Exercise training alters skeletal muscle microvascular endothelial cell properties in recent postmenopausal females.

The present study examined and compared the impact of exercise training on redox and molecular properties of human microvascular endothelial cells derived from skeletal muscle biopsies from sedentary recent (RPF, ≤ 5 years as postmenopausal) and late (LPF, ≥ 10 years as postmenopausal) postmenopausal females. Resting skeletal muscle biopsies were obtained before and after 8 weeks of intense aerobic exercise training for isolation of microvascular endothelial cells and determination of skeletal muscle angiogenic proteins and capillarisation. The microvascular endothelial cells were analysed for mitochondrial respiration and production of reactive oxygen species (ROS), glycolysis and proteins related to vascular function, redox balance and oestrogen receptors. Exercise training led to a reduced endothelial cell ROS formation (∼50%; P = 0.009 and P = 0.020 for intact and permeabilized cells (state 3), respectively) in RPF only, with no effect on endothelial mitochondrial capacity in either group. Basal endothelial cell lactate formation was higher (7%; P = 0.028), indicating increased glycolysis, after compared to before the exercise training period in RPF only. Baseline endothelial G protein-coupled oestrogen receptor (P = 0.028) and muscle capillarisation (P = 0.028) was lower in LPF than in RPF. Muscle vascular endothelial growth factor protein was higher (32%; P = 0.002) following exercise training in LPF only. Exercise training did not influence endothelial cell proliferation or skeletal muscle capillarisation in either group, but the CD31 level in the muscle tissue, indicating endothelial cell content, was higher (>50%; P < 0.05) in both groups. In conclusion, 8 weeks of intense aerobic exercise training reduces ROS formation and enhances glycolysis in microvascular endothelial cells from RPF but does not induce skeletal muscle angiogenesis. KEY POINTS: Late postmenopausal females have been reported to achieve limited vascular adaptations to exercise training. There is a paucity of data on the effect of exercise training on isolated skeletal muscle microvascular endothelial cells (MMECs). In this study the formation of reactive oxygen species in MMECs was reduced and glycolysis increased after 8 weeks of aerobic exercise training in recent but not late postmenopausal females. Late postmenopausal females had lower levels of G protein-coupled oestrogen receptor in MMECs and lower skeletal muscle capillary density at baseline. Eight weeks of intense exercise training altered MMEC properties but did not induce skeletal muscle angiogenesis in postmenopausal females.

Angiogenic potential is reduced in skeletal muscle of aged women.

KEY POINTS: The risk of cardiovascular disease and associated skeletal muscle microvascular rarefaction is enhanced in women after menopause, yet knowledge about the angiogenic potential in ageing women is generally sparse. Aged healthy and sedentary women were found to present a markedly impaired capacity for proliferation of skeletal muscle derived microvascular endothelial cells compared to young women. Vascular endothelial growth factor (VEGF) levels in skeletal muscle myocytes and release of VEGF from myocytes tended to be lower in aged compared to young women. The aged women did not show a detectable increase in skeletal muscle capillarization with 8 weeks of intense aerobic cycle training. Combined, the findings indicate that aged women have a reduced potential for capillary growth in skeletal muscle which, with ageing, may lead to age-induced microvascular rarefaction. ABSTRACT: Skeletal muscle angiogenic potential was examined in cell cultures derived from aged and young women, and the effect of 8 weeks of intense cycle training on muscle capillary growth was determined in the group of aged women. Basal muscle samples were obtained from healthy sedentary aged (n = 12; 64 ± 4.2 years) and young women (n = 5; 24 ± 3.2 years) for endothelial cell and skeletal muscle myocyte isolation and experiments. In addition, the aged women completed an 8-week training intervention. Peak oxygen uptake and muscle samples for histology and protein determination were obtained before and after the training period. Before training, muscle microdialysate was collected from the aged women at rest and during exercise. In Part 1 of the experiments, growth-supplement stimulated proliferation of endothelial cells was ∼75% lower in cells from aged compared to young women (P < 0.001). There was a tendency for a lower vascular endothelial growth factor (VEGF) concentration in muscle conditioned media (P = 0.0696) and for a lower VEGF content in the myocytes (P = 0.0705) from aged compared to young women. Endothelial proliferation was found to be highly dependent on mitochondrial function. Acute exercise resulted in a modest (1.3-fold; P = 0.0073) increase in muscle interstitial VEGF protein in the aged women. In Part 2, 8 weeks of intense training did not change muscle capillarization (P ≥ 0.1502) in the aged women, but led to an increased amount of muscle VEGF (P = 0.0339). In conclusion, aged women have impaired angiogenic potential, which is associated with a compromised response both at the skeletal muscle myocyte and microvascular endothelial cell level.

