Showing papers in "Journal of Applied Physiology in 1992"
TL;DR: This work proposes four themes that provide a basis for the systematic evaluation of the neural and neuromuscular fatigue mechanisms and suggests a number of experiments to advance the understanding of the neurobiology of muscle fatigue.
Abstract: Muscle fatigue encompasses a class of acute effects that impair motor performance. The mechanisms that can produce fatigue involve all elements of the motor system, from a failure of the formulation of the descending drive provided by suprasegmental centers to a reduction in the activity of the contractile proteins. We propose four themes that provide a basis for the systematic evaluation of the neural and neuromuscular fatigue mechanisms: 1) task dependency to identify the conditions that activate the various mechanisms; 2) force-fatigability relationship to explore the interaction between the mechanisms that results in a hyperbolic relationship between force and endurance time; 3) muscle wisdom to examine the association among a concurrent decline in force, relaxation rate, and motor neuron discharge that results in an optimization of force; and 4) sense of effort to determine the role of effort in the impairment of performance. On the basis of this perspective with an emphasis on neural mechanisms, we suggest a number of experiments to advance our understanding of the neurobiology of muscle fatigue.
1,391 citations
TL;DR: The magnitude of increase in core temperature and HR and the decline in SV are graded in proportion to the amount of dehydration accrued during exercise, which was linearly related with the increase in Tes, HR, and SV.
Abstract: This investigation determined the effect of different rates of dehydration, induced by ingesting different volumes of fluid during prolonged exercise, on hyperthermia, heart rate (HR), and stroke v...
792 citations
TL;DR: Results of simulation studies based on a lung model consisting of a central airway and a number of peripheral units withAirway and tissue parameters that were given independent wide distributions were in agreement with the experimental findings and showed that even an extremely inhomogeneous lung structure can produce virtually homogeneous mechanical behavior at the input.
Abstract: Tracheal pressure, central airflow, and alveolar capsule pressures in cardiac lobes were measured in open-chest dogs during 0.1- to 20-Hz pseudorandom forced oscillations applied at the airway open...
790 citations
TL;DR: The results of this study demonstrate that MRI offers a reliable measure of regional and total AT distribution in humans and, thus, is of value as a research tool.
Abstract: This study had two objectives: 1) to establish magnetic resonance imaging (MRI) as a tool for measuring total and regional adipose tissue (AT) distribution in humans and 2) to assess the relationship between selected anthropometric variables and MRI-measured AT. Twenty-seven healthy men varying in age [40.8 +/- 14.5 (SD) yr], body mass index (28.5 +/- 4.8), and waist-to-hip ratio (WHR, 0.96 +/- 0.07) participated in the study. Total AT volume was determined using a linear interpolation of AT areas obtained on consecutive slices (n = 41) taken from head to toe (10-mm thickness, 50-mm centers). The mean change for repeated measures of total AT volume was 2.9% (range 0.9-–4.3%). Large interindividual differences were observed for total AT volume (6.9–59.3 liters), subcutaneous AT (6.3–49.8 liters), and visceral AT (0.5–8.5 liters). Visceral AT represented 18.3% of the total AT. The single best predictor of total adiposity was waist circumference (R2 = 0.92). For visceral AT volume, WHR was the strongest anth...
530 citations
TL;DR: It is concluded that diaphragm fiber bundles produce reactive oxygen intermediates, including O2-.
Abstract: We hypothesized that muscle fiber bundles produce reactive oxygen intermediates and that reactive oxidant species contribute to muscular fatigue in vitro. Fiber bundles from rat diaphragm were moun...
482 citations
TL;DR: The results indicate that a single bout of heavy resistance exercise can increase biceps MPS for up to 24 h postexercise, and these increases appear to be due to changes in posttranscriptional events.
