Effect of high intensity training on capillarization and presence of angiogenic factors in human skeletal muscle

Resveratrol modulates the angiogenic response to exercise training in skeletal muscles of aged men

In animal studies, the polyphenol resveratrol has been shown to influence several pathways of importance for angiogenesis in skeletal muscle. The aim of the present study was to examine the angiogenic effect of resveratrol supplementation with parallel exercise training in aged men. Forty-three healthy physically inactive aged men (65 ± 1 yr) were divided into 1) a training group that conducted 8 wk of intense exercise training where half of the subjects received a daily intake of either 250 mg trans-resveratrol (n = 14) and the other half received placebo (n = 13) and 2) a nontraining group that received either 250 mg trans-resveratrol (n = 9) or placebo (n = 7). The group that trained with placebo showed a ~20% increase in the capillary-to-fiber ratio, an increase in muscle protein expression of VEGF, VEGF receptor-2, and tissue inhibitor of matrix metalloproteinase (TIMP-1) but unaltered thrombospodin-1 levels. Muscle interstitial VEGF and thrombospodin-1 protein levels were unchanged after the training period. The group that trained with resveratrol supplementation did not show an increase in the capillary-to-fiber ratio or an increase in muscle VEGF protein. Muscle TIMP-1 protein levels were lower in the training and resveratrol group than in the training and placebo group. Both training groups showed an increase in forkhead box O1 protein. In nontraining groups, TIMP-1 protein was lower in the resveratrol-treated group than the placebo-treated group after 8 wk. In conclusion, these data show that exercise training has a strong angiogenic effect, whereas resveratrol supplementation may limit basal and training-induced angiogenesis.

The effect of rowing ergometry and resistive exercise on skeletal muscle structure and function during bed rest

Exposure to microgravity causes functional and structural impairment of skeletal muscle. Current exercise regimens are time-consuming and insufficiently effective; an integrated countermeasure is needed that addresses musculoskeletal along with cardiovascular health. High-intensity, short-duration rowing ergometry and supplemental resistive strength exercise may achieve these goals. Twenty-seven healthy volunteers completed 5 wk of head-down-tilt bed rest (HDBR): 18 were randomized to exercise, 9 remained sedentary. Exercise consisted of rowing ergometry 6 days/wk, including interval training, and supplemental strength training 2 days/wk. Measurements before and after HDBR and following reambulation included assessment of strength, skeletal muscle volume (MRI), and muscle metabolism (magnetic resonance spectroscopy); quadriceps muscle biopsies were obtained to assess muscle fiber types, capillarization, and oxidative capacity. Sedentary bed rest (BR) led to decreased muscle volume (quadriceps: -9 ± 4%, P < 0.001; plantar flexors: -19 ± 6%, P < 0.001). Exercise (ExBR) reduced atrophy in the quadriceps (-5 ± 4%, interaction P = 0.018) and calf muscle, although to a lesser degree (-14 ± 6%, interaction P = 0.076). Knee extensor and plantar flexor strength was impaired by BR (-14 ± 15%, P = 0.014 and -22 ± 7%, P = 0.001) but preserved by ExBR (-4 ± 13%, P = 0.238 and +13 ± 28%, P = 0.011). Metabolic capacity, as assessed by maximal O2 consumption, (31)P-MRS, and oxidative chain enzyme activity, was impaired in BR but stable or improved in ExBR. Reambulation reversed the negative impact of BR. High-intensity, short-duration rowing and supplemental strength training effectively preserved skeletal muscle function and structure while partially preventing atrophy in key antigravity muscles. Due to its integrated cardiovascular benefits, rowing ergometry could be a primary component of exercise prescriptions for astronauts or patients suffering from severe deconditioning.

Effects of high intensity training and high volume training on endothelial microparticles and angiogenic growth factors

Aims

Endothelial microparticles (EMP) are complex vesicular structures shed from activated or apoptotic endothelial cells. As endurance exercise affects the endothelium, the objective of the study was to examine levels of EMP and angiogenic growth factors following different endurance exercise protocols.

Methods

12 subjects performed 3 different endurance exercise protocols: 1. High volume training (HVT; 130 min at 55% peak power output (PPO); 2. 4×4 min at 95% PPO; 3. 4×30 sec all-out. EMPs were quantified using flow cytometry after staining platelet-poor-plasma. Events positive for Annexin-V and CD31, and negative for CD42b, were classified as EMPs. Vascular endothelial growth factor (VEGF), migratory inhibiting factor (MIF) and hepatocyte growth factor (HGF) were determined by ELISA technique. For all these measurements venous blood samples were taken pre, 0′, 30′, 60′ and 180′ after each intervention. Furthermore, in vitro experiments were performed to explore the effect of collected sera on target endothelial functions and MP uptake capacities.

Results

VEGF and HGF significantly increased after HIT interventions. All three interventions caused a significant decrease in EMP levels post exercise compared to pre values. The sera taken after exercise increased the uptake of EMP in target endothelial cells compared to sera taken under resting conditions, which was shown to be phosphatidylserin-dependent. Increased EMP uptake was associated with an improved protection of target cells against apoptosis. Sera taken prior and after exercise promoted target endothelial cell migration, which was abrogated after inhibition of VEGF.

Conclusion

Physical exercise leads to decreased EMP levels and promotes a phosphatidylserin-dependent uptake of EMP into target endothelial cells, which is associated with a protection of target cells against apoptosis.

Effects of interval and continuous training on O2 uptake kinetics during severe-intensity exercise initiated from an elevated metabolic baseline

The purpose of this study was to test the hypothesis that V̇o2 kinetics would be speeded to a greater extent following repeated sprint training (RST), compared with continuous endurance training (ET), in the transition from moderate- to severe-intensity exercise. Twenty-three recreationally active subjects were randomly assigned to complete six sessions of ET (60–110 min of moderate-intensity cycling) or RST (four to seven 30-s all-out Wingate tests) over a 2-wk period. Subjects completed three identical work-to-work cycling exercise tests before and after the intervention period, consisting of baseline cycling at 20 W followed by sequential step increments to moderate- and severe-intensity work rates. The severe-intensity bout was continued to exhaustion on one occasion and was followed by a 60-s all-out sprint on another occasion. Phase II pulmonary V̇o2 kinetics were speeded by a similar magnitude in both the lower (ET pre, 28 ± 4; ET post, 22 ± 4 s; RST pre, 25 ± 8; RST post, 20 ± 7 s) and upper (ET pre, 50 ± 10; ET post, 39 ± 11 s; RST pre, 54 ± 7; RST post, 40 ± 11 s) steps of the work-to-work test following ET and RST ( P < 0.05). The tolerable duration of exercise and the total amount of sprint work completed in the exercise performance test were also similarly enhanced by ET and RST ( P < 0.05). Therefore, ET and RST provoked comparable improvements in V̇o2 kinetics and exercise performance in the transition from an elevated baseline work rate, with RST being a more time-efficient approach to elicit these adaptations.

Circulating angiogenic and inflammatory cytokine responses to acute aerobic exercise in trained and sedentary young men

PURPOSE

Endurance exercise training can ameliorate many cardiovascular and metabolic disorders and attenuate responses to inflammatory stimuli. The purpose of this study was to determine whether the angiogenic and pro-inflammatory cytokine response to acute endurance exercise differs between endurance-trained and sedentary young men.

