Search PubMed⌕ Search

Biomedical subjects

B Saltin

Publications and source records attributed to B Saltin.

At least 181 records · Page 10Linked to original sources
PubMed1986

Is peak quadriceps blood flow in humans even higher during exercise with hypoxemia?

Blood flow (Q) to quadriceps muscles was measured by thermal dilution in six men during rest and dynamic exercise [20, 38, and 42.5-60 W (peak load)] restricted to quadriceps of one leg in normoxia (N) and hypoxemia (H; 10-11% O2). Without exception Q and quadriceps vascular conductance were higher in H. Arterial mean pressure, lactate, norepinephrine, and epinephrine all rose when work exceeded 20 W. Q in N was 0.25, 3.28, 4.27, and 5.81 l/min (rest to peak exercise) and in H was 0.25, 4.08, 5.24, and 6.58 l/min. Peak Q per 100 grams of muscle (quadriceps mass = 2.2 kg) was 273.3 (N) and 308.8 ml/min (H). Quadriceps VO2 (Q X femoral A-VO2 difference) was 25, 388, 556, and 771 ml/min (N) and 25, 390, 556, and 743 (lower peak load in H)-net mechanical efficiency was 23%. Muscle O2 delivery (Q X arterial O2 content) was unaffected by H; O2 extraction fell in H but femoral venous O2 content remained near 6 (N) and 5 ml/100 ml (H) at all workloads, in contrast to much lower values in whole body exercise. In H muscle Q can rise to even higher peak values, without apparent limit, when the mass of active muscle is too small to overwhelm the pumping capacity of the heart.

Adult↗
PubMed1986

Role of hemoglobin and capillarization for oxygen delivery and extraction in muscular exercise.

Through the years the role of the various links in the transport of oxygen in the human body has been discussed extensively, and especially whether one of these links could be singled out as limiting oxygen uptake during exercise. In his thesis work Lars Hermansen dealt with several of these variables related to oxygen transport and uptake. Two of these were the hemoglobin concentration of the blood (Hb) and skeletal muscle capillarization. These are the focus of this article. It can be demonstrated that variation in arterial oxygen content due to different Hb concentrations is fully compensated for at the level of the muscle, i.e. the amount of oxygen delivered to contracting muscles is adjusted by a variation in the blood flow so that it is the same regardless of Hb concentration in the range of 118-172 g X l-1. At the systemic level, with a large fraction of the muscle exercising, this causes an increase in submaximal heart rate and a lowering in maximal oxygen uptake in people with low as compared to normal or high Hb concentration. The primary significance of an enlarged capillary network in the muscle does not appear to be for accommodating a larger flow, but rather to allow for a long enough mean transit time and large enough surface area for optimal exchange of gases, substrates and metabolites.

Capillaries↗
PubMed1985

Hemodynamic adaptations to exercise.

It is not currently known whether central hemodynamic or peripheral (vascular or metabolic) factors limit maximal oxygen uptake. By measuring the blood flow and oxygen uptake of exercising muscles when only a small fraction of the total muscle mass is engaged in exercise, it has been demonstrated that the skeletal muscle of man could accommodate a blood flow of at least 200 ml/100 g min, and consume 300 ml O2/100 g min at exhaustive exercise. Thus, in whole body exercise the limiting factor is the capacity of the heart to deliver oxygen, not the muscle. It has also been observed that at high perfusion of the muscle the arteriovenous O2 difference is small (14 to 15 vol %), and that the low extraction of oxygen is related to the mean transit time (MTT) of red blood cells passing through the capillaries. It has been concluded that the primary importance of enlargement of the capillary bed with endurance training is not to accommodate flow but to maintain or elongate MTT. It has also been concluded that, in whole body exercise, the capacity of the muscles to receive a flow exceeds by a factor of 2 to 3 the capacity of the heart to supply the flow. Thus, vasoconstrictor tone must also be present in the arteries that "feed" exercising muscles.

Blood Flow Velocity↗
PubMed1985

Fibre types, capillary supply and enzyme activities in human intercostal muscles.