Abstract: The purpose of this study was to investigate the magnitude and time course for changes in muscle protein synthesis (MPS) after a single bout of resistance exercise. Two groups of six male subjects performed heavy resistance exercise with the elbow flexors of one arm while the opposite arm served as a control. MPS from exercised (ex) and control (con) biceps brachii was assessed 4 (group A) and 24 h (group B) postexercise by the increment in L-[1–13C]leucine incorporation into muscle biopsy samples. In addition, RNA capacity and RNA activity were determined to assess whether transcriptional and/or translational processes affected MPS. MPS was significantly elevated in biceps of the ex compared with the con arms of both groups (group A, ex 0.1007 +/- 0.0330 vs. con 0.067 +/- 0.0204%/h; group B ex 0.0944 +/- 0.0363 vs. con 0.0452 +/- 0.0126%/h). RNA capacity was unchanged in the ex biceps of both groups relative to the con biceps, whereas RNA activity was significantly elevated in the ex biceps of both group...
451 citations
TL;DR: 23 healthy older men and women before and after they had trained by walking/jogging at 80% of maximal heart rate for 45 min/day 4 days/wk for 9-12 mo resulted in a 23% increase in maximal O2 consumption.
Abstract: Previous studies of endurance exercise training in older men and women generally have found only minimal skeletal muscle adaptations to training. To evaluate the possibility that this may have been...
449 citations
TL;DR: A reduction in hamstring coactivity in the trained and untrained legs indicates that these muscles provide less opposing force to the contracting quadriceps in response to static resistance training of this type.
Abstract: Twenty sedentary male university students were randomly assigned to an experimental or a control group. The experimental group trained the knee extensors of one leg by producing 30 isometric extension maximal voluntary contractions (MVC) per day, three times per week for 8 wk. After 8 wk of training, extensor MVC in the trained leg increased 32.8% (P less than 0.05), but there was no change in vastus lateralis maximal integrated electromyographic activity (IEMGmax). The most important finding was that the degree of hamstring coactivation during extension MVC decreased by approximately 20% (P less than 0.05) after the 1st wk of training. Less pronounced adaptations occurred in the untrained leg: extension MVC force increased 16.2% (P less than 0.05), hamstring coactivity decreased 13% (P less than 0.05) after 2 wk of training, and vastus lateralis IEMGmax was unchanged. The same measures in legs of the control group were not changed during the study. There were no changes in flexion MVC, biceps femoris IEMGmax, or the degree of quadriceps coactivity during flexion MVC in either leg of the control or experimental group. A reduction in hamstring coactivity in the trained and untrained legs indicates that these muscles provide less opposing force to the contracting quadriceps. We conclude that this small but significant decrease in hamstring coactivation that occurs during the early stages of training is a nonhypertrophic adaptation of the neuromuscular system in response to static resistance training of this type.
443 citations
TL;DR: It is hypothesized that afferent information from the peripheral chemoreceptors may be necessary to produce diurnal blood pressure elevation in this Hypoxia model, a rat model that responds to repetitive episodic hypoxia with an increase in diurnal systemic blood pressure.
Abstract: We have described a rat model that responds to repetitive episodic hypoxia (12-s infusions of nitrogen into daytime sleeping chambers every 30 s, 7 h/day for 35 days) with an increase in diurnal sy...
417 citations
TL;DR: It is concluded that during maximal exercise, highly trained individuals often reach the mechanical limits of the lung and respiratory muscle for producing alveolar ventilation, which is achieved at a considerable metabolic cost but with a mechanically optimal pattern of breathing and respiratory Muscle recruitment and without sacrifice of a significantAlveolar hyperventilation.
Abstract: We determined how close highly trained athletes [n = 8; maximal oxygen consumption (VO2max) = 73 +/- 1 mlkg-1min-1] came to their mechanical limits for generating expiratory airflow and inspirato
374 citations
TL;DR: The O2 cost of exercise hyperpnea is a significant fraction of the total VO2max but is not sufficient to cause a critical level of "useful"hyperpnea to be achieved in healthy subjects.