METHODS

Ten endurance-trained and ten sedentary healthy young men performed 30 min of treadmill running at 75 % VO2max with blood sampling before and after exercise. Plasma concentrations of tumor necrosis factor (TNF)-alpha, interleukin (IL)-8, IL-6, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), placental growth factor (PlGF), and soluble VEGF receptor-1 (sFlt-1) were measured by multiplex ELISA.

RESULTS

Acute exercise increased IL-6 by 165 % (P < 0.05), IL-8 by 32 % (P < 0.05), PlGF by ~16 % (P < 0.05), sFlt-1 by 36 % (P < 0.001), and tended to increase bFGF by ~25 % (P = 0.06) in main effects analyses. TNF-α and VEGF did not change significantly with exercise in either group. Contrary to our hypothesis, there were no significant differences in TNF-α, IL-6, VEGF, bFGF, PlGF, or sFlt-1 between groups before or after acute exercise; however, there was a tendency for IL-8 concentrations to be higher in endurance-trained subjects compared to sedentary subjects (P = 0.06).

CONCLUSIONS

These results indicate that 30 min of treadmill running at 75 % VO2max produces a systemic angiogenic and inflammatory reaction, but endurance exercise training does not appear to significantly alter these responses in healthy young men.

Epigenetic mechanisms underlying cardiac degeneration and regeneration

Epigenetic modifications which are defined by DNA methylation, histone modifications and microRNA mediated gene regulation, have been found to be associated with cardiac dysfunction and cardiac regeneration but the mechanisms are unclear. MicroRNA therapies have been proposed for cardiac regeneration and proliferation of stem cells into cardiomyocytes. Cardiovascular disorders are represented by abnormal methylation of CpG islands and drugs that inhibit DNA methyltransferases such as 5-methyl Aza cytidine are under trials. Histone modifications which include acetylation, methylation, phosphorylation, ADP ribosylation, sumoylation and biotinylation are represented within abnormal phenotypes of cardiac hypertrophy, cardiac development and contractility. MicroRNAs have been used efficiently to epigenetically reprogram fibroblasts into cardiomyocytes. MicroRNAs represent themselves as potential biomarkers for early detection of cardiac disorders which are difficult to diagnose and are captured at later stages. Because microRNAs regulate circadian genes, for example a nocturnin gene of circadian clockwork is regulated by miR122, they have a profound role in regulating biological clock and this may explain the high cardiovascular risk during the morning time. This review highlights the role of epigenetics which can be helpful in disease management strategies.

Free radicals and sprint exercise in humans

Sprint exercise ability has been critical for survival. The remarkably high-power output levels attained during sprint exercise are achieved through strong activation of anaerobic, and to a lesser extent, aerobic energy supplying metabolic reactions, which generate reactive oxygen and nitrogen species (RONS). Sprint exercise may cause oxidative stress leading to muscle damage, particularly when performed in severe acute hypoxia. However, with training oxidative stress is reduced. Paradoxically, total plasma antioxidant capacity increases during the subsequent 2 h after a short sprint due to the increase in plasma urate concentration. The RONS produced during and immediately after sprint exercise play a capital role in signaling the adaptive response to sprint. Antioxidant supplementation blunts the normal AMPKα and CaMKII phosphorylation in response to sprint exercise. However, under conditions of increased glycolytic energy turnover and muscle acidification, as during sprint exercise in severe acute hypoxia, AMPKα phosphorylation is also blunted. This indicates that an optimal level of RONS-mediated stimulation is required for the normal signaling response to sprint exercise. Although RONS are implicated in fatigue, most studies convey that antioxidants do not enhance sprint performance in humans. Although currently controversial, it has been reported that antioxidant ingestion during training may jeopardize some of the beneficial adaptations to sprint training.

Repeated supra-maximal sprint cycling with and without sodium bicarbonate supplementation induces endothelial microparticle release

Under normal homeostatic conditions, the endothelium releases microparticles (MPs), which are known to increase under stressful conditions and in disease states. CD105 (endoglin) and CD106 (vascular cell adhesion molecule-1) are expressed on the surface of endothelial cells and increased expression in response to stress may be observed. A randomised-controlled double-blinded study aimed to examine the use of endothelial MPs as a marker for the state of one's endothelium, as well as whether maintaining acid-base homeostasis affects the release of these MPs. This study tested seven healthy male volunteers, who completed a strenuous cycling protocol, with venous blood analysed for CD105+ and CD106+ MPs by flow cytometry at regular intervals. Prior to each trial participants consumed either 0.3 g·kg(-1) body mass of sodium bicarbonate (NaHCO3), or 0.045 g·kg(-1) body mass of sodium chloride (NaCl). A significant rise in endothelial CD105+ MPs and CD106+ MPs (p<0.05) was observed at 90 min post-exercise. A significant trend was shown for these MPs to return to resting levels 180 min post-exercise in both groups. No significance was found between experimental groups, suggesting that maintaining acid-base variables closer to basal levels has little effect upon the endothelial stress response for this particular exercise mode. In conclusion, strenuous exercise is accompanied by MP release and the endothelium is able to rapidly recover in healthy individuals, whilst maintaining acid-base homeostasis does not attenuate the MP release from the endothelium after exercise.

Sodium nitrate supplementation does not enhance performance of endurance athletes

PURPOSE

Supplementation with inorganic nitrate has been suggested to be an ergogenic aid for athletes as nitric oxide donor. The purpose of this study was to determine whether ingestion of inorganic sodium nitrate benefits well-trained athletes performing a 40-min exercise test in laboratory conditions. In addition, we investigated the effect of this supplement on plasma levels of endothelin-1 (ET-1) and in nitrated proteins.

METHODS

Thirteen trained athletes participated in this randomized, double-blind, crossover study. They performed a 40-min cycle ergometer distance-trial test after two 3-d periods of dietary supplementation with sodium nitrate (10 mg·kg of body mass) or placebo.

RESULTS

Concentration of plasma nitrate (256 ± 35 μM) and nitrite (334 ± 86 nM) increased significantly (P < 0.05) after nitrate supplementation compared with placebo (nitrate: 44 ± 11 μM; nitrite: 187 ± 43 nM). In terms of exercise performance, there were no differences in either the mean distance (nitrate: 26.4 ± 1.1 km; placebo: 26.3 ± 1.2 km; P = 0.61) or mean power output (nitrate: 258 ± 28 W; placebo: 257 ± 28 W; P = 0.89) between treatments. Plasma ET-1 increased significantly (P < 0.05) just after exercise in nitrate (4.0 ± 0.8 pg·mL) and placebo (2.4 ± 0.4 pg·mL) conditions. This increase was significantly greater (P < 0.05) in the nitrate group. Levels of nitrated proteins did not differ between treatments (nitrate: preexercise, 91% ± 23%; postexercise, 81% ± 23%; placebo: preexercise, 95% ± 20%; postexercise, 99% ± 19%).

CONCLUSION

Sodium nitrate supplementation did not improve a 40-min distance-trial performance in endurance athletes. In addition, concentration of plasma ET-1 increased significantly after exercise after supplementation with sodium nitrate.

