Differential effects of training on the control of skeletal muscle perfusion

Exercise-induced changes in lower limbs skin temperature against plasma ATP among individuals with various type and level of physical activity

The objective of the study was to examine the lower limbs skin temperature (TSK) changes in response to exhaustive whole-body exercise in trained individuals in reference to changes in plasma adenosine triphosphate (ATP). Eighteen trained participants from distinct sport type ‒ endurance (25.2 ± 4.9 yr) and speed-power (25.8 ± 3.1 yr), and 9 controls (24,9 ± 4,3 yr) ‒ were examined. Lower limbs TSK and plasma ATP measures were applied in parallel in response to incremental treadmill test and during 30-min recovery period. Plasma ATP kinetics were inversely associated to changes in TSK. The first significant decrease in TSK (76-89% of V˙ O2MAX) occurred shortly before a significant plasma ATP increase (86-97% of V˙ O2MAX). During recovery, TSK increased, reaching pre-exercise values (before exercise vs. after 30-min recovery: 31.6 ± 0.4 °C vs. 32.0 ± 0.8 °C, p = 0.855 in endurance; 32.4 ± 0.5 °C vs. 32.9 ± 0.5 °C, p = 0.061 in speed-power; 31.9 ± 0.7 °C vs. 32.4 ± 0.8 °C, p = 0.222 in controls). Plasma ATP concentration did not returned to pre-exercise values in well trained participants (before exercise vs. after 30-min recovery: 699 ± 57 nmol l-1 vs. 854 ± 31 nmol l-1, p < 0.001, η2 = 0.961 and 812 ± 35 nmol l-1 vs. 975 ± 55 nmol l-1, p < 0.001, η2 = 0.974 in endurance and speed-power, respectively), unlike in controls (651 ± 40 nmol l-1 vs. 687 ± 61 nmol·l-1, p = 0.58, η2 = 0.918). The magnitude of TSK and plasma ATP response differed between the groups (p < 0.001, η2 = 0.410 for TSK; p < 0.001, η2 = 0.833 for plasma ATP). We conclude that lower limbs TSK change indirectly corresponds to the reverse course of plasma ATP during incremental exercise and the magnitude of the response depends on the level of physical activity and the associated to it long-term metabolic adaptation.

Maternal physical activity affects yolk sac size and growth in early pregnancy, but girls and boys use different strategies

This longitudinal study investigated the impact of actigraphy-measured maternal physical activity on yolk sac size during early development. The yolk sac, a transient extraembryonic organ, plays a crucial role in embryonic development and is involved in metabolism, nutrition, growth, and hematopoiesis. Prospectively collected data from 190 healthy women indicated that their total daily physical activity, including both light and moderate-vigorous activity, was associated with yolk sac growth dynamics depending on embryonic sex and gestational age. Higher preconception maternal physical activity was linked to a larger yolk sac at 7 weeks (95% CI [0.02-0.13 mm]) and a smaller yolk sac at 10 weeks' gestation (95% CI [- 0.18 to - 0.00]) in male embryos; in female embryos, the yolk sac size was increased at 10 weeks' gestation (95% CI [0.06-0.26]) and was, on average, 24% larger than that in male embryos (95% CI [0.12-0.38]). Considering the pattern of other maternal effects on yolk sac size-e.g., body composition and sleep duration-we suggest that physiological yolk sac adaptations occur in short, sex-specific time windows and can be influenced by various maternal factors.

Cardiovascular responses of exercises performed within the extreme exercise domain

Stroke volume (SV), heart rate (HR) and arterio-venous O2 difference (a-vO2diff) responses to heavy and severe-intensity exercise have been well documented; however, there is a lack of information on the SV, HR and a v-O2diff responses of work rates within extreme exercise domain. The aim of this study was, therefore, to focus on central and peripheral components of VO2 responses to exercises performed within the heavy, severe and extreme exercise domain. Eight well-trained male cyclists participated in this study. Maximal O2 consumption (VO2max) and corresponding work rate (P@VO2max) were determined by multisession constant work rate exercises. Cardiovascular responses to exercises were evaluated by nitrous-oxide rebreathing method with work rates from 40 % to 160 % of P@VO2max, VO2max corresponded to 324+/-39.4 W; however, maximal SV responses occurred at 205+/-54.3 W (p<0.01). Maximal cardiac output (Q), HR, and a vO2diff responses were revealed by the P@VO2max. VO2 response to exercise significantly decreased from severe-intense exercises to the first work rate of extreme exercise domain due to significant decreases in Q, SV, and HR responses (p<0.05), except a v-O2diff (p>0.05). Moreover, non-significant decreases in Q, SV, and a v-O2diff were evaluated as response to increase in work rate belonging to extreme work rates (p>0.05), except the HR (p<0.05). Work rates within the lower district of the extreme exercise domain have an important potential to improve peripheral component of VO2, while the P@VO2max seems the most appropriate intensity for aerobic endurance development as it maximizes the central component of VO2max.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

Acute (-)-Epicatechin Consumption: Effects on Local Vasodilation Following Resistance Exercise and High-Intensity Exercise Performance

(-)-Epicatechin is a polyphenol previously shown to enhance vascular health. The purposes of the current studies were to determine the effect of acute (-)-epicatechin supplementation on local vasodilation in conjunction with resistance exercise (study 1) and on high-intensity exercise performance (study 2). For study 1, 11 men participated in two resistance exercise sessions, where they performed three sets of barbell curls while consuming 200 mg of 98% pure (-)-epicatechin or placebo. Measurements of total serum nitrate/nitrite and brachial artery diameter were acquired at baseline (pre-supplement), 90 min after supplement consumption (post-supplement), immediately post-exercise (post-exercise), and 30 min post-exercise (30 min post-exercise). For serum nitric oxide metabolites, no significant interaction between supplement and time nor significant main effect of time was observed (p = 0.38 and p = 0.20; respectively). For brachial artery diameter, no significant interaction between supplement and time was observed (p = 0.24). A significant main effect of time was observed for brachial artery diameter (p < 0.01) with post-exercise brachial artery diameter significantly greater diameter than all other time points (all p < 0.01). For study 2, six women and five men completed the 15.5 CrossFit^® Open Workout three times. A familiarization session was performed first where the workout was performed without the consumption of a supplement. In a randomized, balanced fashion, 100 mg of 98% pure (-)-epicatechin or cellulose (placebo) was consumed two times per day for two days before testing sessions two and three. On the day of testing sessions two and three, 60 to 90 min before completing the workout, 200 mg of the assigned supplement was ingested with water. No significant difference was observed for time to complete the workout between testing sessions (p = 0.49). In conclusion, under the conditions of the current studies, acute (-)-epicatechin supplementation did not augment vasodilation in combination with resistance exercise, nor did it increase exercise performance in humans.

Cycle Training improves vascular function and neuropathic symptoms in patients with type 2 diabetes and peripheral neuropathy: A randomized controlled trial

Diabetic peripheral neuropathy (DPN) is associated with peripheral arterial disease and endothelial dysfunction. We investigated the effect of exercise training on the measures of superficial femoral artery (SFA) and neuropathic symptoms in patients with DPN. In a randomized-controlled trial, 31 volunteers with established DPN were randomly assigned to experimental or control groups. Experimental group performed cycling exercise training (50%-70% of heart rate reserve, 30-45 min, 3 sessions/week) over 12 weeks. Before and 48 h after the experimental period a 5-min flow mediated dilation (FMD) response in SFA using Color Doppler Ultrasonography, fasting glucose level, HbA1c and neuropathic score were assessed. FMD% significantly increased in the experimental group (from 3.2 ± 1.1% to 5.7 ± 1.2%) compared to the control condition (P = 0.0001). However, no significant alteration occurred in baseline membrane diameter and intima media thickness (P > 0.05). We also observed a significant improvement in fasting glucose, HbA1c and Michigan Diabetic Neuropathy Score (MDNS) following exercise intervention (all P < 0.05). Linear regression analysis indicated that the change in MDNS was significantly associated with the change in HbA1c (R Square = 0.34, standardized coefficients Beta = -0.58, P = .001) and FMD (R Square = 0.37, standardized coefficients Beta = 0.61, P = .001). This finding may be clinically of considerable importance as metabolic and vascular factors have been indicated to be involved in the development of DPN.

