Rat muscle blood flows during high-speed locomotion

We previously studied blood flow distribution within and among rat muscles as a function of speed from walking (15 m/min) through galloping (75 m/min) on a motor-driven treadmill. The results showed that muscle blood flows continued to increase as a function of speed through 75 m/min. The purpose of the present study was to have rats run up to maximal treadmill speeds to determine if blood flows in the muscles reach a plateau as a function of running speed over the animals' normal range of locomotory speeds. Muscle blood flows were measured with radiolabeled microspheres at 1 min of running at 75, 90, and 105 m/min in male Sprague-Dawley rats. The data indicate that even at these relatively high treadmill speeds there was still no clear evidence of a plateau in blood flow in most of the hindlimb muscles. Flows in most muscles continued to increase as a function of speed. These observed patterns of blood flow vs. running speed may have resulted from the rigorous selection of rats that were capable of performing the high-intensity exercise and thus only be representative of a highly specific population of animals. On the other hand, the data could be interpreted to indicate that the cardiovascular potential during exercise is considerably higher in laboratory rats than has normally been assumed and that inadequate blood flow delivery to the muscles does not serve as a major limitation to their locomotory performance.     

Influence of higher-grade walking on metabolic demands in young untrained Japanese women

The primary purpose of this study was to document the physiological responses of level walking and running (LW/R) at various speeds, and grade walking (GW) at various grades on a treadmill. Twenty-four young untrained Japanese women performed 2 tests on the specially designed treadmill for a higher grade exercise. The first test was the LW/R with increase of speeds, 33.3, 66.7, 91.7, and 116.7 m.min(-1). The first 3 progressions were for walking and the last progression was for running. The second test was the GW with increase of grades 0, 10, 20, and 30% with the velocity of 33.3 m.min(-1) in all progressions. The different combinations of speeds and grade for the progressions used in this study were selected based on the results of preliminary pilot studies, so that the percent heart rate maximim (%HRmax) was reached at the minimum intensities recommended to allow improving cardiorespiratory fitness by the American College of Sports Medicine (ACSM). Significant (p 相似文献   

Muscle blood flow and fiber activity in partially curarized rats during exercise

We previously reported that low doses of d-tubocurarine attenuated glycogen loss in red muscles of rats during treadmill walking but that the initial hyperemia in the muscles was normal. The present studies were performed to 1) determine with electromyography (EMG) whether red muscle fiber activity is reduced in walking, curarized rats and 2) study muscle blood flow and glycogen loss during running with different doses of curare (dose response). At 0.5 min of treadmill walking (15 m/min), integrated EMG in vastus intermedius (VI) muscle was reduced by an average of 18% in curarized (60 micrograms/kg) rats, although blood flow (measured with microspheres) was the same as in saline control rats. Comparison of blood flows and glycogen loss in quadriceps muscles at 1 min of treadmill running (30 m/min) with different curare doses (20-60 micrograms/kg) demonstrated that red muscle glycogen loss was inversely related to curare dose but that blood flows in the same muscles were unaffected by curare. These findings provide support for our previous conclusion that at the initiation of low to moderate treadmill exercise, red muscle blood flow is not proportional to the activity or metabolism of the muscle fibers.     

Regional muscle blood flow capacity and exercise hyperemia in high-intensity trained rats

The purpose of this study was to determine the effects of high-intensity treadmill exercise training on 1) the regional distribution of muscle blood flow within and among muscles in rats during high-intensity treadmill exercise (phase I) and 2) on the total and regional hindlimb skeletal muscle blood flow capacities as measured in isolated perfused rat hindquarters during maximal papaverine vasodilation (phase II). Two groups of male Sprague-Dawley rats were trained 5 days/wk for 6 wk with a program consisting of 6 bouts/day of 2.5-min runs at 60 m/min up a 15% grade with 4.5-min rest periods between bouts. After training, blood flows were measured with the radiolabeled microsphere technique (phase I) in pair-weighted sedentary control and exercise-trained rats while they ran at 60 m/min (0% grade). In phase II of the study, regional vascular flow capacities were determined at three perfusion pressures (30, 40, and 50 mmHg) in isolated perfused hindquarters of control and trained rats maximally vasodilated with papaverine. The results indicate that this exercise training program produces increases in the vascular flow capacity of fast-twitch glycolytic muscle tissue of rats. However, these changes were not apparent in the magnitude or distribution of muscle blood flow in conscious rats running at 60 m/min, since blood flows within and among muscles during exercise were the same in trained and control rats.     