Abstract: We addressed two questions concerned with the metabolic cost and performance of respiratory muscles in healthy young subjects during exercise: 1) does exercise hyperpnea ever attain a “critical use...
TL;DR: It is demonstrated that RI with body weight can predict FFB with good accuracy in Whites 10-19 yr old.
Abstract: The purposes of this study were to develop and cross-validate the “best” prediction equations for estimating fat-free body mass (FFB) from bioelectrical impedance in children and youth. Predictor v...
TL;DR: The results suggest that postexercise muscle glycogen storage can be enhanced with a carbohydrate-protein supplement as a result of the interaction of carbohydrate and protein on insulin secretion.
Abstract: Carbohydrate, protein, and carbohydrate-protein supplements were compared to determine their effects on muscle glycogen storage during recovery from prolonged exhaustive exercise. Nine male subjects cycled for 2 h on three separate occasions to deplete their muscle glycogen stores. Immediately and 2 h after each exercise bout, they ingested 112.0 g carbohydrate (CHO), 40.7 g protein (PRO), or 112.0 g carbohydrate and 40.7 g protein (CHO-PRO). Blood samples were drawn before exercise, immediately after exercise, and throughout recovery. Muscle biopsies were taken from the vastus lateralis immediately and 4 h after exercise. During recovery the plasma glucose response of the CHO treatment was significantly greater than that of the CHO-PRO treatment, but the plasma insulin response of the CHO-PRO treatment was significantly greater than that of the CHO treatment. Both the CHO and CHO-PRO treatments produced plasma glucose and insulin responses that were greater than those produced by the PRO treatment (P less than 0.05). The rate of muscle glycogen storage during the CHO-PRO treatment [35.5 +/- 3.3 (SE) mumol.g protein-1.h-1] was significantly faster than during the CHO treatment (25.6 +/- 2.3 mumol.g protein-1.h-1), which was significantly faster than during the PRO treatment (7.6 +/- 1.4 mumol.g protein-1.h-1). The results suggest that postexercise muscle glycogen storage can be enhanced with a carbohydrate-protein supplement as a result of the interaction of carbohydrate and protein on insulin secretion.
TL;DR: There is great variability in the degree and location of muscle loss in bed rest and that the lower limb muscles are primarily affected, suggesting that muscle atrophy continued throughout bed rest with rapid recovery after reambulation.
Abstract: This work reports on the muscle loss and recovery after 17 wk of continuous bed rest and 8 wk of reambulation in eight normal male volunteers. Muscle changes were assessed by urinary levels of 3-methylhistidine (3-MeH), nitrogen balance, dual-photon absorptiometry (DPA), magnetic resonance imaging (MRI), and isokinetic muscle performance. The total body lean tissue loss during bed rest calculated from nitrogen balance was 3.9 +/- 2.1 (SD) kg (P < 0.05). Although the total loss is minimal, DPA scans showed that nearly all of the lean tissue loss occurred in the lower limbs. Similarly, MRI muscle volume measurements showed greater percent loss in the limbs relative to the back muscles. MRI, DPA, and nitrogen balance suggest that muscle atrophy continued throughout bed rest with rapid recovery after reambulation. Isokinetic muscle strength decreased significantly (P < 0.05) in the thigh and calf with no loss in the arms and with rapid recovery during reambulation. We conclude that there is great variability in the degree and location of muscle loss in bed rest and that the lower limb muscles are primarily affected.
TL;DR: Observations suggest that peripheral airways are the predominant site of airflow obstruction, irrespective of the different pathogenesis of chronic airflow obstruction.
