Increased expression of xanthine oxidase and insulin-like growth factor I (IGF-I) immunoreactivity in skeletal muscle after strenuous exercise in humans

Oral angiotensin-converting enzyme inhibitor captopril protects the heart from Porphyromonas gingivalis LPS-induced cardiac dysfunction in mice

Although angiotensin converting enzyme (ACE) inhibitors are considered useful for the treatment of human heart failure, some experimental failing-heart models have shown little beneficial effect of ACE inhibitors in animals with poor oral health, particularly periodontitis. In this study, we examined the effects of the ACE inhibitor captopril (Cap; 0.1 mg/mL in drinking water) on cardiac dysfunction in mice treated with Porphyromonas gingivalis lipopolysaccharide (PG-LPS) at a dose (0.8 mg/kg/day) equivalent to the circulating level in patients with periodontal disease. Mice were divided into four groups: 1) Control, 2) PG-LPS, 3) Cap, and 4) PG-LPS + Cap. After1 week, we evaluated cardiac function by echocardiography. The left ventricular ejection fraction was significantly decreased in PG-LPS-treated mice compared to the control (from 66 ± 1.8 to 59 ± 2.5%), while Cap ameliorated the dysfunction (63 ± 1.1%). The area of cardiac fibrosis was significantly increased (approximately 2.9-fold) and the number of apoptotic myocytes was significantly increased (approximately 5.6-fold) in the heart of PG-LPS-treated group versus the control, and these changes were suppressed by Cap. The impairment of cardiac function in PG-LPS-treated mice was associated with protein kinase C δ phosphorylation (Tyr-311), leading to upregulation of NADPH oxidase 4 and xanthine oxidase, and calmodulin kinase II phosphorylation (Thr-286) with increased phospholamban phosphorylation (Thr-17). These changes were also suppressed by Cap. Our results suggest that the renin-angiotensin system might play an important role in the development of cardiac diseases induced by PG-LPS.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Xanthine Oxidoreductase Inhibitor Use Associated With Reduced Risk of Sarcopenia and Severe Sarcopenia in Patients Undergoing Hemodialysis

Background

Xanthine oxidoreductase (XOR) inhibition reduces reactive oxygen species (ROS) production and enhances adenosine triphosphate (ATP) synthesis. We investigated the protective effects of XOR inhibitor treatment on sarcopenia, frequently observed in patients undergoing hemodialysis (HD), in which increased ROS and ATP shortage are known to be involved.

Methods

This retrospective cross-sectional study included 296 HD patient (203 males, 93 females). Muscle mass, physical performance, and muscle strength were assessed using dual-energy X-ray absorptiometry, five-time chair stand testing, and handgrip strength, respectively. The Asian Working Group for Sarcopenia 2019 criteria were used to define low muscle mass, low physical performance, and low muscle strength, as well as sarcopenia and severe sarcopenia.

Results

Sarcopenia and severe sarcopenia prevalence rates were 42.2 and 20.9%, respectively. XOR inhibitor users (n = 119) showed a significantly (p < 0.05) lower prevalence of sarcopenia and severe sarcopenia, as well as reduced muscle mass, physical performance, and muscle strength than non-users (n = 177). Multivariate logistic regression analyses also revealed XOR inhibitor use to be significantly associated with low muscle mass [odds ratio (OR), 0.384; 95% confidence interval (CI), 0.183–0.806; p = 0.011] and low physical performance (OR, 0.286; 95% CI, 0.142–0.578; p < 0.001), while significance with low muscle strength was borderline. Furthermore, XOR inhibitor use was significantly associated with sarcopenia (OR, 0.462; 95% CI, 0.226–0.947; p = 0.035) and severe sarcopenia (OR, 0.236; 95% CI, 0.091–0.614; p = 0.003).

Conclusions

XOR inhibitor use was significantly associated with reduced risk of sarcopenia/severe sarcopenia in HD patients, suggesting that XOR inhibitor treatment has protective effects on sarcopenia in HD patients.

Could intramuscular storage of dietary nitrate contribute to its ergogenic effect? A mini-review

Extensive research performed over the past 10 years has resulted in dietary nitrate being considered a nutritional supplement that can improve exercise performance. However, there is still limited insight in the metabolic fate of dietary nitrate following the appearance of nitrate and nitrite in the circulation. Recent observations in humans suggest the storage of nitrate in skeletal muscle tissue. This short review discusses the possibility of nitrate being stored and utilized in human skeletal muscle tissue, and why confirming this may increase our understanding of how the nitrate-nitrite-NO pathway improves exercise performance. Further insight in skeletal muscle nitrate storage and metabolism may provide answers to current gaps in knowledge, such as the ergogenic benefit of acute vs multiday dietary nitrate supplementation, as well as the suggested muscle fiber-type specific effects on exercise performance. In this mini-review, specific questions that need further exploration are also discussed.

Treatment with Nitrate, but Not Nitrite, Lowers the Oxygen Cost of Exercise and Decreases Glycolytic Intermediates While Increasing Fatty Acid Metabolites in Exercised Zebrafish

BACKGROUND

Dietary nitrate improves exercise performance by reducing the oxygen cost of exercise, although the mechanisms responsible are not fully understood.

OBJECTIVES

We tested the hypothesis that nitrate and nitrite treatment would lower the oxygen cost of exercise by improving mitochondrial function and stimulating changes in the availability of metabolic fuels for energy production.

METHODS

We treated 9-mo-old zebrafish with nitrate (sodium nitrate, 606.9 mg/L), nitrite (sodium nitrite, 19.5 mg/L), or control (no treatment) water for 21 d. We measured oxygen consumption during a 2-h, strenuous exercise test; assessed the respiration of skeletal muscle mitochondria; and performed untargeted metabolomics on treated fish, with and without exercise.

RESULTS

Nitrate and nitrite treatment increased blood nitrate and nitrite levels. Nitrate treatment significantly lowered the oxygen cost of exercise, as compared with pretreatment values. In contrast, nitrite treatment significantly increased oxygen consumption with exercise. Nitrate and nitrite treatments did not change mitochondrial function measured ex vivo, but significantly increased the abundances of ATP, ADP, lactate, glycolytic intermediates (e.g., fructose 1,6-bisphosphate), tricarboxylic acid (TCA) cycle intermediates (e.g., succinate), and ketone bodies (e.g., β-hydroxybutyrate) by 1.8- to 3.8-fold, relative to controls. Exercise significantly depleted glycolytic and TCA intermediates in nitrate- and nitrite-treated fish, as compared with their rested counterparts, while exercise did not change, or increased, these metabolites in control fish. There was a significant net depletion of fatty acids, acyl carnitines, and ketone bodies in exercised, nitrite-treated fish (2- to 4-fold), while exercise increased net fatty acids and acyl carnitines in nitrate-treated fish (1.5- to 12-fold), relative to their treated and rested counterparts.