Metabolism of rats running up and down an incline

The purpose of these experiments was to determine oxygen consumption (VO2) in rats as a function of treadmill speed (10, 20, 30, 40, and 50 m . min-1) as they ran on the level and up and down a 16 degree (17.8%) incline. The slopes of the regression lines relating VO2 (ml O2 . kg-1 . min-1) to running speed (m . min-1) were linear for all three inclines. The regression slope for uphill runners (y = 1.25x + 47.7) was greater than the regression slopes for level (y = 0.88x + 41.2) (P less than 0.025) or downhill (y = 0.68x + 39.7) (P less than 0.005) runners, and the regression slope for level runners was greater than that for downhill runners (P less than 0.10). All VO2 measurements were submaximal. In conclusion, incline has a significant effect on the metabolism of rats running on a motor-driven treadmill.     

Effect of hindlimb unweighting on tissue blood flow in the rat.

The purpose of this study was to characterize the distribution of blood flow in the rat during hindlimb unweighting (HU) and post-HU standing and exercise and examine whether the previously reported (Witzmann et al., J. Appl. Physiol. 54: 1242-1248, 1983) elevation in anaerobic metabolism observed with contractile activity in the atrophied soleus muscle was caused by a reduced hindlimb blood flow. After either 15 days of HU or cage control, blood flow was measured with radioactive microspheres during unweighting, normal standing, and running on a treadmill (15 m/min). In another group of control and experimental animals, blood flow was measured during preexercise (PE) treadmill standing and treadmill running (15 m/min). Soleus muscle blood flow was not different between groups during unweighting, PE standing, and running at 15 m/min. Chronic unweighting resulted in the tendency for greater blood flow to muscles composed of predominantly fast-twitch glycolytic fibers. With exercise, blood flow to visceral organs was reduced compared with PE values in the control rats, whereas flow to visceral organs in 15-day HU animals was unaltered by exercise. These higher flows to the viscera and to muscles composed of predominantly fast-twitch glycolytic fibers suggest an apparent reduction in the ability of the sympathetic nervous system to distribute cardiac output after chronic HU. In conclusion, because 15 days of HU did not affect blood flow to the soleus during exercise, the increased dependence of the atrophied soleus on anerobic energy production during contractile activity cannot be explained by a reduced muscle blood flow.     

Thermoregulation during marathon running in cool, moderate, and hot environments.

A well-trained subject, age 38, ran continously for periods ranging from 60 to 165 min on a motor-driven treadmill at 255.7 m/min while confronted with an airflow equivalent to running speed in cool, moderate, and hot environments. After a period of intensive heat acclimatization, treadmill runs were repeated in the moderate and hot conditions. Measurements were also obtained outdoors in a competitive marathon race. Sweat rate (SR) and mean skin temperature (Ts) were linearly related to Tdb. Acclimatization did not alter VO2max or metabolic rate during the treadmill runs, but heart rat (HR),rectal temperature (Tre), and Ts were lower, SR was higher, and maximal run duration longer in the hot environment, postacclimatization. Maximum runs in the hot environment were terminated by a spiralling increase in Tre to hyperthermic levels, due largely to a marked reduction in cutaneous blood flow, probably reflecting cardiovascular overload from the combined muscular and thermoregulatory blood flow demands, coupled with the effects of progressive dehydration. Utilizing partitional calorimetry and the subject's metabolic heat production, two examples of limiting environmental conditions for his marathon running speed were given.     