Hormetic modulation of angiogenic factors by exercise-induced mechanical and metabolic stress in human skeletal muscle.

This study used an integrative experimental model in humans to investigate whether muscle angiogenic factors are differentially modulated by exercise stimuli eliciting different degrees of mechanical and metabolic stress. In a randomized crossover design, 12 men performed two low-volume high-intensity exercise regimens, including short sprint intervals (SSI) or long sprint intervals (LSI) inducing pronounced mechanical/metabolic stress, and a high-volume moderate-intensity continuous exercise protocol (MIC) inducing mild but prolonged mechanical/metabolic stress. Gene and protein expression of angiogenic factors was determined in vastus lateralis muscle samples obtained before and after exercise. Exercise upregulated muscle VEGF mRNA to a greater extent in LSI and MIC compared with SSI. Analysis of angiogenic factors sensitive to shear stress revealed more marked exercise-induced VEGF receptor 2 (VEGF-R2) mRNA responses in MIC than SSI, as well as greater platelet endothelial cell adhesion molecule (PECAM-1) and endothelial nitric oxide synthase (eNOS) mRNA responses in LSI than SSI. No apparent exercise-induced phosphorylation of shear stress-sensory proteins VEGF-R2Tyr1175, PECAM-1Tyr713, and eNOSSer1177 was observed despite robust elevations in femoral artery shear stress. Exercise evoked greater mRNA responses of the mechanical stretch sensor matrix metalloproteinase-9 (MMP9) in SSI than MIC. Exercise-induced mRNA responses of the metabolic stress sensor hypoxia-inducible factor-1α (HIF-1α) were more profound in LSI than SSI. These results suggest that low-volume high-intensity exercise transcriptionally activates angiogenic factors in a mechanical/metabolic stress-dependent manner. Furthermore, the angiogenic potency of low-volume high-intensity exercise appears similar to that of high-volume moderate-intensity exercise, but only on condition of eliciting severe mechanical/metabolic stress. We conclude that the angiogenic stimulus produced by exercise depends on both magnitude and protraction of myocellular homeostatic perturbations.NEW & NOTEWORTHY Skeletal muscle capillary growth is orchestrated by angiogenic factors sensitive to mechanical and metabolic signals. In this study, we employed an integrative exercise model to synergistically target, yet to different extents and for different durations, the mechanical and metabolic components of muscle activity that promote angiogenesis. Our results suggest that the magnitude of the myocellular perturbations incurred during exercise determines the amplitude of the angiogenic molecular signals, implying hormetic modulation of skeletal muscle angiogenesis by exercise-induced mechanical and metabolic stress.

Inactivity and exercise training differentially regulate abundance of Na+-K+-ATPase in human skeletal muscle.

Physical inactivity is a global health risk that can be addressed through application of exercise training suitable for an individual's health and age. People's willingness to participate in physical activity is often limited by an initially poor physical capability and early onset of fatigue. One factor associated with muscle fatigue during intense contractions is an inexcitability of skeletal muscle cells, reflecting impaired transmembrane Na+/K+ exchange and membrane depolarization, which are regulated via the transmembranous protein Na+-K+-ATPase (NKA). This short review focuses on the plasticity of NKA in skeletal muscle in humans after periods of altered usage, exploring NKA upregulation with exercise training and downregulation with physical inactivity. In human skeletal muscle, the NKA content quantified by [3H]ouabain binding site content shows robust, yet tightly constrained, upregulation of 8-22% with physical training, across a broad range of exercise training types. Muscle NKA content in humans undergoes extensive downregulation with injury that involves substantial muscular inactivity. Surprisingly, however, no reduction in NKA content was found in the single study that investigated short-term disuse. Despite clear findings that exercise training and injury modulate NKA content, the adaptability of the individual NKA isoforms in muscle (α1-3 and ß1-3) and of the accessory and regulatory protein FXYD1 are surprisingly inconsistent across studies, for exercise training as well as for injury/disuse. Potential reasons for this are explored. Finally, we provide suggestions for future studies to provide greater understanding of NKA regulation during exercise training and inactivity in humans.

