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Biomedical subjects

B Saltin

Publications and source records attributed to B Saltin.

At least 145 records · Page 8Linked to original sources
PubMed1992

The metabolic and circulatory response to beta-blockade in hypertensive men is correlated to muscle capillary density.

Both haemodynamic and metabolic variables have been shown to be related to the fibre composition and capillary density of skeletal muscle in man. In the present study, the change of several metabolic variables during beta-blockade was investigated and related to muscle fibre composition and capillary density in 28 men with essential hypertension. They had been given atenolol (50 mg/day) or metoprolol (200 mg/day) or propranolol (160 mg/day) for 4-12 months. Serum triglycerides increased during treatment and individual changes were significantly inversely correlated with capillary density. Insulin concentrations in the fasting state and at the end of an i.v. glucose tolerance test were significantly higher during beta-blockade, and individual changes were inversely correlated with capillary density. Furthermore, body weight increased and heart rate decreased, changes that were also correlated with capillary density. It is concluded that many of the previously but poorly understood large interindividual differences in response to beta-blocker treatment may be explained by the degree of development of the capillary net in muscle tissue. Obesity, physical training as well as genetic factors are known determinants of capillary density.

Adrenergic beta-Antagonists↗
PubMed1992

Maximal oxygen uptake: "old" and "new" arguments for a cardiovascular limitation.

The research performed over the last 100 yr in regard to oxygen transport during exercise is reviewed. Special focus is on major shifts in views held on which link may limit maximal oxygen uptake of an individual exercising with a large fraction of the muscle mass. Initially the pump capacity of the heart was proposed as the critical factor, a view basically unchallenged until results on the plasticity of muscle came about in the 1960-70s. The capillary bed of the muscle and its mitochondrial volumes can be enhanced with training. These adaptations were then suggested to be prerequisites for maximal oxygen uptake to become elevated. The pendulum is slowly swinging back again toward heart and lungs setting the upper limit for the oxygen transport. It appears to be in the range of 80-90 ml.kg-1.min-1 or 150-200 ml.kg-1 muscle.min-1, which can easily be consumed by a fraction of the muscle mass intensely contracting.

Adaptation, Physiological↗
PubMed1991

Responses of glucose and glucoregulatory hormones to exercise in thyrotoxic and myxoedematous patients before and after 3 months of treatment.

1. The effect of moderate endurance exercise on blood glucose concentration and on glucoregulatory hormones was studied in nine thyrotoxic and five myxoedematous humans before and 3 months after anti-thyroid and substitution therapy, respectively. 2. At rest, the fasting concentrations of insulin and pro-insulin correlated positively with the prevailing total tri-iodothyronine concentration, whereas the concentrations of noradrenaline and cortisol correlated inversely with the tri-iodothyronine concentration. 3. During exercise the plasma insulin, pro-insulin and C-peptide concentrations decreased. The plasma glucagon concentration increased slightly in thyrotoxic patients before and after treatment and was largely unchanged in myxoedematous patients in either state. 4. The plasma noradrenaline concentration increased before and after treatment in both groups, with concentrations two times higher in the myxoedematous than in the thyrotoxic patients. Treatment for 3 months did not change this pattern. The plasma adrenaline concentration increased in both groups, but in the untreated thyrotoxic patients the increase was two to three times greater than that after treatment or that in the myxoedematous group. 5. The blood glucose concentration decreased in eight of nine untreated thyrotoxic patients, but was largely unchanged after treatment or in the myxoedematous patients. A strong negative correlation was found between the decline in blood glucose concentration and the increase in plasma adrenaline concentration in the thyrotoxic group. 6. Thus, during exercise untreated thyrotoxic patients are prone to hypoglycaemia, show an inadequate glucagon response, and exhibit a large counter-regulatory increase in plasma adrenaline concentration.

Adult↗
PubMed1991

Substrates for muscle glycogen synthesis in recovery from intense exercise in man.