CONCLUSIONS

Nitrate and nitrite treatment increased the availability of metabolic fuels (ATP, glycolytic and TCA intermediates, lactate, and ketone bodies) in rested zebrafish. Nitrate treatment may improve exercise performance, in part, by stimulating the preferential use of fuels that require less oxygen for energy production.

Sodium nitrate ingestion increases skeletal muscle nitrate content in humans

Nitrate ([Formula: see text]) ingestion has been shown to have vasoactive and ergogenic effects that have been attributed to increased nitric oxide (NO) production. Recent observations in rodents suggest that skeletal muscle tissue serves as an endogenous [Formula: see text] "reservoir." The present study determined [Formula: see text] contents in human skeletal muscle tissue in a postabsorptive state and following ingestion of a sodium nitrate bolus (NaNO₃). Seventeen male, type 2 diabetes patients (age 72 ± 1 yr; body mass index 26.5 ± 0.5 kg/m²; means ± SE) were randomized to ingest a dose of NaNO₃ (NIT; 9.3 mg [Formula: see text]/kg body wt) or placebo (PLA; 8.8 mg NaCl/kg body wt). Blood and muscle biopsy samples were taken before and up to 7 h following [Formula: see text] or placebo ingestion to assess [Formula: see text] [and plasma nitrite ([Formula: see text])] concentrations. Additionally, basal plasma and muscle [Formula: see text] concentrations were assessed in 10 healthy young (CON-Y; age 21 ± 1 yr) and 10 healthy older (CON-O; age 75 ± 1 yr) control subjects. In all groups, baseline [Formula: see text] concentrations were higher in muscle (NIT, 57 ± 7; PLA, 61 ± 7; CON-Y, 80 ± 10; CON-O, 54 ± 6 µmol/l) than in plasma (NIT, 35 ± 3; PLA, 32 ± 3; CON-Y, 38 ± 3; CON-O, 33 ± 3 µmol/l; P ≤ 0.011). Ingestion of NaNO₃ resulted in a sustained increase in plasma [Formula: see text], plasma [Formula: see text], and muscle [Formula: see text] concentrations (up to 185 ± 25 µmol/l) in the NIT group (time effect P < 0.001) compared with PLA (treatment effect P < 0.05). In conclusion, basal [Formula: see text] concentrations are substantially higher in human skeletal muscle tissue compared with plasma. Ingestion of a bolus of dietary [Formula: see text] increases both plasma and muscle [Formula: see text] contents in humans.NEW & NOTEWORTHY Literature of the pharmacokinetics following dietary nitrate ingestion is usually limited to the changes observed in plasma nitrate and nitrite concentrations. The present investigation assessed the skeletal muscle nitrate content in humans during the postabsorptive state, as well as following dietary nitrate ingestion. We show that basal nitrate content is higher in skeletal muscle tissue than in plasma and that ingestion of a dietary nitrate bolus strongly increases both plasma and muscle nitrate concentrations.

Cellular mechanisms underlying oxidative stress in human exercise

A relative increase in oxidation of lipids, proteins and DNA has been recognised to occur in the circulation and tissues of exercising humans and animals since the late 1970s and throughout the ensuing 40 years a great deal of work has been undertaken to elucidate the potential source(s) of this exercise-induced "oxidative stress". Specific aspects of physical exercise (e.g. contractile activity, relative hypoxia, hyperaemia) may theoretically induce increased generation of reactive oxygen species in a number of potential tissues, but data strongly indicate that contractile activity of skeletal muscle predominates as the source of oxidants and contributes to local oxidation and that of extracellular biomaterials. Taken together with the relatively large mass of muscle compared with other tissues and cells it appears that muscle fibres are the major contributor to the relative increase in whole body "oxidative stress" during some forms of exercise. The sub-cellular sources of this increased oxidation have also been the subject of considerable research with early studies predominantly indicating that muscle mitochondria were the likely increased source of oxidants, such as hydrogen peroxide, but assessments of the relative concentrations of hydrogen peroxide in skeletal muscle fibres at rest and during contractile activity do not support this possibility. In contrast, several recent studies have identified NADPH oxidase enzymes in skeletal muscle that appear to play a signalling role in physiological responses exercise and together with xanthine oxidase enzymes may contribute to the relative increase in whole body oxidation. A fuller understanding of the relative roles of these sources and the function(s) of the species generated appears increasingly important in attempts to harness the beneficial effects of exercise for maintenance of health in aging and a variety of chronic conditions.

Effects of exercise training on insulin-like growth factor-I expression in the skeletal muscle of non-cachectic patients with chronic heart failure

Background Chronic heart failure (CHF) is associated with progressive muscle atrophy and reduced local expression of insulin-like growth factor I (IGF-I).

Design The present study was designed to test the hypothesis that the local deficiency of IGF-I in the skeletal muscle of patients with CHF would respond to a 6-months aerobic training intervention. Therefore, 18 patients [mean age 52.4 (SD 4.8) years, left ventricular ejection function (LVEF) 27 (SD 6)%] were prospectively randomized to either 6 months of training or sedentary lifestyle.

Methods Serum levels of growth hormone (GH) were measured by immunofluorometric assay, IGF-I by competitive solid phase immunoassay. IGF-I expression was assessed in vastus lateralis biopsies by real-time PCR.

Results Exercise training led to a significant increase in peak oxygen uptake by 26% [from 20.3 (SD 3.3) ml/kg per min to 25.5 (SD 5.7) ml/kg per min, P=0.003 versus control]. Local expression of IGF-I increased significantly after exercise training by 81% [from 6.3 (SE 0.8) to 11.4 (SE 1.4) relative units, P=0.007 versus control] while IGF-I receptor expression was reduced by 33% [from 20.0 (SE 2.1) to 13.8 (SE 1.7) relative units, P=0.008 versus control]. Serum growth hormone (GH) rose modestly from 0.12 (SE 0.07) to 0.65 (SE 0.37) ng/ml in the training group ( P=0.043 versus baseline), however, this change was not significant compared to the control group ( P=0.848). IGF-I serum levels remained virtually unchanged.

Conclusions Exercise training improves local IGF-I expression without significant changes of systemic parameters of the GH/IGF-I axis. These findings indicate that exercise training has the therapeutic potential to attenuate peripheral skeletal muscle alterations in particular with respect to local IGF-I expression in patients with moderate CHF.

Satellite cells in human skeletal muscle plasticity

Skeletal muscle satellite cells are considered to play a crucial role in muscle fiber maintenance, repair and remodeling. Our knowledge of the role of satellite cells in muscle fiber adaptation has traditionally relied on in vitro cell and in vivo animal models. Over the past decade, a genuine effort has been made to translate these results to humans under physiological conditions. Findings from in vivo human studies suggest that satellite cells play a key role in skeletal muscle fiber repair/remodeling in response to exercise. Mounting evidence indicates that aging has a profound impact on the regulation of satellite cells in human skeletal muscle. Yet, the precise role of satellite cells in the development of muscle fiber atrophy with age remains unresolved. This review seeks to integrate recent results from in vivo human studies on satellite cell function in muscle fiber repair/remodeling in the wider context of satellite cell biology whose literature is largely based on animal and cell models.

