Showing papers in "Journal of Applied Physiology in 1996"
TL;DR: A rapid way to "creatine load" human skeletal muscle is to ingest 20 g of creatine for 6 days, which can be maintained by ingestion of 2 g/day thereafter, and the ingestion of 3 g creatine/day is in the long term likely to be as effective at raising tissue levels as this higher dose.
Abstract: The effect of dietary creatine and supplementation on skeletal muscle creatine accumulation and subsequent degradation and on urinary creatinine excretion was investigated in 31 male subjects who ingested creatine in different quantities over varying time periods. Muscle total creatine concentration increased by approximately 20% after 6 days of creatine supplementation at a rate of 20 g/day. This elevated concentration was maintained when supplementation was continued at a rate of 2 g/day for a further 30 days. In the absence of 2 g/day supplementation, total creatine concentration gradually declined, such that 30 days after the cessation of supplementation the concentration was no different from the presupplementation value. During this period, urinary creatinine excretion was correspondingly increased. A similar, but more gradual, 20% increase in muscle total creatine concentration was observed over a period of 28 days when supplementation was undertaken at a rate of 3 g/day. In conclusion, a rapid way to "creatine load" human skeletal muscle is to ingest 20 g of creatine for 6 days. This elevated tissue concentration can then be maintained by ingestion of 2 g/day thereafter. The ingestion of 3 g creatine/day is in the long term likely to be as effective at raising tissue levels as this higher dose.
749 citations
TL;DR: It is demonstrated that type IID/X fibers make up a significant portion of the adult rat muscle mass and are intermediate to type IIA and IIB fibers in regard to fiber size and oxidative potential.
Abstract: A population of muscle fibers containing a myosin heavy-chain isoform IId (or 2x) has recently been identified in rat muscle. The purpose of this study was to histochemically determine the relative population and size of muscle fibers composed of type IID/X fibers as well as type I, IIA, and IIB fibers to estimate the absolute mass of the different types of fibers in rat muscle. In addition, muscle citrate synthase activity was measured to determine the relationship between fiber composition and muscle oxidative capacity. Seventy-six muscles or muscle parts from the face, neck, shoulder, arm, trunk, hip, thigh, and leg of three adult (4.5-5 mo of age) male Sprague-Dawley rats were removed, weighed, and frozen for histochemical and biochemical analyses. The data demonstrated that type IIB fibers make up 71% of the total muscle mass, type IID/X fibers 18%, type IIA fibers 5%, and type I fibers 6%. The mean cross-sectional area across all muscles was 5,078 +/- 175 microns 2 for type IIB fibers, 3,078 +/- 105 microns2 for type IID/X fibers, 2,045 +/- 80 microns2 for type IIA fibers, and 1,898 +/- 90 microns2 for type I fibers. Citrate synthase activity, an indicator of muscle mitochondrial content, was most closely related to the population of type IIA fibers and was in the rank order of type IIA > I > IID/X > IIB. NADH-tetrazolium reductase staining intensity also confirmed this order. These data demonstrate that type IID/X fibers make up a significant portion of the adult rat muscle mass and are intermediate to type IIA and IIB fibers in regard to fiber size and oxidative potential.
704 citations
TL;DR: This review examines the experimental evidence that provides the foundation for the current understanding of the benefits, consequences, and control of eccentric contractions and suggests a new hypothesis: that the neural commands controlling eccentric contraction are unique.
Abstract: Enoka, Roger M. Eccentric contractions require unique activation strategies by the nervous system. J. Appl. Physiol. 81(6): 2339–2346, 1996.—Eccentric contractions occur when activated muscles are ...
645 citations
TL;DR: The data suggest that aerobic metabolism provides a significant part (approximately 49%) of the energy during the second sprint, whereas PCr availability is important for high power output during the initial 10 s.
