalence of hyperglycemic periods correlated strongly with baseline blood HbA1c concentrations (Pearson's R = 0.69, P < 0.05). CONCLUSION: An acute bout of exercise effectively reduces the prevalence of hyperglycemia during a 24-h period under free-living conditions in long-standing type 2 diabetes patients on exogenous insulin therapy.

Effect of exercise on activation of the p38 mitogen-activated protein kinase pathway, c-Jun NH2 terminal kinase, and heat shock protein 27 in equine skeletal muscle.

OBJECTIVE: To investigate the effects of exercise on activation of mitogen-activated protein kinase (MAPK) signaling proteins in horses. ANIMALS: 6 young trained Standardbred geldings. PROCEDURE: Horses performed a 20-minute bout of exercise on a treadmill at 80% of maximal heart rate. Muscle biopsy specimens were obtained from the vastus lateralis and pectoralis descendens muscles before and after exercise. Amount of expression and intracellular location of phosphospecific MAPK pathway intermediates were determined by use of western blotting and immunofluorescence staining. RESULTS: Exercise resulted in a significant increase in phosphorylation of p38 pathway intermediates, c-Jun NH2 terminal kinase (JNK), and heat shock protein 27 (HSP27) in the vastus lateralis muscle, whereas no significant changes were found in phosphorylation of extracellular regulated kinase. In the pectoralis descendens muscle, phosphorylation of p38 and HSP27 was significantly increased after exercise. Immunohistochemical analysis revealed fiber-type- specific locations of phosphorylated JNK in type 2a/b intermediate and 2b fibers and phosphorylated p38 in type 1 fibers. Phosphorylated HSP27 was strongly increased after exercise in type 1 and 2a fibers. CONCLUSIONS AND CLINICAL RELEVANCE: The p38 pathway and JNK are activated in the vastus lateralis muscle after a single 20-minute bout of submaximal exercise in trained horses. Phosphorylation of HSP27 as detected in the study reported here is most likely induced through the p38 signaling pathway.

Glycaemic instability is an underestimated problem in Type II diabetes.

The aim of the present study was to assess the level of glycaemic control by the measurement of 24 h blood glucose profiles and standard blood analyses under identical nutritional and physical activity conditions in patients with Type II diabetes and healthy normoglycaemic controls. A total of 11 male patients with Type II diabetes and 11 healthy matched controls participated in a 24 h CGMS (continuous subcutaneous glucose-monitoring system) assessment trial under strictly standardized dietary and physical activity conditions. In addition, fasting plasma glucose, insulin and HbA(1c) (glycated haemoglobin) concentrations were measured, and an OGTT (oral glucose tolerance test) was performed to calculate indices of whole-body insulin sensitivity, oral glucose tolerance and/or glycaemic control. In the healthy control group, hyperglycaemia (blood glucose concentration >10 mmol/l) was hardly present (2+/-1% or 0.4+/-0.2/24 h). However, in the patients with Type II diabetes, hyperglycaemia was experienced for as much as 55+/-7% of the time (13+/-2 h over 24 h) while using the same standardized diet. Breakfast-related hyperglycaemia contributed most (46+/-7%; P<0.01 as determined by ANOVA) to the total amount of hyperglycaemia and postprandial glycaemic instability. In the diabetes patients, blood HbA(1c) content correlated well with the duration of hyperglycaemia and the postprandial glucose responses (P<0.05). In conclusion, CGMS determinations show that standard measurements of glycaemic control underestimate the amount of hyperglycaemia prevalent during real-life conditions in Type II diabetes. Given the macro- and micro-vascular damage caused by postprandial hyperglycaemia, CGMS provides an excellent tool to evaluate alternative therapeutic strategies to reduce hyperglycaemic blood glucose excursions.

Effects of increasing insulin secretion on acute postexercise blood glucose disposal.