Cell therapy of peripheral arterial disease: from experimental findings to clinical trials

The age-adjusted prevalence of peripheral arterial disease in the US population was estimated to approach 12% in 1985, and as the population ages, the overall population having peripheral arterial disease is predicted to rise. The clinical consequences of occlusive peripheral arterial disease include intermittent claudication, that is, pain with walking, and critical limb ischemia (CLI), which includes pain at rest and loss of tissue integrity in the distal limbs, which may ultimately lead to amputation of a portion of the lower extremity. The risk factors for CLI are similar to those linked to coronary artery disease and include advanced age, smoking, diabetes mellitus, hyperlipidemia, and hypertension. The worldwide incidence of CLI was estimated to be 500 to 1000 cases per million people per year in 1991. The prognosis is poor for CLI subjects with advanced limb disease. One study of >400 such subjects in the United Kingdom found that 25% required amputation and 20% (including some subjects who had required amputation) died within 1 year. In the United States, ≈280 lower-limb amputations for ischemic disease are performed per million people each year. The first objective in treating CLI is to increase blood circulation to the affected limb. Theoretically, increased blood flow could be achieved by increasing the number of vessels that supply the ischemic tissue with blood. The use of pharmacological agents to induce new blood vessel growth for the treatment or prevention of pathological clinical conditions has been called therapeutic angiogenesis. Since the identification of the endothelial progenitor cell in 1997 by Asahara and Isner, the field of cell-based therapies for peripheral arterial disease has been in a state of continuous evolution. Here, we review the current state of that field.

The angiotensin converting enzyme insertion/deletion polymorphism alters the response of muscle energy supply lines to exercise

The presence of a silencing sequence (the I-allele) in the gene for the upstream regulator of blood flow, angiotensin I-converting enzyme (ACE), is associated with superior endurance performance and its trainability. We tested in a retrospective study with 36 Caucasian men of Swiss descent whether carriers of the ACE I-allele demonstrate a modified adaptive response of energy supply lines in knee extensor muscle, and aerobic fitness, to endurance training based on 6 weeks of supervised bicycle exercise or 6 months of self-regulated running (p value <Bonferroni-corrected 5 %). Body weight related maximal oxygen uptake and capillary density in vastus lateralis muscle before training were 20 and 23 % lower, respectively, in carriers of the I-allele. Bicycle (n = 16) but not running type endurance training (n = 19) increased the volume content of subsarcolemmal mitochondria (2.5-fold) and intramyocellular lipid (2.1-fold). This was specifically amplified in I-allele carriers after 6 weeks of bicycle exercise. The enhanced adjustment in myocellular organelles of aerobic metabolism with bicycle training corresponded to ACE I-allele dependent upregulation of 23 muscle transcripts during recovery from the bicycle stimulus and with training. The majority of affected transcripts were associated with glucose (i.e. ALDOC, Glut2, LDHC) and lipid metabolism (i.e. ACADL, CPTI, CPTII, LIPE, LPL, FATP, CD36/FAT); all demonstrating an enhanced magnitude of change in carriers of the ACE I-allele. Our observations suggest that local improvements in mitochondrial metabolism, through a novel expression pathway, contribute to the varying trainability in endurance performance between subjects with genetically modified expression of the regulator of vascular tone, ACE.

Nitric Oxide and the Biological Cascades Underlying Increased Neurogenesis, Enhanced Learning Ability, and Academic Ability as an Effect of Increased Bouts of Physical Activity

The consummate principle underlying all physiological research is corporeal adaptation at every level of the organism observed. With respect to humans, the body learns to function based on the external stimuli from the environment, beginning in the womb, throughout the developmental stages of life. Nitric Oxide (NO) appears to be the governor of the plasticity of several systems in mammals implicit in their proper development. It is the purpose of this review to describe the physiological pathways that lead to plasticity of not only the vasculature but also of the brain and how physical activity plays a key role in those alterations by initiating the mechanism that triggers NO production. Further, this review hopes to show a connection between these changes and learning, comprising both motor learning and cognitive learning. This review will show how NO plays a significant role in vascularization and neurogenesis, necessary to enhance the mind-body connection and comprehensive physical performance and adaptation. It is our belief that this review effectively demonstrates, using a multidisciplinary approach, the causal mechanisms underlying the increases in neurogenesis as related to improved learning and academic performance as a result of adequate bouts of physical activity of a vigorous nature.

Effects of physical activity and inactivity on muscle fatigue

The aim of this review was to examine the mechanisms by which physical activity and inactivity modify muscle fatigue. It is well known that acute or chronic increases in physical activity result in structural, metabolic, hormonal, neural, and molecular adaptations that increase the level of force or power that can be sustained by a muscle. These adaptations depend on the type, intensity, and volume of the exercise stimulus, but recent studies have highlighted the role of high intensity, short-duration exercise as a time-efficient method to achieve both anaerobic and aerobic/endurance type adaptations. The factors that determine the fatigue profile of a muscle during intense exercise include muscle fiber composition, neuromuscular characteristics, high energy metabolite stores, buffering capacity, ionic regulation, capillarization, and mitochondrial density. Muscle fiber-type transformation during exercise training is usually toward the intermediate type IIA at the expense of both type I and IIx myosin heavy-chain isoforms. High-intensity training results in increases of both glycolytic and oxidative enzymes, muscle capillarization, improved phosphocreatine resynthesis and regulation of K⁺, H⁺, and lactate ions. Decreases of the habitual activity level due to injury or sedentary lifestyle result in partial or even compete reversal of the adaptations due to previous training, manifested by reductions in fiber cross-sectional area, decreased oxidative capacity, and capillarization. Complete immobilization due to injury results in markedly decreased force output and fatigue resistance. Muscle unloading reduces electromyographic activity and causes muscle atrophy and significant decreases in capillarization and oxidative enzymes activity. The last part of the review discusses the beneficial effects of intermittent high-intensity exercise training in patients with different health conditions to demonstrate the powerful effect of exercise on health and well being.

Influence of acute dietary nitrate supplementation on 50 mile time trial performance in well-trained cyclists

Dietary nitrate supplementation has been reported to improve short distance time trial (TT) performance by 1-3 % in club-level cyclists. It is not known if these ergogenic effects persist in longer endurance events or if dietary nitrate supplementation can enhance performance to the same extent in better trained individuals. Eight well-trained male cyclists performed two laboratory-based 50 mile TTs: (1) 2.5 h after consuming 0.5 L of nitrate-rich beetroot juice (BR) and (2) 2.5 h after consuming 0.5 L of nitrate-depleted BR as a placebo (PL). BR significantly elevated plasma [NO(2) (-)] (BR: 472 ± 96 vs. PL: 379 ± 94 nM; P < 0.05) and reduced completion time for the 50 mile TT by 0.8 % (BR: 136.7 ± 5.6 vs. PL: 137.9 ± 6.4 min), which was not statistically significant (P > 0.05). There was a significant correlation between the increased post-beverage plasma [NO(2) (-)] with BR and the reduction in TT completion time (r = -0.83, P = 0.01). Power output (PO) was not different between the conditions at any point (P > 0.05) but oxygen uptake ([Formula: see text]O(2)) tended to be lower in BR (P = 0.06), resulting in a significantly greater PO/[Formula: see text]O(2) ratio (BR: 67.4 ± 5.5 vs. PL: 65.3 ± 4.8 W L min(-1); P < 0.05). In conclusion, acute dietary supplementation with beetroot juice did not significantly improve 50 mile TT performance in well-trained cyclists. It is possible that the better training status of the cyclists in this study might reduce the physiological and performance response to NO(3) (-) supplementation compared with the moderately trained cyclists tested in earlier studies.