Abstract: This study examined the contribution of phosphocreatine (PCr) and aerobic metabolism during repeated bouts of sprint exercise. Eight male subjects performed two cycle ergometer sprints separated by 4 min of recovery during two separate main trials. Sprint 1 lasted 30 s during both main trials, whereas sprint 2 lasted either 10 or 30 s. Muscle biopsies were obtained at rest, immediately after the first 30-s sprint, after 3.8 min of recovery, and after the second 10- and 30-s sprints. At the end of sprint 1, PCr was 16.9 +/- 1.4% of the resting value, and muscle pH dropped to 6.69 +/- 0.02. After 3.8 min of recovery, muscle pH remained unchanged (6.80 +/- 0.03), but PCr was resynthesized to 78.7 +/- 3.3% of the resting value. PCr during sprint 2 was almost completely utilized in the first 10 s and remained unchanged thereafter. High correlations were found between the percentage of PCr resynthesis and the percentage recovery of power output and pedaling speed during the initial 10 s of sprint 2 (r = 0.84, P < 0.05 and r = 0.91, P < 0.01). The anaerobic ATP turnover, as calculated from changes in ATP, PCr, and lactate, was 235 +/- 9 mmol/kg dry muscle during the first sprint but was decreased to 139 +/- 7 mmol/kg dry muscle during the second 30-s sprint, mainly as a result of a approximately 45% decrease in glycolysis. Despite this approximately 41% reduction in anaerobic energy, the total work done during the second 30-s sprint was reduced by only approximately 18%. This mismatch between anaerobic energy release and power output during sprint 2 was partly compensated for by an increased contribution of aerobic metabolism, as calculated from the increase in oxygen uptake during sprint 2 (2.68 +/- 0.10 vs. 3.17 +/- 0.13 l/min; sprint 1 vs. sprint 2; P < 0.01). These data suggest that aerobic metabolism provides a significant part (approximately 49%) of the energy during the second sprint, whereas PCr availability is important for high power output during the initial 10 s.
640 citations
TL;DR: The analysis of the early phase (first 10-15 s) of the on-transition indicates that bulk delivery of O2 to the working muscles is not limiting VO2leg kinetics, but the present results cannot discriminate between maldistribution of blood flow/VO2 vs. inertia the intracellular oxidative machinery as the limiting factor.
Abstract: Muscle O2 uptake (VO2) kinetics in response to an augmented energetic requirement (on-transition) has never been directly determined in humans. We have developed a constant-infusion thermodilution technique that allowed rapid measurements of leg blood flow (Qleg) and, in conjunction with frequent serial measurement of arteriovenous O2 content difference across the leg [(Ca - Cv)O2leg], permitted the determination of the VO2 of the leg (VO2leg) at 3- to 4-s time intervals. VO2leg kinetics during the on-transition was taken as a close approximation of muscle VO2 (VO2mus) kinetics. Alveolar VO2 (VO2A), Qleg, leg O2 delivery [(Q.CaO2leg)], (Ca - Cv)O2leg, and VO2leg kinetics were determined in six trained subjects [age 22.8 +/- 4.4 (SD) yr; maximal O2 uptake 59.1 +/- 5.3 ml.kg-1.min-1] during the transition from unloaded pedaling to a workload (loaded pedaling; LP) (183 +/- 20 W) well below the previously determined ventilatory threshold. For all variables, two distinct phases were recognized. During the first 10-15 s of loaded pedaling (phase I), VO2A, Qleg, and (Q.CaO2)leg increased rapidly, whereas VO2leg increased only slightly and (Ca - Cv)O2leg actually decreased. After phase I, all variables showed a monoexponential increase (phase II), with similar time courses [slightly faster for (Ca - CV)O2leg]. In a consideration of both phases, the half times of the responses among variables were not significantly different: 25.5 +/- 2.6 s for VO2A, 26.6 +/- 7.6 s for Qleg, 26.9 +/- 8.3 s for (Q.CaO2leg, 23.5 +/- 1.3 s for (Ca - Cv)O2leg, and 27.9 +/- 5.7 s for VO2leg. We conclude that during the on-transition the kinetics of VO2A and VO2leg, as measured by these methods, are similar. The analysis of the early phase (first 10-15 s) of the on-transition indicates that bulk delivery of O2 to the working muscles is not limiting VO2leg kinetics. However, the present results cannot discriminate between maldistribution of blood flow/VO2 vs. inertia the intracellular oxidative machinery as the limiting factor.