1. Intramuscular glyconeogenesis from lactate after intense exercise was examined by using the one-legged knee extension model which enables evaluation of metabolism in a well-defined muscle group. 2. In seven subjects measurements of leg blood flow and arterial-venous differences of various substrates were performed in individuals after intense, exhaustive knee extensor exercise lasting 3.0 min. Muscle glycogen and lactate concentrations were determined in the quadriceps muscle immediately after exercise and three times during 1 h of recovery. 3. Muscle glycogen increased from 93.7 +/- 6.7 (+/- S.E.M.) to 108.8 +/- 8.1 mmol (kg wet wt)-1 during the recovery period. Muscle lactate was 27.1 +/- 2.1 mmol (kg wet wt)-1 at the end of exercise and decreased to 14.5 +/- 2.1, 6.7 +/- 1.1, and 3.0 +/- 0.5 mmol (kg wet wt)-1 after 3, 10 and 60 min of recovery, respectively. 4. More than two-thirds of the lactate that accumulated in the muscle during the intense exercise was released into the blood. It was estimated that between 13 and 27% of the lactate could have been converted to glycogen. This corresponded to a glycogen resynthesis rate from lactate of 0.17-0.34 and 0.002 mmol glucosyl units min-1 (kg wet wt)-1 for the first 10 and last 50 min of recovery, respectively. 5. The O2 debt of the leg was 1.5 l of which the resynthesis of ATP, creatine phosphate (CP) and glycogen and reloading of haemoglobin (Hb) and myoglobin (Mb) only could account for one-third. It is proposed that the elevated oxygen uptake during recovery is linked to the metabolic use of intramuscular triacylglycerol.

Adult↗
PubMed1991

The skeletal muscle Na:K ratio is not increased in hypertension: evidence for the importance of obesity and glucose intolerance.

Several previous studies have suggested that hypertension is associated with altered sodium transport across the cell membrane. The aim of the present study was to study the skeletal muscle Na:K ratio in relation to blood pressure and glucose tolerance in obese and non-obese men. Muscle biopsies were taken from the femoral vastus lateralis muscle in men aged 52 +/- 5 years and the electrolytes were analyzed. Ten obese men with impaired glucose tolerance and hypertension, 10 obese normotensive controls, 10 lean men with hypertension and 10 lean normotensive controls participated in the study. Higher insulin levels were found in both hypertensive groups compared with the respective normotensive groups. Increased muscle Na:K ratio was found in obesity (P less than 0.01) and this was further enhanced when combined with hypertension and impaired glucose tolerance (P less than 0.001). However, hypertension in lean individuals was not associated with an increased muscle Na:K ratio. These data suggest that the increased muscle Na:K ratio in obese subjects and those with impaired glucose tolerance is not solely due to insulin resistance and hyperinsulinemia. Furthermore, the data clearly suggest that there is no important general perturbation of the Na-K pump in hypertension per se.

Biological Transport, Active↗
PubMed1990

Co-existence of myosin heavy chain I and IIa isoforms in human skeletal muscle fibres with endurance training.

The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis was analysed by one-dimensional electrophoresis and immunoblotting in three groups of young men with distinct difference in physical activity patterns. No major co-existence of MHC isoforms was found in the group with some daily physical activity. In the very sedentary group, however, 19 +/- 5% (P less than 0.05) of the fibres exhibited coexistence of MHC type IIa and IIb. Further, in the endurance trained group co-existence of MHC type I and IIa was manifested in 36 +/- 4% (P less than 0.05) of the fibres. Disuse and extreme usage of muscle both give rise to an elevation in co-expression of MHC isoforms in single muscle fibres but of markedly different combination of isoforms.

Adult↗
PubMed1990

Cardiovascular responses to carotid sinus baroreceptor stimulation during moderate to severe exercise in man.

Our objective was to assess the importance of arterial baroreflexes in maintaining vasoconstriction in active muscle during moderate to severe exercise. Eight subjects exercised for 8-15 min on a cycle ergometer at three levels (averages 94, 194, 261 W) requiring 40-88% of VO2 max. Four times during each exercise level pulsatile negative pressure (-50 mmHg) was applied over the carotid sinuses for 30 s; suction was applied at each ECG R-wave for 250-400 ms. Before and during each neck suction, femoral venous blood flow (FVBF) was measured by constant infusion thermal dilution. At 94 W neck suction significantly reduced blood pressure (BP) (15 mmHg) and heart rate (HR) (7 beats min-1), and raised leg vascular conductance (LVC) (11.4%) without changing FVBF. At 194 W, neck suction reduced BP (9 mmHg), HR (4 beats min-1) and FVBF (5.1%, 240 ml min-1), and raised LVC (5.2%). At 261 W, LVC was unchanged by neck suction, but BP and FVBF both fell (9 mmHg and 650 ml min-1 or 7.4%). We conclude that competing local vasodilation and sympathetic vasoconstriction control muscle blood flow during moderate exercise, and vasoconstrictor tone can be withdrawn by baroreceptor stimulation. High levels of vasoconstrictor outflow to muscle in severe exercise may not originate from baroreflexes.

Adult↗
PubMed1990

Cardiovascular and metabolic responses to static contraction in man.

