Showing papers in "Journal of Applied Physiology in 1982"
TL;DR: The exponential behavior of VE, VO2, and VCO2 in response to moderate exercise is best described by a model that incorporates only the second phase of the response.
Abstract: To determine the precise nonsteady-state characteristics of ventilation (VE), O2 uptake (VO2), and CO2 output (VCO2) during moderate-intensity exercise, six subjects each underwent eight repetition...
669 citations
TL;DR: The relationship between the mean transdiaphragmatic pressure swing developed with each inspiration (Pdi) and the fraction of the breathing cycle time spent in inspiration (TI/Ttot) was related to the maximal time that such a run could be sustained (Tlim).
Abstract: The relationship between the mean transdiaphragmatic pressure swing developed with each inspiration (Pdi) and the fraction of the breathing cycle time spent in inspiration (TI/Ttot) (Pdi X TI/Ttot)...
639 citations
TL;DR: The utility of the doubly labeled water method for the determination of energy expenditure and water output was investigated in humans, and subjects could maintain their daily activities without restriction.
Abstract: The utility of the doubly labeled water method for the determination of energy expenditure and water output was investigated in humans. Approximately 10 g of 18O and 0.5 g of 2H as water was orally administered to four healthy adults. Total body water was determined from the isotope dilution, and the ensuing 18O and 2H disappearance rates from body water were determined for 13 days by mass spectrometric isotope ratio analysis of the urinary water. During this period, subjects were maintained on a measured diet to determine energy and water intake. The energy expenditure from the doubly labeled water method differed from dietary intake plus change in body composition by an average of 2%, with a coefficient of variation of 6%. The water outputs determined by the two methods differed by 1%, with a coefficient of variation of 7%. The doubly labeled water method is noninvasive, and the subjects could maintain their daily activities without restriction.
576 citations
TL;DR: A general model is developed to account for all kinds of periodic breathing resulting from instability in respiratory control: in normals during sleep and on acute exposure to high altitude, in sleeping infants, and in patients with cardiovascular or neurologic lesions.
Abstract: A general model is developed to account for all kinds of periodic breathing (PB) resulting from instability in respiratory control: in normals during sleep and on acute exposure to high altitude, in sleeping infants, and in patients with cardiovascular or neurologic lesions. It is found that in almost every case the ventilatory oscillation is mediated predominantly by the peripheral controller. System stability is decreased by hypoxia, hypercapnia, increased lung washout times, prolonged lung-chemoreceptor delays, and high controller sensitivity. Stability is enhanced by large lung CO2 and O2 storage volumes but little affected by body tissue stores. Using our own measurements of lung-ear delays, the model predicts that the mean cycle time of PB decreases from about 30 s at sea level to 20 s at 14,000 ft, in excellent agreement with data from other studies. Allometric scaling of the relevant parameters also shows close agreement between model predictions and data obtained on infants.
558 citations
TL;DR: The results favor the use of VE/VO2 for noninvasive detection of the AT because it proved to be the most sensitive and reliable ventilatory or gas exchange index studied.
Abstract: This study was undertaken to determine which of four commonly used ventilatory or gas exchange indices provides the most accurate and reliable detection of the anaerobic threshold (AT). Sixteen subjects performed two cycle ergometer tests to volitional fatigue. After 4 min of unloaded cycling, the work rate was increased 20 W/min. Ventilatory and gas exchange measurements were made every 30 s throughout each test. During one of the two tests (randomly assigned), venous blood was also sampled every 30 s for subsequent determinations of blood lactate (HLa) concentration. Four ventilatory and gas exchange indices (VE, VCO2, R, VE/VO2) were used separately to detect the AT. The AT determined from systematic increases in HLa concentration was used as the criterion measure. AT values (means +/- SE) (VO2, l/min) using VE, VCO2, R, VE/VO2, and HLa were 1.79 +/- 0.11, 1.74 +/- 0.11, 1.58 +/- 0.06, 1.84 +/- 0.11, and 1.85 +/- 0.11 l/min, respectively. The highest correlation between a ventilatory or gas exchange AT and ATHLa (i.e., criterion measure) was found for VE/VO2 (r=0.93, P less than 0.001). The VE/VO2 also provided the highest test-retest correlation for detection of the AT (r = 0.93, P less than 0.001). Multiple correlational analyses did not significantly enhance detection of the AT. These results favor the use of VE/VO2 for noninvasive detection of the AT because it proved to be the most sensitive and reliable ventilatory or gas exchange index studied.