β-Adrenoreceptors do not oppose sympathetic vasoconstriction in resting and contracting skeletal muscle of male rats

Sympathetic nervous system (SNS) vasoconstriction is primarily achieved through the binding of norepinephrine (NE) to α-adrenoreceptors. However, NE may also bind to β-adrenoreceptors and cause vasodilation that may oppose/blunt SNS-mediated vasoconstriction. Therefore, this study investigated the hypothesis that β-adrenoreceptor–mediated vasodilation opposes evoked vasoconstriction in resting and contracting skeletal muscle. Male (n = 9) Sprague–Dawley rats were anesthetized and surgically instrumented for stimulation of the lumbar sympathetic chain and measurement of arterial blood pressure and femoral artery blood flow. The percentage change of femoral vascular conductance in response to sympathetic chain stimulation delivered at 2 and 5 Hz was determined at rest and during triceps surae skeletal muscle contraction before (control) and after β-adrenoreceptor blockade (propranolol; 0.075 mg·kg−1, intravenously). β-Adrenoreceptor blockade did not alter (P > 0.05) baseline hemodynamics or the hyperemic response to exercise. At the 2 Hz stimulation frequency, sympathetic vasoconstriction was similar (P > 0.05) in control and β-blockade conditions in resting (control, −34% ± 6%; β-blockade, −33% ± 8%) and contracting (control, −16% ± 6%; β-blockade, −14% ± 7%) muscle. At the 5 Hz stimulation frequency, sympathetic vasoconstrictor responsiveness was reduced (main effect of drug, P < 0.05) following β-blockade (rest: control, −52% ± 7%; β-blockade, −51% ± 9%; contraction: control, −32% ± 11%; β-blockade, −29% ± 13%).

Novelty These data indicate that β-adrenoreceptor blockade did not augment sympathetic vasoconstriction at rest or during exercise. The study demonstrates that β-adrenoreceptors do not oppose evoked sympathetic vasoconstriction in resting or contracting skeletal muscle or contribute to functional sympatholysis.

Expert's Choice: 2018's Most Exciting Research in the Field of Pediatric Exercise Science

This commentary highlights 23 noteworthy publications from 2018, selected by leading scientists in pediatric exercise science. These publications have been deemed as significant or exciting in the field as they (a) reveal a new mechanism, (b) highlight a new measurement tool, (c) discuss a new concept or interpretation/application of an existing concept, or (d) describe a new therapeutic approach or clinical tool in youth. In some cases, findings in adults are highlighted, as they may have important implications in youth. The selected publications span the field of pediatric exercise science, specifically focusing on: aerobic exercise and training; neuromuscular physiology, exercise, and training; endocrinology and exercise; resistance training; physical activity and bone strength; growth, maturation, and exercise; physical activity and cognition; childhood obesity, physical activity, and exercise; pulmonary physiology or diseases, exercise, and training; immunology and exercise; cardiovascular physiology and disease; and physical activity, inactivity, and health.

Exercise as a therapeutic intervention to optimize fetal weight

The Developmental Origins of Health and Disease suggest the in utero environment programs offspring obesity and cardiovascular disease. Therefore, there is a need to implement safe therapeutic interventions that do not involve the intake of medications or biological products during pregnancy that can improve maternal and fetal health. Prenatal exercise is established to promote maternal and fetal health. It is generally recommended that women accumulate at least 150 min per week of moderate-intensity exercise. It has been demonstrated that prenatal exercise maintains healthy weight gain and improves maternal glucose control, maternal cardiac autonomic control, placental efficiency (increases angiogenesis, downregulates genes involved in fatty acid transport and insulin transport across the placenta, and upregulates genes involved in amino acid transport across the placenta), and oxidative stress. These adaptations following exercise improve maternal metabolism and provide adequate uteroplacental perfusion. In this review, we will focus on exercise as a therapeutic intervention to optimize fetal weight. It has been established that prenatal exercise does not increase the risk of having a small for gestational age baby. To the contrary, prenatal exercise has been associated with the prevention of excessive fat accumulation in the newborn and the maintenance of fetal muscle mass.

Attenuation of Adverse Effects of Aging on Skeletal Muscle by Regular Exercise and Nutritional Support

Beginning early in midlife, natural/primary aging is inevitably associated with a progressive reduction in muscle mass and function. This process can progress with aging to a substantial loss of strength, particularly in the lower extremities, reducing mobility. This condition, commonly referred to as sarcopenia, can result in frailty, reducing one's ability to live independently. This article reviews the underlying biological process contributing to the development of sarcopenia and the roles of regular exercise and nutritional support for attenuating aging-associated muscle loss as well as risk and management of sarcopenia and associated frailty.

Endurance training attenuates the increase in peripheral chemoreflex sensitivity with intermittent hypoxia

Patients with heart failure and sleep apnea have greater chemoreflex sensitivity, presumably due to intermittent hypoxia (IH), and this is predictive of mortality. We hypothesized that endurance training would attenuate the effect of IH on peripheral chemoreflex sensitivity in healthy humans. Fifteen young healthy subjects (9 female, 26 ± 1 yr) participated. Between visits, 11 subjects underwent 8 wk of endurance training that included running four times/wk at 80% predicted maximum heart rate and interval training, and four control subjects did not change activity. Chemoreflex sensitivity (the slope of ventilation responses to serial oxygen desaturations), blood pressure, heart rate, and muscle sympathetic nerve activity (MSNA) were assessed before and after 30 min of IH. Endurance training decreased resting systolic blood pressure (119 ± 3 to 113 ± 3 mmHg; P = 0.027) and heart rate (67 ± 3 to 61 ± 2 beats/min; P = 0.004) but did not alter respiratory parameters at rest (P > 0.2). Endurance training attenuated the IH-induced increase in chemoreflex sensitivity (pretraining: Δ 0.045 ± 0.026 vs. posttraining: Δ -0.028 ± 0.040 l·min^-1·% O₂ desaturation^-1; P = 0.045). Furthermore, IH increased mean blood pressure and MSNA burst rate before training (P < 0.05), but IH did not alter these measures after training (P > 0.2). All measurements were similar in the control subjects at both visits (P > 0.05). Endurance training attenuates chemoreflex sensitization to IH, which may partially explain the beneficial effects of exercise training in patients with cardiovascular disease.

Vascular function and brain-derived neurotrophic factor: The functional capacity factor

Brain-derived neurotrophic factor (BDNF) is essential for neurocognitive function. This study aims at establishing a plausible link between level of serum BDNF, functional capacity (FC), and vascular function in 181 young (age 25.5±9.1 years old), apparently healthy adults. Fasting blood samples were drawn from participants' antecubital veins into plain glass tubes while they were in a sitting position to evaluate serum BDNF using enzyme-linked immunosorbent assay (ELISA). Mercury-in-silastic strain-gauge plethysmography was used to determine arterial function indices, blood flow and vascular resistance at rest and following 5 minutes of arterial ischemia. The 6-minute walk distance (6MWD) test was used to determine FC, according to the American Thoracic Society Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories guidelines. It was conducted in an enclosed corridor on a flat surface with a circular track 33 meters long. The walking course was demarcated with bright colored cones. The 6MWD correlated with BDNF (r=0.3, p=0.000), as well as with forearm blood inflow (r=0.5, p=0.000) and vascular resistance (r = -0.4, p=0.000). Subsequent comparison showed that BDNF and blood inflow were greater (p<0.05) while vascular resistance was less (p<0.05) in participants who achieved a longer 6MWD. Similarly, BDNF correlated with forearm blood inflow (r=0.4, p=0.000) and vascular resistance (r = -0.4, p=0.000). Subsequent comparison showed improved vascular function (p<0.05) in the participants with greater BDNF. In conclusion, these findings might suggest that improved vascular function in individuals with greater FC is mediated, at least partially, by an enhanced serum BDNF level.

Highly athletic terrestrial mammals: horses and dogs

Evolutionary forces drive beneficial adaptations in response to a complex array of environmental conditions. In contrast, over several millennia, humans have been so enamored by the running/athletic prowess of horses and dogs that they have sculpted their anatomy and physiology based solely upon running speed. Thus, through hundreds of generations, those structural and functional traits crucial for running fast have been optimized. Central among these traits is the capacity to uptake, transport and utilize oxygen at spectacular rates. Moreover, the coupling of the key systems--pulmonary-cardiovascular-muscular is so exquisitely tuned in horses and dogs that oxygen uptake response kinetics evidence little inertia as the animal transitions from rest to exercise. These fast oxygen uptake kinetics minimize Intramyocyte perturbations that can limit exercise tolerance. For the physiologist, study of horses and dogs allows investigation not only of a broader range of oxidative function than available in humans, but explores the very limits of mammalian biological adaptability. Specifically, the unparalleled equine cardiovascular and muscular systems can transport and utilize more oxygen than the lungs can supply. Two consequences of this situation, particularly in the horse, are profound exercise-induced arterial hypoxemia and hypercapnia as well as structural failure of the delicate blood-gas barrier causing pulmonary hemorrhage and, in the extreme, overt epistaxis. This chapter compares and contrasts horses and dogs with humans with respect to the structural and functional features that enable these extraordinary mammals to support their prodigious oxidative and therefore athletic capabilities.

Short-term training alters the control of mitochondrial respiration rate before maximal oxidative ATP synthesis

AIM

Short-term exercise training may induce metabolic and performance adaptations before any changes in mitochondrial enzyme potential. However, there has not been a study that has directly assessed changes in mitochondrial oxidative capacity or metabolic control as a consequence of such training in vivo. Therefore, we used (31) P-magnetic resonance spectroscopy ((31) P-MRS) to examine the effect of short-term plantar flexion exercise training on phosphocreatine (PCr) recovery kinetics and the control of respiration rate.