Abstract: To partition the central and peripheral airway resistance in awake humans, a catheter-tipped micromanometer sensing lateral pressure of the airway was wedged into the right lower lobe of a 3-mm-ID bronchus in 5 normal subjects, 7 patients with chronic bronchitis, 8 patients with emphysema, and 20 patients with bronchial asthma. We simultaneously measured mouth flow, transpulmonary pressure, and intra-airway lateral pressure during quiet tidal breathing. Total pulmonary resistance (RL) was calculated from transpulmonary pressure and mouth flow and central airway resistance (Rc) from intra-airway lateral pressure and mouth flow. Peripheral airway resistance (Rp) was obtained by the subtraction of Rc from RL. The technique permitted identification of the site of airway resistance changes. In normal subjects, RL was 3.2 +/- 0.2 (SE) cmH2O.l-1.s and the ratio of Rp to RL was 0.24 during inspiration. Patients with bronchial asthma without airflow obstruction showed values of Rc and Rp similar to those of normal subjects. Although Rc showed a tendency to increase, only Rp significantly increased in those patients with bronchial asthma with airflow obstruction and patients with chronic bronchitis and emphysema. The ratio of Rp to RL significantly increased in three groups of patients with airflow obstruction (P less than 0.01). These observations suggest that peripheral airways are the predominant site of airflow obstruction, irrespective of the different pathogenesis of chronic airflow obstruction.
TL;DR: It is concluded that O2-.
Abstract: We have tested the hypothesis that diaphragm muscle fibers release superoxide anion radicals (O2-.) into the extracellular space. Fiber bundles were isolated from rat diaphragm and incubated in Krebs-Ringer solution containing cytochrome c (10(-5) M), a standard assay for O2-.. Bundles were either passive or active, i.e., directly stimulated to contract rhythmically. After 1 h, absorbance of reduced cytochrome c in the incubation medium was measured at 550 nm. Absorbance was greater in medium exposed to passive muscle than in medium without muscle (P < 0.01), indicating O2-. release by passive muscle. Absorbance was greater in medium exposed to active muscle than in that exposed to passive muscle (P < 0.01), an increase inhibited by superoxide dismutase (10(3) U/ml). Active bundles fatigued; bundles developing the lowest final stresses produced the greatest absorbance increases (P < 0.001), suggesting that the magnitude of fatigue was inversely related to O2-. release. We conclude that O2-. is released by diaphragm myocytes into the interstitium and surrounding medium, a process accelerated by fatiguing muscular contractions.
TL;DR: The findings provide a physiological mechanism for other studies showing increased capillary permeability at high states of lung inflation, and are compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O.
Abstract: We previously showed that when pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to test whether stress failure occurred more frequently at high than at low lung volumes for the same Ptm. Lungs of anesthetized rabbits were inflated to a transpulmonary pressure of 20 cmH2O, perfused with autologous blood at 32.5 or 2.5 cmH2O Ptm, and fixed by intravascular perfusion. Samples were examined by both transmission and scanning electron microscopy. The results were compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O. There was a large increase in the frequency of stress failure of the capillary walls at the higher lung volume. For example, at 32.5 cmH2O Ptm, the number of endothelial breaks per millimeter cell lining was 7.1 +/- 2.2 at the high lung volume compared with 0.7 +/- 0.4 at the low lung volume. The corresponding values for epithelium were 8.5 +/- 1.6 and 0.9 +/- 0.6. Both differences were significant (P less than 0.05). At 52.5 cmH2O Ptm, the results for endothelium were 20.7 +/- 7.6 (high volume) and 7.1 +/- 2.1 (low volume), and the corresponding results for epithelium were 32.8 +/- 11.9 and 11.4 +/- 3.7. At 32.5 cmH2O Ptm, the thickness of the blood-gas barrier was greater at the higher lung volume, consistent with the development of more interstitial edema. Ballooning of the epithelium caused by accumulation of edema fluid between the epithelial cell and its basement membrane was seen at 32.5 and 52.5 cmH2O Ptm. At high lung volume, the breaks tended to be narrower and fewer were oriented perpendicular to the axis of the pulmonary capillaries than at low lung volumes. Transmission and scanning electron microscopy measurements agreed well. Our findings provide a physiological mechanism for other studies showing increased capillary permeability at high states of lung inflation.