Blood flow restricted exercise and vascular function

It is established that regular aerobic training improves vascular function, for example, endothelium-dependent vasodilatation and arterial stiffness or compliance and thereby constitutes a preventative measure against cardiovascular disease. In contrast, high-intensity resistance training impairs vascular function, while the influence of moderate-intensity resistance training on vascular function is still controversial. However, aerobic training is insufficient to inhibit loss in muscular strength with advancing age; thus, resistance training is recommended to prevent sarcopenia. Recently, several lines of study have provided compelling data showing that exercise and training with blood flow restriction (BFR) leads to muscle hypertrophy and strength increase. As such, BFR training might be a novel means of overcoming the contradiction between aerobic and high-intensity resistance training. Although it is not enough evidence to obtain consensus about impact of BFR training on vascular function, available evidences suggested that BFR training did not change coagulation factors and arterial compliance though with inconsistence results in endothelial function. This paper is a review of the literature on the impact of BFR exercise and training on vascular function, such as endothelial function, arterial compliance, or other potential factors in comparison with those of aerobic and resistance training.

Circulating cell-free DNA: an up-coming molecular marker in exercise physiology

The phenomenon of circulating cell-free DNA (cfDNA) concentrations is of importance for many biomedical disciplines including the field of exercise physiology. Increases of cfDNA due to exercise are described to be a potential hallmark for the overtraining syndrome and might be related to, or trigger adaptations of, immune function induced by strenuous exercise. At the same time, exercise provides a practicable model for studying the phenomenon of cfDNA that is described to be of pathophysiological relevance for different topics in clinical medicine like autoimmune diseases and cancer. In this review, we are summarizing the current knowledge of exercise-based acute and chronic alterations in cfDNA levels and their physiological significance. The effects of acute exercise on cfDNA concentrations have been investigated in resistance exercises and in continuous, stepwise and interval endurance exercises of different durations. cfDNA concentrations peaked immediately after acute exercise and showed a rapid return to baseline levels. Typical markers of skeletal muscle damage (creatine kinase, uric acid, C-reactive protein) show delayed kinetics compared with the cfDNA peak response. Exercise parameters such as intensity, duration or average energy expenditure do not explain the extent of increasing cfDNA concentrations after strenuous exercise. This could be due to complex processes inside the human organism during and after physical activity. Therefore, we hypothesize composite effects of different physiological stress parameters that come along with exercise to be responsible for increasing cfDNA concentrations. We suggest that due to acute stress, cfDNA levels increase rapidly by a spontaneous active or passive release mechanism that is not yet known. As a result of the rapid and parallel increase of cfDNA and lactate in an incremental treadmill test leading to exhaustion within 15-20 minutes, it is unlikely that cfDNA is released into the plasma by typical necrosis or apoptosis of cells in acute exercise settings. Recently, rapid DNA release mechanisms of activated immune-competent cells like NETosis (pathogen-induced cell death including the release of neutrophil extracellular traps [NETs]) have been discovered. cfDNA accumulations might comprise a similar kind of cell death including trap formation or an active release of cfDNA. Just like chronic diseases, chronic high-intensity resistance training protocols induced persistent increases of cfDNA levels. Chronic, strenuous exercise protocols, either long-duration endurance exercise or regular high-intensity workouts, induce chronic inflammation that might lead to a slow, constant release of DNA. This could be due to mechanisms of cell death like apoptosis or necrosis. Yet, it has neither been implicated nor proven sufficiently whether cfDNA can serve as a marker for overtraining. The relevance of cfDNA with regard to overtraining status, performance level, and the degree of physical exhaustion still remains unclear. Longitudinal studies are required that take into account standardized and controlled exercise, serial blood sampling, and large and homogeneous cohorts of different athletic achievement. Furthermore, it is important to establish standardized laboratory procedures for the measurement of genomic cfDNA concentrations by quantitative real-time polymerase chain reaction (PCR). We introduce a new hypothesis based on acute exercise and chronic exposure to stress, and rapid active and passive chronic release of cfDNA fragments into the circulation.

Resistance loading and signaling assays for oxidative stress in rodent skeletal muscle

Resistance loading provides an important tool for understanding skeletal muscle responses and adaptations to various perturbations. A model using anesthetized rodents provides the means to control the input parameters carefully, and to measure the output parameters of each muscle contraction. Unilateral models of anesthetized loading also provide the advantage of comparing an unloaded and loaded muscle from the same animal. Voluntary models for resistance loading arguably provide a more "physiological response" but it also introduces more variability in the input parameters, which can be affected by the stimulus used to motivate the animal to exercise. After either acute or chronic periods of muscle loading, the loaded muscles can be removed and various signaling proteins can be determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) or enzyme assays. Several assays are described, which provide an indication of downstream markers for oxidative stress.

Cell-free plasma DNA and purine nucleotide degradation markers following weightlifting exercise

The present study aimed to investigate the acute effects of a single bout of high-intensive strength training on the production of cell-free plasma DNA (cf-DNA), as well as on the degradation of purine nucleotides as assessed by the concentration of xanthine (XA) and hypoxanthine (HX) in urine and serum. Twelve trained weightlifters performed six sets of six lifting exercises with 90-95% of the one repetition maximum. Blood samples and urine were obtained 1 h before training, immediately after finishing the exercise session and following 2 h of recovery. Cf-DNA, HX, and XA (in serum) significantly increased (P < 0.05-P < 0.001) immediately after heavy lifting exercise when compared with baseline levels, and significantly decreased (P < 0.05-P < 0.001) after 2 h of recovery. These results indicate that, cf-DNA and oxypurines might be relevant biomarkers for cellular damage, mechanical, energetic, and/or ischemic stress in context with exercise.

Suppression of oxidative stress by resveratrol after isometric contractions in gastrocnemius muscles of aged mice

This study tested the hypothesis that resveratrol supplementation would lower oxidative stress in exercised muscles of aged mice. Young (3 months) and aged (27 months) C57BL/6 mice received a control or a 0.05% trans-resveratrol-supplemented diet for 10 days. After 7 days of dietary intervention, 20 maximal electrically evoked isometric contractions were obtained from the plantar flexors of one limb in anesthetized mice. Exercise was conducted for three consecutive days. Resveratrol supplementation blunted the exercise-induced increase in xanthine oxidase activity in muscles from young (25%) and aged (53%) mice. Resveratrol lowered H(2)O(2) levels in control (13%) and exercised (38%) muscles from aged animals, reduced Nox4 protein in both control and exercised muscles of young (30%) and aged mice (40%), and increased the ratio of reduced glutathione to oxidized glutathione in exercised muscles from young (38%) and aged (135%) mice. Resveratrol prevented the increase in lipid oxidation, increased catalase activity, and increased MnSOD activity in exercised muscles from aged mice. These data show that dietary resveratrol suppresses muscle indicators of oxidative stress in response to isometric contractions in aged mice.