The relative occurrence of slow twitch (ST) and fast twitch (FTa and FTb) fibres, fibre size, capillary supply, and glycolytic and oxidative enzyme activities in external (EXT) and internal (INT) intercostal muscles was determined on biopsies obtained during thoracotomy from the mid-axillary line in six patients with normal lung function. EXT and INT showed a similar occurrence of ST fibres. Both FTa and FTb fibres were seen in EXT while only FTa fibres were seen in INT. The size of the three fibre types in EXT was similar. In INT the fibre size was larger for FTa than for ST (P less than 0.05). INT appeared to have a larger number of capillaries per fibre than EXT (P less than 0.05). A positive correlation was demonstrated between variables measured during spirometry and fibre size in INT only. No difference in glycolytic and oxidative enzyme activities between EXT and INT was observed. The histochemical characteristics suggest that, in the mid-axillary line, INT are more used than EXT, though this conclusion did not appear to be confirmed by the enzyme activities determined.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1985

Skeletal muscle in paramyotonia congenita: biochemistry, histochemistry and morphology.

In 12 patients with paramyotonia congenita, percutaneous needle biopsies from the brachial biceps muscle were performed. Muscle fibre area, distribution of muscle fibre types I, II-A and II-B and capillarization were not different from healthy controls. Signs of myopathy with central nuclei in the muscle cells were noted in 9 of the patients. 4 of these patients also had small areas with degeneration and, in one, vacuoles were observed. Quantitative determination of muscle glycogen, water and protein content were within normal range as were enzyme activities for hexokinase, lactate dehydrogenase, citrate synthetase and 3-hydroxy-acyl-CoA dehydrogenase.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1985

Partial neuromuscular blockade and cardiovascular responses to static exercise in man.

In human subjects sustained static contractions of the quadriceps femoris in one leg were performed with the same absolute and the same relative intensity before and after partial neuromuscular blockade with either decamethonium or tubocurarine which reduced strength to about 50% of the control value. During the contractions performed with the same absolute force, the magnitude of the cardiovascular responses (heart rate and blood pressure) was greater during neuromuscular blockade than during control contractions. During the contractions involving the same relative force the magnitude of the cardiovascular responses was almost the same with and without neuromuscular blockade. These findings were independent of the drug used. The metabolic part of the exercise pressor reflex was assessed by the application of an arterial cuff 1/2 min before cessation of exercise and for the following 3 min of rest. Although heart rate and blood pressure decreased after cessation of exercise, application of the tourniquet resulted in higher post-exercise values and this effect was seen both with and without neuromuscular blockade. Muscle biopsies from the subjects' m. vastus lateralis were analysed for fast- and slow-twitch fibre composition showing 27-66% slow-twitch fibres. No correlation was found between cardiovascular responses to static exercise, with or without neuromuscular blockade, and fibre type predominance. The results suggest that the involvement of fast- or slow-twitch muscle fibres does not play a dominant role in the cardiovascular responses to static exercise in man. Both central command and reflex neural mechanisms are of importance, and it appears that these two control mechanisms are redundant and that neural occlusion may be operative. However, when partial neuromuscular blockade induces a disproportion between an increase in central command and a constant or decreasing muscle tension and metabolism, the larger signal arising from central command determines the magnitude of the cardiovascular responses.

Adult↗
PubMed1985

Maximal perfusion of skeletal muscle in man.