522 citations
TL;DR: The relationship between running speed (RS) and heart rate (HR) was determined in 210 runners and the velocity at the anaerobic threshold (AT), established by means of blood lactate measurements, and Vd were coincident in 10 runners, showing that AT is critical in determining the running pace in aerobic competitive events.
Abstract: The relationship between running speed (RS) and heart rate (HR) was determined in 210 runners. On a 400-m track the athletes ran continuously from an initial velocity of 12–14 km/h to submaximal ve...
474 citations
TL;DR: The influence of intensity and daily duration of exercise on cytochrome c concentration in the three muscle fiber types was assessed in rats that were treadmill trained for 8 wk (5 days/wk) by 1 of 19 protocols.
Abstract: The influence of intensity and daily duration of exercise on cytochrome c concentration in the three muscle fiber types was assessed in rats that were treadmill trained for 8 wk (5 days/wk) by 1 of 19 protocols. The importance of exercise duration was determined at six running intensities (10, 20, 30, 40, 50, and 60 m/min). Daily run times resulted in a maximal adaptive change for each running intensity. The general pattern of cytochrome c change, caused by increasing daily run times, followed a first-order manner in all fiber types. The final time-independent asymptotic values were dependent on the intensity of running. In addition, as running intensity was increased, the length of daily run time required to achieve the peak adaptive response was shortened. The intensity influence was very different between fiber types. In the fast-twitch red fiber, the maximal time-independent response at each work intensity was altered by exercise intensity at only submaximal work loads (i.e., the adaptation from 19 to 29 nmol/g was not further increased at 50 and 60 m/min). In contrast, the adaptive response in the fast-twitch white fiber began at 30 m/min (approx 80% VO2max) and increased exponentially as intensity was increased (200% increase at 60 m/min). Whether this different adaptive response between fiber types is due solely to the ordered recruitment of motor units remains to be determined.
421 citations
TL;DR: In this article, the authors measured the mass, thickness, area, and length of diaphragm muscle at necropsy to assess the consequences of alterations in body weight and muscularity.
Abstract: To assess the consequences to the human diaphragm of alterations in body weight and muscularity, we measured the mass, thickness, area, and length of diaphragm muscle at necropsy. Of 33 subjects who were clinically well until sudden death, 27 had sedentary occupations and normal weight (group N), while 6 were nonobese laborers whose average weight was 40% greater than normal (group M). Among 37 patients dying of more prolonged illness, 23 were of normal weight (group W), while 14 weighed 71% of normal (group U). Subjects with obesity, chronic pulmonary disease, or edema were excluded. Disease per se did not significantly affect diaphragm dimensions. However, in group M diaphragm muscle mass, thickness, area, and length were 165, 129, 125, and 117% of normal (P less than 0.005), whereas in group U the corresponding values were 57, 73, 77, and 83% (P less than 0.001). Thus alterations in body weight and muscularity profoundly affect diaphragm muscle mass, causing a nearly threefold variation between muscular normal subjects and underweight patients.
359 citations
TL;DR: Although the position of the ankle joint affected electromyographic (EMG) activity recorded during maximal voluntary contraction, there was little change in the EMG-to-M wave ratio.