METHOD

To this aim, we investigated 12 healthy men, experienced with this exercise modality (TRA), and 7 time-control subjects (TC).

RESULTS

After 5 days of training, maximum work rate during incremental plantar flexion exercise was significantly improved (P < 0.01). During the recovery period, the maximal rate of oxidative adenosine triphosphate synthesis (PRE: 28 ± 13 mm min(-1) ; POST: 26 ± 15 mm min(-1) ) and the PCr recovery time constant (PRE: 31 ± 19 s; POST: 29 ± 16) were not significantly altered. In contrast, the Hill coefficient (nH ) describing the co-operativity between respiration rate and ADP was significantly increased in TRA (PRE: nH = 2.7 ± 1.4; POST: nH = 3.4 ± 1.9, P < 0.05). Meanwhile, there were no systematic variations in any of these variables in TC.

CONCLUSION

This study reveals that 5 days of training induces rapid adaptation in the allosteric control of respiration rate by ADP before any substantial improvement in muscle oxidative capacity occurs.

Short-term exercise training enhances functional sympatholysis through a nitric oxide-dependent mechanism

We tested the hypothesis that short-term mild- (M) and heavy-intensity (H) exercise training would enhance sympatholysis through a nitric oxide (NO)-dependent mechanism. Sprague-Dawley rats (n = 36) were randomly assigned to sedentary (S) or to M (20 m min(-1) 5% gradient) or H exercise training groups (40 m min(-1) 5% gradient). Rats assigned to M and H groups trained on 5 days week(-1) for 4 weeks, with the volume of training being matched between groups. Rats were anaesthetized and instrumented for stimulation of the lumbar sympathetic chain and the measurement of arterial blood pressure and femoral artery blood flow. The triceps surae muscle group was stimulated to contract rhythmically at 30 and 60% of maximal contractile force (MCF). The percentage change of femoral vascular conductance (%FVC) in response to sympathetic stimulation delivered at 2 and 5 Hz was determined at rest and during contraction at 30 and 60% MCF. The vascular response to sympathetic stimulation was reduced as a function of MCF in all rats (P < 0.05). At 30% MCF, the magnitude of sympatholysis (%FVC rest - contraction; %FVC) was greater in H compared with M and S groups (%FVC at 2 Hz, S, 9 ± 5; M, 11 ± 8; and H, 18 ± 7; and %FVC at 5 Hz, S, 6 ± 6; M, 12 ± 9; and H, 18 ± 7; P < 0.05) and was greater in H and M compared with S at 60% MCF (%FVC at 2 Hz, S, 15 ± 5; M, 25 ± 3; and H, 36 ± 6; and %FVC at 5 Hz, S, 22 ± 6; M, 33 ± 9; and H, 39 ± 9; P < 0.05). Blockade of NO synthase did not alter the magnitude of sympatholysis in S during contraction at 30 or 60% MCF. In contrast, NO synthase inhibition diminished sympatholysis in H at 30% MCF and in M and H at 60% MCF (P < 0.05). The present findings indicate that short-term exercise training augments sympatholysis in a training-intensity-dependent manner and through an NO-dependent mechanism.

A Mechanism-Based Approach to Prevention of and Therapy for Fibromyalgia

Fibromyalgia syndrome (FMS) is characterized by pain referred to deep tissues. Diagnosis and treatment of FMS are complicated by a variable coexistence with regional pain, fatigue, sleep disruption, difficulty with mentation, and depression. The widespread, deep pain of FMS can be a consequence of chronic psychological stress with autonomic dysregulation. Stress acts centrally to facilitate pain and acts peripherally, via sympathetic vasoconstriction, to establish painful muscular ischemia. FMS pain, with or without a coexistent regional pain condition, is stressful, setting up a vicious circle of reciprocal interaction. Also, stress interacts reciprocally with systems of control over depression, mentation, and sleep, establishing FMS as a multiple-system disorder. Thus, stress and the ischemic pain it generates are fundamental to the multiple disorders of FMS, and a therapeutic procedure that attenuates stress and peripheral vasoconstriction should be highly beneficial for FMS. Physical exercise has been shown to counteract peripheral vasoconstriction and to attenuate stress, depression, and fatigue and improve mentation and sleep quality. Thus, exercise can interrupt the reciprocal interactions between psychological stress and each of the multiple-system disorders of FMS. The large literature supporting these conclusions indicates that exercise should be considered strongly as a first-line approach to FMS therapy.

Short-term exercise training augments sympathetic vasoconstrictor responsiveness and endothelium-dependent vasodilation in resting skeletal muscle

We tested the hypotheses that 4 wk of exercise training would diminish the magnitude of vasoconstriction in response to sympathetic nerve stimulation and augment endothelium-dependent vasodilation (EDD) in resting skeletal muscle in a training intensity-dependent manner. Sprague-Dawley rats were randomly assigned to sedentary time-control (S), mild- (M; 20 m/min, 5% grade), or heavy-intensity (H; 40 m/min, 5% grade) treadmill exercise groups. Animals trained 5 days/wk for 4 wk with training volume matched between groups. Rats were anesthetized and instrumented for study 24 h after the last training session. Arterial pressure and femoral artery blood flow were measured, and femoral vascular conductance (FVC) was calculated. Lumbar sympathetic chain stimulation was delivered continuously at 2 Hz and in patterns at 20 and 40 Hz. EDD was assessed by the vascular response to intra-arterial bolus injections of ACh. The response (% change FVC) to sympathetic stimulation increased ( P < 0.05) in a training intensity-dependent manner at 2 Hz (S: −20.2 ± 9.8%, M: −34.0 ± 6.7%, and H: −44.9 ± 2.0%), 20 Hz (S: −22.0 ± 10.6%, M: −31.2 ± 8.4%, and H: −42.8 ± 5.9%), and 40 Hz (S: H −24.5 ± 8.5%, M: −35.1 ± 8.9%, H: −44.9 ± 6.5%). The magnitude of EDD also increased in a training intensity-dependent manner ( P < 0.05). These data demonstrate that short-term exercise training augments the magnitude of vasoconstriction in response to sympathetic stimulation and EDD in resting skeletal muscle in a training intensity-dependent manner.

The clinical and nonclinical values of nonexercise estimation of cardiovascular endurance in young asymptomatic individuals

Exercise testing is associated with barriers prevent using cardiovascular (CV) endurance (CVE) measure frequently. A recent nonexercise model (NM) is alleged to estimate CVE without exercise. This study examined CVE relationships, using the NM model, with measures of obesity, physical fitness (PF), blood glucose and lipid, and circulation in 188 asymptomatic young (18–40 years) adults. Estimated CVE correlated favorably with measures of PF (r = 0.4 − 0.5) including handgrip strength, distance in 6 munities walking test, and shoulder press, and leg extension strengths, obesity (r = 0.2 − 0.7) including % body fat, body water content, fat mass, muscle mass, BMI, waist and hip circumferences and waist/hip ratio, and circulation (r = 0.2 − 0.3) including blood pressures, blood flow, vascular resistance, and blood (r = 0.2 − 0.5) profile including glucose, total cholesterol, LDL-C, HDL-C, and triglycerides. Additionally, differences (P < 0.05) in examined measures were found between the high, average, and low estimated CVE groups. Obviously the majority of these measures are CV disease risk factors and metabolic syndrome components. These results enhance the NM scientific value, and thus, can be further used in clinical and nonclinical settings.

Decreased muscle blood flow in fibromyalgia patients during standardised muscle exercise: A contrast media enhanced colour doppler study

The aim of the study was to investigate if contrast enhanced ultrasound (US) imaging of muscular blood flow during and following exercise could detect alterations in vascularity in fibromyalgia (FM) patients. Ten FM patients and 10 matched controls were examined with US during standardised static and directly following static and dynamic muscular contractions of the infraspinatus muscle. Doppler ultrasound evaluation was performed before and after the administration of ultrasound contrast media. The FM patients had lower magnitude of muscle vascularity following dynamic (p<0.001) and during (p<0.002) static exercise compared to controls. The immediate flow response to muscular activity was not only of a lower magnitude, but also of a shorter duration in FM patients following dynamic exercise (p<0.001) and during static exercise (p<0.01). There were no statistically significant group differences in blood flow intensity or duration following static contraction. In conclusion, contrast enhanced US was found useful to study real-time muscle blood flow changes during and following standardised, low-intensity exercise in FM patients and healthy controls. Our results support the suggestion that muscle ischemia can contribute to pain in FM, possibly by maintaining the central nervous changes such as central sensitisation/disinhibition. US with contrast can be a new valuable approach to assess muscle perfusion in pain patients during standardised exercise.