599 citations
TL;DR: The fractal dynamics of spontaneous stride interval are normally quite robust and intrinsic to the locomotor system, and this fractal property of neural output may be related to the higher nervous centers responsible for the control of walking rhythm.
Abstract: Fractal dynamics were recently detected in the apparently “noisy” variations in the stride interval of human walking. Dynamical analysis of these step-to-step fluctuations revealed a self-similar p...
590 citations
TL;DR: It is concluded that the primary systemic hemodynamic event, i.e., the postural decrease in stroke volume, was similar in finishers and nonfinishers and the heart rate response and cardiac output during standing were not significantly different, but thePostural vasoconstrictor response was significantly greater among the finishers.
Abstract: Orthostatic intolerance occurs commonly after spaceflight, and important aspects of the underlying mechanisms remain unclear. We studied 14 individuals supine and standing before and after three sp...
571 citations
TL;DR: The hypothesis that the amplitude of the additional slow component of O2 uptake (VO2) during heavy exercise is correlated with the percentage of type II (fast-twitch) fibers in the contracting muscles is tested is tested and it is concluded that fiber type distribution significantly affects both the fast and slow components of VO2 duringheavy exercise.
Abstract: We tested the hypothesis that the amplitude of the additional slow component of O2 uptake (VO2) during heavy exercise is correlated with the percentage of type II (fast-twitch) fibers in the contracting muscles. Ten subjects performed transitions to a work rate calculated to require a VO2 equal to 50% between the estimated lactate (Lac) threshold and maximal VO2 (50% delta). Nine subjects consented to a muscle biopsy of the vastus lateralis. To enhance the influence of differences in fiber type among subjects, transitions were made while subjects were pedaling at 45, 60, 75, and 90 rpm in different trials. Baseline VO2 was designed to be similar at the different pedal rates by adjusting baseline work rate while the absolute increase in work rate above the baseline was the same. The VO2 response after the onset of exercise was described by a three-exponential model. The relative magnitude of the slow component at the end of 8-min exercise was significantly negatively correlated with % type I fibers at every pedal rate (r = 0.64 to 0.83, P 0.05). We conclude that fiber type distribution significantly affects both the fast and slow components of VO2 during heavy exercise and that fiber type and fitness may have both codependent and independent influences on the metabolic and gas-exchange responses to heavy exercise.
497 citations
TL;DR: Ecc is more effective than Con isokinetics training for developing strength in Ecc isokinetic muscle actions and that Con is moreeffective than Ecc iskinetic training fordeveloping strength in Con iskinetics muscle actions.
Abstract: Higbie, Elizabeth J., Kirk J. Cureton, Gordon L. Warren III, and Barry M. Prior. Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation.J. Appl...
477 citations
TL;DR: It is concluded that adaptations to training with maximal eccentric contractions are specific to eccentric muscle actions that are associated with greater neural adaptation and muscle hypertrophy than concentric exercise.
Abstract: We tested the hypothesis that exercise training with maximal eccentric (lengthening) muscle actions results in greater gains in muscle strength and size than training with concentric (shortening) a...
430 citations
TL;DR: Effect of leucine metabolite β-hydroxy-β-methylbutyrate on muscle metabolism during resis...
Abstract: Nissen, S., R. Sharp, M. Ray, J. A. Rathmacher, D. Rice, J. C. Fuller, Jr., A. S. Connelly, and N. Abumrad. Effect of leucine metabolite β-hydroxy-β-methylbutyrate on muscle metabolism during resis...
TL;DR: The data suggest that factors other than PCSA contribute to the force output potential of ankle plantar flexors and dorsiflexors in humans.