Vascular remodelling in human skeletal muscle

Exercise-induced angiogenesis in skeletal muscle involves both non-sprouting and sprouting angiogenesis and results from the integrated responses of multiple systems and stimuli. VEGF-A (vascular endothelial growth factor A) levels are increased in exercised muscle and have been demonstrated to be critical for exercise-induced capillary growth. Only limited information is available regarding the role of other angiogenic and angiostatic factors in exercise, but changes in the angiopoietin family following repetitive bouts of exercise occur in a pattern that is favourable for angiogenesis. Results from other angiogenic model systems, indicate that miRNAs (microRNAs) are important factors in the regulation of angiogenesis and thus to explore their role as regulators of exercise induced angiogenesis will be an important avenue of study in the future. ECM (extracellular matrix) remodelling and activation of MMPs (matrix metalloproteinases) are, to some extent, overlooked players in skeletal muscle adaptation. Degradation of ECM proteins liberates angiogenic factors from immobilized matrix stores and make cell migration possible. In fact, it is known that MMPs become activated by a single bout of exercise in humans, rapid interstitial changes occur long before any changes in gene transcription could result in protein synthesis and inhibition of MMP activity completely abolishes sprouting angiogenesis. A growing body of evidence suggests that circulating and resident progenitor cells, in addition to other cell types located in skeletal muscle tissue, participate in skeletal muscle angiogenesis by various mechanisms. However, more studies are needed before these can be confirmed as mechanisms of exercise-induced capillary growth.

The effect of interval training combined with thigh cuffs pressure on maximal and submaximal exercise performance

The purpose of the study was to investigate the effect of interval training combined with a thigh cuffs pressure of +90 mmHg on maximal and submaximal cycling performance. Twenty untrained individuals were assigned either to a control (CON) or to an experimental (CUFF) training group. Both groups trained 3 days per week for 6 weeks at the same relative intensity; each training session consisted of 2-min work bout at 90% of VO(2max): 2-min active recovery bout at 50% of VO(2max). An incremental exercise test to exhaustion, a 6-min constant-power test at 80% of VO(2max) (Sub(80)) and a maximal constant-power test to exhaustion (TF(150)) were performed pre- and post-training. Despite the unchanged VO(2max), both groups significantly increased peak power output (CON: ∼12%, CUFF: ∼20%) that was accompanied by higher deoxygenation (ΔStO(2)) measured with near-infrared muscle spectroscopy. These changes were more pronounced in the CUFF group. Moreover, both groups reduced VO(2) during the Sub(80) test without concomitant changes in ΔStO(2). TF(150) was enhanced in both groups. Thus, an interval exercise training protocol under moderate restricted blood flow conditions does not provide any additive effect on maximal and submaximal cycling performance. However, it seems to induce peripheral muscular adaptations, despite the lower absolute training intensity.

Pro- and anti-angiogenic factors in human skeletal muscle in response to acute exercise and training

This study examined the effect of acute exercise and 4 weeks of aerobic training on skeletal muscle gene and protein expression of pro- and anti-angiogenic factors in 14 young male subjects. Training consisted of 60 min of cycling (∼60% of ), 3 times/week. Biopsies were obtained from vastus lateralis muscle before and after training. Muscle interstitial fluid was collected during cycling at weeks 0 and 4. Training increased (P < 0.05) the capillary: fibre ratio and capillary density by 23% and 12%, respectively. The concentration of interstitial vascular endothelial growth factor (VEGF) in response to acute exercise increased similarly (>6-fold; P < 0.05) before and after training. Resting protein levels of soluble VEGF receptor-1 in interstitial fluid, and of VEGF, thrombospondin-1 (TSP-1) and tissue inhibitor of matrix metalloproteinase-1 (TIMP1) in muscle were unaffected by training, whereas endothelial nitric oxide synthase protein levels in muscle increased by 50% (P < 0.05). Before and after training, acute exercise induced a similar increase (P < 0.05) in the mRNA level of angiopoietin 2, matrix metalloproteinase 9 and TSP-1. After training, TIMP1 mRNA content increased with exercise (P < 0.05). In conclusion, acute exercise induced a similar increase in the gene-expression of both pro- and anti-angiogenic factors in untrained and trained muscle. We propose that the increase in anti-angiogenic factors with exercise is important for modulation of angiogenesis. The lack of effect of training on basal muscle VEGF protein levels and VEGF secretion during exercise suggests that increased VEGF levels are not a prerequisite for exercise-induced capillary growth in healthy muscle.

Climbing-specific finger flexor performance and forearm muscle oxygenation in elite male and female sport climbers

Climbing performance relies to a great extent on the performance of the finger flexor muscles. Only a few studies investigated this performance in top class climbers and only one study compared gender-specific differences. This study investigated the climbing-specific finger flexor strength and endurance and related muscular oxygenation in 12 elite female and male climbers and 12 non-climbers. After the assessment of maximum voluntary finger flexor contraction (MVC), two isometric finger flexor endurance tests were performed at 40% MVC until exhaustion. A continuous isometric test was followed by an intermittent isometric test (10 s contraction, 3 s rest). Changes in oxygenation of finger flexor muscles were recorded using near infrared spectroscopy. MVC and strength-to-weight ratio were greater in climbers than non-climbers (P = 0.003; P < 0.001) and greater in men than women (P < 0.001; P = 0.002). Time to task failure for the intermittent test and the force-time integrals for the continuous and the intermittent test were also significantly greater in climbers (P = 0.030; P = 0.027; P = 0.005). During the intermittent test, re-oxygenation of the working muscles was faster in climbers (P < 0.05) without gender-specific differences. Close correlations were demonstrated between the best on-sight climbing performance and strength-to-weight ratio (r (2) = 0.946, P < 0.001) only in female climbers. The superior intermittent finger flexor endurance of climbers over non-climbers may be explained by the faster re-oxygenation of the finger flexor muscles during the short rest phases.

Frequent low-load ischemic resistance exercise to failure enhances muscle oxygen delivery and endurance capacity

This study investigated the effects of frequent low-load ischemic resistance exercise performed to failure on quadriceps size and performance, muscle activation, oxygen kinetics and cardiovascular responses. Ten healthy males performed knee-extension exercise for 4 weeks (4 sessions/week) at 15% maximal voluntary muscle contraction (MVC). One leg was trained with free blood flow (C-leg) while in the other leg (I-leg) ischemia was induced by an inflatable cuff (≥230 mmHg). Quadriceps cross-sectional area (CSA) of the I-leg increased by 3.4% (P<0.05). A tendency for smaller increase in muscle CSAs at the cuff level was observed. MVC force did not change in either leg, whereas the number of repetitions during exercise test to failure increased (P<0.01) by 63% in I-leg and 36% in C-leg. The decrease in muscle oxygenated hemoglobin concentration acquired by NIRS was attenuated (P<0.01) by 56% in I-leg and 21% in C-leg. Electromyographic amplitude of rectus femoris in I-leg was ∼45% lower (P<0.025) during the ischemic test. Also, ∼9% increase (P<0.05) in pre-exercise diastolic pressure was observed. In conclusion, substantial gains in muscle endurance capacity were induced, which were associated with enhanced muscle oxygen delivery. The potential negative effects of ischemic exercise with high cuff pressure on muscle and nerve and on arterial pressure regulation need further investigation.