Blood pressure and circulatory relationships with physical activity level in young normotensive individuals: IPAQ validity and reliability considerations

Physical activity (PA) reduces risk of cardiovascular diseases, including hypertension. However, the international physical activity questionnaire (IPAQ) relationships with blood pressure (BP) and flow (BF) and vascular resistance (VR) in healthy young individuals have not been studied. Therefore, BP, BF, and VR relationships with the IPAQ were evaluated in college normotensive students (18-23 yrs). Additionally, the IPAQ relationships with body fat (%BF), muscle mass (MM), body mass index (BMI), waist/hip (W/H) ratio, maximum walking distance in 6 min (6MWD), and handgrip strength (MHG) were examined to evaluate the questionnaire validity against fitness. Subsequently, the IPAQ was administered three times to examine its reliability. Walking, moderate, and total PAs correlated negatively with sysbolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) (range: r = -3 to -0.5, p < 0.05). Additionally, all BP measures were greater in least physically active individuals. In a subgroup of 42 students, IPAQ sitting time correlated with BF (r = -0.3) and VR (r = 0.4). The intraclass correlation coefficient (ICC) for walking, moderate, vigorous, and total PAs and sitting time/week were, 0.97, 0.96, 0.97, 0.97, and 0.96, respectively. The males scored greater vigorous PA (p = 0.001) than the females, while moderate, walking, and total PAs were the same (p > 0.05). Additionally, vigorous PA correlated with %BF (r = -0.2), MM (r = 0.3), MHG (r = 0.3), and 6MWD (r = 0.3) and total PA correlated with MM (r = 0.2), MHG (r =0.2), and 6MWD (r = 0.3). The IPAQ association with the circulatory measures demonstrates PA importance for controlling BP and adds clinical value to the IPAQ. Additionally, the IPAQ is reliable, can discriminate between populations, and reasonably valid against health-related fitness.

Rapid vascular modifications to localized rhythmic handgrip training and detraining: vascular conditioning and deconditioning

Despite the evidence describing the rapid vascular function modifications to commencement and cessation of large muscle exercises (i.e. cycling), no studies examined the time-course vascular modifications to localized training and detraining. This study aimed to examine the effects of 4-week rhythmic handgrip exercise training and 2-week detraining on reactive hyperemic forearm blood flow and vascular resistance in 11 young men. Rhythmic handgrip exercise was performed in the non-dominant forearm for 20 min/day, 5 days/week, at 60% of maximum voluntary contraction for 4 weeks, followed by 2 weeks of no training. Forearm blood flow and vascular resistance were evaluated, in both arms, at rest and following arterial occlusion. These vascular function indices were obtained in five visits; before, after 1 and 4 week(s) of training as well as after 1 and 2 week(s) of training cessation. Resting cardiovascular measures were not altered during the study period. A 2 (arms) x 5 (visits) ANOVA revealed significant arms-by-visits interactions for reactive hyperemic forearm blood flow (p = 0.02) and vascular resistance (p = 0.02). Subsequent comparison demonstrated increased trained forearm reactive hyperemic blood flow 1 week after training, then returned to pre-training values 1 week following training cessation. In contrast, vascular resistance decreased 1 week after training commencement, only to return to pretraining level 1 week after training cessation. These results indicate a rapid, unilateral improvement in regional reactive hyperemic blood flow and vascular resistance following localized exercise-training. However, the improvements are transient and return to pretraining levels 1 week after detraining.

Circulatory effects of apnoea in elite breath-hold divers

AIM

Voluntary apnoea induces several physiological adaptations, including bradycardia, arterial hypertension and redistribution of regional blood flows. Elite breath-hold divers (BHDs) are able to maintain very long apnoea, inducing severe hypoxaemia without brain injury or black-out. It has thus been hypothesized that they develop protection mechanisms against hypoxia, as well as a decrease in overall oxygen uptake.

METHODS

To test this hypothesis, the apnoea response was studied in BHDs and non-divers (NDs) during static and dynamic apnoeas (SA, DA). Heart rate, arterial oxygen saturation (SaO(2)), and popliteal artery blood flow were recorded to investigate the oxygen-conserving effect of apnoea response, and the internal carotid artery blood flow was used to examine the mechanisms of cerebral protection.

RESULTS

The bradycardia and peripheral vasoconstriction were accentuated in BHDs compared with NDs (P < 0.01), in association with a smaller SaO(2) decrease (-2.7% vs. -4.9% during SA, P < 0.01 and -6% vs. -11.3% during DA, P < 0.01). Greater increase in carotid artery blood flow was also measured during apnoea in BHDs than in controls.

CONCLUSION

These results confirm that elite divers present a potentiation of the well-known apnoea response in both SA and DA conditions. This response is associated with higher brain perfusion which may partly explain the high levels of world apnoea records.

Bioenergetic provision of energy for muscular activity

A complex series of metabolic pathways are present in human muscle that break down substrates from nutritional sources to produce energy for different types of muscular activity. However, depending on the activity in which an individual is engaged, the body will make use of different energy systems that have been adapted for the particular activity. More specifically, utilization of bioenergetic substrates depends on the type, intensity, and duration of the exercise. The aerobic oxidative system is used for longer duration activities of low to moderate intensity, the anaerobic glycolytic system is used for short to moderate duration activities of higher intensity, and the high energy phosphagen system is used for short duration activities of high intensity. The efficiency and effectiveness of these pathways can be enhanced through physical activity and training. It is these bioenergetic pathways that are the focus of this review.

Effect of Endothelin 1 Genotype on Blood Pressure Is Dependent on Physical Activity or Fitness Levels

Contributions of the DNA sequence variation at the endothelin 1 locus to the risk of hypertension and to endurance training–induced changes in blood pressure were investigated in the Aerobics Center Longitudinal Study and the Health, Risk Factors, Exercise Training and Genetics Family Study cohorts. We identified 586 normotensive control subjects and 607 incident hypertensive case subjects from the Aerobics Center Longitudinal Study cohort (all whites) who were normotensive and healthy at their first clinic visit. The case subjects were diagnosed with hypertension during an average follow-up of 9.5 years, whereas the control subjects remained normotensive. The allele and genotype frequencies of 5 endothelin 1 haplotype tagging single nucleotide polymorphisms did not differ significantly between the case and control subjects. However, we observed a significant ( P =0.0025) interaction between the endothelin 1 rs5370 (G/T; Lys198Asn) genotype and cardiorespiratory fitness level on the risk of hypertension: among low-fit subjects, the rs5370 minor allele (T; 198Asn) was associated with higher risk of hypertension (odds ratio: 1.95; 95% CI: 1.36 to 2.81; P =0.0003), whereas the risk did not differ among genotypes in high-fit subjects. In the white Health, Risk Factors, Exercise Training and Genetics subjects (N=480), the rs5370 T allele was associated with blunted systolic blood pressure ( P =0.0046) and pulse pressure ( P =0.0016) responses to a 20-week endurance training program. The Lys198Asn variant of the endothelin 1 locus is associated with blood pressure phenotypes in whites. However, the expression of the genotype effect is modulated by physical activity or cardiorespiratory fitness level. Our study provides an illustrative example of how physical activity and fitness level modifies the associations between a candidate gene and outcome phenotype.

What Maintains Energy Supply at Peak Aerobic Exercise in Trained and Untrained Older Men?

BACKGROUND

Aging-related changes occur mainly in the cardiopulmonary system and skeletal muscles, bringing about a reduction in physical performance. Consequently, maximal oxygen uptake (VO(2)max) decreases.

OBJECTIVES

The current study investigated exercise oxygen utilization during maximal aerobic exercise in trained and untrained elderly.

METHODS

Fifteen trained (59.3 +/- 1.1 years) and 15 untrained (60.1 +/- 1.1 years) elderly underwent a peak cardiopulmonary exercise test on a bicycle ergometer. Arterial O(2 )was defined from echocardiograph and venous oxygen content.

RESULTS

At rest, trained compared to untrained elderly had significantly (p < 0.05) higher values of end diastolic volume (108.1 +/- 5.8 and 100.7 +/- 6.2 ml, respectively) and stroke volume (68.1 +/- 4.3 and 57.3 +/- 6.5 ml, respectively), while heart rate (68.7 +/- 9.3 and 81.3 +/- 8.2 beats . min(-1), respectively), and mean arterial blood pressure (90.6 +/- 6.9 and 95.4 +/- 7.2 mm Hg, respectively) were significantly lower. At peak aerobic test, the trained elderly, compared to the untrained subjects, achieved significantly (p < 0.05) higher values of end diastolic volume (156.1 +/- 8.2 and 134.1 +/- 7.6 ml, respectively), stroke volume (123.0 +/- 7.9 and 96.0 +/- 4.8 ml, respectively), cardiac output (20.2 +/- 1.5 and 15.0 +/- 1.3 liters.min(-1), respectively) and oxygen uptake (42.1 +/- 2.1 and 31.1 +/- 2.4 ml.kg(-1).min(-1), respectively), while diastolic blood pressure (70.3 +/- 5.6 and 77.5 +/- 4.2 mm Hg, respectively) and total peripheral resistance [4.3 +/- 0.8 and 5.9 +/- 1.41 (dyn.s(-1).cm(-5)).10(-1), respectively], were significantly (p < 0.05) lower.