Abstract: Reported specific tension measurements for human skeletal muscle vary widely. This variability could be due, at least in part, to the determination of the physiological cross-sectional area (PCSA) of the muscles. In the present study, serial magnetic resonance images were taken every 10 mm along the lower leg of 8 male subjects to calculate the volume and subsequently the PCSAs of the individual muscles producing plantar flexor and dorsiflexor torques. Maximum plantar flexor and dorsiflexor voluntary isometric torques were determined at ankle joint angles of 90, 100, 110, and 120 degrees. Peak tendon force estimated from torque and moment arm measurements was more than fourfold higher in the plantar flexors (3,623 +/- 136 N) than in the dorsiflexors (832 +/- 19 N). PCSAs were about eight- and threefold higher than the anatomic cross-sectional areas at the level of maximum girth of the calf for the plantar flexor and dorsiflexor groups, respectively. Mean muscle volume and PCSA were 4.6 and 12 times larger in the plantar flexors compared with the dorsiflexors, respectively. The PCSAs of both plantar flexors (r = 0.92) and dorsiflexors (r = 0.80) were highly correlated with the tendon tension of the respective muscle groups. The maximum specific tension was more than twofold higher in dorsiflexors than in plantar flexors. These data suggest that factors other than PCSA contribute to the force output potential of ankle plantar flexors and dorsiflexors in humans.
TL;DR: Resistance training resulted in hypertrophy of the total muscle CSA and fiber areas with no change in estimated fiber number, whereas capillary changes were proportional to muscle fiber growth.
Abstract: McCall, G. E., W. C. Byrnes, A. Dickinson, P. M. Pattany, and S. J. Fleck. Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training.J. Appl. Physiol. 81...
TL;DR: It is suggested that an improved muscle perfusion during the exercise may be involved consequent to the residual metabolic acidemia from the high-intensity warm-up.
Abstract: The effects of prior exercise on O2 uptake (VO2) kinetics during supra-lactate threshold (LT) cycling were assessed in 11 subjects. Protocols consisted of two consecutive 6-min work bouts separated...
TL;DR: In this paper, Chest wall and lung volume estimation by optical reflectance motion analysis is presented. But the method is not suitable for the analysis of lung tissue. And it cannot be used for lung cancer diagnosis.
Abstract: Cala, S. J., C. M. Kenyon, G. Ferrigno, P. Carnevali, A. Aliverti, A. Pedotti, P. T. Macklem, and D. F. Rochester. Chest wall and lung volume estimation by optical reflectance motion analysis.J. Ap...
TL;DR: Insight is led into the etiology of fetal lung hypoplasia and how it may be remedied in utero and links between lung tissue stress, increased growth, structural remodeling, and the endocrine environment are defined.
Abstract: Fetal lung growth depends on the degree to which lungs are distended with luminal liquid. Fetal lungs are highly distended such that mean luminal volume exceeds the static relaxation volume. This high level of expansion is maintained by fetal breathing movements and by resistive effects of the upper airway during apnea; both factors oppose lung recoil. Mechanical stress in lung and other tissues stimulates cell division and tissue remodeling. Potential transduction mechanisms involve direct effects of cellular tension and mediation of locally released mitogenic factors. Further studies are required to further define links between lung tissue stress, increased growth, structural remodeling, and the endocrine environment. A common cause of fetal lung hypoplasia is a sustained reduction in mean lung expansion. Studies of mechanisms controlling fetal lung expansion have led to insights into the etiology of fetal lung hypoplasia and how it may be remedied in utero. Fetal lung hypoplasia can have long-lasting effects on postnatal lung function, as airway and alveolar formation may be compromised. Preterm birth may also result in incomplete structural development of the lungs as it shortens the period of increased intrauterine lung expansion.
TL;DR: The results indicate that the muscles from rats with both normal and severely depressed systemic levels of IGF-1 respond to functional overload with an increase in local IGF- 1 expression and this elevated IGF-2 may be contributing to the hypertrophy response, possibly via the mobilization of satellite cells to provide increases in muscle DNA.
