PubMed Health⌕ Search

Biomedical subjects

G Sjøgaard

Publications and source records attributed to G Sjøgaard.

68 records · Page 4Linked to original sources
PubMed1986

Fluid balance in exercise dehydration and rehydration with different glucose-electrolyte drinks.

After exercise dehydration (3% of body weight) the restoration of water and electrolyte balance was followed in 6 male subjects. During a 2 h rest period after exercise, a drink of one of four solutions was given as 9 X 300 ml portions at 15 min intervals: control (C-drink), high potassium (K-drink), high sodium (Na-drink) or high sugar (S-drink). An exercise test (submaximal and supramaximal work) was performed before dehydration and after rehydration. Dehydration reduced plasma volume by 16%, a process reversed on resting even before fluid ingestion began, due to release of water accumulated in the muscles during exercise. After 2 h rehydration, plasma volume was above the initial resting value with all 4 drinks. The final plasma volumes after the Na-drink (+14%) and C-drink (+9%) were significantly higher than after the K- and S-drinks. The Na-drink favoured filling of the extracellular compartment, whereas the K- and S-drinks favoured intracellular rehydration. In spite of the higher than normal plasma volume after rehydration, mean heart rate during the submaximal test was 10 bpm higher after rest and rehydration than in the initial test, and was not different between the drinks. The amount of work which could be performed in the supramaximal test (105% VO2max) was 20% less after exercise dehydration and subsequent rest and rehydration than before. This reduction was similar for all drinks, and may be due to a decreased muscle glycogen content (70% of initial) at the time of the second test.

Adolescent↗
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↗
PubMed1986

Water and electrolyte fluxes during exercise and their relation to muscle fatigue.

UNLABELLED: Muscle fatigue - defined as impaired contractility - coincided in rat skeletal muscle during in vitro experiments with a decrease in intracellular potassium concentration, [K], and a decrease in resting membrane potential, RMP. In man changes in intra- and extracellular electrolyte concentrations and RMP were calculated from muscle biopsies and blood samples during voluntary contractions. At exhaustion in maximal exercise the intracellular [K] decreased by 20-40 mM from a resting value of 165 mM. Simultaneously extracellular [K] increased by 1-2 mM, and also the intra- as well as extracellular [Na] tended to increase. The calculated RMP therefore decreased from a resting value of -89 mV to -75 mV. During prolonged submaximal exercise similar changes occurred although the rate of these changes was slower. The K lost from the exercising muscles was being taken up by other tissues, and during recovery the fatigued muscles regain the previously lost K. IN CONCLUSION: the K-gradient across the muscle membrane decreased significantly during maximal as well as submaximal exercise. At exhaustion this change is of an order of magnitude, which may well impair the excitability of the muscle membrane and thereby the contractility of the muscle fibres.

Animals↗
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↗
PubMed1984

Cardiovascular, hormonal and body fluid changes during prolonged exercise.

During prolonged heavy exercise a gradual upward drift in heart rate (HR) is seen after the first 100 min of exercise. This "secondary rise" might be caused by a reduction in stroke volume due to reduced filling of the heart, which is dependent upon both hemodynamic pressure and blood volume. Swimming and bicycling differ with respect to hydrostatic pressure and to water loss, due to sweating. Five subjects were studied during 90 min of bicycle exercise, and swimming the leg kick of free style. The horizontal position during swimming resulted in a larger cardiac output and stroke volume. After the initial rise in heart rate the "secondary rise" followed parallel courses in the two situations. The rises were positively related to the measured increments in plasma catecholamine concentrations, which continued to increase as exercise progressed. The secondary rise in HR could not be explained by changes in plasma volume or in water balance, nor by changes in plasma [K]. The plasma volume decreased 5-6% (225-250 ml) within the first 5 to 10 min of exercise both in bicycling and swimming, but thereafter remained virtually unchanged. The sweat loss during bicycling was four times greater than during swimming; but during swimming the hydrostatic conditions induced a diuresis, so that the total water loss was only 25% less than during bicycling.

Adult↗
PubMed1984

Muscle morphology and metabolic potential in elite road cyclists during a season.

The purpose of this investigation was to study muscle adaptation to high endurance performance. Muscle biopsies were taken from the m. vastus lateralis of 23 road cyclists, and their VO2 max was measured repeatedly during the season. At the beginning of their training season, VO2 max was 56 (37-66) ml X min-1 X kg-1 in competitive amateurs and 71 (64-76) ml X min-1 X kg-1 in elite professionals. Muscle capillary density determined at the same time was correspondingly roughly 30% higher in elite than in competitive cyclists while muscle enzyme activities (CS, HAD, and HK) were 30%-60% higher and LDH 50% lower in elite compared to competitive cyclists. Some elite cyclists were retested 5 months later when each of them had completed more than 15,000 km of bicycling during training and competition. During this period VO2 max remained unchanged, and the same was true for capillary density, while muscle enzyme activity (CS, HAD, and HK) increased 40%-70%, and LDH slightly decreased. The present results suggest that there may not be a close coupling between whole body VO2 max and the oxidative capacity of a local muscle group. Rather, the changes in muscle enzyme activities may be of importance for the regulation of muscle metabolism enhancing the endurance capacity. It is suggested that capillary density of the working muscles is of significance for VO2 max.

Adaptation, Physiological↗
PubMed1983

Electrolytes in slow and fast muscle fibers of humans at rest and with dynamic exercise.