L-carnitine modulates blood platelet oxidative stress

The oxidative stress induced by acute exertion may interfere with blood platelet activation. The beneficial effect of L-carnitine (gamma-trimethylamino-beta-hydroxybutyric acid) on oxidative stress in blood platelets has not been fully investigated; however, different studies indicate that this compound modulates platelet functions. The aim of our study was to assess the effects of L-carnitine on platelet activation and oxidative/nitrative protein damage (determined by the levels of protein carbonyl groups, thiol groups, and 3-nitrotyrosine residues) in resting blood platelets or platelets treated with peroxynitrite (ONOO(-), a strong physiological oxidant) in vitro. We also investigated the effects of L-carnitine on the level of platelet glutathione and on the formation of superoxide anion radicals O2(-*), lipid peroxidation measured by thiobarbituric acid reactive substances (TBARS) in blood platelets stimulated by thrombin (a strong physiological agonist), and platelet aggregation induced by adenosine diphosphate (a strong physiological stimulator). We have observed that carnitine decreases platelet activation (measured by platelet aggregation, the generation of O2(-*), and TBARS production). Moreover, our results in vitro demonstrate that carnitine may protect against oxidation of thiol groups induced by ONOO(-). Thus, carnitine may have some protectory effects against oxidative changes induced in blood platelets.

Redox regulation of adaptive responses in skeletal muscle to contractile activity

Skeletal muscle is a highly malleable tissue that responds to changes in its pattern of activity or the mechanical and environmental stresses placed upon it. The signaling pathways involved in these multiple adaptations are increasingly well described, but there is a lack of information on the factors responsible for initiating these processes. Reactive oxygen species (ROS) are produced at various sites in skeletal muscle and there is increasing evidence that these species play targeted roles in modulating redox-sensitive signaling pathways that are important to the muscle for making adaptations. This review will outline some of the processes involved and the types of experimental approaches that seem necessary to fully evaluate these redox signaling systems in muscle. To understand how labile, highly reactive ROS can play a role in cell signaling that is discrete and yet regulated to prevent oxidative damage, an increased knowledge of the subcellular localization and compartmentalization of both ROS generation and the redox-sensitive targets of ROS activity is required. It seems likely that application of this increased knowledge will lead to new approaches to manipulating muscle metabolism to maintain health and prevent loss of muscle function in age-related diseases.

Effects of L-carnitine L-tartrate supplementation on muscle oxygenation responses to resistance exercise

Previous research has shown that L-carnitine L-tartrate (LCLT) supplementation beneficially affects markers of hypoxic stress following resistance exercise. However, the mechanism of this response is unclear. Therefore, the primary purpose of this study was to determine the effects of LCLT supplementation on muscle tissue oxygenation during and after multiple sets of squat exercise. Nine healthy, previously resistance-trained men (25.2 +/- 6.years, 91.2 +/- 10.2 kg, 180.2 +/- 6.3 cm) ingested 2 g.d of LCLT or an identical placebo for 23 days in a randomized, balanced, crossover, double-blind, placebo-controlled, repeated-measures study design. On day 21, forearm muscle oxygenation was measured during and after an upper arm occlusion protocol using near infrared spectroscopy (NIRS), which measures the balance of oxygen delivery in relation to oxygen consumption. On day 22, subjects performed 5 sets of 15 to 20 repetitions of squat exercise with corresponding measures of thigh muscle oxygenation, via NIRS, and serial blood draws. Compared to the placebo trial, muscle oxygenation was reduced in the LCLT trial during upper arm occlusion and following each set of resistance exercise. Despite reduced oxygenation, plasma malondealdehyde, a marker of membrane damage, was attenuated during the LCLT trial. There were no differences between trials in the vasoactive substance prostacyclin. In conclusion, because oxygen delivery was occluded during the forearm protocol, it is proposed that enhanced oxygen consumption mediated the reduced muscle oxygenation during the LCLT trial. Enhanced oxygen consumption would explain why hypoxic stress was attenuated with LCLT supplementation.

Single bouts of exercise affect albumin redox state and carbonyl groups on plasma protein of trained men in a workload-dependent manner

The purpose of this study was to investigate the effect of single bouts of exercise at three different intensities on the redox state of human serum albumin (HSA) and on carbonyl groups on protein (CP) concentrations in plasma. Trained men [n = 44, maximal oxygen consumption (Vo(2max)): 55 +/- 5 ml.kg(-1).min(-1), nonsmokers, 34 +/- 5 years of age] from a homogenous population, volunteers from a police special forces unit, were randomly assigned to perform on a cycle ergometer either at 70% (n = 14), 75% (n = 14), or 80% (n = 16) of Vo(2max) for 40 min. Blood was collected before exercise, immediately after the exercise test (IE), and 30 min after each test (30M) and 30 h after each test (30H). The reduced fraction of HSA, human mercaptalbumin (HMA), decreased at all three exercise intensities IE and 30M, returning to preexercise values by 30H (P < 0.05). HMA was primarily oxidized to its reversible fraction human nonmercaptalbumin 1 (HNA1). CP concentrations increased at 75% of Vo(2max) IE and 30M with a tendency (P < 0.1) and at 80% Vo(2max) IE and 30M significantly, returning to preexercise concentrations by 30H (P < 0.01). These results indicate that the HSA redox system in plasma is activated after a single bout of cycle ergometer exercise at 70% Vo(2max) and 40 min duration. The extent of the HSA modification increased with exercise intensity. Oxidative protein damage, as indicated by CP, was only significantly increased at 80% Vo(2max) intensity in this homogenous cohort of trained men.

Implications of chronic heart failure on peripheral vasculature and skeletal muscle before and after exercise training

The pathophysiology of chronic heart failure (CHF) is typically conceptualized in terms of cardiac dysfunction. However, alterations in peripheral blood flow and intrinsic skeletal muscle properties are also now recognized as mechanisms for exercise intolerance that can be modified by therapeutic exercise. This overview focuses on blood delivery, oxygen extraction and utilization that result from heart failure. Related features of inflammation, changes in skeletal muscle signaling pathways, and vulnerability to skeletal muscle atrophy are discussed. Specific focus is given to the ways in which perfusion and skeletal muscle properties affect exercise intolerance and how peripheral improvements following exercise training increase aerobic capacity. We also identify gaps in the literature that may constitute priorities for further investigation.

Free radicals generated by contracting muscle: by-products of metabolism or key regulators of muscle function?