Effect of exercise modality on oxygen uptake kinetics during heavy exercise

The mechanisms responsible for the oxygen uptake (VO2) slow component during high-intensity exercise have yet to be established. In order to explore the possibility that the VO2 slow component is related to the muscle contraction regimen used, we examined the pulmonary VO2 kinetics during constant-load treadmill and cycle exercise at an exercise intensity that produced the same level of lactacidaemia for both exercise modes. Eight healthy subjects, aged 22-37 years, completed incremental exercise tests to exhaustion on both a cycle ergometer and a treadmill for the determination of the ventilatory threshold (defined as the lactate threshold, Th1a) and maximum VO2 (VO2max). Subsequently, the subjects completed two "square-wave" transitions from rest to a running speed or power output that required a VO2 that was halfway between the mode-specific Th1a and VO2max. Arterialised blood lactate concentration was determined immediately before and after each transition. The VO2 responses to the two transitions for each exercise mode were time-aligned and averaged. The increase in blood lactate concentration produced by the transitions was not significantly different between cycling [mean (SD) 5.9 (1.5) mM] and running [5.5 (1.6) mM]. The increase in VO2 between 3 and 6 min of exercise; (i.e. the slow component) was significantly greater in cycling than in running, both in absolute terms [290 (102) vs 200 (45) ml x min(-1); P<0.05] and as a proportion of the total VO2 response above baseline [10 (3)% vs 6 (1)%; P < 0.05]. These data indicate that: (a) a VO2 slow component does exist for high-intensity treadmill running, and (b) the magnitude of the slow component is less for running than for cycling at equivalent levels of lactacidaemia. The greater slow component observed in cycling compared to running may be related to differences in the muscle contraction regimen that is required for the two exercise modes.     

Gastric emptying during walking and running: effects of varied exercise intensity

Gastric emptying is increased during running (50%-70% maximal aerobic uptake, VO2max) as compared to rest. Whether this increase varies as a function of mode (i.e. walking vs running) and intensity of treadmill exercise is unknown. To examine the gastric emptying characteristics of water during treadmill exercise performed over a wide range of intensities relative to resting conditions, 10 men ingested 400 ml of water prior to each of six 15 min exercise bouts or 15 min of seated rest. Three bouts of walking exercise (1.57 m.s-1) were performed at increasing grades eliciting approximately 28%, 41% or 56% of VO2max. On a separate day, three bouts of running (2.68 ms-1) exercise were performed at grades eliciting approximately 57%, 65% or 75% of VO2max. Gastric emptying was increased during treadmill exercise at all intensities excluding 75% VO2max as compared to rest. Gastric emptying was similar for all intensities during walking and at 57% and 65% VO2max during running. However, running at 74% VO2max decreased the volume of original drink emptied as compared to all lower exercise intensities. Stomach secretions were markedly less during running as compared to walking and rest. These data demonstrate that gastric emptying is similarly increased during both moderate intensity (approximately 28%-65% VO2max) walking or running exercise as compared to resting conditions. However, gastric emptying decreases during high intensity exercise. Increases in gastric emptying during moderate intensity treadmill exercise may be related to increases in intragastric pressure brought about by contractile activity of the abdominal muscles.     

Cardiorespiratory and lactate responses to a 1-hour submaximal running at the lactate threshold

Cardiorespiratory and blood lactate (La) responses to prolonged submaximal running at an intensity relative to lactate threshold (LT) were examined in 15 recreational runners, aged 19 to 32. In test 1 where treadmill speed was progressively incremented by 10-20m/min until exhaustion, oxygen uptake at the LT (VO2 @ LT: 2.34 +/- 0.331/min or 41.6 +/- 5.7 ml/kg/min) and VO2max (3.58 +/- 0.341/min or 63.6 +/- 5.5 ml/kg/min) were measured. In test 2, the subject was required to run on the treadmill for 1 hour at a fixed velocity (Vt) which corresponded to his Vt @ LT. As expected, mean VO2 ranged during the 1-h submaximal running from 2.31 +/- 0.411/min or 63.0 +/- 7.8% VO2max at min 10-20 to 2.52 +/- 0.351/min or 69.2 +/- 6.2% VO2max at min 50-60, both of which were close to VO2 @ LT (65.2 +/- 4.4% VO2max). The slight decrease in blood La was found from min 20 to min 60, and this was accompanied by a parallel decline in respiratory exchange ratio. Shifts in the energy substrate toward a reliance on fat oxidation may occur during the course of 1-h running at Vt @t LT. The small oxygen debt observed after the 1-h running may confirm the assumption that prolonged running at Vt at LT would be performed in an almost fully aerobic steady state. We conclude that prolonged running at Vt @ LT may possibly maximize health-related benefits in the healthy adult.     