Sodium, potassium, and magnesium were analyzed in human slow-twitch (ST) and fast-twitch (FT) skeletal muscles. In contrast to other species, no relation was found between fiber composition and electrolyte distribution. In soleus (S), vastus lateralis (VL), and triceps brachii (TB) the overall mean values for 6 men and 6 women were 44 mmol K/100 g dry wt and 11 mmol Na/100 g dry wt; the intracellular concentrations were 161 mmol K/l and 26 mmol Na/l with no differences between the muscles. Analysis of fragments of single ST and FT fibers from each of the muscles also showed no difference between the fiber types in Na and K content. Small differences were seen between the muscles with regard to Mg, but these were not related to fiber composition compared with other species. During exercise to exhaustion (3 bouts of bicycling for 3 min at 325-395 W, 6 men) the extracellular electrolyte concentrations for Na, K, and Mg increased from 134 to 140, 4.5 to 5.8, and 0.75 to 0.87 mmol/l, respectively (P less than 0.05). In VL Na content increased from 9.8 to 16.5 mmol/100 g dry wt, while intracellular [Na] remained constant. In contrast, intracellular [K] decreased from 161 to 141 mmol/l (P less than 0.05). No such changes occurred in TB. In concert with other studies the present changes in electrolytes in the working muscles indicate that muscle fatigue may be related to changes at the muscle fiber membrane.

Adult↗
PubMed1982

Capillary supply and cross-sectional area of slow and fast twitch muscle fibres in man.

The muscles triceps brachii, quadriceps femoris (part vastus lateralis) and soleus were analysed in 6 men and 6 women for fibre composition (% slow twitch, ST-fibres and % fast twitch, FT-fibres), fibre cross sectional areas, and capillarization. Also the fraction of fibres enclosed by their own fibre type was analysed together with the capillary supply of these fibres. Fibre composition was 39(19-60)% ST in m. triceps brachii, 60(29-78)% ST in m. vastus lateralis and 73(49-88)% ST in m. soleus. Fibre areas ranged from 2,320 to 16,667 microns2 being smallest in m. triceps brachii and largest in m. soleus (p less than 0.05) and with ST fibres being significantly smaller than FT fibres in some of the muscles. In all muscles the shape of the fibres was elliptical with the larger diameter being about twice the smaller diameter. Capillary density per cross sectional muscle area was not related to the fibre composition and was 379(302-500) cap/mm2 in m. triceps brachii, 404(284-529) cap/mm2 in m. vastus lateralis and 417(333-592) cap/mm2 in m. soleus. However, capillary supply expressed as fibre type area per capillary was up to 40% larger for FT-fibres than for ST-fibres within the same muscle (p less than 0.05). The capillary supply of enclosed fibres was not different from that of fibres surrounded also by the other fibre type. The results demonstrate that the difference in capillary supply to ST and FT-fibres is less distinct in humans than in other mammals, which is consistent with the metabolic potentials also being more alike.

Adult↗
PubMed1982

Extra- and intracellular water spaces in muscles of man at rest and with dynamic exercise.

A method was established to analyze the extracellular water space (H2Oe) in small muscle tissue samples as [3H]inulin distribution space. After initial experiments on rats, the method was applied on 13 men and 6 women. Muscles with different fiber compositions (soleus, S; vastus lateralis, (VL; gastrocnemius, G; triceps brachii, TB) were studied at rest. The total water content was the same for all muscles, 320 (313-330) ml/100 g dry wt. However, differences were demonstrated for H2Oe, with 26-34 ml/100 g dry wt in VL and 38-54 ml/100 g dry wt in S, (P less than 0.05); the values for G and TB were in between those for VL and S. The differences in H2Oe were not related to the fiber composition of the muscles. During 3 x 3 min of intense bicycle exercise demanding about 120% VO2 max (6 men), total water content increased in VL from 313 to 359 ml/100 g dry wt and H2Oe increased from 34 to 60 ml/100 g dry wt (P less than 0.05), In TB, which is relatively inactive during bicycle exercise, no such changes occurred. The calculated intracellular lactate concentration increased in VL from 5.7 to 30.6 mmol/l H2Oi. The extracellular lactate concentration amounted to 13.6 mmol/l H2Oe at the end of exercise. The concentration gradient for lactate of 2 from intra- to extracellular space favored a flux of water to the intracellular space. The relative large increase in H2Oe may then be caused by a hydrostatic rather than an osmotic factor.U

Adult↗
PubMed1978

NAD in muscle of man at rest and during exercise.

NAD can be used to assess the adequacy of oxygen availability to the respiratory chain. An enzymatic assay was established for NAD in human muscle biopsy samples. It gave reliable, reproducible results. The variation within and between subjects was less than 12%. Muscle NAD and lactate were determined at rest, and after bicycle ergometry work requiring approximately 75 and approximately 100% VO2 max (six subjects, four tests each). A positive (P less than 0.01) linear relationship between resting muscle NAD and percent slow twitch fibers was found, suggesting that fiber types may have different NAD content. Muscle NAD decreased during submaximal and maximal work (P less than 0.05). A large portion (73%) of the NAD reduction could be accounted for by increased muscle water. No relationship could be established between NAD and lactate. The negative linear relationship (P less than 0.01) between the muscle/blood ratio and percent slow twitch fibers is another indication of the fiber having different metabolic responses to the activity.

Adult↗