The effect of repeated periods of speed endurance training on performance, running economy, and muscle adaptations.

The effect of repeated intense training interventions was investigated in eight trained male runners (maximum oxygen uptake [VO2 -max]: 59.3±3.2 mL/kg/min, mean±SD) who performed 10 speed endurance training (SET; repeated 30-seconds "all-out" bouts) and 10 aerobic moderate-intensity training sessions during two 40-day periods (P1 and P2) separated by ~80 days of habitual training. Before and after both P1 and P2, subjects completed an incremental test to exhaustion to determine VO2 -max and a repeated running test at 90% vVO2 -max to exhaustion (RRT) to determine short-term endurance capacity. In addition, running economy (RE) was measured at 60% vVO2 -max (11.9±0.5 km/h) and v10-km (14.3±0.9 km/h), a 10-km track-running test was performed, and a biopsy from m. vastus lateralis was collected. 10-km performance and VO2 -max (mL/min) were the same prior to P1 and P2, whereas RE was better (P<.05) before P2 than before P1. During P1 and P2, 10-km performance (2.9% and 2.3%), VO2 -max (2.1% and 2.6%), and RE (1.9% and 1.8% at 60% vVO2 -max; 1.6% and 2.0% at v10-km) improved (P<.05) to the same extent, respectively. Performance in RRT was 20% better (P<.05) after compared to before P2, with no change in P1. No changes in muscle expression of Na+ ,K+ -ATPase α1, α2 and ß1, NHE1, SERCA1 and SERCA2, actin, and CaMKII were found during neither P1 nor P2. Thus, the present study demonstrates that a second period of intense training leads to improved short-term performance and further improved RE, whereas 10-km performance and VO2 -max improve to the same extent as during the first period.

Performance in sports--With specific emphasis on the effect of intensified training.

Performance in most sports is determined by the athlete's technical, tactical, physiological and psychological/social characteristics. In the present article, the physical aspect will be evaluated with a focus on what limits performance, and how training can be conducted to improve performance. Specifically how intensified training, i.e., increasing the amount of aerobic high-intensity and speed endurance training, affects physiological adaptations and performance of trained subjects. Periods of speed endurance training do improve performance in events lasting 30 s-4 min, and when combined with aerobic high-intensity sessions, also performance during longer events. Athletes in team sports involving intense exercise actions and endurance aspects, such as soccer and basketball, can also benefit from intensified training. Speed endurance training does reduce energy expenditure and increase expression of muscle Na(+), K(+) pump α subunits, which may preserve muscle cell excitability and delay fatigue development during intense exercise. When various types of training are conducted in the same period (concurrent training), as done in a number of sports, one type of training may blunt the effect of other types of training. It is not, however, clear how various training modalities are affecting each other, and this issue should be addressed in future studies.

Effects of long-term football training on the expression profile of genes involved in muscle oxidative metabolism.

We investigated whether long-term recreational football training affects the expression of health-related biochemical and molecular markers in healthy untrained subjects. Five untrained healthy men trained for 1 h 2.4 times/week for 12 weeks and 1.3 times/week for another 52 weeks. Blood samples and a muscle biopsy from the vastus lateralis were collected at T0 (pre intervention) and at T1 (post intervention). Gene expression was measured by RTqPCR on RNA extracted from muscle biopsies. The expression levels of the genes principally involved in energy metabolism (PPARγ, adiponectin, AMPKα1/α2, TFAM, NAMPT, PGC1α and SIRT1) were measured at T0 and T1. Up-regulation of PPARγ (p < 0.0005), AMPKα1 (p < 0.01), AMPKα2 (p < 0.0005) and adiponectin was observed at T1 vs T0. Increases were also found in the expression of TFAM (p < 0.001), NAMPT (p < 0.01), PGC1α (p < 0.01) and SIRT1 (p < 0.01), which are directly or indirectly involved in the glucose and lipid oxidative metabolism. Multiple linear regression analysis revealed that fat percentage was independently associated with NAMPT, PPARγ and adiponectin expression. In conclusion, long-term recreational football training could be a useful tool to improve the expression of muscle molecular biomarkers that are correlated to oxidative metabolism in healthy males.