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean +/- 1 SD) was 0.4 +/- 0.3, 1.76 +/- 0.65, 0.90 +/- 0.32 and 1.06 +/- 0.59 1 min-1, and mean arterial pressures (MAP) were 104 +/- 13, 140 +/- 14, 160 +/- 17 and 161 +/- 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation. Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3-3.5 1 min-1, which corresponded to 150 ml 100 g-1 min-1. When both O2 uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found. When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood flow became reduced.

Adult↗
PubMed1990

Function, morphology and protein expression of ageing skeletal muscle: a cross-sectional study of elderly men with different training backgrounds.

The function and morphology of knee extension/m. vastus lateralis and elbow flexion/m. biceps brachii were studied in young (28 +/- 0.1 years, n = 7) and elderly (68 +/- 0.5 years, n = 8) sedentary subjects and in elderly swimmers (69 +/- 1.9 years, n = 6), runners (70 +/- 0.7 years, n = 5) and strength-trained subjects (68 +/- 0.8 years, n = 7). On average, the training groups had, for the 12-17 years before the measurements were taken, performed their training regimen 3 +/- 0.1 times a week. Compared with the young subjects, the maximal isometric torque of the sedentary elderly subjects was 44% (P less than 0.05) lower in knee extension and 32% (P less than 0.05) lower in elbow flexion, and speed of movement was between 20 and 26% (P less than 0.05) lower in both knee extension and elbow flexion. The cross-sectional area of m. quadriceps femoris and the elbow flexors was also 24% (P less than 0.05) and 20% lower respectively, and the specific tension was 27% (P less than 0.05) lower in m. quadriceps femoris and 14% (P less than 0.05) lower in the elbow flexors. A 27% (P less than 0.05) higher content of myosin heavy chain type I and a 39% (P less than 0.05) higher content of the slow-type myosin light chain--2 was observed in m. vastus lateralis of the sedentary elderly subjects as compared with the young subjects. The same tendency was also seen with m. biceps brachii. Since the histochemical fibre-type distribution was identical and no major co-expression of type I and type II myosin heavy-chain isoforms was observed with immunocytochemistry, the increase in slow myosin isoforms with ageing seems mainly related to a larger relative area of type I fibres, induced by a selective atrophy of type II fibre area. An increased content of the beta-isoform of tropomyosin was also demonstrated with ageing. In contrast to the swimmers and runners, the elderly strength-trained subjects had maximal isometric torques, speed of movements, cross-sectional areas, specific tensions and a content of myosin and tropomyosin isoforms in both muscles studied identical to those of the young controls. These results seem to suggest that strength training can counteract the age-related changes in function and morphology of the ageing human skeletal muscle.

Aged↗
PubMed1990

Ageing alters the myosin heavy chain composition of single fibres from human skeletal muscle.

The myosin heavy chain composition of single fibres (n = 1088) was analysed with an electrophoretic technique in biopsy material from m. vastus lateralis (n = 5) and m. biceps brachii (n = 4) of young (23-31 years old) and elderly men (68-70 years old). In m. vastus lateralis, elderly subjects had a higher proportion of fibres showing a coexistence of myosin heavy chain types I and IIa (20 +/- 3% vs 8 +/- 1%, P less than 0.05) and of myosin heavy chain types IIa and IIb (33 +/- 2% vs 12 +/- 4%, P less than 0.05). In contrast, the young subjects had a higher proportion of fibres containing only myosin heavy chain type I (50 +/- 5% vs 33 +/- %, P less than 0.05) and type IIa (26 +/- 3% vs 12 +/- 2%, P less than 0.05). A similar pattern of myosin heavy chain expression was found in single fibres from m. biceps brachii, with the exception that the elderly subjects had a lower proportion of fibres with coexistence of types IIa and IIb (23 +/- 1% vs 34 +/- 2%, P less than 0.05) and a higher proportion of fibres containing only myosin heavy chain type IIa (25 +/- 5% vs 12 +/- 2%, P less than 0.05). Three fibres from m. biceps brachii contained all three isoforms. These results indicate that coexistence of myosin heavy chain isoforms in single fibres is present in skeletal muscles of young adults, and that there is an increased occurrence of this phenomenon with ageing.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Lactate and potassium fluxes from human skeletal muscle during and after intense, dynamic, knee extensor exercise.

