Carbohydrate and lipid metabolites and blood serum enzymes in humans during graded exercise test in long-term anti-orthostatic hypokinesia

Exercise tests were carried out before as well as on days 128 and 248 of a 370-day head-down tilt study. The test subjects, who took part in the study, were divided into two groups that used different regimens of countermeasures (drugs and exercise). During exercise tests the following serum parameters were measured: lactate, pyruvate, glucose, triglycerides, nonesterified fatty acids, lactate dehydrogenase, alpha-hydroxybutyrate dehydrogenase, malate dehydrogenase, creatine phosphokinase. Decrease or delayed increase in the concentration of energy substrates (nonesterified fatty acids and triglycerides) after a standard exercise test is a metabolic manifestation of deconditioning changes induced by head-down tilting. Insufficient supply of a working human body with readily utilizable lipid substrates causes inadequate activation of energy forming enzymes and excessive buildup of metabolites, i. e. lactate and pyruvate. The efficacy of corrective and prophylactic measures was verified by biochemical data.     

Changes in serotonin and histamine levels in human blood after 370-day anti-orthostatic hypokinesia

Ten healthy men took part in a 360-day antiorthostatic hypokinesia study. They were subdivided into two equal groups that differed in terms of time when they started using counter-measures: Group A began exercising on the first day of exposure and Group B on bed rest day 120. As compared to the baseline, the test subjects showed a decrease of serotonin (Ser) and histamine (HA). The only exception was HA increase on bed rest day 50 in the Group A subjects. The difference in Ser and HA concentrations in Group A and B subjects was insignificant on bed rest days 110 through 350. On the 60th day after the study Ser and HA concentrations did not yet return to norm. These observations indicate that changes in the serotonin- and histaminergic systems cannot be compensated within the above period of time.     

Functional status of the human cardiorespiratory system after 30 hours' antiorthostatic hypokinesia

Before and after 30-day head-down tilt (-8 degrees) the cardiorespiratory function of six healthy volunteers was assessed using an exercise test (aerobic workload on the treadmill that grew to the maximal level). After hypokinesia the maximal oxygen consumption decreased by 9.9% and total oxygen debt by 23% (P less than 0.05). The bioelectric activity of the heart showed a decrease of the TA wave by 34% and the TD wave by 30% (P less than 0.05). These changes give evidence that the functional capacity of the cardiorespiratory system declined and as a consequence the ability of the test subjects to perform sustained physical work of aerobic character also decreased.     

Intensive cycle training with artificial gravity maintains muscle size during bed rest

INTRODUCTION: The present study aimed to investigate the effect of intensive cycle training with short-arm centrifuge-induced hypergravity during bed rest on muscle size and function. METHODS: This study involved 10 healthy men who were divided into 2 groups: a countermeasure group, BR-CM (n = 5); and a control group, BR-Cont (n = 5). The BR-CM subjects partook in intensive cycle training (to 90% of maximum HR) with short-arm centrifuge-induced artificial gravity on alternate days during 20-d bed rest. Muscle volume of the thigh and maximum voluntary contraction (MVC) during isometric knee extensions was measured before and after bed rest. Muscle functional magnetic resonance imaging (mfMRI) and electromyogram (EMG) of the quadriceps femoris were obtained during submaximal knee extension exercises at a load of 30% MVC. RESULTS: The volume of the total thigh muscles was maintained in the BR-CM group (-1%), whereas it was not in the BR-Cont group (-9%, p < 0.05). MVC decreased in the BR-CM (7%) and BR-Cont groups (23%). EMG activity in the BR-CM group after bed rest was significantly lower than that of before; however, no significant change was found in the BR-Cont group. There were no significant changes in the resting and exercised mfMRI signals in either the BR-CM or BR-Cont groups. CONCLUSION: These results suggest that intensive cycle training with hypergravity maintained the size of human skeletal muscles during bed rest.     