Abstract: The contractile properties of the triceps surae (medial and lateral gastrocnemii and soleus) have been studied in humans. In comparison with most other human muscles, the triceps complex had a slow twitch (mean contraction and half-relaxation times 112.4 +/- 11.1 and 99.6 +/- 14.4 ms, respectively) and a low tetanus fusion frequency (60 Hz). Stretching the muscle caused both the contraction and half-relaxation times to become longer. With the knee bent, the optimum length for torque development corresponded to almost full dorsiflexion of the ankle. Similar results were obtained with the knee extended. The optimum position of the ankle differed considerably from the position of the joint when the leg was at rest. Although the position of the ankle joint affected electromyographic (EMG) activity recorded during maximal voluntary contraction, there was little change in the EMG-to-M wave ratio.
334 citations
TL;DR: Observations suggested that metabolic changes in muscles have a retrograde trophic influence on motor nerves, and the model of limb immobilization permits the study of many fundamental problems concerned with mechanisms by which a muscle adapts so that it can meet the requirements of the external environment.
Abstract: The immobilization of limbs resulted in atrophy of those muscles that are fixed either at or less than resting length. The loss in protein in these muscles can be described by a first-order equation. Decreases in protein synthesis rate in muscles of immobilized limbs occur during the first 6 h of immobilization, and this decrease probably played a role in initiating muscular atrophy. After weeks of immobilization, muscles composed predominately of slow-twitch fibers took on properties characteristic of fast twitch muscles. The EMG activity of muscles in immobilized limbs was reduced to 5--15% of control levels. Insulin responsiveness for 2-deoxyglucose uptake into the soleus muscle of a limb is decreased at the 24th h of limb immobilization. Muscles of immobilized limbs have either no change or a decrease in resting membrane potential, an increase in extrajunctional acetylcholine receptors of lesser magnitude than the increase that occurred in denervated muscle, and no change in acetylcholinesterase activity in neuromuscular junctions. Immobilizing muscles at stretched lengths prevented the decrease in nerve afterhyperpolarization that was seen in muscles immobilized at shortened positions. These observations suggested that metabolic changes in muscles have a retrograde trophic influence on motor nerves. The model of limb immobilization permits the study of many fundamental problems concerned with mechanisms by which a muscle adapts so that it can meet the requirements of the external environment.
330 citations
TL;DR: It is concluded that the model is suitable for the quantitative study of sympathetic/parasympathetic heart rate control in humans, and that the lower resting heart rate in oarsmen is solely due to a reduction in intrinsic cardiac rate, and not to an increase in parasympathy tone.
Abstract: A simple model to characterize sympathetic and parasympathetic effects on heart rate (R) was tested during rest in 10 nonathletes and 8 world-class oarsmen. The model states that R = mnR0, where R0 is the intrinsic cardiac rate, and m and n depend only on sympathetic and parasympathetic activity, respectively. The multipliers, m and n, were determined by dual pharmacological blockade in two sessions under similar conditions, but in one session propranolol and in the other atropine was given first. In agreement with the model, when corrections were made for atropine-induced blood pressure changes, m and n did not depend on which blocking agent was administered first. In athletes the control heart rate [55 +/- 3.3 (SD) beats/min] and R0 (81 +/- 8.3 beats/min) were lower than in nonathletes (62 +/- 6.0, P less than 0.01 and 102 +/- 11, P less than 0.001, respectively). The sympathetic multiplier, m, was similar (1.18 +/- 0.06 vs. 1.20 +/- 0.05, P greater than 0.4) in the two groups, but n, the parasympathetic multiplier, was closer to 1 in the athletes (0.57 +/- 0.03 vs. 0.51 +/- 0.05, P less than 0.01). We conclude that the model is suitable for the quantitative study of sympathetic/parasympathetic heart rate control in humans, and that the lower resting heart rate in oarsmen is solely due to a reduction in intrinsic cardiac rate, and not to an increase in parasympathetic tone.
TL;DR: The exponential character of the cardiodeceleration seen after peak exercise appears to be an intrinsic property of the circulation because it occurred under each experimental condition.
