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Biomedical subjects

B Saltin

Publications and source records attributed to B Saltin.

At least 163 records · Page 9Linked to original sources
PubMed1989

Increased skeletal muscle Na/K-ratio in obese men, but not in women, with glucose intolerance.

Obesity is associated with glucose intolerance. Glucose is to a large extent disposed in the skeletal muscle. Peripheral insulin resistance, as well as decreased enzymatic activity in the skeletal muscle, has been suggested in type II diabetes. Potassium is essential for such enzymatic reactions. In this study, obese men, but not women, with glucose intolerance tended to have a lower total body potassium per kg body weight, indicating a smaller muscle mass, than weight-matched normoglycaemic men. They also had a lower skeletal muscle potassium content per 100 g dry weight (P less than 0.05) and a higher muscle Na/K-ratio (P less than 0.05) compared with obese men with normal glucose tolerance. Muscle fat and muscle sodium content were higher in obese men than in women with the same body mass index (P less than 0.01). The muscle electrolyte changes can be explained by a decrease in the insulin mediated Na/k-pump activity across the cell membrane or a smaller number of insulin receptors on the skeletal muscle cell in patients with glucose intolerance.

Anthropometry↗
PubMed1989

Risk factors for cardiovascular disease in 16-19-year-old teenagers.

In a representative sample of Danish school children (124 boys and 169 girls), 16-19 years of age, blood pressure, blood lipids, body fat content, maximal aerobic power, alcohol consumption and smoking habits were studied. No systematic variation was noticed within this age in the risk factor profile. The mean values for blood pressure (BP) (systolic/diastolic) were 125/73 mmHg for the boys and 117/71 mmHg for the girls. As much as 14% of the boys and 5% of the girls had either a systolic BP above 140 mmHg or a diastolic BP above 90 mmHg. Total serum cholesterol averaged 4.13 mmol l-1 for the boys and 4.53 mmol l-1 for the girls, which is also high compared with adolescents from other countries. The ratios for high density lipoprotein cholesterol to total serum cholesterol were normal and in the range of 0.25-0.28 for both sexes. Other factors associated with coronary heart disease in adults, such as body fat content, serum triglycerides, physical activity, as well as smoking and alcohol habits were similar to that reported for teenagers in other countries. No correlation was found between aerobic power (ml min-1.kg-1) and the risk factors measured.

Adipose Tissue↗
PubMed1989

Temporal relationship between blood flow changes and release of ions and metabolites from muscles upon single weak contractions.

The temporal changes in muscular blood flow and in the release of ions and metabolites have been studied during and after short-lasting isometric contractions. Blood velocities in the human femoral artery were measured using pulsed bidirectional Doppler ultrasound equipment during single contractions of the quadriceps muscle group. Contractions of 5 s and 30 s duration and at a tension of 10% MVC (maximal voluntary contraction) were investigated. Even the contractions of 5 s duration caused conspicuous post-contraction increases in femoral arterial flow. The following substances were analysed in the femoral vein during and following the contractions: potassium, lactate, inorganic phosphate, calcium, sodium, oxygen and haemoglobin. Following contractions of 5 s duration, an increase in the venous potassium concentration (by 0.9 mM) was found, but there was no change in concentration of any of the other substances analysed. Following contractions of 30 s duration a more marked increase in the venous potassium concentration (by 1.5 mM) was found, and in addition substantial changes in venous lactate concentration and oxygen saturation. There were small but statistically significant changes in the concentrations of inorganic phosphate and calcium, but no change in the sodium concentration. The time-course and magnitude of the changes in venous potassium concentration fit well with the idea that potassium is important in the initiation and regulation of the functional hyperaemia in contracting muscles.

Adult↗
PubMed1989

Norepinephrine spillover from skeletal muscle during exercise in humans: role of muscle mass.