CONCLUSIONS

The present study suggests that the differences between trained and untrained elderly in absolute oxygen uptake of the working muscles and peak power output at maximal exercise test are due to physical activity status. The higher aerobic capacity in the trained elderly is related to increased cardiovascular function and to a lesser extent to increased muscle mitochondria concentration and capillarity. Although untrained elderly have reduced maximal oxygen uptake at peak aerobic exercise, intrinsic regulation of mitochondrial function does not seem to be significantly altered because of aging associated physical inactivity. Therefore, untrained elderly can partially compensate for their lower cardiac output by increasing oxygen extraction to levels comparable with those of trained elderly.

Exercise training enhances flow-induced vasodilation in skeletal muscle resistance arteries of aged rats: role of PGI2 and nitric oxide

Flow-induced vasodilation is attenuated with old age in rat skeletal muscle arterioles. The purpose of this study was to determine whether diminished cyclooxygenase (COX) signaling contributes to the age-induced attenuation of flow-induced vasodilation in gastrocnemius muscle arterioles and to determine whether, and through which mechanism(s), exercise training restores this deficit in old rats. Fischer 344 rats (3 and 22 mo old) were assigned to a sedentary or exercise-trained group. First-order arterioles were isolated from the gastrocnemius muscles, cannulated, and pressurized to 70 cm H(2)O. Diameter changes were determined in response to graded increases in intraluminal flow in the presence and absence of nitric oxide synthase (NOS) inhibition [10(-5) M N(G)-nitro-L-arginine methyl ester (L-NAME)], COX inhibition (10(-5) M indomethacin), or combination NOS (10(-5) M L-NAME) plus COX (10(-5) M indomethacin) inhibition. Aging reduced flow-induced vasodilation in gastrocnemius muscle arterioles. Exercise training restored responsiveness to flow in arterioles of aged rats and enhanced flow-induced vasodilation in arterioles from young rats. L-NAME inhibition of flow-induced vasodilation was greater in arterioles from old rats compared with those from young rats and was increased after exercise training in arterioles from both young and old rats. Although the indomethacin-sensitive portion of flow-induced dilation was not altered by age or training, both COX-1 mRNA expression and PGI(2) production increased with training in arterioles from old rats. These data demonstrate that exercise training restores flow-induced vasodilation in gastrocnemius muscle arterioles from old rats and enhances flow-induced vasodilation in gastrocnemius muscle arterioles from young rats. In arterioles from both old and young rats, the exercise training-induced enhancement of flow-induced dilation occurs primarily through a NOS mechanism.

Acute sympathetic vasoconstriction at rest and during dynamic exercise in cyclists and sedentary humans

The impact of exercise training on sympathetic activation is not well understood, especially across untrained and trained limbs in athletes. Therefore, in eight sedentary subjects (maximal oxygen consumption = 40 ± 2 ml·kg−1·min−1) and eight competitive cyclists (maximal oxygen consumption= 64 ± 2 ml·kg−1·min−1), we evaluated heart rate, blood pressure, blood flow, vascular conductance, and vascular resistance in the leg and arm during acute sympathetic stimulation [cold pressor test (CPT)]. The CPT was also performed during dynamic leg (knee extensor) or arm (handgrip) exercise at 50% of maximal work rate (WRmax) with measurements in the exercising limb. At rest, the CPT decreased vascular conductance similarly in the leg and arm of sedentary subjects (−33 ± 8% leg, −38 ± 6% arm) and cyclists (−34 ± 4% leg, −31 ± 9% arm), and during exercise CPT-induced vasoconstriction was blunted (i.e., sympatholysis) in both the leg and arm of both groups. However, the magnitude of sympatholysis was significantly different between the arm and leg of the sedentary group (−47 ± 11% arm, −25 ± 8% leg), and it was less in the arm of cyclists (−28 ± 11%) than sedentary controls. Taken together, these data provide evidence that sympathetically mediated vasoconstriction is expressed equally and globally at rest in both sedentary and trained individuals, with a differential pattern of vasoconstriction during acute exercise according to limb and exercise training status.

Regional changes in reactive hyperemic blood flow during exercise training: time-course adaptations

Background

Few studies have examined the time-course of localized exercise training on regional blood flow in humans. The study examined the influence of handgrip exercise training on forearm reactive hyperemic blood flow and vascular resistance in apparently healthy men.

Methods

Forearm blood flow and vascular resistance were evaluated, in 17 individuals [Age: 22.6 ± 3.5], in both arms, at rest and following 5 minutes of arterial occlusion, using strain gauge plethysmography, prior to training (V1) and every week thereafter (V2-5) for 4 weeks. Handgrip exercise was performed in the non-dominant arm 5 d/wk for 20 minutes at 60% of maximum voluntary contraction, while the dominant arm served as control.

Results

Resting HR, BP, and forearm blood flow and vascular resistance were not altered with training. The trained arm handgrip strength and circumference increased by 14.5% (p = 0.014) and 1.56% (p = 0.03), respectively. ANOVA tests revealed an arms by visit interaction for the trained arm for reactive hyperemic blood flow (p = 0.02) and vascular resistance (p = 0.009). Post-hoc comparison demonstrated increased reactive hyperemic blood flow (p = 0.0013), and decreased post-occlusion vascular resistance (p = 0.05), following the 1^st week of training, with no significant changes in subsequent visits.

Conclusion

The results indicate unilateral improvements in forearm reactive hyperemic blood flow and vascular resistance following 1 week of handgrip exercise training and leveled off for the rest of the study.

Ageing and exercise training alter adrenergic vasomotor responses of rat skeletal muscle arterioles

Ageing is associated with increased leg vascular resistance and reductions in leg blood flow during rest and exercise, potentially predisposing older adults to a host of functional and cardiovascular complications. The purpose of these studies was to examine the effects and possible mechanisms of ageing and exercise training on arteriolar adrenergic vasoreactivity. Young and old male Fischer 344 rats were divided into young sedentary (YS), old sedentary (OS), young exercise-trained (YT) or old exercise-trained (OT) groups, where training consisted of chronic treadmill exercise. Isolated soleus (SOL) and gastrocnemius (GAS) muscle arterioles were studied in vitro. Responses to noradrenaline in endothelium-intact and endothelium-denuded arterioles, as well as during nitric oxide synthase (NOS) inhibition were determined. Vasodilator responses to isoproterenol and forskolin were also determined.

RESULTS

Noradrenaline-mediated vasoconstriction was increased in SOL arterioles with ageing, and exercise training in old rats attenuated alpha-adrenergic vasoconstriction in arterioles from both muscle types. Removal of the endothelium and NOS inhibition eliminated these ageing and training effects. Isoproterenol-mediated vasodilatation was impaired with ageing in SOL and GAS arterioles, and exercise training had little effect on this response. Forskolin-induced vasodilatation was not affected by age. The data demonstrate that ageing augments alpha-adrenergic vasoconstriction while exercise training attenuates this response, and both of these alterations are mediated through an endothelial alpha-receptor-NOS-signalling pathway. In contrast, ageing diminishes beta-receptor-mediated vasodilatation, but this impairment is specific to the smooth muscle. These studies indicate that alpha- and beta-adrenergic mechanisms may serve to increase systemic vascular resistance with ageing, and that the effects of exercise training on adrenergic vasomotor properties could contribute to the beneficial effects of exercise on cardiovascular disease.

Mechanisms underlying development of spatially distributed chronic pain (fibromyalgia)

Chronic fibromyalgia (FM) pain is prevalent (estimated as high as 13%), predominantly affects women, and is associated with a variety of focal pain conditions. Ongoing FM pain is referred to deep tissues and is described as widespread but usually is maximally located within a restricted region such as the shoulders. Palpation of deep tissues reveals an enhanced nociceptive sensitivity that is not restricted to regions of clinical pain. Similarly, psychophysical testing reveals allodynia and hyperalgesia for cutaneous stimulation at locations beyond regions of clinical pain referral. The combination of widely distributed clinical pain and generalized hypersensitivity is highly disabling, but no satisfactory treatment is regularly prescribed. A thorough understanding of mechanisms will likely be required to develop and document adequate therapies. The generalized hypersensitivity associated with FM has focused considerable interest on central (CNS) mechanisms for the disorder. These include central sensitization, central disinhibition and a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis. However, the central effects associated with FM can be produced by a peripheral source of pain. Chronic nociceptive input induces central sensitization, magnifying pain, and it activates the HPA and the sympathetic nervous system. Chronic sympathetic activation indirectly sensitizes peripheral nociceptors and sets up a vicious cycle. Thus, it appears that central mechanisms of FM pain are dependent on abnormal peripheral input(s) for development and maintenance of this condition. A substantial literature defines peripheral-CNS-peripheral interactions that are integral to FM pain. These reciprocal actions and related phenomena of relevance to FM pain are reviewed here, leading to suggestions for testing of therapeutic approaches.