Distinctive effects of three different modes of exercise on oxygen uptake, heart rate and blood lactate and pyruvate.

We intended to investigate the effects of different modes of exercise on oxygen uptake (VO2), the heart rate and the levels of lactate and pyruvate in venous blood. For this, untrained male subjects performed three modes of exercise with a treadmill (TR), a bicycle ergometer (UP) and a supine leg ergometer (SU). The percentage of maximal oxygen uptake (% VO2max) and VO2/weight for TR were significantly higher than those for UP or SU at lactate levels of 2, 3 and 4 mmol/l. The heart rate was also higher for TR than for SU at these lactate levels. The correlations of blood lactate with % VO2max, VO2/weight and the heart rate were significant for TR and SU, but not for UP. Blood lactate levels were lower for TR than for SU or UP at 60, 70, 80% VO2max, whereas the values for UP were lower than those for SU only at 60% VO2max. Blood pyruvate levels were always lower for TR than for SU. The ratios of lactate/pyruvate differed for TR and SU only at 60% VO2max. For a given mode of exercise, blood lactate and the ratio of lactate/pyruvate increased with an increase in % VO2max, but those of pyruvate did not. These results reveal that the relationships between any two of lactate, pyruvate, VO2 and the heart rate are different at different modes of exercise, and that blood lactate depends on adaptation of muscles to a mode of exercise rather than on the quantity of muscles mobilized.     

Various individual features of human adaptation to altitude

Two groups of young healthy men--natives of lowlands who for one year lived and worked in chronic hypoxia (Group 1 at an altitude of 1680 m with PO2 = 120 mm Hg and Group 2 at an altitude of 3650 with PO2 = 90 mm Hg) were examined. It was found that after this prolonged exposure the subjects showed a higher sensitivity of the respiration system to hypoxia, an enhanced lung ventilation and circulation, a lower gas exchange and physical work capacity. The concentration of lactic acid at rest in the Group 2 subjects was 47% higher than in the Group 1 subjects. The lactate/pyruvate ratio in the Group 2 subjects increased by 46% thus indicating an enhanced rate of anaerobic processes. A higher deficiency of buffer bases, a lower concentration of bicarbonates in blood at rest and during exercise tests of the Group 2 subjects pointed to metabolic acidosis. The subjects with a higher rate of anaerobic metabolism in a low PO2 environment displayed a diminished sensitivity of the hypoxic stimulation of respiration, an increased tolerance to the very low PAO2 and a reduced work capacity in chronic hypoxia.     

Glycolytic changes after local hyperthermia in mouse liver and adenocarcinoma

Glycolytic changes in an adenocarcinoma and in liver of C57B1 mice were determined for up to twelve hours after local hyperthermia at 43 degrees C for 30 min. The metabolites studied included glucose, glucose-6-phosphate, pyruvate, lactate, acetoacetate and beta-hydroxybutyrate. Both the glucose and glucose-6-phosphate levels decreased significantly in liver and tumour and remained low for up to twelve hours. The lactate levels increased slightly immediately after heating but were decreased at later times. However, the hepatic pyruvate levels decreased for up to two hours after heating but increased later reaching control levels. In both liver and tumour the levels of beta-hydroxybutyrate were significantly enhanced immediately after hyperthermia, whereas those of acetoacetate were lowered.     

Status of metabolism and peripheral circulation in man during antiorthostatic hypokinesia

Metabolism and peripheral circulation were investigated in head-down tilt tests of varying duration. The greatest changes were seen on test day 30 when the subjects showed venous hyperoxia, lower oxygen arterio-venous difference and a significant (p less than 0.05) decrease of oxygen tension in arterial blood and oxygen utilization in tissues (p less than 0.05). At the same time the subjects exhibited an increase in Pi and lactate and a maximum growth of 2,3-diphosphoglyceric acid (p less than 0.05). This exposure seems to produce a discrepancy between oxygen supply and oxygen requirements in tissues which gives rise to secondary tissue hypoxia. It is believed that the basic cause of these changes is disordered oxygen transport from blood to tissues.     