This study examines lactate and K+ fluxes from muscle to blood during and after intense exercise. Ten men performed exhaustive dynamic exercise (mean load 65 W, mean duration 3.18 min) with the knee extensors of one leg. The mean lactate efflux was 15.5 (range 8.9-24.0) mmol min-1 at exhaustion, and it was linearly related to the lactate gradient. A linear relationship was also obtained if the H+ gradient was taken into account. Muscle pH decreased from 7.14 at rest to 6.71 (range 6.50-6.87) at exhaustion. At rest and during late recovery blood lactate was distributed across the erythrocyte membrane according to the membrane potential (intra-/extracellular ratio of 0.5), but during rapid lactate release this ratio decreased to 0.2. In-vitro experiments demonstrated a time constant of 1.2 min for lactate efflux from the erythrocytes. Approximately 70% of the K+ ions released from the muscle to the blood accumulated in the plasma; the rest were taken up by other tissues. However, erythrocytes were not involved as a dilution space. The small change in erythrocyte K+ concentration was due to cellular volume changes. During recovery the kinetics of K+ reuptake by the muscle were described by a very fast (less than 1 min) and a slow component (greater than 1 min): the magnitude of the former was equivalent to what had accumulated in the plasma. Individuals displayed a wide range of intramuscular lactate concentrations and pH values at exhaustion. Further, the pH changes were not as extreme as previously reported, suggesting that pH may not be the only factor involved in the fatigue process. A possible role for the potassium shifts as a limiting factor for muscle function is discussed.

Adult↗
PubMed1990

Anaerobic energy production and O2 deficit-debt relationship during exhaustive exercise in humans.

1. Eight subjects performed one-legged, dynamic, knee-extensor exercise, first at 10 W followed by 10 min rest, then at an intense, exhaustive exercise load (65 W) lasting 3.2 min. After 60 min recovery, exercise was performed for 8-10 min each at 20, 30, 40 and 50 W. Measurements of pulmonary oxygen uptake, heart rate, blood pressure, leg blood flow, and femoral arterial-venous differences of oxygen content and lactate were performed as well as determination of ATP, creatine phosphate (CP) inosine monophosphate (IMP) and lactate concentrations on biopsy material from the quadriceps muscle before and immediately after the intense exercise, and at 3, 10 and 60 min into recovery. 2. Individual linear relations (r = 0.95-1.00) between the power outputs for submaximal exercise and oxygen uptakes (leg and pulmonary) were used to estimate the energy demand during intense exercise. Pulmonary and leg oxygen deficits determined as the difference between energy demand and oxygen uptake were 0.46 and 0.48 l (kg active muscle)-1, respectively. Limb and pulmonary oxygen debts (oxygen uptake during 60 min of recovery - pre-exercise oxygen uptake) were 0.55 and 1.65 l (kg active muscle)-1, respectively. 3. During the intense exercise, muscle [ATP] decreased by 30% and [CP] by 60% from resting concentrations of 6.2 and 22.4 mmol (kg wet wt)-1, respectively, and [IMP] increased to 1.1 mmol (kg wet wt)-1. Muscle [lactate] increased from 2 to 28.1 mmol (kg wet wt)-1, and the concomitant net lactate release was 14.8 mmol (kg wet wt)-1 or about 1/3 of the total net lactate production. During recovery 70% of the accumulated lactate was released to the blood, and the nucleotides and CP returned to about 40 and 85% of pre-exercise values at 3 and 10 min of recovery, respectively. 4. Total reduction in ATP and CP (and elevation of IMP) during the intense exercise amounted to 16.4 mmol ATP (kg wet wt)-1, which together with the lactate production accounted for 83.1 mmol ATP (kg wet wt)-1. In addition 6-8 mmol ATP (kg wet wt)-1 are made available related to accumulation of glycolytic intermediates including pyruvate (and alanine). Estimated leg oxygen deficit corresponded to an ATP production of 94.7 mmol ATP kg-1; this value included 3.1 mmol kg-1 related to unloading of HbO2 and MbO2.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1990

Ammonia metabolism during intense dynamic exercise and recovery in humans.

This study examined the dynamics for ammonia (NH3) metabolism in human skeletal muscle during and after intense one-legged exercise. Subjects (n = 8) performed dynamic leg extensor exercise to exhaustion (3.2 min). Muscle NH3 release increased rapidly to a maximum of 314 +/- 42 mumol/min and declined immediately on cessation of exercise. Recovery was complete in approximately 20 min. Arterial [NH3] increased less rapidly and reached its maximum 2-3 min into recovery. These data demonstrate that NH3 clearance is more sensitive to the cessation of exercise than is NH3 release from skeletal muscle. Muscle [NH3] increased three to fourfold during exercise and represented 74 +/- 8% of the total net NH3 formation. Thus the change in muscle [NH3] alone underestimates the NH3 production. There was no evidence that the muscle-to-venous blood NH3 ratio shifts in accordance with the H+ data. Thus other factors must contribute to the NH3 release from active muscle. The total net NH3 formed corresponded with the intramuscular inosine 5'-monophosphate accumulation, suggesting that the NH3 was derived from AMP deamination. Changes in the known modulators of AMP deaminase (ATP, ADP, H+) were moderate, so the mechanisms initiating the deamination remain obscure.