Skeletal muscle fibers generate reactive oxygen species (ROS) at a number of subcellular sites and this generation is increased by contractile activity. Early studies suggested that generation of superoxide as a by-product of mitochondrial oxygen consumption was the major source of muscle ROS generation and that the species produced were inevitably damaging to muscle, but recent data argue against both of these possibilities. Developments in analytical approaches have shown that specific ROS are generated in a controlled manner by skeletal muscle fibers in response to physiological stimuli and play important roles in the physiological adaptations of muscle to contractions. These include optimization of contractile performance and initiation of key adaptive changes in gene expression to the stresses of contractions. These positive benefits of the ROS that are induced by contractile activity contrast starkly with the increasing evidence that ROS-induced degenerative pathways are fundamental to aging processes in skeletal muscle. A fuller understanding of these contrasting roles is recognized to be important in the design of strategies to maintain and optimize skeletal muscle function during exercise and to help prevent the devastating effects of sarcopenia and other muscle-wasting conditions.

Effects of oral l-carnitine supplementation in racing Greyhounds

l-Carnitine supplementation can stimulate erythropoiesis, reduce exercise-induced plasma lactate concentrations and decrease post-exercise muscle damage. Next to horses, Greyhounds represent the premier animal racing species and perform short-duration, very high-intensity exercise that has the potential to incur substantial muscle damage. Under resting and standard racing conditions (5/16 mile), we tested the novel hypotheses that l-carnitine supplementation in Greyhounds would: (1) elevate haematocrit at rest and immediately post-exercise; (2) reduce peak post-exercise plasma lactate; and (3) reduce indices of muscle damage (plasma creatine phosphokinase, CPK and aspartate aminotransferase, AST). Six conditioned Greyhounds (30.1 ± 1.6 kg) underwent a randomized placebo-controlled crossover study to determine the effects of 6 weeks of l-carnitine supplementation (100 mg kg− 1 of body weight/day) at rest and following a maximal speed 5/16 mile race. In accordance with our hypotheses, l-carnitine elevated resting and immediately post-race haematocrit (control, 60.1 ± 1.7, l-carnitine, 63.6 ± 1.7; P < 0.05) and reduced peak post-race plasma CPK and AST concentrations (both P < 0.05). Those dogs with the highest peak post-exercise plasma CPK concentrations under placebo conditions evidenced the greatest reduction with l-carnitine supplementation (r = 0.99, P < 0.01). However, contrary to our hypotheses, l-carnitine did not change peak post-exercise plasma lactate concentrations (control, 27.0 ± 2.1, l-carnitine, 27.7 ± 1.3; P>0.05). We conclude that l-carnitine supplementation increases the potential for oxygen transport and reduces plasma indicators of muscle damage, CPK and AST in racing Greyhounds.

Insulin-like growth factor 1 and muscle growth: implication for satellite cell proliferation

Insulin-like growth factor 1 (IGF-1) has been shown to rescue the aging-related or inactivity-induced loss of muscle mass through the activation of satellite cells. However, the signalling pathways and the mechanism by which IGF-1 affects satellite cells have not been not completely identified. The purpose of the present review is to provide current understanding of the cellular and molecular events underlying IGF-1 induced proliferation of satellite cells.

Short-term strength training and the expression of myostatin and IGF-I isoforms in rat muscle and tendon: differential effects of specific contraction types

In skeletal muscle, an increased expression of insulin like growth factor-I isoforms IGF-IEa and mechano-growth factor (MGF) combined with downregulation of myostatin is thought to be essential for training-induced hypertrophy. However, the specific effects of different contraction types on regulation of these factors in muscle are still unclear, and in tendon the functions of myostatin, IGF-IEa, and MGF in relation to training are unknown. Female Sprague-Dawley rats were subjected to 4 days of concentric, eccentric, or isometric training ( n = 7–9 per group) of the medial gastrocnemius, by stimulation of the sciatic nerve during general anesthesia. mRNA levels for myostatin, IGF-IEa, and MGF in muscle and Achilles' tendon were measured by real-time RT-PCR. Muscle myostatin mRNA decreased in response to all types of training (2- to 8-fold) ( P < 0.05), but the effect of eccentric training was greater than concentric and isometric training ( P < 0.05). In tendon, myostatin mRNA was detected, but no changes were seen after exercise. IGF-IEa and MGF increased in muscle (up to 15-fold) and tendon (up to 4-fold) in response to training ( P < 0.01). In tendon no difference was seen between training types, but in muscle the effect of eccentric training was greater than concentric training for both IGF-IEa and MGF ( P < 0.05), and for IGF-IEa isometric training had greater effect than concentric ( P < 0.05). The results indicate a possible role for IGF-IEa and MGF in adaptation of tendon to training, and the combined changes in myostatin and IGF-IEa/MGF expression could explain the important effect of eccentric actions for muscle hypertrophy.

The production of reactive oxygen and nitrogen species by skeletal muscle

Skeletal muscle has been recognized as a potential source for generation of reactive oxygen and nitrogen species for more than 20 years. Initial investigations concentrated on the potential role of mitochondria as a major source for generation of superoxide as a "by-product" of normal oxidative metabolism, but recent studies have identified multiple subcellular sites, where superoxide or nitric oxide are generated in regulated and controlled systems in response to cellular stimuli. Full evaluation of the factors regulating these processes and the functions of the reactive oxygen species generated are important in understanding the redox biology of skeletal muscle.

Local changes in the insulin-like growth factor system in human skeletal muscle assessed by microdialysis and arterio-venous differences technique

IGF-I plays a direct role in whole body glucose homeostasis primarily by stimulating skeletal muscle glucose uptake. IGF-I is also involved in exercise induced muscle hypertrophy. Knowledge regarding local changes in muscle IGF-I bioavailability and its regulation by IGFBPs at rest and during exercise is limited. We have therefore explored changes in total IGF-I levels as well as circulating IGFBP levels and their post-translational modifications over an exercising leg. For the first time we have determined IGF-I levels in exercising skeletal muscle microdialysate in an attempt to assess local IGF-I bioavailability. Eighteen healthy young men performed one legged knee-extension exercise during 45min. Blood samples were taken from the femoral artery and vein of the exercising leg. No significant differences between arterial and venous concentrations of total IGF-I or IGFBP-1 were detected over the leg at any time. IGF-I concentrations increased significantly during exercise in the artery but not in the vein. Total IGFBP-1 increased after exercise in both artery and vein. The increase in non-plus less phosphorylated forms of IGFBP-1 was less pronounced and did not reach statistical significance. The proportion of fragmented IGFBP-3 (IGFBP-3 proteolysis) assessed by Western immunoblotting did not change significantly during or after exercise. Although optimization and validation of IGF-I determinations in muscle microdialysate (md) will be required, our first results using this technique demonstrate a significant 2-fold increase in mdIGF-I collected during and after exercise. We conclude that determination of A-V-differences appears to be of limited value in the assessments of local muscle change in the IGF-system. A substantial release of IGF-I during short time is required to detect significant change in the large circulating store of IGF-I. We suggest that an optimized and validated microdialysis technique for determination of local IGF-I may be advantageous in future studies.