Exercise-induced pyruvate dehydrogenase activation is not affected by 7 days of bed rest

To test the hypothesis that physical inactivity impairs the exercise-induced modulation of pyruvate dehydrogenase (PDH), six healthy normally physically active male subjects completed 7 days of bed rest. Before and immediately after the bed rest, the subjects completed an oral glucose tolerance test (OGTT) and a one-legged knee extensor exercise bout [45 min at 60% maximal load (Wmax)] with muscle biopsies obtained from vastus lateralis before, immediately after exercise, and at 3 h of recovery. Blood samples were taken from the femoral vein and artery before and after 40 min of exercise. Glucose intake elicited a larger ( P ≤ 0.05) insulin response after bed rest than before, indicating glucose intolerance. There were no differences in lactate release/uptake across the exercising muscle before and after bed rest, but glucose uptake after 40 min of exercise was larger ( P ≤ 0.05) before bed rest than after. Muscle glycogen content tended to be higher (0.05< P ≤ 0.10) after bed rest than before, but muscle glycogen breakdown in response to exercise was similar before and after bed rest. PDH-E1α protein content did not change in response to bed rest or in response to the exercise intervention. Exercise increased ( P ≤ 0.05) the activity of PDH in the active form (PDHa) and induced ( P ≤ 0.05) dephosphorylation of PDH-E1α on Ser293, Ser295 and Ser300, with no difference before and after bed rest. In conclusion, although 7 days of bed rest induced whole body glucose intolerance, exercise-induced PDH regulation in skeletal muscle was not changed. This suggests that exercise-induced PDH regulation in skeletal muscle is maintained in glucose-intolerant (e.g., insulin resistant) individuals.

Relationship between performance at different exercise intensities and skeletal muscle characteristics

The hypothesis investigated whether exercise performance over a broad range of intensities is determined by specific skeletal muscle characteristics. Seven subjects performed 8–10 exhaustive cycle trials at different workloads, ranging from 150 to 700 W (150 min to 20 s). No relationships between the performance times at high and low workloads were observed. A relationship ( P < 0.05) was noticed between the percentage of fast-twitch x fibers and the exercise time at 579 ± 21 W (∼30 s; r2 = 0.88). Capillary-to-fiber-ratio ( r2: 0.58–0.85) was related ( P < 0.05) to exercise time at work intensities ranging from 395 to 270 W (2.5–21 min). Capillary density was correlated ( r2 = 0.68; P < 0.05) with the net rate of plasma K+ accumulation during an ∼3-min bout and was estimated to explain 50–80% ( P < 0.05) of the total variance observed in exercise performances lasting ∼30 s to 3 min. The Na+-K+ pump β1-subunit expression was found to account for 13–34% ( P < 0.05) during exhaustive exercise of ∼1–4 min. In conclusion, exercise performance at different intensities is related to specific physiological variables. A large distribution of fast-twitch x fibers may play a role during very intense efforts, i.e., ∼30 s. Muscle capillaries and the Na+-K+ pump β1-subunit seem to be important determinants for performance during exhaustive high-intensity exercises lasting between 30 s and 4 min.

Exercise and Duchenne muscular dystrophy: toward evidence-based exercise prescription

To develop a rational framework for answering questions about the role of exercise in Duchenne muscular dystrophy (DMD), we focused on five pathophysiological mechanisms and offer brief hypotheses regarding how exercise may beneficially modulate pertinent cellular and molecular pathways. We aimed to provide an integrative overview of mechanisms of DMD pathology that may improve or worsen as a result of exercise. We also sought to stimulate discussion of what outcomes/dependent variables most appropriately measure these mechanisms, with the purpose of defining criteria for well-designed, controlled studies of exercise in DMD. The five mechanisms include pathways that are both intrinsic and extrinsic to the diseased muscle cells.

Short-term resistance training with blood flow restriction enhances microvascular filtration capacity of human calf muscles

Resistance training increases muscle strength and endurance but may require high intensity and long duration to enhance capillarity. Vascular occlusion during low-load resistance training augments the strength and endurance gains compared with low-load resistance training alone, but in this study we investigated whether it also promotes microvascular filtration capacity, an index of capillarity. Nine healthy males performed short-term low-intensity resistance training of the calf muscles (four sets of 50 heel raises, three times a week for 4 weeks) under restricted (thigh cuff inflated to 150 mmHg on the non-dominant leg) or unrestricted (dominant leg without thigh cuff) blood flow conditions. Before and after resistance training, calf filtration capacity and resting blood flow were assessed by strain gauge plethysmography, and calf muscle strength and fatigue were assessed respectively by maximal voluntary contraction and force decline during electrically evoked ischaemic contractions in both legs. Calf filtration capacity increased by 26% in the restricted leg but did not increase significantly in the unrestricted leg. Calf muscle strength was 18% greater in the restricted leg but unchanged in the unrestricted leg. Calf muscle fatigue and resting blood flow did not change in either leg. Resistance training promoted microvascular filtration capacity, an effect that was somewhat enhanced by blood flow restriction, and could be due to increased capillarization.

Exercise and PGC-1α-independent synchronization of type I muscle metabolism and vasculature by ERRγ

How type I skeletal muscle inherently maintains high oxidative and vascular capacity in the absence of exercise is unclear. We show that nuclear receptor ERRγ is highly expressed in type I muscle and, when transgenically expressed in anaerobic type II muscles (ERRGO mice), dually induces metabolic and vascular transformation in the absence of exercise. ERRGO mice show increased expression of genes promoting fat metabolism, mitochondrial respiration, and type I fiber specification. Muscles in ERRGO mice also display an activated angiogenic program marked by myofibrillar induction and secretion of proangiogenic factors, neovascularization, and a 100% increase in running endurance. Surprisingly, the induction of type I muscle properties by ERRγ does not involve PGC-1α. Instead, ERRγ genetically activates the energy sensor AMPK in mediating the metabovascular changes in ERRGO mice. Therefore, ERRγ represents a previously unrecognized determinant that specifies intrinsic vascular and oxidative metabolic features that distinguish type I from type II muscle.

Increased cellular proliferation in rat skeletal muscle and tendon in response to exercise: use of FLT and PET/CT

PURPOSE

The purpose of this study is to investigate exercise-induced cellular proliferation in rat skeletal muscle/tendon with the use of 3'-[F-18]fluoro-3'deoxythymidine (FLT) and to quantitatively study concomitant changes in the proliferation-associated factor, Ki67.

PROCEDURES

Wistar rats (n = 13) performed 3 days of treadmill running. Cellular proliferation was investigated 3 days before and 48 h after the running exercise with the use of FLT and positron emission tomography/computed tomography (PET/CT). Results were compared to a sedentary control group (n = 10). Image-derived standardized uptake values were calculated for Achilles tendons and calf muscles and compared to gene expression and immunohistochemical evaluations of Ki67.

RESULTS

Treadmill running induced increased uptake of FLT uptake in calf muscles (30%; p < 0.001) and in Achilles tendon (21%, p < 0.001). The image-derived results were supported by a correlation in calf muscle to Ki67 (protein and mRNA level), while this coherence was not found in tendon.