Physical exertion tolerance after water immersion

Before and after 24-hour water immersion test subjects performed a submaximal workload on a bicycle ergometer. Changes in their hematocrit, circulating plasma volume and fluid balance were compared with those during immersion. As a result, the test subjects were subdivided into two groups. For one group the workload was very hard; adaptation to immersion was accompanied by significant renal losses of fluid from the intra- and extravascular space. The bicycle ergometry test after immersion demonstrated a decrease of exercise tolerance combined with circulatory disorders. The other group showed a higher exercise tolerance; after immersion exercise tolerance remained high at the expense of the reserves that maintained optimal blood supply to the working muscles.     

Effects of 20 days of bed rest on the viscoelastic properties of tendon structures in lower limb muscles

Objectives: The purpose of this study was to investigate the effects of 20 days' bed rest on the viscoelastic properties of human tendon structures in knee extensor and plantar flexor muscles in vivo.

Methods: Eight healthy men (age: 24±4 years, height: 172±9 m, body mass: 69±13 kg) carried out a 6° head-down bed rest for 20 days. Before and after bed rest, elongation (L) of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and plantar flexion, respectively, were determined using real-time ultrasonic apparatus, while the subjects performed ramp isometric contraction up to the voluntary maximum, followed by ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve.

Results: L values above 100 N were significantly greater after bed rest for VL, while there were no significant differences in L values between before and after for MG. The stiffness decreased after bed rest for VL (70.3±27.4 v 50.1±24.8 N/mm, before and after bed rest, respectively; p = 0.003) and MG (29.4±7.5 v 25.6±7.8 N/mm, before and after bed rest, respectively; p = 0.054). In addition, hysteresis increased after bed rest for VL (16.5±7.1% v 28.2±12.9%, before and after bed rest, respectively; p = 0.017), but not for MG (17.4±4.4% v 17.7±6.1%, before and after bed rest, respectively; p = 0.925).

Conclusions: These results suggested that bed rest decreased the stiffness of human tendon structures and increased their hysteresis, and that these changes were found in knee extensors, but not the plantar flexors.

     

Effects of prior exercise on eccentric exercise-induced neutrophilia and enzyme release

PURPOSE: The purpose of this study was to determine the effects of prior exercise on changes in circulating neutrophils, neutrophil activation, and myocellular enzymes following a standardized bout of eccentric exercise. METHODS: Twenty-four male volunteers were randomized into three groups (N = 8). Group C performed 10 sets of 10 eccentric contractions of the quadriceps muscles with both legs (100% of the concentric IRM). Group D and Group F exercised for 2 h at 56%VO2max on a cycle ergometer followed by a similar bout of eccentric contractions. Group F also received 7.5 mL x kg(-1) of a carbohydrate-electrolyte beverage every 30 min during the submaximal exercise, whereas group D received no fluid. RESULTS: Body weight remained unchanged in groups C and F and decreased in group D by 1.56 +/- 0.34 kg. Ultrastructural Z-Band damage increased three-fold following exercise and remained elevated 3 d after exercise but was not different among groups. Circulating neutrophils were elevated more in group D compared with those in group C immediately after the exercise or rest period, and this difference persisted 3 h after the eccentric exercise. Serum lactoferrin concentrations increased 3.3-fold after exercise in all groups (P < 0.01). Creatine kinase levels (CK) rose in all subjects, with subjects in Group F and D having a significantly greater rise in CK after exercise compared with those in group C. CONCLUSIONS: These data indicate that submaximal exercise followed by a bout of eccentric exercise results in similar amounts of myofibrillar injury with a larger neutrophil response and CK release.     