Exercise-induced oxidative stress:myths, realities and physiological relevance

Although assays for the most popular markers of exercise-induced oxidative stress may experience methodological flaws, there is sufficient credible evidence to suggest that exercise is accompanied by an increased generation of free radicals, resulting in a measurable degree of oxidative modifications to various molecules. However, the mechanisms responsible are unclear. A common assumption that increased mitochondrial oxygen consumption leads per se to increased reactive oxygen species (ROS) production is not supported by in vitro and in vivo data. The specific contributions of other systems (xanthine oxidase, inflammation, haem protein auto-oxidation) are poorly characterised. It has been demonstrated that ROS have the capacity to contribute to the development of muscle fatigue in situ, but there is still a lack of convincing direct evidence that ROS impair exercise performance in vivo in humans. It remains unclear whether exercise-induced oxidative modifications have little significance, induce harmful oxidative damage, or are an integral part of redox regulation. It is clear that ROS play important roles in numerous physiological processes at rest; however, the detailed physiological functions of ROS in exercise remain to be elucidated.

Insulin-like growth factor-1 and muscle wasting in chronic heart failure

Chronic heart failure is a clinical syndrome of cardiac origin, which affects various organ systems. It is associated with metabolic abnormalities leading to a catabolic syndrome in advanced stages of the disease. As in several other chronic diseases, skeletal muscle dysfunction and structural muscle abnormalities result in progressive muscle wasting and cachexia. These changes are accompanied by increased expression of proinflammatory cytokines, increased rate of apoptosis and activation of the proteolytic ubiquitin-proteasome pathway. Further, reduced expression of the local anabolic insulin-like growth factor-1 has been demonstrated in skeletal muscle of animals and patients with chronic heart failure. This suppression occurs in the presence of normal serum levels of insulin-like growth factor-1. In addition to catabolic effects of proinflammatory cytokines, these recent findings are consistent with reduced anabolism involving altered local insulin-like growth factor-1 levels in progressive muscle atrophy in chronic heart failure. This article describes local effects of insulin-like growth factor-1 on skeletal muscle function and morphology, its role in stem cell recruitment and muscle regeneration as well as its regulation in circumstances of muscle inflammation and wasting.

The behaviour of satellite cells in response to exercise: what have we learned from human studies?

Understanding the complex role played by satellite cells in the adaptive response to exercise in human skeletal muscle has just begun. The development of reliable markers for the identification of satellite cell status (quiescence/activation/proliferation) is an important step towards the understanding of satellite cell behaviour in exercised human muscles. It is hypothesised currently that exercise in humans can induce (1) the activation of satellite cells without proliferation, (2) proliferation and withdrawal from differentiation, (3) proliferation and differentiation to provide myonuclei and (4) proliferation and differentiation to generate new muscle fibres or to repair segmental fibre injuries. In humans, the satellite cell pool can increase as early as 4 days following a single bout of exercise and is maintained at higher level following several weeks of training. Cessation of training is associated with a gradual reduction of the previously enhanced satellite cell pool. In the elderly, training counteracts the normal decline in satellite cell number seen with ageing. When the transcriptional activity of existing myonuclei reaches its maximum, daughter cells generated by satellite cell proliferation are involved in protein synthesis by enhancing the number of nuclear domains. Clearly, delineating the events and the mechanisms behind the activation of satellite cells both under physiological and pathological conditions in human skeletal muscles remains an important challenge.

Coordinated collagen and muscle protein synthesis in human patella tendon and quadriceps muscle after exercise

We hypothesized that an acute bout of strenuous, non-damaging exercise would increase rates of protein synthesis of collagen in tendon and skeletal muscle but these would be less than those of muscle myofibrillar and sarcoplasmic proteins. Two groups (n = 8 and 6) of healthy young men were studied over 72 h after 1 h of one-legged kicking exercise at 67% of maximum workload (W(max)). To label tissue proteins in muscle and tendon primed, constant infusions of [1-(13)C]leucine or [1-(13)C]valine and flooding doses of [(15)N] or [(13)C]proline were given intravenously, with estimation of labelling in target proteins by gas chromatography-mass spectrometry. Patellar tendon and quadriceps biopsies were taken in exercised and rested legs at 6, 24, 42 or 48 and 72 h after exercise. The fractional synthetic rates of all proteins were elevated at 6 h and rose rapidly to peak at 24 h post exercise (tendon collagen (0.077% h(-1)), muscle collagen (0.054% h(-1)), myofibrillar protein (0.121% h(-1)), and sarcoplasmic protein (0.134% h(-1))). The rates decreased toward basal values by 72 h although rates of tendon collagen and myofibrillar protein synthesis remained elevated. There was no tissue damage of muscle visible on histological evaluation. Neither tissue microdialysate nor serum concentrations of IGF-I and IGF binding proteins (IGFBP-3 and IGFBP-4) or procollagen type I N-terminal propeptide changed from resting values. Thus, there is a rapid increase in collagen synthesis after strenuous exercise in human tendon and muscle. The similar time course of changes of protein synthetic rates in different cell types supports the idea of coordinated musculotendinous adaptation.

Exercise and circulating insulin-like growth factor I

Determinations of serum concentrations of total insulin-like growth factor I (tIGF-I) are important in the diagnosis, monitoring of treatment and safety evaluation of patients with growth disorders and/or metabolic disease. It is well established that tIGF-I status varies over time. Changes in tIGF-I levels in relation to an acute bout of exercise or repeated bouts, known as training, are likely to contribute to this variation. Serum tIGF-I has also been found to be of predictive value in growth prediction models employed before the start of growth hormone (GH) treatment. Furthermore, IGF-I generation tests have been suggested to be of value in the assessment of the growth response to GH administration in patients suspected of GH deficiency with or without some degree of GH insensitivity. This is discussed elsewhere in this issue. Recent progress in our understanding of growth hormone-dependent and -independent expression of the IGF1 gene in skeletal muscle and the role of sufficient energy intake during training for muscle and liver generation of IGF-I raises important questions regarding their relative contribution to the circulating pool of IGF-I. The present review is focused on circulating levels of tIGF-I in relation to a single bout of exercise or to a period of training. In addition, the expression of IGF-I locally in muscle in response to these stimuli will be discussed.