CONCLUSION

FLT-PET seems to be a promising tool for imaging of exercise-induced cellular proliferation in musculo-tendinous tissue.

The effect of passive movement training on angiogenic factors and capillary growth in human skeletal muscle

The effect of a period of passive movement training on angiogenic factors and capillarization in skeletal muscle was examined. Seven young males were subjected to passive training for 90 min, four times per week in a motor-driven knee extensor device that extended one knee passively at 80 cycles min₋₁. The other leg was used as control. Muscle biopsies were obtained from m. v. lateralis of both legs before as well as after 2 and 4 weeks of training. After the training period, passive movement and active exercise were performed with both legs, and muscle interstitial fluid was sampled from microdialysis probes in the thigh. After 2 weeks of training there was a 2-fold higher level of Ki-67 positive cells, co-localized with endothelial cells, in the passively trained leg which was paralleled by an increase in the number of capillaries around a fibre (P <0.05). Capillary density was higher than pre-training at 4 weeks of training (P <0.05). The training induced an increase in the mRNA level of endothelial nitric oxide synthase (eNOS), the angiopoietin receptor Tie-2 and matrix metalloproteinase (MMP)-9 in the passively trained leg and MMP-2 and tissue inhibitor of MMP (TIMP)-1 mRNA were elevated in both legs. Acute passive movement increased (P <0.05) muscle interstitial vascular endothelial growth factor (VEGF) levels 4- to 6-fold above rest and the proliferative effect, determined in vitro, of the muscle interstitial fluid ~16-fold compared to perfusate. The magnitude of increase was similar for active exercise. The results demonstrate that a period of passive movement promotes endothelial cell proliferation and angiogenic factors and initiates capillarization in skeletal muscle.

Blood vessels and the satellite cell niche

The fate of stem cell is regulated by cues received from the surrounding area. Recently, the concept of "stem cell zone"--rather than a predefined niche--introduced the notion of dynamic and permanent interactions between stem cells and their microenvironment. In adult skeletal muscle, satellite cells are considered as the main stem cells responsible for muscle repair and maintenance. They are localized close to vessels regardless their state of activation and differentiation. Moreover, the number of satellite cells is positively correlated to the capillarization of the myofiber. Angiogenesis has been known for a long time to be essential for muscle repair. However, relationships between vessel cells and satellite/myogenic cells that govern myogenic cell expansion, myogenesis, and angiogenesis have been only recently investigated. In this chapter, we discuss the possible existence of a vascular amplifying/differentiating niche, in an attempt to reconciliate several recent observations showing that satellite/myogenic cells interact with various cell types during the time course of muscle regeneration. Indeed, endothelial cells (ECs) stimulate myogenic cell growth and, inversely, differentiating myogenic cells promote angiogenesis. However, stromal cells may also provide some proliferating or differentiating cues to satellite/myogenic cells in this vascular area. Although some molecular effectors have been identified, including growth factors and cytokines, molecular regulations that occur within this vascular amplifying/differentiating niche requires further investigation. At the end of muscle repair, maturation of newly formed vessels takes place. In this context, we discuss the potential quiescence niche of satellite cells and the specific role of periendothelial cells. Indeed, periendothelial cells promote the return to quiescence of a subset of satellite/myogenic cells and maintain their quiescence (through Angiopoietin-1/Tie-2 signaling). We ask to what extent the environment may control the fate choice of satellite/myogenic cells and we also question the "hypoxic niche" in skeletal muscle, such a quiescence niche having being observed in the bone marrow.

Contraction-induced secretion of VEGF from skeletal muscle cells is mediated by adenosine

The role of adenosine and contraction for secretion of vascular endothelial growth factor (VEGF) in skeletal muscle was investigated in human subjects and rat primary skeletal muscle cells. Microdialysis probes were inserted in the thigh muscle of seven male subjects, and dialysate was collected at rest, during infusion of adenosine, and during knee extensor exercise. The dialysate was analyzed for content of VEGF protein and adenosine. The mechanism of VEGF secretion from muscle cells in culture was examined in resting and electrostimulated cells and in response to the adenosine analog NECA and the adenosine A2A receptor specific analog CGS-21680. Adenosine receptors A1, A2A, and A2B were blocked with DPCPX, ZM-241385, and enprofylline, respectively. cAMP-dependent protein kinase A (PKA) and mitogen-activated protein kinase (MAPK) were inhibited by H-89 and PD-98509, respectively. The human experiment showed that adenosine infusion enhanced ( P < 0.05) the interstitial concentration of VEGF protein approximately fourfold above baseline. Exercise increased ( P < 0.05) the interstitial VEGF concentration approximately sixfold above rest in parallel with an approximately threefold increase in adenosine concentration. In accordance, in cultured muscle cells, NECA and contraction caused secretion of VEGF ( P < 0.05). The contraction-induced secretion of VEGF was abolished by the A2B antagonist enprofylline and by inhibition of PKA or MAPK. The results demonstrate that adenosine causes secretion of VEGF from human skeletal muscle cells and that the contraction-induced secretion of VEGF protein is partially mediated via adenosine acting on A2B adenosine receptors. Moreover, the contraction-induced secretion of VEGF protein from muscle is dependent on both PKA and MAPK activation, but only the MAPK pathway appears to be adenosine dependent, revealing involvement of additional pathways in VEGF secretion.

Exercise training normalizes skeletal muscle vascular endothelial growth factor levels in patients with essential hypertension

METHODS

Vascular endothelial growth factor (VEGF) protein and capillarization were determined in muscle vastus lateralis biopsy samples in individuals with essential hypertension (n = 10) and normotensive controls (n = 10). The hypertensive individuals performed exercise training for 16 weeks. Muscle samples as well as muscle microdialysis fluid samples were obtained at rest, during and after an acute exercise bout, performed prior to and after the training period, for the determination of muscle VEGF levels, VEGF release, endothelial cell proliferative effect and capillarization.

RESULTS

Prior to training, the hypertensive individuals had 36% lower levels of VEGF protein and 22% lower capillary density in the muscle compared to controls. Training in the hypertensive group reduced (P < 0.01) mean arterial blood pressure by 7.1 +/- 0.8 mmHg, enhanced (P < 0.01) the capillary-to-fiber ratio by 17% and elevated (P < 0.05) muscle VEGF protein by 67%. Before training, acute exercise did not induce an increase in muscle interstitial VEGF levels above resting levels, but a five-fold increase (P < 0.05) was observed after the training period. Acute exercise induced an elevated (P < 0.05) endothelial cell proliferative effect of muscle dialysate after, but not before, training.

CONCLUSION

In summary, exercise training markedly elevates VEGF protein levels in muscle tissue, increases exercise-induced VEGF release from muscle and the cell proliferative effect of muscle dialysate. These alterations are paralleled by a lowering of blood pressure and an increased capillary-per-fiber ratio, but unaltered capillary density.

Exercise training stimulates ischemia-induced neovascularization via phosphatidylinositol 3-kinase/Akt-dependent hypoxia-induced factor-1 alpha reactivation in mice of advanced age

BACKGROUND

Exercise stimulates the vascular response in pathological conditions, including ischemia; however, the molecular mechanisms by which exercise improves the impaired hypoxia-induced factor (HIF)-1 alpha-mediated response to hypoxia associated with aging are poorly understood. Here, we report that swimming training (ST) modulates the vascular response to ischemia in aged (24-month-old) mice.