TL;DR: Protein requirements for athletes performing strength training are greater than for sedentary individuals and are above current Canadian and US recommended daily protein intake requirements for young healthy males.
Abstract: Leucine kinetic and nitrogen balance (NBAL) methods were used to determine the dietary protein requirements of strength athletes (SA) compared with sedentary subjects (S). Individual subjects were ...
TL;DR: In this article, the factors affecting the electromyographic power spectrum discussed in this review are action potential velocity decrease, firing statistics alterations, action potential modification, muscle temperature, additional recruitment at fatigue, and force level.
Abstract: Alterations of the electromyographic power spectrum have been studied extensively to assess fatigue development in the neuromuscular system. Usually, a data reduction has been applied to create an index based on the mean power frequency or the median frequency. The physiological origin of the spectrum alterations has been (and to some extent still is) incompletely known. However, during the 1980s, substantial progress has been made in this field. The factors affecting the electromyographic power spectrum discussed in this review are action potential velocity decrease, firing statistics alterations, action potential modification, muscle temperature, additional recruitment at fatigue, and force level. Their impact on three commonly used fatigue indexes, mean power frequency, median frequency, and zero crossing rate, is also reviewed.
TL;DR: The electrical stimulation protocol used in this study enhanced the oxidative capacity and endurance properties of the paralyzed muscles but had no effect on fiber size and strength.
Abstract: Selected morphological and metabolic properties of single fibers were studied in biopsy samples from the tibialis anterior of normal control and spinal cord-injured (SCI) subjects. In the SCI subje...
TL;DR: The results confirm that satellite cell proliferation is a prerequisite for muscle hypertrophy induced by synergist incapacitation, but it appears not to be required for the maintenance of, or change in, normal muscle fiber myosin heavy chain phenotype expression.
Abstract: Mouse extensor digitorum longus (EDL) muscle was subjected to a dose of gamma irradiation that causes reproductive death of satellite cells and/or to chronic compensatory overload, achieved by removal of the distal portion of the tibialis anterior muscle. Four weeks later the mass, fiber type percentage, and fiber size of the EDL muscle were measured. Both the irradiated + overloaded and the irradiated only EDL muscles were significantly lighter and contained significantly smaller fibers than untreated muscle or muscle subjected to chronic overload only. Overload muscle, whether irradiated or not, had a larger percentage of type IIx fibers and a smaller percentage of type IIb fibers than muscle that had not been overloaded. The results confirm that satellite cell proliferation is a prerequisite for muscle hypertrophy induced by synergist incapacitation, but it appears not to be required for the maintenance of, or change in, normal muscle fiber myosin heavy chain phenotype expression.
TL;DR: The magnitude of the blood pressure response depends on the degree of effort or central command and not actual force production, and the greatest increase in blood pressure occurred at the joint angle corresponding to the weakest point in the strength curve.
Abstract: Brachial arterial pressure was directly recorded in 31 healthy male volunteers through protocols examining the effects of the Valsalva maneuver, muscle size and strength, contraction force, contraction type (concentric, isometric, eccentric), changes in joint angle, and muscle fatigue on the blood pressure response to resistance exercise. Weight lifting at the same relative intensity produced similar increases in blood pressure, regardless of individual differences in muscle size or strength. Concentric, isometric, or eccentric exercise at the same relative intensity caused similar increases despite differences in force production. In weight lifting, the greatest increase in blood pressure occurred at the joint angle corresponding to the weakest point in the strength curve and the least at the angle corresponding to the strongest point. Isometric contractions of the same relative intensity at different joint angles produced identical blood pressures despite differences in absolute force production. When subjects attempted to maintain a maximum isometric contraction for 45 s, the blood pressure increase remained the same despite a marked diminution in force. Thus the magnitude of the blood pressure response depends on the degree of effort or central command and not actual force production. A brief Valsalva maneuver, which exaggerates the increase in blood pressure, is unavoidable when desired force production exceeds approximately 80% maximum voluntary contraction.