Leukocytes, cytokines, growth factors and hormones in human skeletal muscle and blood after uphill or downhill running

Muscular adaptation to physical exercise has previously been described as a repair process following tissue damage. Recently, evidence has been published to question this hypothesis. The purpose of this study was to investigate inflammatory processes in human skeletal muscle and epimysium after acute physical exercise with large eccentric components. Three groups of subjects (n= 19) performed 45 min treadmill running at either 4 deg (n= 5) or 8 deg (n= 9) downhill or 4 deg uphill (n= 5) and one group served as control (n= 9). One biopsy was taken from each subject 48 h post exercise. Blood samples were taken up to 7 days post exercise. Compared to the control group, none of the markers of inflammation in muscle and epimysium samples was different in any exercised group. Only subjects in the Downhill groups experienced delayed onset of muscle soreness (DOMS) and increased serum creatine kinase activity (CK). The detected levels of immunohistochemical markers for T cells (CD3), granulocytes (CD11b), leukaemia inhibitory factor (LIF) and hypoxia-inducible factor 1beta (HIF-1beta) were greater in epimysium from exercised subjects with DOMS ratings >3 (0-10 scale) compared to exercised subjects without DOMS but not higher than controls. Eccentric physical exercise (downhill running) did not result in skeletal muscle inflammation 48 h post exercise, despite DOMS and increased CK. It is suggested that exercise can induce DOMS by activating inflammatory factors present in the epimysium before exercise. Repeated physical training may alter the content of inflammatory factors in the epimysium and thus reduce DOMS.

Oxidative stress, exercise, and antioxidant supplementation

Cells continuously produce free radicals and reactive oxygen species (ROS) as part of metabolic processes. These free radicals are neutralized by an elaborate antioxidant defense system consisting of enzymes such as catalase, superoxide dismutase, glutathione peroxidase, and numerous non-enzymatic antioxidants, including vitamins A, E and C, glutathione, ubiquinone, and flavonoids. Exercise can produce an imbalance between ROS and antioxidants, which is referred to as oxidative stress. Dietary antioxidant supplements are marketed to and used by athletes as a means to counteract the oxidative stress of exercise. Whether strenuous exercise does, in fact, increase the need for additional antioxidants in the diet is not clear. This review examines the markers used to determine oxidative stress in blood and muscle samples (e.g. lipid peroxidation, expired pentane, malondialdehyde (MDA), F2-isoprostanes, congugated dienes, and 8-hydroxy-2'-deoxyguanosine (8-OhdG)), the changes in oxidative stress markers induced by exercise, and whether athletes require antioxidant supplements.

Exercise-induced muscle damage in humans

Exercise-induced muscle injury in humans frequently occurs after unaccustomed exercise, particularly if the exercise involves a large amount of eccentric (muscle lengthening) contractions. Direct measures of exercise-induced muscle damage include cellular and subcellular disturbances, particularly Z-line streaming. Several indirectly assessed markers of muscle damage after exercise include increases in T2 signal intensity via magnetic resonance imaging techniques, prolonged decreases in force production measured during both voluntary and electrically stimulated contractions (particularly at low stimulation frequencies), increases in inflammatory markers both within the injured muscle and in the blood, increased appearance of muscle proteins in the blood, and muscular soreness. Although the exact mechanisms to explain these changes have not been delineated, the initial injury is ascribed to mechanical disruption of the fiber, and subsequent damage is linked to inflammatory processes and to changes in excitation-contraction coupling within the muscle. Performance of one bout of eccentric exercise induces an adaptation such that the muscle is less vulnerable to a subsequent bout of eccentric exercise. Although several theories have been proposed to explain this "repeated bout effect," including altered motor unit recruitment, an increase in sarcomeres in series, a blunted inflammatory response, and a reduction in stress-susceptible fibers, there is no general agreement as to its cause. In addition, there is controversy concerning the presence of sex differences in the response of muscle to damage-inducing exercise. In contrast to the animal literature, which clearly shows that females experience less damage than males, research using human studies suggests that there is either no difference between men and women or that women are more prone to exercise-induced muscle damage than are men.

Chronic heart failure and skeletal muscle catabolism: effects of exercise training

Although the clinical picture of cardiac cachexia is well-known in patients with advanced chronic heart failure (CHF) the factors that determine who is at risk for this progressive catabolic syndrome and who is not remain unclear. Different endocrine systems have been accused of being involved in this process: an imbalance between catabolic and anabolic steroids with an elevated cortisol/dihydroepiandrosterone ratio, an increased resting metabolic rate due to high levels of circulating catecholamines, various cytokines are activated in CHF (i.e. TNF-alpha, IL-6, IL-1beta and others), and elevated levels of growth hormone (GH) with inappropriately normal or low serum levels of insulin-like growth factor-I (IGF-I) have been described in cardiac cachexia. These catabolic factors contribute to peripheral muscle atrophy, augment the expression of the inducible nitric oxide synthase (iNOS), which in turn inhibits the aerobic cellular metabolism. The present review examines whether the catabolic factors can be influenced by a classical anabolic intervention: regular physical exercise training. Long-term training programs increase skeletal muscle cytochrome c oxidase activity and are associated with reduced local expression of pro-inflammatory cytokines as well as iNOS, and augment local IGF-I production. In concert, these beneficial effects of exercise training may help to retard the catabolic process in CHF finally leading to cardiac cachexia and death.

L-Carnitine L-tartrate supplementation favorably affects markers of recovery from exercise stress

We examined the influence of L-carnitine L-tartrate (LCLT) on markers of purine catabolism, free radical formation, and muscle tissue disruption after squat exercise. With the use of a balanced, crossover design (1 wk washout), 10 resistance-trained men consumed a placebo or LCLT supplement (2 g L-carnitine/day) for 3 wk before obtaining blood samples on six consecutive days (D1 to D6). Blood was also sampled before and after a squat protocol (5 sets, 15-20 repetitions) on D2. Muscle tissue disruption at the midthigh was assessed using magnetic resonance imaging (MRI) before exercise and on D3 and D6. Exercise-induced increases in plasma markers of purine catabolism (hypoxanthine, xanthine oxidase, and serum uric acid) and circulating cytosolic proteins (myoglobin, fatty acid-binding protein, and creatine kinase) were significantly (P < or = 0.05) attenuated by LCLT. Exercise-induced increases in plasma malondialdehyde returned to resting values sooner during LCLT compared with placebo. The amount of muscle disruption from MRI scans during LCLT was 41-45% of the placebo area. These data indicate that LCLT supplementation is effective in assisting recovery from high-repetition squat exercise.

Exercise-induced muscle damage and inflammation: fact or fiction?

Physical exercise is necessary for maintaining normal function of skeletal muscle. The mechanisms governing normal muscle function and maintenance are vastly unknown but synergistic function of hormones, neurosignalling, growth factors, cytokines and other factors, is undoubtedly important. Because of the complex interaction among these systems the lack of complete understanding of muscle function is not surprising. The purpose of exercise-induced changes in muscle cell function is to adapt the tissue to a demand of increased physical work capacity. Some of the approaches used to investigate changes in skeletal muscle cell function are exercise and electrical stimulation in animals and human models and isolated animal muscle. From these models, it has been concluded that during physical exercise, in an intensity and duration dependent manner, skeletal muscle is damaged and subsequently inflamed. The purpose of the inflammation would be to repair the exercise-induced damage. Because of the design and methods used in a majority of these studies, concerns must be raised, and the question asked whether the paradigm of exercise-induced muscle inflammation in fact is fiction. In a majority of conducted studies, a non-exercising control group is lacking and because of the invasive nature of the sampling methods used to study inflammation it does not appear impossible that observed inflammatory events in human skeletal muscle after physical exercise are methodological artefacts.