Abstract: To assess the contribution of the autonomic nervous system to heart rate recovery following exertion, heart rate was observed after peak treadmill exercise in six men following parasympathetic blockade (PB) with atropine sulfate (0.03 mg/kg), sympathetic blockade (SB) with propranolol hydrochloride (0.20 mg/kg), double blockade (DB) with both drugs, and no drugs (ND). Least-squares analysis of each subject's heart rate (HR) as an exponential function of recovery time (t) was computed for each treatment giving an equation of the form HR = aebt. HRs at rest, peak exercise, and 10 min of recovery, the coefficients a and b, and the least-squares correlation coefficient (r) were compared among treatments by nonparametric analysis of variance and rank-sum multiple comparisons. HR recovered in an exponential manner after dynamic exercise in each subject with each of the treatment modes (P less than 0.01 for each r, mean across all treatments r = 0.94). Coefficients a and b differed the most between PB and SB. At the cessation of exercise the decreases in venous return and the systemic need for cardiac output are accompanied by an exponential HR decline. The exponential character of the cardiodeceleration seen after peak exercise appears to be an intrinsic property of the circulation because it occurred under each experimental condition.
TL;DR: Observations indicate the presence of reflex pathways that regulate GG muscle activity in response to upper airway pressure loads and could be important in ensuring pharyngeal airway patency.
Abstract: The effects of change in pharyngeal airway pressure on electromyographic (EMG) activity of a pharyngeal dilating muscle (genioglossus) were investigated in 20 anesthetized rabbits. In vagotomized a...
TL;DR: A mathematical model of maximal expiratory flow was developed and bronchial mechanical properties were obtained from measurements in excised human lungs for the central airways and by extrapolations of these data for the peripheral airways.
Abstract: A mathematical model of maximal expiratory flow was developed. Coupled equations describing the pressure losses in the flow and the pressure-area behavior of the airway were integrated along the airway from the periphery to the flow-limiting site. Equations describing pressure losses in the flow were adapted from studied of bronchial casts. The bronchial anatomy utilized was that described by Weibel. Bronchial mechanical properties were obtained from measurements in excised human lungs for the central airways and by extrapolations of these data for the peripheral airways. The maximal flow for air and helium predicted by the model agrees with that of five lungs from which mechanical properties were obtained. The model predictions agree with published values of density and viscosity dependence of maximal flow. At high and midlung volumes, maximal flow is determined primarily by the wave-speed mechanism. At low lung volumes, maximal flow is primarily determined by the coupling of viscous pressure losses and airway mechanical properties.
TL;DR: It is concluded that EMG changes and Tlim are related and are expressions of the metabolic changes induced by the contraction pattern.
Abstract: The time course of the frequency content of the electromyogram (EMG) was studied in the diaphragm of five normal subjects breathing through high inspiratory resistance. The ratio between the power ...
TL;DR: In exercise urea production does not accurately reflect all aspects of amino acid metabolism, and despite the increase in leucine oxidation during exercise, urea concentration and production did not change.
Abstract: We have used the primed constant infusion of di-[15N]urea and [1–13C]leucine to determine the effects of mild exercise (approx 30% Vo2max for 105 min) on urea production and leucine metabolism in h...
TL;DR: The method allows reproducible measurement of ventilatory muscle endurance without dependence on the subject's flow rates or the resistance chosen and both ensures that a constant pressure is generated with each breath and allows the subject to vary his tidal volume freely.
Abstract: We have devised a method for measuring ventilatory muscle endurance as the sustainable inspiratory pressure (SIP), which is the highest pressure a subject can generate in each breath for 10 min. We used a weighted plunger as an inspiratory valve. This both ensures that a constant pressure is generated with each breath and allows the subject to vary his tidal volume freely. Fifteen normal subjects, ages 5--75 yr, had SIP of 82 +/- 6 (SE) cmH2O or 68 +/- 3% of their maximum inspiratory pressure. The respiratory rate was 13 +/- 1 breaths/min with 52 +/- 4% of the respiratory cycle spent in inspiration; end-tidal CO2 pressure increased by 3.3 +/- 1.0 Torr during runs at SIP. Oxygen consumption measured in two subjects rose with increasing pressure below SIP. There was no further increase in oxygen consumption when these subjects breathed with inspiratory pressures above SIP. Our method allows reproducible measurement of ventilatory muscle endurance without dependence on the subject's flow rates or the resistance chosen.