状态相关脑波复杂度分析方法的研究

目的 建立状态相关脑波复杂度（Ｃｓ）分析方法，探讨安静状态及心算作业时的脑波复杂度及心算引起Ｃｓ改变的规律。方法 记录１０名２６～３０岁男性安静及心算状态的１６导ＥＥＧ，用自行编制的状态相关脑波复杂度分析程序进行处理，分析两种状态下的Ｃｓ及其与脑功能状态相关的变化。结果 心算作业使Ｃｓ显著改变：Ａ类（８名）安静时Ｃｓ较低，心算作业时Ｃｓ在全脑均呈上升趋势或显著上升，且以左右颞及枕顶区最显著；Ｂ类（     

Effect of 120-day antiorthostatic hypokinesia on gas exchange and pulmonary circulation in humans

Parameters of gas exchange and pulmonary circulation were measured in five healthy test subjects during 120-day head-down tilt test and early recovery. During the first half of the bed rest study CO2 tension in arterial blood increased significantly. During the second half of the study oxygen and carbon dioxide tension decreased significantly. The mechanisms of these changes are discussed.     

Change in hemoglobin mass during prolonged hypokinesia]

The total hemoglobin mass was measured by the carbon monoxide method in 33 male test subjects, 21 of whom were exposed to 30-day bed rest and 6 of whom were exposed to 100-day bed rest. The hypokinetic test subjects showed a decrease in hemoglobin mass by 11-24%. During readaptation the test subjects who had a noticeable reduction of hemoglobin displayed a 2.7-fold increase of the reticulocyte count. It is suggested that the gravity decrease during bed rest and antiorthostatic hypokinesia results in a reduced rate of hemoglobin synthesis in bone marrow.     

Whole-body energy mapping under physical exercise using positron emission tomography

We attempted to visualize dynamic adjustment of glucose utilization in humans in the whole-body organs during physical exercise by using three-dimensional positron emission tomography (3D-PET) and [18F]-2-fluoro-deoxy-glucose (FDG). Twelve healthy male volunteers collaborated on the study; six subjects were assigned to the resting control group (C) and the other six to the running group (E). Group E subjects performed running on a flat road for 35 min. After 15 min of running, subjects injected FDG and kept on running thereafter for another 20 min. Group C subjects sat on a comfortable chair in a quiet room for 35 min after the injection of FDG. After scanning by PET, the regions of interest (ROIs) were manually set on brain, heart, thorax, abdomen, lower extremities, and the rest of the body on the corresponding transaxial images. The uptake of FDG in each region was evaluated as the % fraction of FDG accumulation relative to the total amount of whole-body accumulation. The results revealed increase of FDG uptake after running in the lower leg muscles from 24.6 +/- 9.5% to 43.1 +/- 4.7% and in the heart from 2.3 +/- 0.4% to 2.8 +/- 0.6%. The differences were significant (P < 0.05). These increases reflect the rise in energy consumption in leg and heart muscles and were balanced by the reduction of energy consumption in the other part of the body. FDG uptake in the abdominal region reduced from 37.3 +/- 7.2% to 19.7 +/- 4.9%. However, FDG uptake in the brain remained stable, i.e., 11.9 +/- 2.8% at rest and 10.3 +/- 2.5% after exercise. Thus, 3D-PET is a tool to visualize the dynamic adjustment of energy consumption during physical exercise in humans.     

Neuro-muscular fatigue and recovery dynamics following anaerobic interval workload