Distribution of blood flow in muscles of miniature swine during exercise

The purpose of this study was to determine how the distribution of blood flow within and among the skeletal muscles of miniature swine (22 +/- 1 kg body wt) varies as a function of treadmill speed. Radiolabeled microspheres were used to measure cardiac output (Q) and tissue blood flows in preexercise and at 3-5 min of treadmill exercise at 4.8, 8.0, 11.3, 14.5, and 17.7 km/h. All pigs (n = 8) attained maximal O2 consumption (VO2max) (60 +/- 4 ml X min-1 X kg-1) by the time they ran at 17.7 km/h. At VO2max, 87% of Q (9.9 +/- 0.5 l/min) was to skeletal muscle, which constituted 36 +/- 1% of body mass. Average total muscle blood flow at VO2max was 127 +/- 14 ml X min-1 X 100 g-1; average limb muscle flow was 135 +/- 17 ml X min-1 X 100 g-1. Within the limb muscles, blood flow was distributed so that the deep red parts of extensor muscles had flows about two times higher than the more superficial white portions of the same muscles; the highest muscle blood flows occurred in the elbow flexors (brachialis: 290 +/- 44 ml X min-1 X 100 g-1). Peak exercise blood flows in the limb muscles were proportional (P less than 0.05) to the succinate dehydrogenase activities (r = 0.84), capillary densities (r = 0.78), and populations of oxidative (slow-twitch oxidative + fast-twitch oxidative-glycolytic) fiber types (r = 0.93) in the muscles. Total muscle blood flow plotted as a function of exercise intensity did not peak until the pigs attained VO2max, although flows in some individual muscles showed a plateau in this relationship at submaximal exercise intensities. The data demonstrate that blood flow in skeletal muscles of miniature swine is distributed heterogeneously and varies in relation to fiber type composition and exercise intensity.     

Oxygen uptake during running as related to body mass in circumpubertal boys: a longitudinal study

To investigate the effect of endurance training on physiological characteristics during circumpubertal growth, eight young runners (mean starting age 12 years) were studied every 6 months for 8 years. Four other boys served as untrained controls. Oxygen uptake (VO2) and blood lactate concentrations were measured during submaximal and maximal treadmill running. The data were aligned with each individual's age of peak height velocity. The maximal oxygen uptake (VO2max; ml.kg-1.min-1) decreased with growth in the untrained group but remained almost constant in the training group. The oxygen cost of running at 15 km.h-1 (VO2 15, ml.kg-1.min-1) was persistently lower in the trained group but decreased similarly with age in both groups. The development of VO2max and VO2 15 (l.min-1) was related to each individual's increase in body mass so that power functions were obtained. The mean body mass scaling factor was 0.78 (SEM 0.07) and 1.01 (SEM 0.04) for VO2max and 0.75 (SEM 0.09) and 0.75 (SEM 0.02) for VO2 15 in the untrained and trained groups, respectively. Therefore, expressed as ml.kg-0.75.min-1, VO2 15 was unchanged in both groups and VO2max increased only in the trained group. The running velocity corresponding to 4 mmol.l-1 of blood lactate (nu la4) increased only in the trained group. Blood lactate concentration at exhaustion remained constant in both groups over the years studied. In conclusion, recent and the present findings would suggest that changes in the oxygen cost of running and VO2max (ml.kg-1.min-1) during growth may mainly be due to an overestimation of the body mass dependency of VO2 during running.(ABSTRACT TRUNCATED AT 250 WORDS)     

Downhill running: a model of exercise hyperemia in the rat spinotrapezius muscle.