TL;DR: This study test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise and found that both measures were strongly related.
Abstract: Electromyography (EMG) is commonly used to determine the electrical activity of skeletal muscle during contraction. To date, independent verification of the relationship between muscle use and EMG has not been provided. It has recently been shown that relaxation- (e.g., T2) weighted magnetic resonance images (MRI) of skeletal muscle demonstrate exercise-induced contrast enhancement that is graded with exercise intensity. This study was conducted to test the hypothesis that exercise-induced magnetic resonance (MR) contrast shifts would relate to EMG amplitude if both measures reflect muscle use during exercise. Both MRI and EMG data were collected for separate eccentric (ECC) and concentric (CON) exercise of increasing intensity to take advantage of the fact that the rate of increase and amplitude of EMG activity are markedly greater for CON muscle actions. Seven subjects 30 +/- 2 (SE) yr old performed five sets of 10 CON or ECC arm curls with each of four resistances representing 40, 60, 80, and 100% of their 10 repetition maximum for CON curls. There was 1.5 min between sets and 30 min between bouts (5 sets of 10 actions at each relative resistance). Multiple echo, transaxial T2-weighted MR images (1.5 T, TR/TE 2,000/30) were collected from a 7-cm region in the middle of the arm before exercise and immediately after each bout. Surface EMG signals were collected from both heads of the biceps brachii and the long head of the triceps brachii muscles. CON and ECC actions resulted in increased integrated EMG (IEMG) and T2 values that were strongly related (r = 0.99, P < 0.05) with relative resistance.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Data indicate that, during the early stages of intensive bodybuilding training, PRO needs are approximately 100% greater than current recommendations but that PROIN increases from 1.35 to 2.62 g.kg-1.day-1 do not enhance muscle mass/strength gains, at least during the 1st mo of training.
Abstract: This randomized double-blind cross-over study assessed protein (PRO) requirements during the early stages of intensive bodybuilding training and determined whether supplemental PRO intake (PROIN) e...
TL;DR: Endurance training elevated the antioxidant and detoxicant status of muscle and liver, respectively, and total glutathione decreased in the trained leg muscles.
Abstract: Female beagle dogs were treadmill trained 40 km/day at 5.5–6.8 km/h, 15% upgrade, 5 days/wk for 55 wk. With training, hepatic and red gastrocnemius (RG) total glutathione increased, glutathione per...
TL;DR: The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction, and synergism (explained by the increase in Qleg) seems to be an important contribution to increases in VO2max with training.
Abstract: To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.
TL;DR: Hypohydration reduced the core temperature that could be tolerated and aerobic fitness, per se, did not influence the magnitude of heat strain that could been tolerated, and curves can be developed to estimate exhaustion rates for a given level of physiological strain.
Abstract: This study determined whether 1) exhaustion from heat strain occurs at the same body temperatures during exercise in the heat when subjects are euhydrated as when they are hypohydrated, 2) aerobic fitness influences the body temperature at which exhaustion from heat strain occurs, and 3) curves could be developed to estimate exhaustion rates at a given level of physiological strain. Seventeen heat-acclimated men [maximal oxygen uptake (VO2max) from 45 to 65 ml.kg-1.min-1] attempted two heat stress tests (HSTs): one when euhydrated and one when hypohydrated by 8% of total body water. The HSTs consisted of 180 min of rest and treadmill walking (45% VO2max) in a hot-dry (ambient temperature 49 degrees C, relative humidity 20%) environment. The required evaporative cooling (Ereq) exceeded the maximal evaporative cooling capacity of the environment (Emax); thus thermal equilibrium could not be achieved and 27 of 34 HSTs ended by exhaustion from heat strain. Our findings concerning exhaustion from heat strain are 1) hypohydration reduced the core temperature that could be tolerated; 2) aerobic fitness, per se, did not influence the magnitude of heat strain that could be tolerated; 3) curves can be developed to estimate exhaustion rates for a given level of physiological strain; and 4) exhaustion was rarely associated with a core temperature up to 38 degrees C, and it always occurred before a temperature of 40 degrees C was achieved. These findings are applicable to heat-acclimated individuals performing moderate-intensity exercise under conditions where Ereq approximates or exceeds Emax and who have high skin temperatures.