The purpose of this study was to determine the effect of increasing muscle mass involvement in dynamic exercise on both sympathetic nervous activation and local hemodynamic variables of individual active and inactive skeletal muscle groups. Six male subjects performed 15-min bouts of one-legged knee extension either alone or in combination with the knee extensors of the other leg and/or with the arms. The range of work intensities varied between 24 and 71% (mean) of subjects' maximal aerobic capacity (% VO2max). Leg blood flow, measured in the femoral vein by thermodilution, was determined in both legs. Arterial and venous plasma concentrations of norepinephrine (NE) and epinephrine were analyzed, and the calculated NE spillover was used as an index of sympathetic nervous activity to the limb. NE spillover increased gradually both in the resting, and to a larger extent in the exercising legs, with a steeper rise occurring approximately 70% VO2max. These increases were not associated with any significant changes in leg blood flow or leg vascular conductance at the exercise intensities examined. These results suggest that, as the total active muscle mass increases, the rise in sympathetic nervous activity to skeletal muscle, either resting or working at a constant load, is not associated with any significant neurogenic vasoconstriction and reduction in flow or conductance through the muscle vascular bed, during whole body exercise demanding up to 71% VO2max.

Adult↗
PubMed1989

Estimation of the mitochondrial redox state in human skeletal muscle during exercise.

The mitochondrial redox (NAD+/NADH) state can be used as a reflection of oxygen availability within the mitochondrion. Previous studies using isolated muscle preparations suggest that active muscle is not hypoxic during lactate production, whereas experiments with humans come to the opposite conclusion. Six men exercised for 5 min at 75% maximal O2 consumption (VO2max) and then at 100% VO2max to exhaustion. Ammonia, oxoglutarate (alpha-ketoglutarate), and glutamate, as well as lactate, were measured in biopsies (vastus lateralis) taken at the end of each exercise. The three former metabolites were used to determine the mass action ratio of glutamate dehydrogenase and thus were used as an estimate of the mitochondrial redox state. Muscle lactate increased (P less than 0.05) to 14.5 and 24.5 mmol/kg wet wt after 75 and 100% VO2max, respectively. At both exercise intensities, muscle ammonia rose (P less than 0.05), glutamate fell (P less than 0.05) to only 30-35% of rest levels, and oxoglutarate declined (P less than 0.05). Despite the high levels of muscle lactate accumulation, the estimated mitochondrial redox rate rose 300% (P less than 0.05) in both exercise bouts. This response should increase the activity of key oxidative enzymes and promote increased VO2. Furthermore the data do not support the concept that muscle lactate is formed because of tissue hypoxia.

Adult↗
PubMed1989

Skeletal muscle potassium increases after diet and weight reduction in obese subjects with normal and impaired glucose tolerance.

Body composition calculated from total body potassium and skeletal muscle potassium were studied in middle-aged obese men and women with normal and impaired glucose tolerance as well as Type II diabetes before and after advice on calorie reduction during twelve months. The subjects were compared with healthy lean men and women. Mean weight loss was 6.6 kg (P less than 0.05). Lean body mass and body fat decreased 2.0 kg (P less than 0.05) and 4.6 kg (P less than 0.05), respectively. Total body potassium decreased by a mean of 146 +/- 49 mmol (P less than 0.01). Obese men with Type II diabetes and impaired glucose tolerance had lower total body potassium and muscle potassium levels than obese healthy men. After dieting, the obese men and women increased their muscle potassium levels with a mean of 2.8 mmol/100 fat-free dry weight to 42.6 +/- 2.6 mmol/100 g fat-free dry weight (P less than 0.05), but they were still below the levels of the lean controls, 44.4 +/- 1.3 MMOL/100 g fat-free dry weight, (P less than 0.01). Increase in skeletal muscle potassium was correlated to decrease in body weight, r = 0.55 (P less than 0.01) and to decrease in fasting blood glucose, r = 0.42 (P less than 0.05).

Blood Glucose↗
PubMed1988

Capacity of blood flow delivery to exercising skeletal muscle in humans.