ß2-adrenergic stimulation enhances Ca2+ release and contractile properties of skeletal muscles, and counteracts exercise-induced reductions in Na+-K+-ATPase Vmax in trained men.

The aim of the present study was to examine the effect of ß2-adrenergic stimulation on skeletal muscle contractile properties, sarcoplasmic reticulum (SR) rates of Ca(2+) release and uptake, and Na(+)-K(+)-ATPase activity before and after fatiguing exercise in trained men. The study consisted of two experiments (EXP1, n = 10 males, EXP2, n = 20 males), where ß2-adrenoceptor agonist (terbutaline) or placebo was randomly administered in double-blinded crossover designs. In EXP1, maximal voluntary isometric contraction (MVC) of m. quadriceps was measured, followed by exercise to fatigue at 120% of maximal oxygen uptake (V̇O2, max ). A muscle biopsy was taken after MVC (non-fatigue) and at time of fatigue. In EXP2, contractile properties of m. quadriceps were measured with electrical stimulations before (non-fatigue) and after two fatiguing 45 s sprints. Non-fatigued MVCs were 6 ± 3 and 6 ± 2% higher (P < 0.05) with terbutaline than placebo in EXP1 and EXP2, respectively. Furthermore, peak twitch force was 11 ± 7% higher (P < 0.01) with terbutaline than placebo at non-fatigue. After sprints, MVC declined (P < 0.05) to the same levels with terbutaline as placebo, whereas peak twitch force was lower (P < 0.05) and half-relaxation time was prolonged (P < 0.05) with terbutaline. Rates of SR Ca(2+) release and uptake at 400 nm [Ca(2+)] were 15 ± 5 and 14 ± 5% (P < 0.05) higher, respectively, with terbutaline than placebo at non-fatigue, but declined (P < 0.05) to similar levels at time of fatigue. Na(+)-K(+)-ATPase activity was unaffected by terbutaline compared with placebo at non-fatigue, but terbutaline counteracted exercise-induced reductions in maximum rate of activity (Vmax) at time of fatigue. In conclusion, increased contractile force induced by ß2-adrenergic stimulation is associated with enhanced rate of Ca(2+) release in humans. While ß2-adrenergic stimulation elicits positive inotropic and lusitropic effects on non-fatigued m. quadriceps, these effects are blunted when muscles fatigue.

Executive summary: Football for health - prevention and treatment of non-communicable diseases across the lifespan through football.

This supplement contains 16 original articles describing how football conducted as small sided games affects fitness and health of untrained individuals across the lifespan. The intermittent nature of football and high exercise intensity result in a broad range of effects. The heart changes its structure and improves its function. Blood pressure is markedly reduced with the mean arterial blood pressure being lowered by ~10 mmHg for hypertensive men and women training 2-3 times/week for 12-26 weeks. Triglycerides and cholesterol are lowered and body fat declines, especially in middle-aged men and women with type 2 diabetes. Furthermore, muscle mass and bone mineral density increases in a number of participant groups, including 65-75-year-old men. The functional capacity is elevated with increases in VO2 max of 10-15%, and 50-100% improvements in the capacity to perform intermittent work within 16 weeks. These effects apply irrespective of whether the participants are young, overweight, elderly or suffering from a disease. The studies clearly show that the participants enjoy playing football and form special relationships with their team mates. Thus, football is a healthy activity, providing a unique opportunity to increase recruitment and adherence to physical activity in a hitherto underserved population, and to treat and rehabilitate patients with hypertension, type 2 diabetes and prostate cancer.

Combined inhalation of beta2 -agonists improves swim ergometer sprint performance but not high-intensity swim performance.