TL;DR: The clearance rates of 50 ml of isosmotic fluids from the lungs of anesthetized, ventilated sheep with lung lymph fistulas and the difference in lymph flow response between the two fluids must be due to the protein in the alveolar fluid.
Abstract: We determined the clearance rates of 50 ml of isosmotic fluids from the lungs of anesthetized, ventilated sheep with lung lymph fistulas. The removal of the liquid volume followed a monoexponential process over 4 h for both Ringer lactate [half time (t 1/2) = 3 h] and autologous serum (t 1/2 = 6 h). Lymph flow did not increase with Ringer lactate, indicating that the alveolar fluid was cleared via the circulation. With serum, however, lymph flow increased 40%. In both groups the lymph-to-plasma protein concentration ratio fell slightly. Using protein tracers in the alveolar instillate, we found that less than 2% of the protein entered the lymph and plasma. Almost all of the protein remained in the air spaces and was concentrated in proportion to the amount of liquid volume that was cleared. Clearance of liquid volume from alveoli to interstitium could be due to subatmospheric interstitial fluid pressure or to active metabolic processes that cause small molecules to leave the alveolar fluid, or both. The results of the serum experiments tend to favor a metabolic process, but passive mechanisms are possible. The difference in lymph flow response between the two fluids must be due to the protein in the alveolar fluid. We believe Ringer lactate dilutes the alveolar wall interstitial protein concentration thereby decreasing local filtration, whereas serum concentrates alveolar wall interstitial fluids proteins thereby increasing local filtration.
TL;DR: Comparison of the normal ranges of oxygen consumption, heart rate, cardiac index, and stroke index indicated that men have significantly higher values than women, but because of a more rapid decline with age in men, the older women had higher heart rates than the older men.
Abstract: The normal range of maximal values for oxygen consumption, heart rate, cardiac index, and stroke index during treadmill exercise testing are presented for 98 men and 104 women for ages 20–75 yr. Th...
TL;DR: Data show that hyperventilation occurs during intense exercise, even when there is no increase in plasma [H+], and it is possible that nonhumoral stimuli originating in the active muscles or in the brain elicit thehyperventilation observed during intense Exercise.
Abstract: This study was undertaken to determine if patients who lack muscle phosphorylase (i.e., McArdle's disease), and therefore the ability to produce lactic acid during exercise, demonstrate a normal hy...
TL;DR: It was concluded that sampling between 3 and 5 sites in the different muscles was necessary to reduce the between-site standard deviation to 5% and to determine the variability of slow-twitch and fast-twitch fiber distributions.
Abstract: The variability of fiber type distributions between different regions of the same human muscle is believed to be small, based on the sampling of between two and four sites. The objective of the present investigation was to determine the variability of slow-twitch (ST) and fast-twitch (FT) fiber distributions using a more extensive sampling technique than those previously employed. The soleus, biceps, triceps, and vastus lateralis muscles were excised from each of four young men who had died suddenly. Between 13 and 17 sites were sampled from each of the muscles; 3 transverse areas were then examined within each sample. Fiber type distributions were determined from photographs of sections stained for myofibrillar adenosine triphosphatase at pH 10.3, 10.0, or 4.3. The numbers of fibers counted in the four muscles ranged between a mean of 13,660 and a mean of 21,601. The variability in fiber type distributions observed between sites and areas within a site were statistically greater (P less than 0.01) than could be expected from muscles whose fiber type distributions are equally distributed throughout the muscle. It was concluded that sampling between 3 and 5 sites in the different muscles was necessary to reduce the between-site standard deviation to 5%.
TL;DR: The data suggest that the stress of treadmill running acts as a stimulus to greater Bh-Ep/Bh-LPH secretion, a reduction in its degradation, or a combination of these, which leads to increased levels of these ligands in venous blood.