Mechanical load increases muscle IGF-I and androgen receptor mRNA concentrations in humans

The mechanism(s) of load-induced muscle hypertrophy is as yet unclear, but increasing evidence suggests a role for locally expressed insulin-like growth factor I (IGF-I). We investigated the effects of concentric (CON) vs. eccentric (ECC) loading on muscle IGF-I mRNA concentration. We hypothesized a greater IGF-I response after ECC compared with CON. Ten healthy subjects (24.4 +/- 0.7 yr, 174.5 +/- 2.6 cm, 70.9 +/- 4.3 kg) completed eight sets of eight CON or ECC squats separated by 6-10 days. IGF-I, IGF binding protein-4 (IGFBP-4), and androgen receptor (AR) mRNA concentrations were determined in vastus lateralis muscle by RT-PCR before and 48 h after ECC and CON. Serum total testosterone (TT) and IGF-I were measured serially across 48 h, and serum creatine kinase activity (CK), isometric maximum voluntary contraction (MVC), and soreness were determined at 48 h. IGF-I mRNA concentration increased 62% and IGFBP-4 mRNA concentration decreased 57% after ECC (P < 0.05). Changes after CON were similar but not significant (P = 0.06-0.12). AR mRNA concentration increased (P < 0.05) after ECC (63%) and CON (102%). Serum TT and IGF-I showed little change. MVC fell 10% and CK rose 183% after ECC (P < 0.05). Perceived soreness was higher (P < 0.01) after ECC compared with CON. Results indicate that a single bout of mechanical loading in humans alters activity of the muscle IGF-I system, and the enhanced response to ECC suggests that IGF-I may somehow modulate tissue regeneration after mechanical damage.

Immunohistochemical detection of components of the insulin-like growth factor system during skeletal muscle growth in the pig

The insulin-like growth factor (IGF) system plays an important role in postnatal somatic and skeletal muscle growth in pigs. There is little information on the occurrence and distribution of components of the IGF system in postnatal porcine skeletal muscle. IGF-I, IGF receptor 1 (IGF1R) and the IGF-binding proteins IGFBP-1 and -3 in longissimus dorsi and triceps brachii were localized in muscle biopsies from 12 commercially crossbred pigs aged from 28 to 199 days as well as from the sire generation, by immunohistochemistry. Plasma IGF-I concentrations were also determined using radio-immunoassays. Unlike other species, IGF-I was localized in porcine skeletal muscle fibres. Staining intensity correlated with the highest plasma IGF-I levels and phases of intensive muscle growth from the 11th to 22nd week. The pattern of IGF1R immunostaining, which was strong, correlated with that of IGF-I, IGF1R was also localized in endomysial tissues. IGFBP-1 was not detected within muscle fibres, but was found in the endomysium and vessel walls, while IGFBP-3 was localized with IGF-1 and its receptor. Higher magnification revealed that IGF1R, IGFBP-3 and probably IGF-I appeared in the tubular system. Inhibitory as well as stimulating controls of IGFBP-1 and -3 on IGF functions are discussed, which may maintain a balance between autocrine growth promoting activities of IGF-I and IGF1R.

Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans

Acute and long-term effects of resistance exercise combined with vascular occlusion on muscular function were investigated. Changes in integrated electromyogram with respect to time (iEMG), vascular resistive index, and plasma lactate concentration were measured in five men either during or after elbow flexion exercises with the proximal end of the arm occluded at 0-100 mmHg. The mean iEMG, postexercise hyperemia, and plasma lactate concentration were all elevated with the increase in occlusion pressure at a low-intensity exercise, whereas they were unchanged with the increase in occlusion pressure at high-intensity exercise. To investigate the long-term effects of low-intensity exercise with occlusion, older women (n = 24) were subjected to a 16-wk exercise training for elbow flexor muscles, in which low-intensity [ approximately 50-30% one repetition maximum (1 RM)] exercise with occlusion at approximately 110 mmHg (LIO), low-intensity exercise without occlusion (LI), and high- to medium-intensity ( approximately 80-50% 1 RM) exercise without occlusion (HI) were performed. Percent increases in both cross-sectional area and isokinetic strength of elbow flexor muscles after LIO were larger than those after LI (P < 0.05) and similar to those after HI. The results suggest that resistance exercise at an intensity even lower than 50% 1 RM is effective in inducing muscular hypertrophy and concomitant increase in strength when combined with vascular occlusion.

Exercise-induced DNA effects in human leukocytes are not accompanied by increased formation of 8-hydroxy-2'-deoxyguanosine or induction of micronuclei

The present study examined the effects of a short-distance triathlon on the induction of DNA effects in peripheral leukocytes, urinary excretion of oxidized DNA bases, and frequency of micronuclei in lymphocytes of human volunteers. Induction of DNA effects was measured as increased DNA migration using the alkaline comet assay. Increased DNA migration was found in leukocytes of all individuals at different time points after exercise and revealed a biphasic pattern. Twenty-four hours postexercise, elevated DNA migration was found, whereas lower values were detected 48 h after exercise. Seventy-two hours postexercise, the maximum increase in DNA migration was found and baseline values were still elevated after 120 h. A modified protocol of the comet assay for the detection of oxidized DNA bases revealed no differences in leukocytes before and directly after the triathlon. Urinary excretion of 8-hydroxy-2'-deoxyguanosine remained unaltered during the 5 consecutive days sampled. No differences were found in the micronucleus-frequency in lymphocytes before or 48 and 96 h after exercise. Our data suggest that DNA effects detected with the comet assay in leukocytes of humans after exercise are secondary effects that do not originate from oxidized DNA bases and do not result in chromosome damage.

Exercise and oxidative stress: Sources of free radicals and their impact on antioxidant systems

Strenuous exercise is characterized by increased oxygen consumption and the disturbance between intracellular pro-oxidant and antioxidant homeostasis. At lease three biochemical pathways (i.e., mitochondrial electron transport chain, xanthine oxidase, and polymorphoneutrophil) have been identified as potential sources of intracellular free radical generation during exercise. These deleterious reactive oxygen species pose a serious threat to the cellular antioxidant defense system, such as diminished reserves of antioxidant vitamins and glutathione. However, enzymatic and non-enzymatic antioxidants have demonstrated great versitility and adaptability in response to acute and chronic exercise. The delicate balance between pro-oxidants and antioxidants suggests that supplementation with antioxidants may be desirable for physically active individuals under certain physiological conditions by providing a larger protective margin.