There is a high prevalence of asthma and airway hyperresponsiveness (AHR) in elite athletes, which leads to a major use of beta2 -agonists. In a randomized double-blinded crossover study, we investigated the effects of combined inhalation of beta2 -agonists (salbutamol, formoterol, and salmeterol), in permitted doses within the World Anti-Doping Agency 2013 prohibited list, in elite swimmers with (AHR, n = 13) or without (non-AHR, n = 17) AHR. Maximal voluntary isometric contraction of m. quadriceps (MVC), sprint performance on a swim ergometer and performance in an exhaustive swim test at 110% of VO2max were determined. Venous plasma interleukin-6 (IL-6) and interleukin-8 (IL-8) were measured post-exercise. No improvement was observed in the exhaustive swim test, but swim ergometer sprint time was improved (P < 0.05) in both groups from 57 ± 1.7 to 56 ± 1.8 s in AHR and 58.3 ± 1 to 57.4 ± 1 s in non-AHR. MVC and post-exercise plasma IL-6 increased (P < 0.05) with beta2 -agonists in both groups, whereas IL-8 only increased in AHR. In summary, inhalation of beta2 -agonists, in permitted doses, did not improve swim performance in elite swimmers. However, swim ergometer sprint performance and MVC were increased, which should be considered when making future anti-doping regulations.

Angiogenic response to passive movement and active exercise in individuals with peripheral arterial disease.

Peripheral arterial disease (PAD) is caused by atherosclerosis and is associated with microcirculatory impairments in skeletal muscle. The present study evaluated the angiogenic response to exercise and passive movement in skeletal muscle of PAD patients compared with healthy control subjects. Twenty-one PAD patients and 17 aged control subjects were randomly assigned to either a passive movement or an active exercise study. Interstitial fluid microdialysate and tissue samples were obtained from the thigh skeletal muscle. Muscle dialysate vascular endothelial growth factor (VEGF) levels were modestly increased in response to either passive movement or active exercise in both subject groups. The basal muscle dialysate level of the angiostatic factor thrombospondin-1 protein was markedly higher (P < 0.05) in PAD patients compared with the control subjects, whereas soluble VEGF receptor-1 dialysate levels were similar in the two groups. The basal VEGF protein content in the muscle tissue samples was ∼27% lower (P < 0.05) in the PAD patients compared with the control subjects. Analysis of mRNA expression for a range of angiogenic and angiostatic factors revealed a modest change with active exercise and passive movement in both groups, except for an increase (P < 0.05) in the ratio of angiopoietin-2 to angiopoietin-1 mRNA in the PAD group with both interventions. PAD patients and aged individuals showed a similar limited angiogenic response to active exercise and passive movement. The limited increase in muscle extracellular VEGF combined with an elevated basal level of thrombospondin-1 in muscle extracellular fluid of PAD patients may restrict capillary growth in these patients.

Intense intermittent exercise provides weak stimulus for vascular endothelial growth factor secretion and capillary growth in skeletal muscle.

The effect of acute intense intermittent exercise compared with moderate-intensity exercise on angiogenic factors and the effect of 4 weeks of intense intermittent training on capillary growth were examined in nine healthy young men, preconditioned by moderate-intensity endurance training. The intense training consisted of 24 bouts of 1 min cycling at an initial work rate of 316 ± 19 W (~117% of pretraining maximal oxygen uptake), performed three times per week. Skeletal muscle biopsies and muscle microdialysates were obtained from the vastus lateralis before, during and after acute exercise performed at either moderate or high intensity. Comparison of the response in angiogenic factors to acute moderate- versus high-intensity exercise, performed prior to the intense training intervention, revealed that intense exercise resulted in a markedly lower (~60%; P < 0.05) increase in interstitial vascular endothelial growth factor than did moderate-intensity exercise. Muscle interstitial fluid obtained during moderate-intensity exercise increased endothelial cell proliferation in vitro more than interstitial fluid obtained during intense exercise (sixfold versus 2.5-fold, respectively; P < 0.05). The 4 weeks of high-intensity training did not lead to an increased capillarization in the muscle but abolished the exercise-induced increase in mRNA for several angiogenic factors, increased the protein levels of endothelial nitric oxide synthase, lowered the protein levels of thrombospondin-1 in muscle but increased the interstitial protein levels of thrombospondin-1. We conclude that intense intermittent exercise provides a weak stimulus for vascular endothelial growth factor secretion and endothelial cell proliferation and that intense intermittent training does not induce a sufficient angiogenic stimulus to induce capillary growth in muscle previously conditioned by moderate-intensity exercise.

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.

Effect of temperature on skeletal muscle energy turnover during dynamic knee-extensor exercise in humans.