Five subjects exercised with the knee extensor of one limb at work loads ranging from 10 to 60 W. Measurements of pulmonary oxygen uptake, heart rate, leg blood flow, blood pressure and femoral arterial-venous differences for oxygen and lactate were made between 5 and 10 min of the exercise. Flow in the femoral vein was measured using constant infusion of saline near 0 degrees C. Since a cuff was inflated just below the knee during the measurements and because the hamstrings were inactive, the measured flow represented primarily the perfusion of the knee extensors. Blood flow increased linearly with work load right up to an average value of 5.7 l min-1. Mean arterial pressure was unchanged up to a work load of 30 W, but increased thereafter from 100 to 130 mmHg. The femoral arterial-venous oxygen difference at maximum work averaged 14.6% (v/v), resulting in an oxygen uptake of 0.80 l min-1. With a mean estimated weight of the knee extensors of 2.30 kg the perfusion of maximally exercising skeletal muscle of man is thus in the order of 2.5 l kg-1 min-1, and the oxygen uptake 0.35 l kg-1 min-1. Limitations in the methods used previously to determine flow and/or the characteristics of the exercise model used may explain why earlier studies in man have failed to demonstrate the high perfusion of muscle reported here. It is concluded that muscle blood flow is closely related to the oxygen demand of the exercising muscles. The hyperaemia at low work intensities is due to vasodilatation, and an elevated mean arterial blood pressure only contributes to the linear increase in flow at high work rates. The magnitude of perfusion observed during intense exercise indicates that the vascular bed of skeletal muscle is not a limiting factor for oxygen transport.

Adult↗
PubMed1985

Water and ion shifts in skeletal muscle of humans with intense dynamic knee extension.

Six subjects performed one-legged dynamic knee-extension. Blood samples were drawn from the femoral artery and vein, and muscle biopsies were obtained from the quadriceps muscle. Leg blood flow was measured by the thermodilution technique, and 3H-inulin was infused for determination of extra- and intracellular muscle water shifts. During the submaximal work load (S) muscle lactate increased, whereas muscle pH remained almost constant; after maximal exercise (M) the values markedly increased for lactate and decreased for pH. Except for a release of lactate from the exercising muscles, K was continuously released throughout S, and this release increased during M. Immediately when the muscles relaxed, the K release was converted to a K re-uptake. The calculated K loss, based on v- a and flow values, agreed with the decrease in muscle K content from 458 mmol/kg dw at rest to 414 mmol/kg dw at exhaustion (P less than 0.05), as analyzed on the muscle biopsies. Muscle water content increased during S mainly because of an increased extracellular H2O, whereas during M the largest increase occurred in intracellular H2O (H2Oi). Because of the simultaneous K loss and H2Oi increase in the exercising muscle the intracellular [K] was calculated to decrease from 165 mM at rest to 129 mM at exhaustion. This decrease and an increase in extracellular [K] from 4.5 mM at rest to greater than 6.0 mM at exhaustion affects the muscle membrane excitability. Muscle fatigue may thus not only be caused by changes within the cell, affecting energy metabolism or actin-myosin reaction, but may be located at the membrane protecting the cell against overload.

Body Water↗
PubMed1985

Dynamic knee extension as model for study of isolated exercising muscle in humans.

In an attempt to approach a system of isolated exercising muscle in humans, a model has been developed that enables the study of muscle activity and metabolism over the quadriceps femoris (QF) muscles while the rest of the body remains relaxed. The simplest version includes the subject sitting on a table with a rod connecting the ankle and the pedal arm of a bicycle ergometer placed behind the subject. Exercise is performed by knee extension from a knee angle of 90 to approximately 170 degrees while flywheel momentum repositions the relaxed leg during flexion. Experiments where electromyographic recordings have been taken from biceps femoris, gastrocnemius, tibialis anterior, and other muscles in addition to QF indicate that only the QF is active and that there is an equal activation of the lateral, medial, and rectus femoris heads relative to maximum. Furthermore, virtually identical pulmonary O2 uptake (Vo2) during and without application of a pressure cuff below the knee emphasizes the inactivity of the lower leg muscles. The advantages of the model are that all external work can be localized to a single muscle group suitable for taking biopsies and that the blood flow in and sampling from the femoral vein are representative of the active muscles. Thus all measurements can be closely related to changes in the working muscle. Using this model we find that a linear relationship exists between external work and pulmonary Vo2 over the submaximal range and the maximal Vo2 per kilogram of muscle may be as much as twice as high as previously estimated.

Adult↗
PubMed1985

Malleability of the system in overcoming limitations: functional elements.