METHODS AND RESULTS

Aged wild-type mice (MMP-2(+/+)) that maintained ST (swimming 1 h/d) from day 1 after surgery were randomly assigned to 4 groups that were treated with either vehicle, LY294002, or deferoxamine for 14 days. Mice that were maintained in a sedentary condition served as controls. ST increased blood flow, capillary density, and levels of p-Akt, HIF-1 alpha, vascular endothelial growth factor, Fit-1, and matrix metalloproteinase-2 (MMP-2) in MMP-2(+/+) mice. ST also increased the numbers of circulating endothelial progenitor cells and their function associated with activation of HIF-1 alpha. All of these effects were diminished by LY294002, an inhibitor of phosphatidylinositol 3-kinase; enhanced by deferoxamine, an HIF-1 alpha stabilizer; and impaired by knockout of MMP-2. Finally, bone marrow transplantation confirmed that ST enhanced endothelial progenitor cell homing to ischemic sites in aged mice.

CONCLUSIONS

ST can improve neovascularization in response to hypoxia via a phosphatidylinositol 3-kinase-dependent mechanism that is mediated by the HIF-1 alpha/vascular endothelial growth factor/MMP-2 pathway in advanced age.

Training modalities: impact on endurance capacity

Endurance athletes demonstrate an exceptional resistance to fatigue when exercising at high intensity. Much research has been devoted to the contribution of aerobic capacity for the economy of endurance performance. Important aspects of the fine-tuning of metabolic processes and power output in the endurance athlete have been overlooked. This review addresses how training paradigms exploit bioenergetic pathways in recruited muscle groups to promote the endurance phenotype. A special focus is laid on the genome-mediated mechanisms that underlie the conditioning of fatigue resistance and aerobic performance by training macrocycles and complements. The available data on work-induced muscle plasticity implies that different biologic strategies are exploited in athletic and untrained populations to boost endurance capacity. Olympic champions are probably endowed with a unique constitution that renders the conditioning of endurance capacity for competition particularly efficient.

High-intensity training in football

This article reviews the major physiological and performance effects of aerobic high-intensity and speed-endurance training in football, and provides insight on implementation of individual game-related physical training. Analysis and physiological measurements have revealed that modern football is highly energetically demanding, and the ability to perform repeated high-intensity work is of importance for the players. Furthermore, the most successful teams perform more high-intensity activities during a game when in possession of the ball. Hence, footballers need a high fitness level to cope with the physical demands of the game. Studies on football players have shown that 8 to 12 wk of aerobic high-intensity running training (> 85% HR(max)) leads to VO2(max) enhancement (5% to 11%), increased running economy (3% to 7%), and lower blood lactate accumulation during submaximal exercise, as well as improvements in the yo-yo intermittent recovery (YYIR) test performance (13%). Similar adaptations are observed when performing aerobic high-intensity training with small-sided games. Speed-endurance training has a positive effect on football-specific endurance, as shown by the marked improvements in the YYIR test (22% to 28%) and the ability to perform repeated sprints (approximately 2%). In conclusion, both aerobic and speed-endurance training can be used during the season to improve high-intensity intermittent exercise performance. The type and amount of training should be game related and specific to the technical, tactical, and physical demands imposed on each player.

Morphological changes in murine skeletal muscle in response to exercise and mesterolone

Light and electron microscopy and quantitative morphometry were used to determine the effects of exercise and mesterolone on the soleus muscles of mice. Both exercise and mesterolone caused a significant hypertrophy of extrafusal muscle fibres. The hypertrophy of Type I fibres was greater than that of Type II fibres. There was no hyperplasia. Mitochondria were more numerous and larger than in the muscles of sedentary animals. Capillarity increased and small centrally nucleated muscle fibres appeared, usually in small clusters and most often in the muscles of animals exposed to mesterolone. A small proportion of satellite cells exhibited signs of activation but there were more in the muscles of mesterolone-treated animals than after exercise. Muscles from animals that had been both exercised and treated with mesterolone exhibited the largest changes: muscle mass and muscle fibre hypertrophy was greater than in all other groups of animals, capillarity was higher and >30% of all recognized satellite cells exhibited signs of activation. Groups of small centrally nucleated muscle fibres were commonly seen in these muscles. They appeared to be the result of splits in the form of sprouts from existing muscle fibres. With both exercise and mesterolone, alone or in combination, there was an increase in the proportion of Type I muscle fibres and a decrease in the proportion of Type II.

Regulation of extracellular matrix compounds involved in angiogenic processes in short- and long-track elite runners

Exercise induces alterations of the extracellular matrix (ECM), e.g. by an increased release of endostatin or by regulation of matrix metalloproteases (MMP)-2/-9, and cathepsin L. To investigate the influence of training status on exercise-induced ECM-processing of angiogenic molecules, alterations of endostatin-, MMP-2, and MMP-9 plasma concentrations during incremental running step tests in male elite short-track (n=6) and male elite long-track runners (n=7) were studied. Three blood samples (pre-exercise, 0, and 1 h post-exercise) were taken from each subject at each running test. In both groups, the basal endostatin plasma concentration was significantly decreased at the second running test, i.e. after the training season. Exercise-related acute alterations of the parameters were also observed only during the second test. In the long-track group, there was a significant increase in endostatin at 0 h and of MMP-2 at 1 h post-exercise. In the short-track group, only MMP-9 was significantly increased at 0 h post-exercise. Cathepsin L was increased at 0 h post-exercise. In conclusion, regular exercise performance decreases the basal endostatin plasma concentration, facilitates ECM-processing of angiogenic molecules by regular performance, and seems to be dependent on the kind of training.

Neuromuscular blockade of slow twitch muscle fibres elevates muscle oxygen uptake and energy turnover during submaximal exercise in humans

We tested the hypothesis that a greater activation of fast-twitch (FT) fibres during dynamic exercise leads to a higher muscle oxygen uptake (VO2 ) and energy turnover as well as a slower muscle on-kinetics. Subjects performed one-legged knee-extensor exercise for 10 min at an intensity of 30 W without (CON) and with (CUR) arterial injections of the non-depolarizing neuromuscular blocking agent cisatracurium. In CUR, creatine phosphate (CP) was unaltered in slow twitch (ST) fibres and decreased (P < 0.05) by 28% in FT fibres, whereas in CON, CP decreased (P < 0.05) by 33% and 23% in ST and FT fibres, respectively. From 127 s of exercise, muscle VO2 was higher (P < 0.05) in CUR compared to CON (425 +/- 25 (+/- S.E.M.) versus 332 +/- 30 ml min(-1)) and remained higher (P < 0.05) throughout exercise. Using monoexponential fitting, the time constant of the exercise-induced muscle VO2 response was slower (P < 0.05) in CUR than in CON (55 +/- 6 versus 33 +/- 5 s). During CUR and CON, muscle homogenate CP was lowered (P < 0.05) by 32 and 35%, respectively, and also muscle lactate production was similar in CUR and CON (37.8 +/- 4.1 versus 35.2 +/- 6.2 mmol). Estimated total muscle ATP turnover was 19% higher (P < 0.05) in CUR than in CON (1196 +/- 90 versus 1011 +/- 59 mmol) and true mechanical efficiency was lower (P < 0.05) in CUR than in CON (26.2 +/- 2.0 versus 30.9 +/- 1.5%). In conclusion, the present findings provide evidence that FT fibres are less efficient than ST fibres in vivo at a contraction frequency of 1 Hz, and that the muscle VO2 kinetics is slowed by FT fibre activation.