Several studies using different techniques to estimate muscle blood flow during exercise in humans support the concept that peak muscle perfusion is at least 150 ml/100 g/min. Such high blood flows are achieved when only part of the muscle mass is recruited during exercise. With 2 or more limbs exercising, the pump capacity of the heart will limit the blood flow available for the muscles. Norepinephrine spillover from an exercising limb is increased when a small muscle group performs the work, but it appears to have no functional effect on blood flow, and alpha-blocking drugs do not significantly elevate peak blood flow. During whole-body exercise, the norepinephrine spillover becomes further elevated, but the functional significance is not apparent until the oxygen uptake reaches more than 80% of maximal oxygen uptake. At these high work rates the sympathetic discharge overrides the local vasodilator factors and causes vasoconstriction. Thus, blood pressure can be maintained.

Animals↗
PubMed1988

Skeletal muscle adaptations to physical training in type II (non-insulin-dependent) diabetes mellitus.

Seven middle-aged men with manifest type II diabetes mellitus underwent an endurance training programme for 10-15 weeks. The maximal aerobic capacity, as well as the endurance capacity, was improved by 10% (p less than 0.05). The intramuscular glycogen store increased by more than 80% (p less than 0.05) from 350 mumol/g dw (dry weight), and the activities of citrate synthase and 3-hydroxy-acyl-CoA dehydrogenase increased by more than 50% (p less than 0.05) and 30% (p less than 0.05). The activity of glycogen synthase was decreased by approximately 20% (p less than 0.05), whereas lactate dehydrogenase remained unchanged. Capillaries/fibre and fibre area increased by more than 50% (p less than 0.05) and 30% (p less than 0.05) leaving the area of supply constant. Training did not influence fasting blood lipids and glucose, glycosylated hemoglobin, oral glucose tolerance, and insulin response to an oral glucose load measured 72 hours post-exercise. It is concluded that patients with manifest type II diabetes, as normoglycaemic individuals, adapt to physical training. However, no persistent effect on glucohomeostasis and lipaemia is produced by short-term training in the diabetic patients.

Adaptation, Physiological↗
PubMed1988

Decreased skeletal muscle potassium in obesity.

The effect of body weight on total body potassium, skeletal muscle electrolytes and fat content was studied in seven lean and seven obese middle-aged men and seven lean and eight obese middle-aged women. Total body potassium and total body fat increased with body weight (p less than 0.01 and less than 0.05 for men, and p less than 0.05 and p less than 0.001 for women, respectively). So did muscle fat in men (p less than 0.01), while muscle tissue potassium was decreased in both obese men (p less than 0.001) and obese women (p less than 0.05). The skeletal muscle Na/K-ratio tended to be higher in obese men (p less than 0.1) but was not related to body weight in women. Skeletal muscle magnesium was higher (p less than 0.01) in obese men than in lean men. No differences between lean and obese women were found. Obese men had higher diastolic blood pressure (p less than 0.05) than lean men, while there was no difference between obese and lean women. Compared with lean subjects, obese subjects thus had lower relative skeletal muscle mass and men, especially, had more fat and less potassium in the skeletal muscle.

Adipose Tissue↗
PubMed1988

The low physical working capacity of thyrotoxic patients is not normalized by oral antithyroid treatment.

The low working capacity in thyrotoxic patients has not been quantified and its causes have not been clarified. We studied the working capacity in nine thyrotoxic patients at diagnosis (test 1), after 3 months of oral antithyroid medication (test 2), and in four of them again after 1 year (test 3). The maximum power output was low in thyrotoxic patients (1.65 +/- 0.15 W/kg-1) and was not significantly higher after 3 months of treatment (1.84 +/- 0.15), although plasma thyroid hormone concentrations had been normalized for approximately 3 months. After 1 year's treatment the maximum power output was still somewhat low in the four tested patients (2.75 +/- 0.34). The rate of oxygen uptake under maximum exercise was low (26 ml/min-1/kg-1) and was not significantly increased at test 2 and 3. The net mechanical efficiency was low at test 1 and 2 (18.9 +/- 2.1% and 20.1 +/- 1.8%, respectively), but was normal at test 3 (25.2%). At all three tests the blood lactate response upon maximum exercise attained only about 50% of normal concentration. Thus, low work capacity in thyrotoxic patients remained for a long period of time after euthyroid conditions had been attained. The low capacity was due to low aerobic and anaerobic capacities and initially also to a low mechanical efficiency.