BACKGROUND: Coingestion of protein and/or free amino acids with carbohydrate has been reported to accelerate postexercise muscle glycogen synthesis due to an increase in the insulin response. PURPOSE: To determine the extent to which the combined ingestion of carbohydrate and a casein protein hydrolysate with or without additional free leucine can increase insulin levels during postexercise recovery in endurance-trained athletes. To determine how this affects whole-body plasma glucose disposal during postexercise recovery. METHODS: Fourteen male athletes (age: 24.3 +/- 0.8 yr; VO2max: 62.9 +/- 1.4 mL.kg.min) were subjected to three randomized crossover trials in which they performed 2 h of exercise (55% Wmax). Thereafter, subjects were studied for 3.5 h during which they ingested carbohydrate (CHO: 0.8 g.kg.h), carbohydrate and a protein hydrolysate (CHO-PRO: 0.8 and 0.4 g.kg.h, respectively), or carbohydrate, a protein hydrolysate, and free leucine (CHO-PRO-LEU: 0.8, 0.4, and 0.1 g.kg.h, respectively) in a double-blind fashion. Continuous infusions with [6,6-H2] glucose were applied to quantify plasma glucose appearance (Ra) and disappearance rates (Rd). RESULTS: Plasma insulin responses were 108 +/- 17 and 190 +/- 33% greater in the CHO-PRO and CHO-PRO-LEU trial, respectively, compared with the CHO-trial (P < 0.01). Plasma glucose responses were lower in the CHO-PRO and CHO-PRO-LEU trial compared with the CHO-trial (35 +/- 5 and 42 +/- 11% lower, respectively; P < 0.01). Plasma glucose Ra and Rd were greater in the CHO versus the CHO-PRO and CHO-PRO-LEU trials (P < 0.05). Glucose Rd represented 100 +/- 0.03% of Ra in all trials. CONCLUSIONS: The combined ingestion of a protein hydrolysate and/or free leucine with carbohydrate (0.8 g.kg.h) substantially augments insulin secretion, but does not affect plasma glucose disposal during the first 3.5 h of postexercise recovery in trained athletes.

Effects of short- and long-term recombinant equine growth hormone and short-term hydrocortisone administration on tissue sensitivity to insulin in horses.

OBJECTIVE: To determine the effects of short-term IV administration of hydrocortisone or equine growth hormone (eGH) or long-term IM administration of eGH to horses on tissue sensitivity to exogenous insulin. ANIMALS: 5 Standardbreds and 4 Dutch Warmblood horses. PROCEDURE: The euglycemic-hyperinsulinemic clamp technique was used to examine sensitivity of peripheral tissues to exogenous insulin 24 hours after administration of a single dose of hydrocortisone (0.06 mg/kg), eGH (20 microg/kg), or saline (0.9% NaCl) solution and after long-term administration (11 to 15 days) of eGH to horses. The amounts of metabolized glucose (M) and plasma insulin concentration (I) were determined. RESULTS: Values for M and the M-to-I ratio were significantly higher 24 hours after administration of a single dose of hydrocortisone than after single-dose administration of eGH or saline solution. After long-term administration of eGH, basal I concentration was increased and the mean M-to-I ratio was 22% lower, compared with values for horses treated with saline solution. CONCLUSIONS AND CLINICAL RELEVANCE: Increases in M and the M-to-I ratio after a single dose of hydrocortisone imply that short-term hydrocortisone treatment increases glucose use by, and insulin sensitivity of, peripheral tissues. Assuming a single dose of hydrocortisone improves sensitivity of peripheral tissues to insulin, it may be an interesting candidate for use in reducing insulin resistance in peripheral tissues of horses with several disease states. In contrast, long-term administration of eGH decreased tissue sensitivity to exogenous insulin associated with hyperinsulinemia. Therefore, increased concentrations of growth hormone may contribute to insulin resistance in horses with various disease states.

Effect of a 2-day very low-energy diet on skeletal muscle insulin sensitivity in obese type 2 diabetic patients on insulin therapy.

This study investigates the molecular mechanisms underlying the blood glucose-lowering effect of a 2-day very low-energy diet (VLED, 1883 kJ/d) in 12 obese (body mass index, 36.3 +/- 1.0 kg/m2 [mean +/- SEM]) type 2 diabetic (HbA(1C) 7.3% +/- 0.4%) patients simultaneously taken off all glucose-lowering therapy, including insulin. Endogenous glucose production (EGP) and glucose disposal ([6,6-2H2]-glucose) were measured before and after the VLED in basal and hyperinsulinemic (40 mU/m2 per minute) euglycemic conditions. Insulin signaling and expression of GLUT-4, FAT/CD36, and triglycerides were assessed in muscle biopsies, obtained before the clamp and after 30 minutes of hyperinsulinemia. Fasting plasma glucose decreased from 11.3 +/- 1.3 to 10.3 +/- 1.0 mmol/L because of a decreased basal EGP (14.2 +/- 1.0 to 11.9 +/- 0.7 micromol/kg per minute, P = .009). Insulin-stimulated glucose disposal did not change. No diet effect was found on the expression of the insulin receptor and insulin receptor substrate-1 or on phosphatidylinositol 3'-kinase activity, or on FAT/CD36 expression pattern, GLUT-4 translocation, or triglyceride distribution in either the basal or insulin-stimulated situation. Unexpectedly, basal PKB/Akt phosphorylation on T308 and S473 increased after the diet, at equal protein expression. In conclusion, a 2-day VLED lowers fasting plasma glucose via a decreased basal EGP without an effect on glucose disposal. Accordingly, no changes in activation of phosphatidylinositol 3'-kinase, triglyceride distribution, FAT/CD36 expression, and GLUT-4 translocation were found in skeletal muscle biopsies.