To utilize the rat spinotrapezius muscle as a model to investigate the microcirculatory consequences of exercise training, it is necessary to design an exercise protocol that recruits this muscle. There is evidence that the spinotrapezius is derecruited during standard treadmill exercise protocols performed on the uphill treadmill (i.e., 6 degrees incline). This investigation tested the hypothesis that downhill running would effectively recruit the spinotrapezius muscle as assessed by the presence of an exercise hyperemia response. We used radioactive 15-microm microspheres to determine blood flows in the spinotrapezius and selected hindlimb muscles of female Sprague-Dawley rats at rest and during downhill (i.e., -14 degrees incline; 331 +/- 5 g body wt, n = 7) and level (i.e., 0 degrees incline; 320 +/- 11 g body wt, n = 5) running at 30 m/min. Both level and downhill exercise increased blood flow to all hindlimb muscles (P < 0.01). However, in marked contrast to the absence of a hyperemic response to level running, blood flow to the spinotrapezius muscle increased from 26 +/- 6 ml.min(-1).100 g(-1) at rest to 69 +/- 8 ml.min(-1).100 g(-1) during downhill running (P < 0.01). These findings indicate that downhill running represents an exercise paradigm that recruits the spinotrapezius muscle and thereby constitutes a tenable physiological model for investigating the adaptations induced by exercise training (i.e., the mechanisms of altered microcirculatory control by transmission light microscopy).     

Effect of graded erythrocythemia on cardiovascular and metabolic responses to exercise

The effects of graded induced erythrocythemia on cardiovascular and metabolic responses to intense treadmill running were studied in four highly trained endurance runners. Three autologous infusions of 1 unit (U) whole blood (450 ml/U) were administered sequentially 2-7 days apart. Maximal O2 consumption (VO2max) increased from 5.04 l/min at control (C) to 5.24 l/min after 2 U (R2) and 5.38 l/min after 3 U (R3). Cardiac output during treadmill running at 91% control VO2max was 28.2 l/min at C, 29.8 l/min at R2, and 33.1 l/min at R3. Corresponding heart rates were unchanged, and stroke volume was increased at R3. Peak lactate concentration was reduced, and arterial acid-base status improved at R2 and R3 after standardized bouts of intense exercise. Arterial blood pressures and electrocardiograms during exercise were not affected by erythrocythemia. We conclude that the reinfusion of up to 3 U of autologous blood into highly trained endurance runners who have normal hematology does not adversely affect their cardiovascular response to maximal exercise. In addition, the increases in VO2max following reinfusion of 2 U, and again after 3 U, suggest that the aerobic power of the working muscles was not surpassed at these levels of erythrocythemia.     

跑台运动促进幼龄大鼠学习能力

为了探讨跑台运动对幼龄大鼠学习能力的影响,实验采用5周龄Sprague-Dawley大鼠,随机分为安静对照组和跑台运动组,其中跑台运动组大鼠以低强度进行为期一周的跑台运动;然后使用Morris水迷宫,对两组大鼠的定位航行和空间探索能力进行分析。在定位航行实验中,运动组大鼠寻找到平台的潜伏期明显短于对照组（P〈0．05）;并且随着训练次数的增加,运动组大鼠的游泳速度明显高于对照组（P〈0．01）;另外,运动轨迹的弯曲度表明运动组大鼠还表现出了较强的寻找平台的动机以及对平台位置较为准确的空间定位能力。在空间探索实验中,两组大鼠的游泳速度并没有明显差异,从大鼠在各象限内穿越平台相应位置的次数来看,运动组大鼠在D象限穿越的次数高于对照组,但无统计学差异（P〉0．05）。上述结果提示,低强度的跑台运动在短时间内便可以明显提高幼龄大鼠的学习能力。     