The aim of this study was to determine the influence of anaerobic running on muscle contractile characteristics and voluntary muscle activation level during MVC as well as the dynamics of their recovery during a 2-hour period. Seven well-trained runners performed 5 x 300 m at submaximal velocity with a 1-minute active recovery interval between the runs. The average run velocity was 6.69 m.s(-1), which represented 77 % of their top velocity. Contractile characteristics of the vastus lateralis and activation level of quadriceps femoris muscles were measured before and immediately after the runs and within the 120-minute time interval that followed the workload. To do this we used: single twitch, low- and high-frequency electrical stimulation, maximal voluntary knee extension test, and muscle activation level test. After the exercise the maximal twitch torque (T(TW)) decreased for 28 +/- 3.7 % (p < 0.001) and torque at stimulation with 20 Hz and 100 Hz were 19.2 +/- 4.6 % (p < 0.01) and 7.5 +/- 2.3 % (p < 0.05) lower, respectively, while MVC torque and activation level remained unchanged. Subjects with higher blood lactate accumulation level showed significant decrease in the torque at low frequency stimulation (T(F20)) (r = - 0.80; p < 0.01) and T(TW) (r = - 0.92; p < 0.01). The restoration of twitch torque took a short time despite the fact that blood lactate concentration remained high. Ten minutes after the last interval run the twitch torque exceeded the pre-workload value by 11 % (p < 0.01). Potentiation lasted until the 40th min. It was concluded that fatigue after the anaerobic interval workload was peripheral in character and caused by contractile mechanisms disturbances.     

Quadriceps oxygenation during isometric exercise in sailing

The aim of the present study was to investigate why blood lactate after prolonged quadriceps contraction during hiking is only marginally increased. Eight sailors performed five 3-min hiking bouts interspersed with 5-s recovery periods. Whole body oxygen uptake, heart rate and lactate were recorded, along with continuous-wave near-infrared spectroscopy measures of quadriceps oxygenation. The time for 50% re-oxygenation was also assessed as an indication of the degree of localized oxygen delivery stress. Hiking elicited a significant (p = 0.001) increase in mean (+/- SD) heart rate (124 +/- 10 beats . min (-1)) which was accompanied by a disproportionately low oxygen uptake (12 +/- 2 ml.kg(-1).min(-1)). Lactate was significantly (p = 0.001) increased throughout hiking manoeuvres, though post-exercise it remained low (3.2 +/- 0.9 mmol.l(-1)). During the hiking bouts mean quadriceps oxygenation was significantly (p = 0.001) reduced compared to baseline (by 33 +/- 5%), indicating an imbalance between muscle oxygen accessibility and oxygen demand. During rest intervals quadriceps oxygenation was partially restored. After the end of the final bout the time for 50 % re-oxygenation was only 8 +/- 2 s, whereas recovery of quadriceps oxygenation and oxygen uptake was completed within 3 min. We conclude that the observed low lactate could be attributed to the small oxygen and energy deficits during hiking as the muscles' oxygen accessibility is presumably partially restored during the brief rest intervals.     

Central blood circulation in the healthy human being during 7 days' head-down tilt hypokinesia

The effect of 7-day head-down tilt (-15 degrees) and lower body negative pressure on circulation and oxidative metabolism was investigated on 13 healthy male test subjects. For 7-10 days they had Swan-Ganz catheters implanted in the pulmonary artery and a special cannula in the radial artery. The most marked changes were seen in the pulmonary artery pressure (PAP) and central venous pressure (CVP) that varied in a phase-like manner. By the 7th hour of bed rest the PAP increased significantly; this was followed by increases in the total lung resistance and the right ventricle function, as well as by a slight decrease of renin and aldosterone. Beginning with bed rest days 2 or 3 the PAP and CVP declined and remained lowered, as compared to the pretest level, till the end of bed rest. The responses to LBNP tests changed by bed rest day 2. Possible mechanisms of the above changes at rest and during LBNP tests are discussed.     

人体运动氧代谢的实时无创测定

为探讨运动过程中肌肉组织氧含量的变化规律，用无损近红外光谱学技术（ＮＩＲＳ）对１０名运动员１２ｍｉｎ递增有氧负荷运动的肌氧含量做了实时连续监测，同时测定了血乳酸和心率，相关分析表明，有氧代谢运动肌氧含量下降与血乳酸上升的测定值呈线性相关（ｒ＝－０．９６２）在相同负荷下对运动员和普通受试者的肌氧和血乳酸等参数的实时变化情况做了比较，此外，还检测和探讨了以无氧运动为主的短跑过程中肌氧含量的下降和恢复规