Exercise training produces nonuniform increases in arteriolar density of rat soleus and gastrocnemius muscle

OBJECTIVE

Exercise training has been shown to increase regional blood flow capacity to muscle tissue containing fibers that experience increased activity during exercise. The purpose of this study was to test the hypothesis that the increased blood flow capacity is partially the result of increases in arteriolar density (number of arterioles/mm2 of tissue), specifically in skeletal muscle tissue, with the largest relative increase in muscle fiber activity during training bouts.

METHODS

This hypothesis was tested by comparing and contrasting the effects of endurance exercise training (ET) and interval sprint training (IST) on arteriolar density in soleus muscle (S) red (Gr) and white (Gw) portions of gastrocnemius muscle of male Sprague Dawley rats. ET rats completed 10 weeks of treadmill training 30 m/min, 15% grade, 60 min/day, 5 days/week, while IST rats completed 10 weeks of IST consisting of six 2.5-min exercise bouts, with 4.5-min rest between bouts (60 m/min, 15% incline), 5 days/week. The hypothesis would be supported if ET increased arteriolar density in S and Gr and if IST increased arteriolar density in Gw.

RESULTS

ET increased arteriolar density above values of sedentary rats (SED) in both the Gw (ET = 0.93 +/- 0.19 arterioles/microm2; SED = 0.44 +/- 0.09 arterioles/microm2) and Gr (ET = 0.97 +/- 0.1 arterioles/microm2; SED = 0.51 +/- 0.06 arterioles/microm2) muscles, but not in S (ET = 1.69 +/- 0.45 arterioles/microm2; SED = 1.51 +/- 0.34 arterioles/microm2) muscle. In contrast, IST did not alter arteriolar density in Gw or Gr muscle tissue. Although arterial wall thickness was greater in S (3.95 +/- 0.40 microm) and Gr (6.24 +/- 0.59 microm) than Gw (2.76 +/- 0.18 microm), neither ET or IST altered mean wall thickness in either muscle.

CONCLUSION

Increases in blood flow capacity produced in Gr and Gw by ET appear to be due in part to increased arteriolar density. In contrast, increased arteriolar density does not contribute to increased blood flow capacity of Gw in IST rats.

Effect of endurance training on muscle microvascular filtration capacity and vascular bed morphometry in the elderly

AIM

Exercise training is a strong stimulus for vascular remodelling and could restore age-induced vascular alterations. The purpose of the study was to test the hypothesis that an increase in vascular bed filtration capacity would corroborate microvascular adaptation with training.

METHODS

We quantified (1) microvascularization from vastus lateralis muscle biopsy to measure the capillary to fibre interface (LC/PF) and (2) the microvascular filtration capacity (K(f)) in lower limbs through a venous congestion plethysmography procedure. Twelve healthy older subjects (74 +/- 4 years) were submitted to a 14-week training programme during which lower-limbs were trained for endurance exercise.

RESULTS

The training programme induced a significant increase in the aerobic exercise capacity of lower limbs (+11% V(O2peak); P < 0.05; +28% Citrate Synthase Activity; P < 0.01). K(f) was largely increased (4.3 +/- 0.9 10(-3) mL min(-1) mmHg(-1) 100 mL(-1) post-training vs. 2.4 +/- 0.8 pre-training, mean +/- SD; P < 0.05) and microvascularization developed as shown by the rise in LC/PF (0.29 +/- 0.06 post- vs. 0.23 +/- 0.06 pre-training; P < 0.05). Furthermore, K(f) and LC/PF were correlated (r = 0.65, P < 0.05).

CONCLUSION

These results demonstrated the microvascular adaptation to endurance training in the elderly. The increase in K(f) with endurance training was probably related to a greater surface of exchange with an increased microvessel/fibre interface area. We conclude that measurement of the microvascular filtration rate reflects the change in the muscle exchange area and is influenced by exercise training.

Electrically stimulated resistance training in SCI individuals increases muscle fatigue resistance but not femoral artery size or blood flow

STUDY DESIGN

Longitudinal.

OBJECTIVES

The purpose of this study was to evaluate the effect of lower extremity resistance training on quadriceps fatigability, femoral artery diameter, and femoral artery blood flow.

SETTING

Academic Institution.

METHODS

Five male chronic spinal cord injury (SCI) individuals (American Spinal Injury Association (ASIA): A complete; C5-T10; 36+/-5 years old) completed 18 weeks of home-based neuromuscular electrical stimulation (NMES) resistance training. Subjects trained the quadriceps muscle group twice a week with four sets of 10 dynamic knee extensions against resistance while in a seated position. All measurements were made before training and after 8, 12, and 18 weeks of training. Ultrasound was used to measure femoral artery diameter and blood flow. Blood flow was measured before and after 5 and 10 min of distal cuff occlusion, and during a 4-min isometric electrical stimulation fatigue protocol.

RESULTS

Training resulted in significant increases in weight lifted and muscle mass, as well as a 60% reduction in muscle fatigue (P = 0.001). However, femoral arterial diameter did not increase. The range was 0.44+/-0.03 to 0.46+/-0.05 cm over the four time points (P = 0.70). Resting, reactive hyperemic, and exercise blood flow did not appear to change with training.

CONCLUSION

NMES resistance training improved muscle size and fatigue despite an absence of response in the supplying vasculature. These results suggest that the decreases in arterial caliber and blood flow seen with SCI are not tightly linked to muscle mass and fatigue resistance. In addition, muscle fatigue in SCI patients can be improved without increases in arterial diameter or blood flow capacity.

Doppler ultrasound assessment of posterior tibial artery size in humans

PURPOSE

The difference between structural remodeling and changes in tone of peripheral arteries in the lower extremities has not been evaluated. The purpose of this study was to (1) evaluate the day-to-day reproducibility and interobserver reliability (IOR) of posterior tibial artery (PTA) diameter measurements and (2) evaluate the effect of posture on PTA diameter at rest (Drest), during 10 minutes of proximal cuff occlusion (Dmin), and after the release of cuff occlusion (Dmax), as well as range (Dmax - Dmin) and constriction [(Dmax - Drest)/(Dmax - Dmin) x 100] in vivo.

METHODS

We used B-mode sonography to image the PTA during each condition.

RESULTS

Day-to-day reliability was good for Drest (intraclass correlation coefficient [ICC] 0.95; mean difference 4.2%), Dmin (ICC 0.93; mean difference 5.4%), and Dmax (ICC 0.99; mean difference 2.2%). The coefficient of repeatability for IOR was 70.5 microm, with a mean interobserver error of 4.7 microm. The seated position decreased Drest (2.6 +/- 0.2 to 2.4 +/- 0.3 mm; p = 0.002), increased Dmin (2.1 +/- 0.2 to 2.4 +/- 0.2 mm; p = 0.001), and decreased Dmax (3.1 +/- 0.4 to 2.8 +/- 0.3 mm; p < 0.001) compared with the supine position. The seated position also decreased arterial range (Dmax - Dmin) from 0.9 +/- 0.2 to 0.5 +/- 0.1 mm (p = 0.003) and increased basal arterial constriction from 57 +/- 19% to 105 +/- 27% (p = 0.007).

CONCLUSIONS

The system employed for measuring PTA diameter yields unbiased and consistent estimates. Furthermore, lower extremity arterial constriction and range change with posture in a manner consistent with known changes in autonomic activity.

Blood Flow to Exercising Limbs Varies With Age, Gender, and Training Status

Understanding the effects of physiological aging on blood flow to active skeletal muscle and its regulation during exercise has important functional, hemodynamic, and metabolic implications for our rapidly expanding elderly population. During peak exercise involving a large muscle mass, blood flow to the legs is lower in healthy older compared to younger persons; this results from central (reduced cardiac output) and peripheral (reduced leg vascular conductance) limitations. There is considerable variability in the literature concerning age-related changes in leg blood flow during submaximal exercise, with reports of similar or reduced leg blood flaw and vascular conductance in older vs. younger subjects depending on the exercise intensity and the gender and training status of the subjects. However, all the studies involving non-endurance-trained subjects are consistent in that older subjects achieve the requisite leg blood flow at higher arterial perfusion pressures than young subjects, suggesting altered local vasoregulatory mechanisms with aging. Although the nature of these age- related alterations is poorly understood, we have preliminary evidence for augmented sympathetic vasoconstrictor responsiveness in the legs of older men during exercise, and blunted leg vasodilator responsiveness in older women. Systematic research will be needed in order to define the central and local mechanisms underlying these age- and gender-specific differences in muscle vascular responsiveness. Such information will be important for designing future interventions aimed at improving muscle blood supply and functional capacity in older persons. Key words: exercise, vascular responsiveness, human

Effect of Endurance Training on the &OV0312;O2???Work Rate Relationship in Normoxia and Hypoxia

PURPOSE

We postulated that the relationship between VO2 and work rate (VO2-WR relationship) during incremental exercise is dependent on O2 availability, and that training-induced adaptations alter this relationship. We therefore studied the effect of endurance training on VO2 response during incremental exercise in normoxia and hypoxia (FIO2=0.134).