The present study examined the effect of elevated temperature on muscle energy turnover during dynamic exercise. Nine male subjects performed 10 min of dynamic knee-extensor exercise at an intensity of 43 W (SD 10) and a frequency of 60 contractions per minute. Exercise was performed under normal (C) and elevated muscle temperature (HT) through passive heating. Thigh oxygen uptake (V(O2)) was determined from measurements of thigh blood flow and femoral arterial-venous differences for oxygen content. Anaerobic energy turnover was estimated from measurements of lactate release as well as muscle lactate accumulation and phosphocreatine utilization based on analysis of muscle biopsies obtained before and after each exercise. At the start of exercise, muscle temperature was 34.5 degrees C (SD 1.7) in C compared with 37.2 degrees C (SD 0.5) during HT (P < 0.05). Thigh V(O2) after 3 min was 0.52 l/min (SD 0.11) in C and 0.63 l/min (SD 0.13) in HT, and at the end of exercise it was 0.60 l/min (SD 0.14) and 0.61 l/min (SD 0.10) in C and HT, respectively (not significant). Total lactate release was the same between the two temperature conditions, as was muscle lactate accumulation and PCr utilization. Total ATP production (aerobic + anaerobic) was the same between each temperature condition [505.0 mmol/kg (SD 107.2) vs. 527.1 mmol/kg (SD 117.6); C and HT, respectively]. In conclusion, within the range of temperatures studied, passively increasing muscle temperature before exercise has no effect on muscle energy turnover during dynamic exercise.

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

The effect of intense training on endothelial proliferation, capillary growth and distribution of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was examined in human skeletal muscle. Two intermittent knee extensor training protocols (at approximately 150% (Study 1) versus approximately 90% (Study 2) of leg (O(2) max)) were conducted. Muscle biopsies were obtained throughout the training periods for immunohistochemical assessment of capillarization, cell proliferation (Ki-67-positive cells), VEGF and bFGF. In Study 1, microdialysis samples were collected from the trained and untrained leg at rest and during exercise and added to endothelial cells to measure the proliferative effect. After 4 weeks of training there was a higher (P < 0.05) capillary-to-fibre ratio (Study 1: 2.4 +/- 0.1 versus 1.7 +/- 0.1) and number of Ki-67-positive cells (Study 1: 0.18 +/- 0.05 versus 0.00 +/- 0.01) than before training. Neither the location of proliferating endothelial cells nor capillarization was related to muscle fibre type. The endothelial cell proliferative effect of the muscle microdialysate increased from rest to exercise in both the untrained leg (from 262 +/- 60 to 573 +/- 87% of control perfusate) and the trained leg (from 303 +/- 75 to 415 +/- 108% of perfusate). VEGF and bFGF were localized in endothelial and skeletal muscle cells and training induced no changes in distribution. The results demonstrate that intense intermittent endurance training induces capillary growth and a transient proliferation of endothelial cells within 4 weeks, with a similar growth occurring around type I versus type II muscle fibres.

Effect of ribose supplementation on resynthesis of adenine nucleotides after intense intermittent training in humans.

The effect of oral ribose supplementation on the resynthesis of adenine nucleotides and performance after 1 wk of intense intermittent exercise was examined. Eight subjects performed a random double-blind crossover design. The subjects performed cycle training consisting of 15 x 10 s of all-out sprinting twice per day for 7 days. After training the subjects received either ribose (200 mg/kg body wt; Rib) or placebo (Pla) three times per day for 3 days. An exercise test was performed at 72 h after the last training session. Immediately after the last training session, muscle ATP was lowered (P < 0.05) by 25 +/- 2 and 22 +/- 3% in Pla and Rib, respectively. In both Pla and Rib, muscle ATP levels at 5 and 24 h after the exercise were still lower (P < 0.05) than pretraining. After 72 h, muscle ATP was similar (P > 0.05) to pretraining in Rib (24.6 +/- 0.6 vs. 26.2 +/- 0.2 mmol/kg dry wt) but still lower (P < 0.05) in Pla (21.1 +/- 0.5 vs. 26.0 +/- 0.2 mmol/kg dry wt) and higher (P < 0.05) in Rib than in Pla. Plasma hypoxanthine levels after the test performed at 72 h were higher (P < 0.05) in Rib compared with Pla. Mean and peak power outputs during the test performed at 72 h were similar (P > 0.05) in Pla and Rib. The results support the hypothesis that the availability of ribose in the muscle is a limiting factor for the rate of resynthesis of ATP. Furthermore, the reduction in muscle ATP observed after intense training does not appear to be limiting for high-intensity exercise performance.