Adult↗
PubMed1988

Skeletal muscle glucose uptake during dynamic exercise in humans: role of muscle mass.

To study the role of muscle mass in glucoregulation, six subjects worked with the knee extensors of one leg on a specially constructed cycle ergometer. The knee extensors of one leg worked either alone or in combination with the knee extensors of the other leg and/or with the arms. Substrate usage was measured across both knee extensors by femoral arterial and venous catheterization and measurement of femoral venous blood flow. Glucose uptake by the working knee extensors was absolutely (by approximately 20%) or relatively decreased when arm cranking was added to knee extensions. The decrease in glucose uptake was not compensated for by increased uptake of free fatty acids but was accompanied by decreases in plasma insulin and increases in plasma epinephrine and norepinephrine. During work with large muscle masses, arterial lactate increased to approximately 6 mM, and net leg lactate release reverted to net lactate uptake. Decreased glucose uptake could not be explained by decreased perfusion. It is concluded that thigh muscle glucose uptake is affected by the size of the total muscle mass engaged in exercise. The decrease in thigh glucose uptake, when arm cranking was added and O2 uptake was increased above 50% of maximum aerobic capacity, may be elicited by neuroendocrine adjustments or lactate-induced inhibition of glycolysis and may represent a mechanism for protecting against premature hypoglycemia during prolonged exercise.

Adult↗
PubMed1988

Muscle blood flow is not reduced in humans during moderate exercise and heat stress.

The effect of heat stress on circulation in an exercising leg was determined using one-legged knee extension and two-legged bicycle exercise, both seated and upright. Subjects exercised for three successive 25-min periods wearing a water-perfused suit: control [CT, mean skin temperature (Tsk) = 35 degrees C], hot (H, Tsk = 38 degrees C), and cold (C, Tsk = 31 degrees C). During the heating period, esophageal temperature increased to a maximum of 37.91, 39.35, and 39.05 degrees C in the three types of exercise, respectively. There were no significant changes in pulmonary O2 uptake (VO2) throughout the entire exercise period with either one or two legs. Leg blood flow (LBF), measured in the femoral vein of one leg by thermodilution, remained unchanged between CT, H, and C periods. Venous plasma lactate concentration gradually declined over time, and no trend for an increased lactate release during the heating period was found. Similarly, femoral arteriovenous O2 difference and leg VO2 remained unchanged between the three exercise periods. Although cardiac output (acetylene rebreathing) was not significantly higher during H, there was a tendency for an increase of 1 and 2 l/min in one- and two-legged exercise, respectively, which could account for part of the increase in total skin blood flow during heating (gauged by changes in forearm blood flow). Because LBF was not reduced during exercise and heat stress in these experiments, the additional increase in skin blood flow must have been met by redistribution of blood away from vascular beds other than active skeletal muscle.

Adult↗
PubMed1987

Maximal oxygen uptake in Danish adolescents 16-19 years of age.

A random sample of schoolchildren, 119 boys and 153 girls, was tested in the fall of 1983. The data presented here are anthropometric data (height, weight, fat % and vital capacity) and oxygen uptake directly measured on a bicycle ergometer. The mean height and weight for boys were 179.1 cm and 67.7 kg, and those for girls were 168.0 cm and 59.6 kg. The mean fat content was 9.1% for boys and 19.1% for girls, and their mean vital capacities were 4.91 and 3.61 respectively. The boys had a high maximal oxygen uptake (51.7 ml X kg-1 X min-1) showing no reduction over the age span studied. The girls' maximal oxygen uptake was lower (overall mean 40.0 ml X kg-1 X min-1) with a small reduction from 16 to 19 years of age. When comparing maximal oxygen uptake per kg lean body mass in the two sexes, the boys had 18.4% higher values than the girls, indicating that girls of this age have the lower fitness level. The results of maximal aerobic power measurement in the boys compare well with findings from other investigations using direct measurements, indicating that the fitness of teenage boys is kept at a high level. Comparable data from various countries for girls show different pictures, but it appears that in general they have a low fitness level.

Adolescent↗
PubMed1987

Noradrenaline spillover during exercise in active versus resting skeletal muscle in man.