Three different views can be found in the literature concerning the classical question in exercise physiology: what limits maximal oxygen uptake in man? Some authors believe that the limitation is the maximal rate of oxygen delivery by the cardiovascular system. Others argue that oxygen uptake is limited by the capillary bed or metabolic capacity of skeletal muscle, and the third line of thought is that no single factor can be found to be directly limiting as all links in the oxygen transport are so closely matched. The stand taken in this paper is that the skeletal muscle of man can be excluded as a limiting factor for maximal oxygen uptake in whole body exercise. It can be shown, by direct measurements, that in sedentary and in trained man maximal perfusion and oxygen utilization of skeletal muscle is so high that if all muscles in the body were engaged in intense exercise, the cardiac pump function would have to be 2-3 fold larger than it is. What happens in whole body exercise is that each muscle group receives only a fraction of the blood it can accommodate. The primary role for a larger capillary network observed in trained muscles is to keep or extend mean transit time. Elevated mitochondrial enzyme activities affect the metabolic response (i.e. lipid oxidation is elevated in trained muscles). However, these adaptations are not necessary for increasing the maximal oxygen uptake of man, as the capacity of the heart is limiting. Improved training techniques (which induce even larger improvements in cardiac pump function) may reveal that pulmonary diffusion capacity is the limiting factor.

Adaptation, Physiological↗
PubMed1984

Is there a change in relative muscle fibre composition with age?

Muscle biopsy was taken from the vastus lateralis muscle during surgery of recent fractures of the neck of the femur in 52 patients aged 66-100 years. The percentage of slow twitch (ST) fibres was close to 55% with no significant change with age and no difference between patients with and without clinical diagnoses prior to the fracture. Also subgrouping of fast twitch (FT) fibres showed insignificant changes in this age range. Muscle fibre areas were smaller for FT than for ST fibres. A comparison between proximal and distal sampling site in the muscle did not show any significant difference. Combining these results and previous results from our laboratories no change in relative fibre composition with age could be proven.

Aged↗
PubMed1984

Static contraction of the quadriceps muscle in man: cardiovascular control and responses to one-legged strength training.

Knee extension strength training of one leg (ST) (120 maximal contractions per day, 5 days per week for 9 weeks) was performed by 9 healthy young men. Before and after ST, biopsies were obtained from the vastus lateralis muscle of each leg and static quadriceps contractions (SQC) lasting 2 min were performed with each leg under control conditions and after combined vagal and beta-adrenergic blockade with atropine and metoprolol. Maximal voluntary contraction strength (MVC) increased more for the trained leg (TL) than for the untrained leg (UTL) but thigh circumferences and muscle fibre diameters gave little evidence for muscle hypertrophy. In pre- vs. post-training comparisons during SQC at the same relative force (40% of MVC) mean blood pressure (MBP), heart rate (HR) and smoothed rectified electromyographic activity were similar for TL and UTL. Similar findings were obtained for MBP after attenuation of the HR response by autonomic blockade, indicating that MBP, per se, was closely linked to the relative force of SQC. Pre- to post-training reductions in MBP and HR during SQC with each leg at an absolute force of 40% of pre-training MVC were likely due to changes in the pattern of motor unit activation. A lower MBP response to SQC and TL than of UTL after training correlated with a greater capillary density and a lower muscle lactate level for TL.

Adaptation, Physiological↗
PubMed1984

Intramuscular pressure, blood flow, and skeletal muscle metabolism in patients with venous claudication.

Nine patients with chronic iliac vein obstruction and venous claudication were investigated. Intramuscular pressure was measured in the anterior tibial and the deep posterior compartments in both legs at rest and during exercise. The pressures were significantly higher in the leg with iliac vein obstruction (39 +/- 10 mm Hg) than in the contralateral leg (26 +/- 12 mm Hg) at rest as well as during exercise (60 +/- 16 mm Hg and 41 +/- 15 mm Hg, respectively) in the deep posterior compartment. Similar changes were observed in the anterior tibial compartment. Muscle water content was higher (P less than 0.01) in the obstructed leg and contributes to the explanation for the high intramuscular pressure in this leg. Muscle blood flow, adenosine triphosphate, phosphocreatine, and lactate were determined in the gastrocnemius muscles at rest and at exercise. Muscle blood flow, measured with the 133xenon clearance technique, was lower in the obstructed leg (17.5 ml/min, 100 gm) than in the control leg (28.1 ml/min, 100 gm) during exercise. Lactate increased more (P less than 0.05) in the obstructed leg. It is suggested that pain in venous claudication is caused by the high intramuscular pressure, and therefore fasciotomy may be useful in the treatment of this disorder.