Determinants of VO2max in rats after high-intensity sprint training

The hemodynamic response to maximal exercise was determined in rats that were subjected to high-intensity sprint training (HIST) and rats that served as sedentary controls. Training consisted of five 1-min bouts of treadmill running at work loads (15% grade, 97 m/min) in excess of the animals' maximal O2 uptake (VO2max) interspersed with 90 s of rest. Training was performed 6 days/wk for 6 wk. After the training regimen, all rats were acutely instrumented with catheters in the right carotid artery and right ventricle. O2 uptakes, hemodynamic parameters, arterial and mixed venous O2 concentrations, blood gases, and acid-base status were determined at rest and during submaximal and maximal exercise. Results demonstrated that VO2max of HIST rats was significantly greater than that found for sedentary control rats. This increase in VO2max was due to an increase in maximal cardiac output (Qmax), since maximal arteriovenous O2 difference was similar between trained and sedentary rats. The increase in Qmax was due to an increase in maximal stroke volume (SVmax), because maximal heart rate in trained rats was similar to that in sedentary control rats. Citrate synthase and phosphofructokinase activities measured in the white gastrocnemius, plantaris, and soleus muscles of trained and sedentary rats were similar. These results suggest that the increase in VO2max produced with HIST in rats is strongly linked to an increase in central cardiac function as indicated by an increase in Qmax and SVmax.     

Dissociation of changes in VO2 max, muscle QO2, and performance with training in rats

Before the start and after 4, 8, and 12 wk of a treadmill training program male rats were randomly selected and tested for running performance, maximum O2 consumption (VO2 max), running economy (VO2 submax), and skeletal muscle oxidative capacity (QO2). Data were compared with values from untrained weight-matched control rats. Maximum running time to exhaustion increased significantly (P less than 0.01) by 4 wk and again at 12 wk (P less than 0.01). Submaximal running endurance increased by 120 (4 wk), 320 (8 wk), and 372% (12 wk) (P less than 0.01). VO2 max was increased only at 12 wk (86.0 +/- 2.7 vs. 75.5 +/- 1.9 ml O2.kg-1.min-1); VO2 submax was decreased at 4 and 8 wk but not at 12 wk. Soleus QO2 was unchanged after 4 wk of training and increased by 50% at 8 wk and by 77% at 12 wk. This study is the first to show a dissociation in both the time course and the magnitude of longitudinal changes in VO2 max, VO2 submax, QO2, and maximal and submaximal running performance. We conclude that factors other than those measured explain the improvement in running performance that resulted from endurance training in these rats.     

Exercise-induced muscle glycogen depletion and repletion in diabetic rats.

The purpose of this experiment was to examine glycogen depletion in muscles of chronic diabetic rats during treadmill running of moderate intensity and glycogen repletion following the exercise bouts. Diabetes was induced with a single intravenous injection of streptozotocin (70 mg × kg^?1). Glycogen concentrations in muscles from diabetic and normal animals were determined at rest, after running either 10 or 30 min at 23 m × min^?1 (5% incline), or 2, 4, or 8 hr following 30 min of running at the same speed and incline. With the exception of soleus muscle after 30 min of running, there were no differences in muscle glycogen contents between normal and diabetic rats before exercise, immediately after exercise, or during the recovery period. All muscles showed a significant loss of glycogen during exercise, and most muscles had completely restored their glycogen by 2 hr following exercise. Blood lactate concentrations were also similar for normal and diabetic rats at rest and after exercise. It is concluded that the diabetic condition studied in this experiment did not significantly alter muscle glycogen metabolism during exercise of moderate intensity or during recovery from the activity.     

Animal models of complex diseases: an initial strategy

We speculated that the rise in atmospheric oxygen from 2 billion years ago was so integral for the evolution of biocomplexity that it must also associate strongly with complex diseases. As a remote test of this idea, we hypothesized that lines contrasting for disease and health would emerge from artificial selection for low and high aerobic treadmill running capacity. Eleven generations of selection in rats produced lines that differed by 347% in running capacity. The low line demonstrated health risk factors including higher visceral adiposity, blood pressure, insulin, and triglycerides. The high line was superior for VO2max, economy of running, heart function, and nitric oxide-induced vascular dilation.