Allantoin formation and urate and glutathione exchange in human muscle during submaximal exercise.

Seven males performed two exhaustive cycling bouts (EX1 and EX2) at a work-rate of 90% of maximal oxygen uptake, separated by 60 min. During EX1 there was a significant accumulation of urate (from 0.16 +/- 0.02 to 0.27 +/- 0.03 micromol/kg d.w.) and allantoin (from 0.39 +/- 0.05 to 0.69 +/- 0.14 micromol/kg d.w.) in the muscle. An uptake of urate was observed in early recovery from EX1 (0-9 min: 486 +/- 136 micromol; p <.05). There was no exchange of total glutathione or cysteine over the muscle either during or after exercise, and muscle and plasma total glutathione remained unaltered (p <.05). The glycogen levels were lowered by 40% at the onset of EX2, yet the level of oxidative stress in EX1 and EX2 was similar as evidenced by a similar increase in muscle allantoin in both exercise bouts. The data suggest that urate is utilized as antioxidant in human skeletal muscle and that reactive oxygen species are formed in muscle during intense submaximal exercise. No net exchange of glutathione appears to occur over the muscle either at rest, during exercise or in recovery. Moreover, when an exhaustive exercise bout is repeated with lowered glycogen levels, the level of oxidative stress is not different than that of the first bout.

The effect of high-intensity exhaustive exercise studied in isolated mitochondria from human skeletal muscle.

Six young men performed five 1-min bicycle exercise bouts to exhaustion. Muscle lactate increased to congruent with 114 mmol x kg(-1) dwt and pH decreased to congruent with 6.6. Mitochondria were prepared from a needle biopsy sample taken from m. vastus lateralis immediately after the last exercise bout. No significant effect of exhaustion on the proton permeability and amount of cytochromes c and aa3 in isolated mitochondria was detected. The activities of the following enzymes and systems were not altered either: citrate synthase, succinate dehydrogenase, cytochrome oxidase, succinate + glutamate respiration, malate + glutamate respiration, the respiratory chain, and the reactions involved in ATP synthesis. Thus, the mitochondria did not appear globally altered upon exhaustion. However, the following NAD-linked activities were significantly lowered: pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, glutamate dehydrogenase and fatty acid beta-oxidation. The activities of alpha-glycerophosphate dehydrogenase and exo-NADH oxidase, enzymes that might catalyze the oxidation of sarcoplasmic NADH, were increased. These changes may be due to the action of reactive oxygen species, protons and Ca2+. Transient opening of the permeability transition pore may also be involved. Some effects may have been reversed during isolation of the mitochondria and the changes in mitochondrial function in situ upon exhaustion may have been more extensive than observed.

Muscle oxygen uptake and energy turnover during dynamic exercise at different contraction frequencies in humans.