Adenosine Triphosphate↗
PubMed1983

Morphology of the brachial biceps muscle and elbow flexion in man.

This study was undertaken to determine whether skeletal muscle fibre characteristics could be demonstrated to be of significance for muscle function in voluntary contraction in man. 4 male and 4 female adult subjects were studied. During elbow flexion force and velocity was measured at the hand with the forearm in a 100 degree position. A motor-driven heavy flywheel guaranteed a constant velocity or movement at the time of measurement. Force was registered by a straingauge dynamometer, and velocity by two sets of photocells. Cross-sectional area of the brachial biceps muscle was determined by computerized tomography scanning. Muscle fibre composition and fibre cross-sectional areas were assessed histochemically on needle biopsy samples obtained superficially from the brachial biceps muscle, the more superficial of the two large elbow flexor muscles. At contraction velocities from 2 to 7 radians per second (rad/s) a close relationship existed between the relative force output and the relative area of fast-twitch fibers (p less than 0.01). Maximal voluntary isometric contraction force averaged 189 N (120 to 309 N), and showed a close relationship with total cross-sectional area of the brachial biceps muscle. The specific tension (maximal isometric tension) of the muscle averaged 33 N/cm2 with no demonstrable difference between subjects of widely different fibre compositions, suggesting that maximal tetanic tension is similar in fast- and slow-twitch fibres in man.

Adenosine Triphosphatases↗
PubMed1983

Intramuscular pressure, muscle blood flow, and skeletal muscle metabolism in chronic anterior tibial compartment syndrome.

One hundred eight patients with lower leg pain of unknown cause underwent intramuscular pressure measurements by the wick technique. Fifteen patients (14%) were found to have a chronic anterior tibial compartment syndrome. In these patients the intramuscular pressure was significantly increased at rest and during and after exercise as compared with normal subjects. The pressure increase after exercise was long-lasting (40 minutes). Biopsies of the anterior tibial muscles showed increased water content, which may explain the elevated pressures. Muscle blood flow during exercise as measured by the xenon-133 clearance technique was decreased, and muscle lactate concentration was increased in the anterior tibial muscles. Fasciotomy relieved pain and normalized intramuscular pressure, muscle blood flow, and skeletal muscle metabolism.

Adolescent↗
PubMed1982

Coupling between dietary changes, reduced body weight, muscle fibre size and improved glucose tolerance in middle-aged men with impaired glucose tolerance.

Fourteen middle-aged med with impaired glucose tolerance were studied prior to and 6 months after exchange of simple carbohydrates for complex carbohydrates rich in fibers and saturated for polyunsaturated fats in their diet when exchangeable. Body weight was reduced by 6.4 kg (p less than 0.001). Physical work capacity was unchanged. Fasting blood glucose and insulin were lowered (p less than 0.001) at 6 months and so were the values during an OGTT at 120 min. Both serum triglyceride and cholesterol concentrations were reduced (p less than 0.01) by the changes diet, the most marked reduction being found in the VLDL fraction. HDL levels increased by 21% (p less than 0.01). Enzyme activities in gastrocnemius muscle specimens were subnormal and uninfluenced by changed dietary habits. The number of capillaries per fiber was normal throughout, but as muscle fiber size was reduced in relation to the decreased body weight, the number of capillaries/mm2 increased during the dieting period. It is suggested that the observed improvement in insulin sensitivity and glucose tolerance after a dietary period with weight reduction is related to and partly explained by shorter diffusing distances in weight-bearing muscles.

Age Factors↗