Adenine Nucleotides↗
PubMed1990

Beta 2-adrenergic stimulation does not prevent potassium loss from exercising quadriceps muscle.

During exercise K+ is released from contracting muscle and plasma K+ concentration rises. Because beta 2-adrenergic agonists stimulate K+ uptake by skeletal muscle in vitro, we tested whether terbutaline, a selective beta 2-agonist, would reduce the loss of K+ from working muscle. Dynamic quadriceps muscle exercise was performed by 12 healthy male volunteers for 50 or 80 min at an average workload of 38 W. A steady K+ loss estimated at 0.16 +/- 0.02 mmol.min-1.kg working muscle-1 and a 0.30 +/- 0.05 mM elevation of arterial plasma K+ concentration were observed. The addition of terbutaline during exercise caused leg blood flow to increase 13% from 5.10 +/- 0.16 to 5.75 +/- 0.13 l/min and arterial K+ concentration to fall monoexponentially by 0.90 +/- 0.05 mM with a rate constant of 0.26 min-1. Terbutaline increased, rather than decreased, the washout of K+ from working quadriceps by 40% to an average value of 0.23 +/- 0.02 mmol.min-1.kg muscle-1. In an additional subject who exercised to exhaustion, terbutaline failed to diminish muscle K+ loss. We conclude that terbutaline does not augment Na(+)-K+ pump activity to a degree sufficient to prevent K+ loss from exercising muscle in humans. On the other hand, the rapid reduction in plasma K+ concentration observed with beta 2-adrenergic stimulation is compatible with an uptake of K+ by nonexercising tissue at an estimated maximal rate of 0.5 micromol.g-1.min-1.

Adrenergic beta-Agonists↗
PubMed1990

Limb skeletal muscle adaptation in athletes after training at altitude.

Morphological and biochemical characteristics of biopsies obtained from gastrocnemius (GAS) and triceps brachii muscle (TRI), as well as maximal O2 uptake (VO2 max) and O2 deficit, were determined in 10 well-trained cross-country skiers before and after a 2-wk stay (2,100 m above sea level) and training (2,700 m above sea level) at altitude. On return to sea level, VO2 max was the same as the prealtitude value, whereas an increase in O2 deficit (29%) and in short-term running performance (17%) was observed (P less than 0.05). GAS showed maintained capillary supply but a 10% decrease in mitochondrial enzyme activities (P less than 0.05), whereas an increase in capillary supply (P less than 0.05) but unchanged mitochondrial enzyme activities were observed in TRI. Buffer capacity was increased by 6% in both GAS and TRI (P less than 0.05). A positive correlation was found between the relative increase in buffer capacity of GAS and short-term running time (P less than 0.05). Thus the present study indicates no effect of 2 wk of altitude training on VO2 max but provides evidence to suggest an improvement in short-term exercise performance, which may be the result of an increase in muscle buffer capacity.

Adaptation, Physiological↗
PubMed1990

Muscle blood flow and muscle metabolism during exercise and heat stress.

The effect of heat stress on blood flow and metabolism in an exercising leg was studied in seven subjects walking uphill (12-17%) at 5 km/h on a treadmill for 90 min or until exhaustion. The first 30 min of exercise were performed in a cool environment (18-21 degrees C); then subjects moved to an adjacent room at 40 degrees C and continued to exercise at the same speed and inclination for a further 60 min or to exhaustion, whichever occurred first. The rate of O2 consumption, 2.6 l/min (1.8-3.3) (average from cool and hot conditions), corresponded to 55-77% of their individual maximums. In the cool environment a steady state was reached at 30 min. When the subjects were shifted to the hot room, the core temperature and heart rate started to rise and reached values greater than 39 degrees C and near-maximal values, respectively, at the termination of the exercise. The leg blood flow (thermodilution method), femoral arteriovenous O2 difference, and consequently leg O2 consumption were unchanged in the hot compared with the cool condition. There was no increase in release of lactate and no reduction in glucose and free net fatty acid uptake in the exercising leg in the heat. Furthermore, the rate of glycogen utilization in the gastrocnemius muscle was not elevated in the hot environment. There was a tendency for cardiac output to increase in the heat (mean 15.2 to 18.4 l/min), which may have contributed to the increase in skin circulation, together with a possible further reduction in flow to other vascular beds, because muscle blood flow was not reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