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one-legged knee-extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for 10 min at each of 50% and 100% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (NAe) or of adrenalin (Ae) is required: NAe was measured by repeating the experiment under constant [3H]NA infusion following a 40-min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this tissue.

Adult↗
PubMed1987

Muscle and blood ammonia and lactate responses to prolonged exercise with hyperoxia.

Investigations using nonsteady-state and fatiguing exercise protocols have demonstrated a strong relationship between ammonia and lactate metabolism and have suggested a cause and effect relationship between these two variables. We investigated the lactate-ammonia response using prolonged exercise and inspiration of hyperoxic gas (60% O2-40% N2). The exercise consisted of either 70-75% maximal O2 uptake (VO2 max) for 40 min (series 1, n = 6) or 75-80% VO2max for 30 min (series 2, n = 6) with the subjects inspiring room air on one occasion and hyperoxia in the other test. In both series blood ammonia rose continuously throughout the exercise regardless of the inspired gas treatment; in contrast blood lactate did not increase after 10 min with room air, and with hyperoxia blood lactate was reduced. Muscle lactate and ammonia (series 2; vastus lateralis) had responses similar to the blood data. The data demonstrated no apparent lactate-ammonia relationship with prolonged exercise or in response to hyperoxia, suggesting that ammonia production can be independent of lactate metabolism. The data also suggest that type I fibers can be a major source of ammonia in humans.

Adult↗
PubMed1986

Physiological adaptation to physical conditioning. Old problems revisited.

Three classical problems in the field of man's adaptive response to exercise are reviewed. A case is made for the pump capacity of the heart limiting maximal oxygen uptake in man. This conclusion is based on findings that the capacity of skeletal muscle of man markedly surpasses that of the heart supplying it with a flow and thereby oxygen. It is suggested that only one third of the muscle mass of man can fully tax the capacity of the heart and consume the oxygen delivered by the heart. If a larger muscle mass is intensely engaged in the exercise, vasoconstriction must occur in the arterioles of the exercising limbs to avoid a reduction in blood pressure. Evidence is presented that a decrease in heart rate at submaximal exercise-observed after a period of physical conditioning, is caused by an altered autonomic chronotropic activity to heart, which most likely is due to a less potent feed back reflex from exercising muscles. The enlarged stroke volume is secondary to a larger diastolic filling, which via a Frank-Starling mechanism results in an elevation in the stroke volume. Last, it is argued that the altered metabolic response to exercise after physical conditioning, i.e. the larger lipid oxidation and reduced lactate production, results from local regulatory mechanisms rather than from changes in supply of oxygen, substrates, or hormones. Further, the muscle metabolic response to exercise is thought to play a major role in modulating systemic cardiovascular regulation in exercise.

Adaptation, Physiological↗
PubMed1986

Intramuscular pressure, EMG and blood flow during low-level prolonged static contraction in man.

Seven men performed one-legged isometric knee-extension at 5% MVC for 1 h. Intramuscular pressure increased with contraction from its resting value of 14 (2-31) mmHg. Some intramuscular pressure recordings stayed at an almost constant level through the 1 h contraction, but most recordings showed large fluctuations from resting values up to 90 mmHg. The overall mean intramuscular pressure was twice the resting value. In some cases, EMG recordings confirmed that the changes in intramuscular pressure were related to alternating recruitment of various parts of the knee-extensors. Blood flow in the femoral vein increased within 3 min of 5% MVC to a level of 1.58 (1.25-2.22) 1 min-1 and no significant changes occurred during the 1 h contraction. In two subjects blood flow was measured also in the recovery period, and this decreased almost immediately when the muscle relaxed. It is concluded that during low-level static contractions, the blood supply to the exercising muscle is maintained at a sufficiently high level, and that the alternating recruitment of muscle fibres may result in a heterogeneously distributed blood flow within the contracting muscle. Despite this the muscle was fatigued after the 1 h at 5% MVC. The rating of perceived exertion (RPE) increased from 1.9 (1-3) at the beginning to 4.5 (2-8) at the end of contraction, and MVC was decreased by 12% after the contraction.

Adult↗