Abstract: Six well-trained endurance athletes were studied to determine if submaximal treadmill exercise results in increased plasma levels of beta-endorphin/beta-lipotropin (Bh-Ep/Bh-LPH) immunoreactivity. Bh-Ep/Bh-LPH immunoreactivity was measured by radio immunoassay in plasma from six experienced runners before and after 30-min treadmill runs at a self-selected pace, 60 and 80% VO2 max, and a control experiment of 30 min rest. All tests were randomized and occurred during the same time of day for a given subject (0600--1500 h). Preexercise Bh-Ep/Bh-LPH values averaged between 10 and 20 pg/ml and increased two- to fivefold after each run. The increase was statistically significant (P less than 0.05) only after the 60% run when Bh-Ep/Bh-LPH increased to a mean of 58.3 pg/ml. A large individual variation in the Bh-Ep/Bh-LPH response to running was noted. Mood state and perceptual data were also collected, and no significant relationship with Bh-Ep/Bh-LPH was evident. These data suggest that the stress of treadmill running acts as a stimulus to greater Bh-Ep/Bh-LPH secretion, a reduction in its degradation, or a combination of these, which leads to increased levels of these ligands in venous blood. The physiological significance of these increased plasma levels is not clear.
TL;DR: The principal stimulus for this apneic reflex is the absence or reduced concentration of Cl- (or small anions that can functionally replace Cl-) in the laryngeal fluid.
Abstract: In neonatal mammals the introduction of water and some other fluids into the larynx causes prolonged reflex apnea by stimulation of afferents in the superior laryngeal nerve (SLN). We have studied ...
TL;DR: The observation that the T(vent) and T(lac) could be manipulated independently of each other reveals limitations in using the T (vent) to estimate the so-called anaerobic threshold.
Abstract: Nine male subjects performed continuous incremental exercise on a bicycle ergometer pedaling at 50 and 90 rpm in a normal glycogen state (NG) and at 50 rpm in a glycogen-depleted state (GD) to dete...
TL;DR: The response to high-dose endotoxin in sheep closely resembles acute respiratory failure in humans following gram-negative septicemia and increased with increasing survival time after endotoxin infusion, suggesting that pulmonary edema accumulated at the same rate in all fatally injured sheep, regardless of other variables.
Abstract: Infusion of Escherichia coli endotoxin (0.12–0.5 micrograms/kg) into unanesthetized sheep causes transient pulmonary hypertension and several hours of increased lung vascular permeability, after wh...
TL;DR: Formaldehyde-induced fluorescence reveals numerous serotonin-containing cells within the primary epithelium of the fish gill, similar to those found within the wall of lung airways in mammals and submammalian vertebrates.
Abstract: Formaldehyde-induced fluorescence reveals numerous serotonin-containing cells within the primary epithelium of the fish gill. These cells are isolated or clustered and are supported by the epithelial basal lamina. They never reach the external medium and are found on the internal side of the primary lamellae, facing the respiratory water flow. With the electron microscope, these cells are found to contain dense-cored vesicles (DCV) of 80-100 nm. Nerve profiles are consistently found close to DCV cells. After having crossed the basal lamina, nerve fibers form endings on DCV-containing cells. These endings display both small clear vesicles and DCV and are in direct contact with DCV cells. Specific membrane alterations are suggestive of efferent synapses. These cells are considered neuroepithelial cells, similar to those found within the wall of lung airways in mammals and submammalian vertebrates. Structure and localization are suggestive of a tissue O2 sensor.
TL;DR: An analysis of the mechanics of this model yields relations among surface area, recoil pressure, lung volume, and surface tension that are consistent with published data for lung volumes below 80% of total lung capacity.
Abstract: The appearance of the microstructure of the lung as revealed in transmission and scanning electron micrographs of perfusion-fixed air- and saline-filled lungs suggests the following model for the s...
TL;DR: In this paper, the authors found that the site of the flow-limiting segment at FRC during maximal expiratory maneuvers is in large proximal airways, similar to the adult; and the relationship of airway size to parenchymal size may be similar in neonates and adults or, in fact, airways may be larger, relative to the parenchyma, in infants.