Inhibition of adipose tissue lipolysis increases intramuscular lipid and glycogen use in vivo in humans.

This study investigates the consequences of inhibition of adipose tissue lipolysis on skeletal muscle substrate use. Ten subjects were studied at rest and during exercise and subsequent recovery under normal, fasting conditions (control trial, CON) and following administration of a nicotinic acid analog (low plasma free fatty acid trial, LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate intramuscular triacylglycerol (IMTG) and glycogen use. Muscle biopsies were collected to measure 1) fiber type-specific IMTG content; 2) allosteric regulators of hormone-sensitive lipase (HSL), glycogen phosphorylase, and pyruvate dehydrogenase; and 3) the phosphorylation status of HSL at Ser563 and Ser565. Administration of a nicotinic acid analog (acipimox) substantially reduced plasma FFA rate of appearance and subsequent plasma FFA concentrations (P < 0.0001). At rest, this substantially reduced plasma FFA oxidation rates, which was compensated by an increase in the estimated IMTG use (P < 0.05). During exercise, the progressive increase in FFA rate of appearance, uptake, and oxidation was prevented in the LFA trial and matched by greater IMTG and glycogen use. Differential phosphorylation of HSL or relief of its allosteric inhibition by long-chain fatty acyl-CoA could not explain the increase in muscle TG use, but there was evidence to support the contention that regulation may reside at the level of the glucose-fatty acid cycle. This study confirms the hypothesis that plasma FFA availability regulates both intramuscular lipid and glycogen use in vivo in humans.

A single session of resistance exercise enhances insulin sensitivity for at least 24 h in healthy men.

The aim of the present study was to determine whether a single session of resistance exercise improves whole-body insulin sensitivity in healthy men for up to 24 h. Twelve male subjects (23 +/- 1 years) were studied over a period of 4 days during which they consumed a standardized diet, providing 0.16 +/- 0.01 MJ.kg(-1).day(-1) containing 15 +/- 0.1 energy% (En%) protein, 29 +/ -0.1 En% fat and 55 +/- 0.3 En% carbohydrate. Insulin sensitivity was determined 24 h before and 24 h after a single resistance exercise session (8 sets of 10 repetitions at 75% of 1 repetition maximum for two leg exercise tasks) using an intravenous insulin tolerance test. Insulin sensitivity index was calculated by the decline in arterial blood glucose concentration following intravenous administration of a single bolus of human insulin (0.075 IU.kg(-1) fat free mass). Basal glucose and insulin concentrations were not changed up to 24 h after the resistance exercise. However, a substantial 13+/-5% improvement in whole-body insulin sensitivity was observed, 24 h after the resistance exercise (P < 0.05). This study shows that even a single session of resistance exercise improves whole-body insulin sensitivity for up to 24 h in healthy men, which is consistent with earlier observations following endurance exercise tasks.

The effects of exercise and adipose tissue lipolysis on plasma adiponectin concentration and adiponectin receptor expression in human skeletal muscle.

OBJECTIVE: It has been suggested that adiponectin regulates plasma free fatty acid (FFA) clearance by stimulating FFA uptake and/or oxidation in muscle. We aimed to determine changes in plasma adiponectin concentration and adiponectin receptor 1 and 2 mRNA expression in skeletal muscle during and after prolonged exercise under normal, fasting conditions (high FFA trial; HFA) and following pharmacological inhibition of adipose tissue lipolysis (low FFA trial; LFA). Furthermore, we aimed to detect and locate adiponectin in skeletal muscle tissue. METHODS: Ten subjects performed two exercise trials (120 min at 50% VO(2max)). Indirect calorimetry was used to determine total fat oxidation rate. Plasma samples were collected at rest, during exercise and during post-exercise recovery to determine adiponectin, FFA and glycerol concentrations. Muscle biopsies were taken to determine adiponectin protein and adiponectin receptor 1 and 2 mRNA expression and to localise intramyocellular adiponectin. RESULTS: Basal plasma adiponectin concentrations averaged 6.57+/-0.7 and 6.63+/-0.8 mg/l in the HFA and LFA trials respectively, and did not change significantly during or after exercise. In the LFA trial, plasma FFA concentrations and total fat oxidation rates were substantially reduced. However, plasma adiponectin and muscle adiponectin receptor 1 and 2 mRNA expression did not differ between trials. Immunohistochemical staining of muscle cross-sections showed the presence of adiponectin in the sarcolemma of individual muscle fibres and within the interfibrillar arterioles. CONCLUSION: Plasma adiponectin concentrations and adiponectin receptor 1 and 2 mRNA expression in muscle are not acutely regulated by changes in adipose tissue lipolysis and/or plasma FFA concentrations. Adiponectin is abundantly expressed in muscle, and, for the first time, it has been shown to be present in/on the sarcolemma of individual muscle fibres.