Abstract: Insulin-like growth factor-1 (IGF-1) is known to have anabolic effects on skeletal muscle cells. This study examined the time course of muscle hypertrophy and associated IGF-1 peptide and mRNA expression. Data were collected at 3, 7, 14, and 28 days after surgical removal of synergistic muscles of both normal and hypophysectomized (HX) animals. Overloading increased the plantaris (Plant) mass, myofiber size, and protein-to-body weight ratio in both groups (normal and HX; P < 0.05). Muscle IGF-1 peptide levels peaked at 3 (normal) and 7 (HX) days of overloading with maximum 4.1-fold (normal) and 6.2-fold (HX) increases. Increases in muscle IGF-1 preceded the hypertrophic response. Total DNA content of the overloaded Plant increased in both groups. There was a strong positive relationship between IGF-1 peptide and DNA content in the overloaded Plant from both groups. These results indicate that 1) the muscles from rats with both normal and severely depressed systemic levels of IGF-1 respond to functional overload with an increase in local IGF-1 expression and 2) this elevated IGF-1 may be contributing to the hypertrophy response, possibly via the mobilization of satellite cells to provide increases in muscle DNA.
TL;DR: Findings indicate that DA and DR result in a greater preservation of MRI-SM, mobilization of SAT from the abdominal region, by comparison with the gluteal-femoral region, and improved functional capacity when compared with DO in obese men.
Abstract: Ross, Robert, John Rissanen, Heather Pedwell, Jennifer Clifford, and Peter Shragge. Influence of diet and exercise on skeletal muscle and visceral adipose tissue in men. J. Appl. Physiol. 81(6): 24...
TL;DR: It is suggested that VEGF, bFGF, and TGF-beta 1 may be involved in the angiogenic response to exercise and that reduced intracellular PO2 (as occurs during normoxic exercise) may be part of the stimulus to such growth factor production.
Abstract: A major adaptation to exercise is new capillary formation in skeletal muscle. On the basis of angiogenesis in tumors and during development, several angiogenic growth factors may be involved, including vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and transforming growth factor-beta 1 (TGF-beta 1). In 9-wk-old female Wistar rats, mRNA expression for these three growth factors in gastrocnemius muscle was examined by quantitative Northern analysis after a single 1-h run at 15 or 20 m/min at 10 degrees incline in room air. A third group ran at 15 m/min in 12% O2, and resting control groups were included at inspired O2 fractions of 0.21 and 0.12. Exercise significantly increased mRNA levels two- to fourfold, which was evident over the first 4 h postexercise; by 8 and 24 h, mRNA levels returned to baseline. For all three factors, mRNA levels were significantly higher after exercise at 20 than at 15 m/min. Hypoxia at rest doubled VEGF and TGF-beta 1 message but had no effect on bFGF. Hypoxic exercise further raised VEGF mRNA levels but had no effect on the other factors. We suggest that VEGF, bFGF, and TGF-beta 1 may be involved in the angiogenic response to exercise and that reduced intracellular PO2 (as occurs during normoxic exercise) may be part of the stimulus to such growth factor production.
TL;DR: The validity, reliability, and protocol for the interpolated twitch technique (ITT) were investigated with isometric plantar flexor and leg extension contractions and there was no significant difference in the ITT sensitivity when twitches, doublets, or quintuplets were used.
Abstract: Behm, D. G., D. M. M. St-Pierre, and D. Perez. Muscle inactivation: assessment of interpolated twitch technique.J. Appl. Physiol. 81(5): 2267–2273, 1996.—The validity, reliability, and protocol for...
TL;DR: Pulmonary clearance of circulating endothelin-1 in dogs in vivo: exclusive role of ETB receptors.
Abstract: Dupuis, Jocelyn, Carl A. Goresky, and Alain Fournier.Pulmonary clearance of circulating endothelin-1 in dogs in vivo: exclusive role of ETB receptors.J. Appl. Physiol. 81(4): 1510–1515, 1996.—The p...
TL;DR: In this paper, the effects of training duration on substrate turnover and oxidation during exercise were investigated, and it was shown that training duration has a significant effect on the substrate turnover during exercise.