METHODS

Before and after training (6 d.wk, 4 wk), eight subjects performed incremental exercises under normoxia and hypoxia and one constant-work rate exercise in normoxia at 80% of pretraining VO2max. The slopes of the VO2-WR relationship during incremental exercise were calculated using all the points (whole slope) or only points before the lactate threshold (pre-LT slope). The difference between VO2max measured and VO2max expected from the pre-LT slope (DeltaVO2) was determined, as was the difference between VO2 at minute 10 and VO2 at minute 4 during the constant-work rate exercise (DeltaVO2(10'-4')).

RESULTS

In normoxia, training induced a significant decrease in the whole slope (11.0+/-1.0 vs 9.9+/-0.4 mL.min.W, P<0.05). In hypoxia, training induced a significant increase in the pre-LT slope (8.7+/-1.2 vs 9.8+/-0.7 mL.min.W; P<0.05) and the whole slope (8.5+/-1.2 vs 9.4+/-0.5 mL.min.W; P<0.05). A significant correlation between the decrease of DeltaVO2 and the decrease of DeltaVO2(10'-4') with training was found in normoxia (P<0.01, r=0.79).

CONCLUSIONS

Taken together, these results indicate that adaptations induced by endurance training are associated with more efficient incremental and constant-workload exercise performed in normoxia. Moreover, training contributes to improved O2 delivery during moderate exercise performed in hypoxia, and to enhanced near-maximal exercise tolerance.

Running for health: how much running for how much health?

Increasing physical activity has been shown to reduce physiological markers of cardiovascular disease, such as high blood pressure, vascular endothelial cell reactivity and arterial stiffness. In this issue of Clinical Science, Hägg and colleagues have chosen the spontaneously hypertensive rat model to investigate the effect of exercise on vascular function. They found that spontaneous running increased aortic compliance and antioxidant capacity with decreased oxidative stress in mesenteric arteries, presenting support for the cardiovascular protective effects of physical activity. Two important aspects of their study include the magnitude of the running stimulus and the choice of artery to evaluate.

Effects of exercise training on the vascular reactivity of the whole kidney circulation in rabbits

Exercise training is known to improve vasodilating mechanisms mediated by endothelium-dependent relaxing factors in the cardiac and skeletal muscle vascular beds. However, the effects of exercise training on visceral vascular reactivity, including the renal circulation, are still unclear. We used the experimental model of the isolated perfused rabbit kidney, which involves both the renal macro- and microcirculation, to test the hypothesis that exercise training improves vasodilator mechanisms in the entire renal circulation. New Zealand White rabbits were pen confined (Sed; n = 24) or treadmill trained (0% grade) for 5 days/wk at a speed of 18 m/min during 60 min over a 12-wk period (ExT; n = 24). Kidneys isolated from Sed and ExT rabbits were continuously perfused in a nonrecirculating system under conditions of constant flow and precontracted with norepinephrine (NE). We assessed the effects of exercise training on renal vascular reactivity using endothelial-dependent [acetylcholine (ACh) and bradykinin (BK)] and -independent [sodium nitroprusside (SNP)] vasodilators. ACh induced marked and dose-related vasodilator responses in kidneys from Sed rabbits, the reduction in perfusion pressure reaching 41 ± 8% ( n = 6; P < 0.05). In the kidneys from ExT rabbits, vasodilation induced by ACh was significantly enhanced to 54 ± 6% ( n = 6; P < 0.05). In contrast, BK-induced renal vasodilation was not enhanced by training [19 ± 8 and 13 ± 4% reduction in perfusion pressure for Sed and ExT rabbits, respectively ( n = 6; P > 0.05)]. Continuous perfusion of isolated kidneys from ExT animals with Nω-nitro-l-arginine methyl ester (l-NAME; 300 μM), an inhibitor of nitric oxide (NO) biosynthesis, completely blunted the additional vasodilation elicited by ACh [reduction in perfusion pressure of 54 ± 6 and 38 ± 5% for ExT and l-NAME + ExT, respectively ( n = 6; P < 0.05)]. On the other hand, l-NAME infusion did not affect ACh-induced vasodilation in Sed animals. Exercise training also increased renal vasodilation induced by SNP [36 ± 7 and 45 ± 10% reduction in perfusion pressure for Sed and ExT rabbits, respectively ( n = 6; P < 0.05)]. It is concluded that exercise training alters the rabbit kidney vascular reactivity, enhancing endothelium-dependent and -independent renal vasodilation. This effect seems to be related not only to an increased bioavailability of NO but also to the enhanced responsiveness of the renal vascular smooth muscle to NO.

The influence of training on oxygen isotope fractionation in healthy subjects

We determined the oxygen isotope fractionation in expired alveolar gas relative to inspired air (delta(A-I)) in eight young, healthy subjects at rest and at five levels of exercise up to maximal workload both before and after a training period of about 4 weeks which increased maximum oxygen uptake by about 10%. The data for delta(A-I) were used to compute the relative difference (deltaU) between the resistances of 16O18O and 16O2 for oxygen transport from the alveolar space and utilization in the mitochondria. Prior to training, deltaU decreased from 15 per thousand at rest to 5 per thousand at the highest level of exercise and after training from 12 to 5 per thousand. The difference between the results for deltaU before and after training was significant for rest (P < or = 5) but not for exercise conditions. Accordingly, we conclude that for exercise conditions the non-fractionating oxygen transport by blood flow to and the fractionating oxygen transport by diffusion in the muscles have improved by training to more or less the same degree. The decrease in deltaU in rest after training suggests that oxygen transport by diffusion in other tissues also benefits from the effects of training.

Cardiovascular responses to endurance training in children: effect of gender

BACKGROUND

The aim of the present study was to determine in healthy children the effect of a well-controlled endurance training programme on cardiac function at maximal exercise and to define whether gender affects the training-induced cardiovascular response. The contribution of factors potentially involved in those adaptations such as cardiac dimensions and diastolic and systolic function was also investigated.

METHODS

Thirty-five l0-11-year-old children took part in this study: 19 children (10 girls and nine boys) were assigned to participate in a 13-week endurance training programme (3 x 1 h week-1, intensity: > 80% HR max), and 16 (seven girls and nine boys) served as a control group. A resting echocardiographic evaluation and a maximal upright cycle test, including measurement of stroke volume (SV), cardiac output (Q) and blood pressure, were performed in all children before and after the study period.

RESULTS

The training programme led to a rise in maximal O2 uptake (VO2max), brought about however, only by an increase in SVmax in both genders. Moreover, the boys increased their VO2max to a greater extent than the girls (boys: +15%; girls: +8%) only because of a higher SVmax improvement (boys: +15%; girls: +11%). No alterations were noticed in the SV pattern from rest to maximal exercise, indicating that the increase in SVrest was a key factor in the improvement of SVmax and thus VO2max. Regarding resting echocardiographic data, an increase in the left ventricular end-diastolic diameter, concomitant with an improvement in diastolic function, was observed after training and constituted an essential element in the rise in VO2max after training in these children. Moreover, during maximal exercise, a decrease in systemic vascular resistances, probably indicating peripheral cardiovascular adaptive changes, might also play an important role in the increase in VO2max.

CONCLUSION

Whatever gender, aerobic training increases VO2max in children, mediated by an improvement in SVmax only. Similar mechanisms, including loading conditions and cardiac morphology, seem to be involved in both genders in order to explain such an improvement.

Endothelial nitric oxide synthase (NOS) deficiency affects energy metabolism pattern in murine oxidative skeletal muscle

Oxidative capacity of muscles correlates with capillary density and with microcirculation, which in turn depend on various regulatory factors, including NO generated by endothelial nitric oxide synthase (eNOS). To determine the role of eNOS in patterns of regulation of energy metabolism in various muscles, we studied mitochondrial respiration in situ in saponin-permeabilized fibres as well as the energy metabolism enzyme profile in the cardiac, soleus (oxidative) and gastrocnemius (glycolytic) muscles isolated from mice lacking eNOS (eNOS(-/-)). In soleus muscle, the absence of eNOS induced a marked decrease in both basal mitochondrial respiration without ADP (-32%; P <0.05) and maximal respiration in the presence of ADP (-29%; P <0.05). Furthermore, the eNOS(-/-) soleus muscle showed a decrease in total creatine kinase (-29%; P <0.05), citrate synthase (-31%; P <0.01), adenylate kinase (-27%; P <0.05), glyceraldehyde-3-phosphate dehydrogenase (-43%; P <0.01) and pyruvate kinase (-26%; P <0.05) activities. The percentage of myosin heavy chains I (slow isoform) was significantly increased from 24.3+/-1.5% in control to 30.1+/-1.1% in eNOS(-/-) soleus muscle ( P <0.05) at the expense of a slight non-significant decrease in the three other (fast) isoforms. Besides, eNOS(-/-) soleus showed a 28% loss of weight. Interestingly, we did not find differences in any parameters in cardiac and gastrocnemius muscles compared with respective controls. These results show that eNOS knockout has an important effect on muscle oxidative capacity as well on the activities of energy metabolism enzymes in oxidative (soleus) muscle. The absence of such effects in cardiac and glycolytic (gastrocnemius) muscle suggests a specific role for eNOS-produced NO in oxidative skeletal muscle.