1. It has been established that pulmonary oxygen uptake is greater during cycle exercise in humans at high compared to low contraction frequencies. However, it is unclear whether this is due to more work being performed at the high frequencies and whether the energy turnover of the working muscles is higher. The present study tested the hypothesis that human skeletal muscle oxygen uptake and energy turnover are elevated during exercise at high compared to low contraction frequency when the total power output is the same. 2. Seven subjects performed single-leg dynamic knee-extensor exercise for 10 min at contraction frequencies of 60 and 100 r.p.m. where the total power output (comprising the sum of external and internal power output) was matched between frequencies (54 +/- 5 vs. 56 +/- 5 W; mean +/- S.E.M.). Muscle oxygen uptake was determined from measurements of thigh blood flow and femoral arterial - venous differences for oxygen content (a-v O(2) diff). Anaerobic energy turnover was estimated from measurements of lactate release and muscle lactate accumulation as well as muscle ATP and phosphocreatine (PCr) utilisation based on analysis of muscle biopsies obtained before and after each exercise bout. 3. Whilst a-v O(2) diff was the same between contraction frequencies during exercise, thigh blood flow was higher (P < 0.05) at 100 compared to 60 r.p.m. Thus, muscle V(O2) was higher (P < 0.05) during exercise at 100 r.p.m. Muscle V(O2) increased (P < 0.05) by 0.06 +/- 0.03 (12 %) and 0.09 +/- 0.03 l min(-1) (14 %) from the third minute to the end of exercise at 60 and 100 r.p.m., respectively, but there was no difference between the two frequencies. 4. Muscle PCr decreased by 8.1 +/- 1.7 and 9.1 +/- 2.0 mmol (kg wet wt)(-1), and muscle lactate increased to 6.8 +/- 2.1 and 9.8 +/- 2.5 mmol (kg wet wt)(-1) during exercise at 60 and 100 r.p.m., respectively. The total release of lactate during exercise was 48.7 +/- 8.8 and 64.3 +/- 10.6 mmol at 60 and 100 r.p.m. (not significant, NS). The total anaerobic ATP production was 47 +/- 8 and 61 +/- 12 mmol kg(-1), respectively (NS). 5. Muscle temperature increased (P < 0.05) from 35.8 +/- 0.3 to 38.2 +/- 0.2 degrees C at 60 r.p.m. and from 35.9 +/- 0.3 to 38.4 +/- 0.3 degrees C at 100 r.p.m. Between 1 and 7 min muscle temperature was higher (P < 0.05) at 100 compared to 60 r.p.m. 6. The estimated mean rate of energy turnover during exercise was higher (P < 0.05) at 100 compared to 60 r.p.m. (238 +/- 16 vs. 194 +/- 11 J s(-1)). Thus, mechanical efficiency was lower (P < 0.05) at 100 r.p.m. (24 +/- 2 %) compared to 60 r.p.m. (28 +/- 3 %). Correspondingly, efficiency expressed as work per mol ATP was lower (P < 0.05) at 100 than at 60 r.p.m. (22.5 +/- 2.1 vs. 26.5 +/- 2.5 J (mmol ATP)(-1)). 7. The present study showed that muscle oxygen uptake and energy turnover are elevated during dynamic contractions at a frequency of 100 compared with 60 r.p.m. It was also observed that muscle oxygen uptake increased as exercise progressed in a manner that was not solely related to the increase in muscle temperature and lactate accumulation.

ATP production and efficiency of human skeletal muscle during intense exercise: effect of previous exercise.

The aim of the present study was to examine whether ATP production increases and mechanical efficiency decreases during intense exercise and to evaluate how previous exercise affects ATP turnover during intense exercise. Six subjects performed two (EX1 and EX2) 3-min one-legged knee-extensor exercise bouts [66.2 +/- 3.9 and 66.1 +/- 3.9 (+/-SE) W] separated by a 6-min rest period. Anaerobic ATP production, estimated from net changes in and release of metabolites from the active muscle, was 3.5 +/- 1.2, 2.4 +/- 0.6, and 1.4 +/- 0.2 mmol ATP x kg dry wt(-1) x s(-1) during the first 5, next 10, and remaining 165 s of EX1, respectively. The corresponding aerobic ATP production, determined from muscle oxygen uptake, was 0.7 +/- 0.1, 1.4 +/- 0.2, and 4.7 +/- 0.4 mmol ATP x kg dry wt(-1) x s(-1), respectively. The mean rate of ATP production during the first 5 s and next 10 s was lower (P < 0.05) than during the rest of the exercise (4.2 +/- 1.2 and 3.8 +/- 0.7 vs. 6.1 +/- 0.3 mmol ATP x kg dry wt(-1) x s(-1)). Thus mechanical efficiency, expressed as work per ATP produced, was lowered (P < 0.05) in the last phase of exercise (39.6 +/- 6.1 and 40.7 +/- 5.8 vs. 25.0 +/- 1.3 J/mmol ATP). The anaerobic ATP production was lower (P < 0.05) in EX2 than in EX1, but the aerobic ATP turnover was higher (P < 0.05) in EX2 than in EX1, resulting in the same muscle ATP production in EX1 and EX2. The present data suggest that the rate of ATP turnover increases during intense exercise at a constant work rate. Thus mechanical efficiency declines as intense exercise is continued. Furthermore, when intense exercise is repeated, there is a shift toward greater aerobic energy contribution, but the total ATP turnover is not significantly altered.