Abstract: Maximal flows at functional residual capacity (VmaxFRC) from partial expiratory flow-volume (PEFV) curves (achieved with rapid compression of the chest) were obtained on 11 healthy newborn babies Mean VmaxFRC, size corrected by dividing absolute values by measured thoracic gas volume, was 190 TGV's/s Specific upstream conductances were high, and the cross-sectional area of the flow-limiting segment was estimated to be approximately 030 cm2 in the three infants on whom recoil pressures at FRC were also measured The cross-sectional area of the major bronchi in the neonate is approximately 026-030 cm2 PEFV curves were convex to the volume axis Many of the neonates increased their flows while breathing a helium-oxygen gas mixture These results suggest 1) size-corrected flows are higher in the neonate than in older children or adults; 2) the site of the flow-limiting segment at FRC during maximal expiratory maneuvers is in large proximal airways, similar to the adult; and 3) the relationship of airway size to parenchymal size may be similar in neonates and adults or, in fact, airways may be larger, relative to parenchyma, in neonates These physiological data do not support the hypothesis, based on pathological studies, that peripheral airways are disproportionately smaller (when compared with central airways) in infants than in adults
TL;DR: The diaphragm length-lung volume relation is curvilinear, with length increasing primarily in the portion of the diaphragem apposed to the chest wall, generally conforming to force-length behavior of isolated muscle.
Abstract: To characterize the in vivo force-length relation of the human diaphragm, we related pressures during static inspiratory efforts (Pmus and Pdi, respiratory muscle and transdiaphragmatic pressures, respectively) to diaphragm lengths measured on chest X rays from 22 normal subjects. At total lung capacity, the intersection of diaphragm and chest wall contours corresponds to the anatomic junction of diaphragm and chest wall. This point is located by skeletal landmarks to reveal the entire diaphragm contour on films taken at lower lung volumes. To validate the X-ray measurements, corresponding diameters were measured on 32 normal diaphragms at necropsy. After correction for height and diaphragm position, in vivo and necropsy length estimates along the coronal section agreed within 9%. The diaphragm length-lung volume relation is curvilinear, with length increasing primarily in the portion of the diaphragm apposed to the chest wall. As length increases, Pmus and Pdi rise sharply then plateau, generally conforming to force-length behavior of isolated muscle. However, absence of a Pdi peak at presumed diaphragm resting length suggests that Pdi is submaximal during voluntary inspiratory effort.
TL;DR: The findings indicate that one- leg exercise, compared with two-leg exercise, involves circulatory adaptations that respond differently to one-leg training and implies that oxygen supply to one large muscle group of exercising muscles may be limited by vasoconstriction when another large group of muscles is exercising simultaneously.
Abstract: Six young healthy male subjects performed submaximal and maximal exercise on bicycle ergometers with one leg and two legs before and after 8 wk of one-leg training with each of both legs. The following variables were measured during one- and two-leg exercise: oxygen uptake, heart rate, mean arterial blood pressure, cardiac output, leg blood flow, and iliac arteriovenous differences for oxygen and lactate. After training the maximal oxygen uptake during one- and two-leg exercise was increased by 19 and 11%, respectively. The corresponding cardiac outputs increased by 16 and 11%, respectively. During submaximal one-leg exercise, heart rate decreased by 11%, whereas a decrease of only 2% was seen during submaximal two-leg exercise. Mean blood pressure decreased by about 10 Torr in both types of exercise and during both submaximal and maximal exercise. Maximal leg blood flow increased only by 1.2 l/min during one-leg exercise. Leg blood flow and leg oxygen uptake were smaller during two-leg exercise than during one-leg exercise and more so after training. These findings indicate that one-leg exercise, compared with two-leg exercise, involves circulatory adaptations that respond differently to one-leg training. The findings further imply that oxygen supply to one large muscle group of exercising muscles may be limited by vasoconstriction when another large group of muscles is exercising simultaneously.