Four weeks of speed endurance training reduces energy expenditure during exercise and maintains muscle oxidative capacity despite a reduction in training volume

We studied the effect of an alteration from regular endurance to speed endurance training on muscle oxidative capacity, capillarization, as well as energy expenditure during submaximal exercise and its relationship to mitochondrial uncoupling protein 3 (UCP3) in humans. Seventeen endurance-trained runners were assigned to either a speed endurance training (SET; n = 9) or a control (Con; n = 8) group. For a 4-wk intervention (IT) period, SET replaced the ordinary training ( approximately 45 km/wk) with frequent high-intensity sessions each consisting of 8-12 30-s sprint runs separated by 3 min of rest (5.7 +/- 0.1 km/wk) with additional 9.9 +/- 0.3 km/wk at low running speed, whereas Con continued the endurance training. After the IT period, oxygen uptake was 6.6, 7.6, 5.7, and 6.4% lower (P < 0.05) at running speeds of 11, 13, 14.5, and 16 km/h, respectively, in SET, whereas remained the same in Con. No changes in blood lactate during submaximal running were observed. After the IT period, the protein expression of skeletal muscle UCP3 tended to be higher in SET (34 +/- 6 vs. 47 +/- 7 arbitrary units; P = 0.06). Activity of muscle citrate synthase and 3-hydroxyacyl-CoA dehydrogenase, as well as maximal oxygen uptake and 10-km performance time, remained unaltered in both groups. In SET, the capillary-to-fiber ratio was the same before and after the IT period. The present study showed that speed endurance training reduces energy expenditure during submaximal exercise, which is not mediated by lowered mitochondrial UCP3 expression. Furthermore, speed endurance training can maintain muscle oxidative capacity, capillarization, and endurance performance in already trained individuals despite significant reduction in the amount of training.

Regulation of pH in human skeletal muscle: adaptations to physical activity

Regulation of pH in skeletal muscle is the sum of mechanisms involved in maintaining intracellular pH within the normal range. Aspects of pH regulation in human skeletal muscle have been studied with various techniques from analysis of membrane proteins, microdialysis, and the nuclear magnetic resonance technique to exercise experiments including blood sampling and muscle biopsies. The present review characterizes the cellular buffering system as well as the most important membrane transport systems involved (Na(+)/H(+) exchange, Na-bicarbonate co-transport and lactate/H(+) co-transport) and describes the contribution of each transport system in pH regulation at rest and during muscle activity. It is reported that the mechanisms involved in pH regulation can undergo adaptational changes in association with physical activity and that these changes are of functional importance.

Passive leg movement enhances interstitial VEGF protein, endothelial cell proliferation, and eNOS mRNA content in human skeletal muscle

The present study used passive limb movement as an experimental model to study the effect of increased blood flow and passive stretch, without enhanced metabolic demand, in young healthy male subjects. The model used was 90 min of passive movement of the leg leading to a 2.8-fold increase ( P < 0.05) in blood flow without a significant enhancement in oxygen uptake. Muscle interstitial fluid was sampled with microdialysis technique and analyzed for vascular endothelial growth factor (VEGF) protein and for the effect on endothelial cell proliferation. Biopsies obtained from the musculus vastus lateralis were analyzed for mRNA content of VEGF, endothelial nitric oxide synthase (eNOS), and matrix metalloproteinase-2 (MMP-2). The passive leg movement caused an increase ( P < 0.05) in interstitial VEGF protein concentration above rest (73 ± 21 vs. 344 ± 83 pg/ml). Addition of muscle dialysate to cultured endothelial cells revealed that dialysate obtained during leg movement induced a 3.2-fold higher proliferation rate ( P < 0.05) than dialysate obtained at rest. Passive movement also enhanced ( P < 0.05) the eNOS mRNA level fourfold above resting levels. VEGF mRNA and MMP-2 mRNA levels were unaffected. The results show that a session of passive leg movement, elevating blood flow and causing passive stretch, augments the interstitial concentrations of VEGF, the proliferative effect of interstitial fluid, and eNOS mRNA content in muscle tissue. We propose that enhanced blood flow and passive stretch are positive physiological stimulators of factors associated with capillary growth in human muscle.

Redox regulation of the VEGF signaling path and tissue vascularization: Hydrogen peroxide, the common link between physical exercise and cutaneous wound healing

Vascularization, under physiological or pathophysiological conditions, typically takes place by one or more of the following processes: angiogenesis, vasculogenesis, arteriogenesis, and lymphangiogenesis. Although all of these mechanisms of vascularization have sufficient contrasting features to warrant consideration under separate cover, one common feature shared by all is their sensitivity to the VEGF signaling pathway. Conditions such as wound healing and physical exercise result in increased production of reactive oxygen species such as H(2)O(2), and both are associated with increased tissue vascularization. Understanding these two scenarios of adult tissue vascularization in tandem offers the potential to unlock the significance of redox regulation of the VEGF signaling pathway. Does H(2)O(2) support tissue vascularization? H(2)O(2) induces the expression of the most angiogenic form of VEGF, VEGF-A, by a HIF-independent and Sp1-dependent mechanism. Ligation of VEGF-A to VEGFR2 results in signal transduction leading to tissue vascularization. Such ligation generates H(2)O(2) via an NADPH oxidase-dependent mechanism. Disruption of VEGF-VEGFR2 ligation-dependent H(2)O(2) production or decomposition of such H(2)O(2) stalls VEGFR2 signaling. Numerous antioxidants exhibit antiangiogenic properties. Current evidence lends firm credence to the hypothesis that low-level endogenous H(2)O(2) supports vascular growth.

Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans

The effect of dexamethasone on Na(+),K(+) pump subunit expression and muscle exchange of K(+) during exercise in humans was investigated. Nine healthy male subjects completed a randomized double blind placebo controlled protocol, with ingestion of dexamethasone (Dex: 2 x 2 mg per day) or placebo (Pla) for 5 days. Na(+),K(+) pump catalytic alpha1 and alpha2 subunit expression was approximately 17% higher (P < 0.05) and the structural beta1 and beta2 subunit expression was approximately 6-8% higher (P < 0.05) after Dex compared with Pla. During one-legged knee-extension for 10 min at low intensity (LI; 18.6 +/- 1.0 W), two moderate intensity (51.7 +/- 2.4 W) exercise bouts (MI(1): 5 min; 2 min recovery; MI(2): exhaustive) and two high-intensity (71.7 +/- 2.5 W) exercise bouts (HI(1): 1 min 40 s; 2 min recovery; HI(2): exhaustive), femoral venous K(+) was lower (P < 0.05) in Dex compared with Pla. Thigh K(+) release was lower (P < 0.05) in Dex compared with Pla in LI and MI, but not in HI. Time to exhaustion in MI(2) tended to improve (393 +/- 50 s versus 294 +/- 41 s; P = 0.07) in Dex compared with Pla, whereas no difference was detected in HI(2) (106 +/- 10 s versus 108 +/- 9 s). The results indicate that an increased Na(+),K(+) pump expression per se is of importance for thigh K(+) reuptake at the onset of low and moderate intensity exercise, but less important during high intensity exercise.