Abstract: Phillips, S. M., H. J. Green, M. A. Tarnopolsky, G. J. F. Heigenhauser, R. E. Hill, and S. M. Grant. Effects of training duration on substrate turnover and oxidation during exercise.J. Appl. Physio...
TL;DR: Loss of desmin staining occurred in the absence of contractile or metabolic protein disruption in rabbit muscles subjected to cyclic eccentric contraction, and represents a very early structural manifestation of muscle injury during eccentric contraction.
Abstract: The time course of loss of the 55,000-Da intermediate filament protein desmin was measured in rabbit muscles subjected to cyclic eccentric conrtraction. Rabbit extensor digitorum longus (EDL) and t...
TL;DR: Increased permeability of capillary membranes may be the most important mechanism causing spaceflight-induced PV reduction, which is probably maintained by increased GFR and other mechanisms.
Abstract: The fluid and electrolyte regulation experiment with seven subjects was designed to describe body fluid, renal, and fluid regulatory hormone responses during the Spacelab Life Sciences-1 (9 days) a...
TL;DR: The results from this study show that the cerebral blood flow response to hypoxia and hypercapnia in humans is much faster than has previously been thought.
Abstract: This study examined the dynamics of the cerebral blood flow response to hypoxia and hypercapnia in humans. Middle cerebral artery blood flow (MCAF) was assessed continuously using transcranial Doppler ultrasound. MCAF was calculated on a beat-by-beat basis as the product of the intensity-weighted mean velocity and the total power of the reflected signal. End-tidal PCO2 (PETCO2) and PO2 (PETO2) were controlled using a dynamic end-tidal forcing system. Six repeats of each of four protocols were administered to six subjects. The first was a control protocol with PETO2 held at 100 Torr and PETCO2 held 1-2 Torr above eucapnia throughout. The second was a hypoxic step protocol with PETO2 lowered from control values to 50 Torr for 20 min. The third was a hypercapnic step protocol with PETCO2 elevated from control by 7.5 Torr for 20 min. The fourth was a hypoxic-and-hypercapnic step protocol lasting 20 min. The total power of the Doppler signal remained relatively constant, suggesting that the cross-sectional area of the vessel changed little. After the initial transient in MCAF at the onset of the stimulus, no adaptation or progressive increase was observed over the remaining 20 min. A simple model consisting of a single pure delay, gain terms, time constants, and offsets for the on and off transients was fitted to the hypoxic and hypercapnic protocols. For hypercapnia, all the parameters for the onset were significantly different from the relief of the stimulus. The asymmetry was characterized by a slower on transient than off transient and also by a degree of undershoot after the relief of hypercapnia. Finally, the results from this study show that the cerebral blood flow response to hypoxia and hypercapnia in humans is much faster than has previously been thought.
TL;DR: It is demonstrated that NO synthase inhibition has a modest effect on peak vasodilation during reactive hyperemia but plays a minimal role later, and prostaglandins appear to be important determinants of peak flow.
Abstract: Engelke, Keith A., John R. Halliwill, David N. Proctor, Niki M. Dietz, and Michael J. Joyner. Contribution of nitric oxide and prostaglandins to reactive hyperemia in the human forearm.J. Appl. Phy...
TL;DR: Because of the significant correlation with regulatory metabolites (ADP and PCr) of oxidative phosphorylation, O2 decline rate in immediate postexercise ischemia determined by near-infrared spectroscopy with continuous wave can be utilized for the quantitative evaluation of localized muscle oxidative metabolism.
Abstract: The purpose of this study was to determine whether the initial rate of hemoglobin and myoglobin deoxygenation during immediate postexercise ischemia, a reflection of muscle O2 consumption (VO2mus),...
TL;DR: The current study results reveal that large errors are present in the Burkinshaw SM method and that substantial refinements in the models that form the basis of this IVNA approach are needed.