Angiotensin-converting enzyme and genetics at high altitude

As part of the renin-angiotensin system (RAS), angiotensin-converting enzyme (ACE) plays a key role in circulatory homeostasis. ACE degrades vasodilator kinins and generates angiotensin II. A polymorphism in intron 16 of the human ACE gene has been identified in which the presence (insertion, I allele) rather than the absence (deletion, D allele) of a 287 bp fragment is associated with lower serum and tissue ACE activity. The I allele has been associated with some aspects of endurance performance, being found with excess frequency in elite distance runners, rowers, and other elite athletes. Mountaineers also demonstrate an allele skew with a significant excess of the I allele and II genotype in elite, male, British mountaineers who have ascended beyond 7000 m without the use of supplemental oxygen. This review evaluates the evidence for and against an association of the I allele with human endurance, and performance at high altitude. We conclude that the I allele does confer an advantage, most likely mediated via improved muscle efficiency with secondary benefits in terms of conservation of non-fat mass.

Influence of training on NIRS muscle oxygen saturation during submaximal exercise

PURPOSE

Endurance training improves the oxygen delivery and muscle metabolism. Muscle oxygen saturation measured by near infrared spectroscopy (IR-SO(2)), which is primarily influenced by the local delivery/demand balance, should thus be modified by training. We examined this effect by determining the influence of change in blood lactate and muscle capillary density with training on IR-SO(2) in seven healthy young subjects.

METHODS

Two submaximal exercise tests at 50% (Ex1) and 80% pretraining VO(2max) (Ex2) were performed before and after a 4-wk endurance-training program.

RESULTS

VO(2max) increased only slightly (+8%, NS) with training but the training effect was confirmed by the increased capillary density (+31%, P < 0.01) and citrate synthase activity (50%, P < 0.01), determined from muscle biopsy samples. Before training, blood lactate increased during the first 5 min of Ex1 and then remained constant (3.8 +/- 0.5 mmol x L(-1), P < 0.01), whereas it increased continuously during Ex2 (8.9 +/- 1.8 mmol x L(-1), P < 0.001). After training, lactate decreased significantly and remained constant during the two bouts of exercise (2.0 +/- 0.4 and 3.7 +/- 1.2 at the end of Ex1 and Ex2, respectively, both P < 0.001). During Ex1, IR-SO(2) dropped initially at the onset of exercise and recovered progressively without reaching the resting level. Training did not change this pattern of IR-SO(2). During Ex2, IR-SO(2) decreased progressively during the 15 min of exercise (P < 0.05); IR-SO2 kept constant after the initial drop after training. We found a significant relationship (r = 0.42, P = 0.03) between blood lactate and IR-SO(2) at the end of both bouts of exercise; this relationship was closer before training. By contrast, IR-SO(2) or IR-BV was not related to the capillary density.

CONCLUSION

The training-induced adaptation in blood lactate influences IR-SO(2) during mild- to hard-intensity exercise. Thus, NIRS could be used as a noninvasive monitoring of training-induced adaptations.

Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury

OBJECTIVE

To test whether a short period of training leads to adaptations in the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with spinal cord injury (SCI).

DESIGN

Before-after trial.

SETTING

Rehabilitation center, academic medical center.

PARTICIPANTS

Nine men with spinal cord lesions.

INTERVENTION

Six weeks of cycling using a functional electrically stimulated leg cycle ergometer (FES-LCE).

MAIN OUTCOME MEASURES

Longitudinal images and simultaneous velocity spectra were measured in the common carotid (CA) and femoral (FA) arteries using quantitative duplex Doppler ultrasound examination. Arterial diameters, peak systolic inflow volumes (PSIVs), mean inflow volumes (MIVs), and a velocity index (VI), representing the peripheral resistance, were obtained at rest. PSIVs and VI were obtained during 3 minutes of hyperemia following 20 minutes of FA occlusion.

RESULTS

Training resulted in significant increases in diameter (p < .01), PSIVs (p < .01), and MIVs (p < .05), and reduced VI (p < .01) of the FA, whereas values in the CA remained unchanged. Postocclusive hyperemic responses were augmented, indicated by significantly higher PSIVs (p <.01) and a trend toward lower VI.

CONCLUSION

Six weeks of FES-LCE training increased the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with SCI.

NOS3 Glu298Asp genotype and blood pressure response to endurance training: the HERITAGE family study

Endothelium-dependent vasodilation is a mechanism that may affect blood pressure response to endurance training. Because NO plays a central role in this process, the endothelial NO synthase gene is a good candidate for the regulation of exercise blood pressure. We investigated the associations between an endothelial NO synthase gene polymorphism (Glu298Asp) and endurance training-induced changes in resting and submaximal exercise blood pressure in 471 white subjects of the HERITAGE Family Study. Two submaximal exercise tests at 50 W were conducted both before and after a 20-week endurance training program. Steady-state exercise blood pressure was measured twice in each test with an automated unit. The Glu298Asp polymorphism was typed with a PCR-based method and digestion with BAN:II. Both systolic and diastolic blood pressure at 50 W decreased in response to the training program, whereas resting blood pressure remained unchanged. The decrease in diastolic blood pressure at 50 W was greater (P=0.0005, adjusted for age, gender, baseline body mass index, and baseline diastolic blood pressure at 50 W) in the Glu/Glu homozygotes (4.4 [SEM 0.4] mm Hg, n=187) than in the heterozygotes (3.1 [0.4] mm Hg, n=213) and the Asp/Asp homozygotes (1.3 [0.7] mm Hg, n=71). The genotype accounted for 2.3% of the variance in diastolic blood pressure at 50 W training response. Both the Glu298 homozygotes and the heterozygotes had a greater (P=0.013) training-induced reduction in rate-pressure product at 50 W than the Asp298 homozygotes. These data suggest that DNA sequence variation in the endothelial NO synthase gene locus is associated with the endurance training-induced decreases in submaximal exercise diastolic blood pressure and rate-pressure product in sedentary normotensive white subjects.

Cardiovascular responses in anticipation of changes in posture and locomotion

Measurements were made in 29 adult baboons that were housed in social groups, allowing the occurrence of the full range of species-specific behavioral interactions. The cardiovascular variables measured included blood pressure, heart rate, renal blood flow, lower limb blood flow, and occasionally mesenteric blood flow. The data were telemetered from backpacks worn by the animals and were recorded in analogue form on a polygraph, digitally on a computer and were also recorded on the audio channels of videotape being made of the behavior and social interactions of the baboons. The video and the computer recordings were synchronized by a timing system that made it possible to relate the cardiovascular responses to the behavioral responses. A numerically based behavioral code was developed that allowed the categorization of the totality of the behavior, including postural and locomotor changes. Comparisons between baseline cardiovascular values and those occurring 1 s before the initiation of a movement or posture change gave no evidence of anticipatory cardiovascular responses unless the movement was associated with behavior that included emotional content. Hypothalamic perifornical lesions reduced or eliminated these anticipatory changes.

The effects of exercise and training on human cardiovascular reflex control

During physical activity, there is a graded withdrawal of vagal cardiac tone and a graded increase in sympathetic cardiac and vasomotor tone, initiated through both central command from the somatic motor cortex and muscle chemoreceptive and mechanoreceptive inputs. In parallel, there is an upward resetting of the operating point of the arterial baroreflex, with preserved reflex sensitivity. In contrast to the traditional interpretation that blood flow through exercising muscle is independent of vasomotor neural influences because of the dominance of local dilator metabolites, recent evidence suggests that both constrictor and dilator sympathetic neural influences may be involved in determining absolute levels of perfusion. Post-exercise, there is a period of relative hypotension that is associated with decreased peripheral resistance. Some, but not all, evidence indicates a causal role for reduced sympathetic drive. Chronic exercise training appears to reduce resting sympathetic activity, with parallel changes in the gain of a variety of cardiovascular autonomic reflexes initiated from cardiovascular sites. These changes may be attributable at least partly to masking of arterial baroreflexes by the impact of elevated blood volume on low-pressure baroreceptors. The reductions in sympathetic drive that follow training are more pronounced in patients with essential hypertension than in normotensive individuals and are likely to underlie the anti-hypertensive effect of exercise.