TL;DR: Evans blue dye bound tightly to albumin (EBA) as determined by lack of transfer through dialysis membranes and specific elution with albumin from a molecular exclusion column and was a more specific marker for protein transfer than lavage fluid protein.
Abstract: Determination of protein transfer across the endothelial barrier or the entire alveolar capillary membrane is critical for investigation of mechanisms leading to pulmonary edema. The purpose of this study was to evaluate Evans blue dye for determination of protein clearance across cultured bovine pulmonary artery endothelial cell monolayers and as a quantitative marker for albumin leakage to the air spaces in isolated perfused rat lungs. Evans blue dye bound tightly to albumin (EBA) as determined by lack of transfer through dialysis membranes and specific elution with albumin from a molecular exclusion column. EBA was equivalent to 125I-labeled albumin for calculation of albumin clearance rates (Calb) across intact and challenged monolayers [Calb (+ vehicle) = 0.12 microliters/min; Calb (+10 nM alpha-thrombin) = 0.47 microliters/min; Calb (+5 mg/ml trypsin) = 1.29 microliters/min]. Transfer of EBA was linear with time in both the endothelial cell monolayer model and the perfused lung. EBA was a sensitive marker for early edema in the perfused lung (before detectable weight gain) as well as for severe edema in the oxidant-injured lung (marked EBA accumulation in lavage fluid) and was a more specific marker for protein transfer than lavage fluid protein. EBA transfer is a convenient, reproducible, and accurate means to assess alterations in vascular permeability.
TL;DR: Blood volume, esophageal and rectal temperatures, forearm blood flow, and elevations in serum osmolality and sodium concentration during 2 h of exercise with fluid ingestion were measured.
Abstract: The purpose of this experiment was to determine whether fluid ingestion attenuates the hyperthermia and cardiovascular drift that occurs during exercise dehydration due to increases in blood volume...
TL;DR: It is concluded that rat DVL muscle is particularly vulnerable to exercise-induced free radical damage and that a disturbance of muscle GSH status is indicative of an oxidative stress.
Abstract: Glutathione status and antioxidant enzymes in various types of rat skeletal muscle were studied after an acute bout of exercise (Ex) at different intensities. Glutathione (GSH) and glutathione disulfide (GSSG) concentrations were the highest in soleus (SO) muscle, followed by those in deep (DVL) and then superficial (SVL) portions of vastus lateralis. In DVL, but not in SO or SVL, muscle GSH increased proportionally with Ex intensity and reached 1.8 +/- 0.08 mumol/g wet wt compared with 1.5 +/- 0.03 (P < 0.05) in resting controls (R). GSSG in DVL was increased from 0.10 +/- 0.01 mumol/g wet wt in R to 0.14 +/- 0.01 (P < 0.05) after Ex. Total glutathione (GSH + GSSG) contents in DVL were also significantly elevated with Ex, whereas GSH/GSSG ratio was unchanged. Activities of GSH peroxidase (GPX), GSSG reductase (GR), and catalase (CAT) were significantly higher in SO than in DVL and SVL, but there was no difference in superoxide dismutase activity between the three muscle types. Furthermore, Ex at moderate intensities elicited significant increases in GPX, GR, and CAT activities in DVL muscle. None of the antioxidant enzymes was affected by exercise in SO. It is concluded that rat DVL muscle is particularly vulnerable to exercise-induced free radical damage and that a disturbance of muscle GSH status is indicative of an oxidative stress.