Abstract: Although skeletal muscle (SM) is a major body component, whole body measurement methods remain limited and inadequately investigated. The aim of the present study was to evaluate the Burkinshaw in vivo neutron activation analysis (IVNA)-whole body 40K-counting and dual-energy X-ray absorptiometry (DXA) methods of estimating SM by comparison to adipose tissue-free SM measured using multiscan computerized axial tomography (CT). In the Burkinshaw method the potassium-to-nitrogen ratios of SM and non-SM lean tissue are assumed constant; in the DXA method the ratio of appendicular SM to total SM is assumed constant at 0.75. Seventeen healthy men [77.5 +/- 13.8 (SD) kg body wt] and eight men with acquired immunodeficiency syndrome (AIDS; 65.5 +/- 7.6 kg) completed CT, IVNA, and DXA studies. SM measured by CT was 34.4 +/- 6.2 kg for the healthy subjects and 27.2 +/- 4.0 kg for the AIDS patients. Compared with CT, the Burkinshaw method underestimated SM by an average of 6.9 kg (20.1%, P = 0.0001) and 6.3 kg (23.2%, P = 0.01) in the healthy men and the men with AIDS, respectively. The DXA method minimally overestimated SM in both groups (2.0 kg and 5.8% in healthy men, P = 0.001; 1.4 kg and 5.1% in men with AIDS, P = 0.16). This overestimate could be explained by a higher actual than assumed ratio of DXA-measured appendicular SM to total body SM (actual = 0.79 +/- 0.05, assumed = 0.75). The current study results reveal that large errors are present in the Burkinshaw SM method and that substantial refinements in the models that form the basis of this IVNA approach are needed. The model on which the DXA-SM method is based also needs further minor refinements, but this is a promising in vivo approach because of less radiation exposure and lower cost than the IVNA and CT methods.
TL;DR: Evidence is provided that in humans, as in rats, the adaptive increase in mitochondrial enzymes in skeletal muscle occurs fairly rapidly in response to exercise training, and there is no support for the claim that this adaptive response is delayed for > 2 wk after the onset of training.
Abstract: Endurance exercise training induces a significant increase in the respiratory capacity of skeletal muscle. This is reflected by a training-induced increase in mitochondrial enzyme activity. One consequence of this adaptation is that there is a decreased reliance on carbohydrate utilization with a concomitant increase in fat utilization, resulting in an improvement in endurance capacity. Recently it has been reported that 7-14 days of cycle ergometer exercise training does not induce an increase in mitochondrial enzyme levels in skeletal muscle but, nevertheless, results in smaller decreases in phosphocreatine and glycogen and smaller increases in Pi and lactate in muscle in response to the same exercise after compared with before training. However, previous studies in rats have shown that an adaptive increase in mitochondrial enzymes is already evident after only 2 days of exercise training. In view of this discrepency, the present study was performed to reevaluate the effect of short-term training (7-10 days) on mitochondrial enzymes in skeletal muscle of humans. Twelve subjects [6 men and 6 women, 27 +/- 5 (SE) yr old] underwent 7 (n = 5) or 10 days (n = 7) of cycle ergometer exercise for 2h/day at 60-70% of peak O2 consumption. Peak O2 consumption was increased by 9% (from 2.97 +/- 0.16 to 3.24 +/- 0.17 l/min) in response to training. Blood lactate levels were lower at the same absolute work rates after than before training. The activities of citrate synthase, beta-hydroxyacyl-CoA dehydrogenase, mitochondrial thiolase, and carnitine acetyltransferase were increased by approximately 30% in response to training. The results of the present study provide evidence that in humans, as in rats, the adaptive increase in mitochondrial enzymes in skeletal muscle occurs fairly rapidly in response to exercise training. They provide no support for the claim that this adaptive response is delayed for > 2 wk after the onset of training.
TL;DR: The morphometric data on the branching pattern and vascular geometry of the human pulmonary arterial and venous trees are presented and the elemental and segmental data are presented.
Abstract: Huang, W., R. T. Yen, M. McLaurine, and G. Bledsoe.Morphometry of the human pulmonary vasculature.J. Appl. Physiol. 81(5): 2123–2133, 1996.—The morphometric data on the branching pattern and vascul...