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Biomedical subjects

J Bangsbo

Publications and source records attributed to J Bangsbo.

At least 37 records · Page 2Linked to original sources
PubMed2000

Interstitial K(+) in human skeletal muscle during and after dynamic graded exercise determined by microdialysis.

Interstitial K(+) concentrations were measured during one-legged knee-extensor exercise by use of microdialysis with probes inserted in the vastus lateralis muscle of the subjects. K(+) in the dialysate was measured either by flame photometry or a K(+)-sensitive electrode placed in the perfusion outlet. The correction for fractional K(+) recovery was based on the assumption of identical fractional thallium loss. The interstitial K(+) was 4. 19 +/- 0.09 mM at rest and increased to 6.17 +/- 0.19, 7.48 +/- 1.18, and 9.04 +/- 0.74 mM at 10, 30, and 50 W exercise, respectively. The individual probes demonstrated large variations in interstitial K(+), and values >10 mM were obtained. The observed interstitial K(+) was markedly higher than previously found for venous K(+) concentrations at similar work intensities. The present data support a potential role for interstitial K(+) in regulation of blood flow and development of fatigue.

Adult↗
PubMed2000

Exercise-induced translocation of Na(+)-K(+) pump subunits to the plasma membrane in human skeletal muscle.

Six human subjects performed one-legged knee extensor exercise (90 +/- 4 W) until fatigue (exercise time 4.6 +/- 0.8 min). Needle biopsies were obtained from vastus lateralis muscle before and immediately after exercise. Production of giant sarcolemmal vesicles from the biopsy material was used as a membrane purification procedure, and Na(+)-K(+) pump alpha- and beta-subunits were quantified by Western blotting. Exercise significantly increased (P < 0.05) the vesicular membrane content of the alpha(2)-, total alpha-, and beta(1)-subunits by 70 +/- 29, 35 +/- 10, and 26 +/- 5%, respectively. The membrane content of alpha(1) was not changed by exercise, and the densities of subunits in muscle homogenates were unchanged. The ratio of vesicular to crude muscle homogenate content of the alpha(2)-, total alpha-, and beta(1)-subunits was elevated during exercise by 67 +/- 33 (P < 0.05), 23 +/- 6 (P < 0.05), and 40 +/- 14% (P = 0.06), respectively. It is concluded that translocation of subunits is an important mechanism involved in the short time upregulation of the Na(+)-K(+) pumps in association with human muscle activity.

Adult↗
PubMed2000

Muscle oxygen kinetics at onset of intense dynamic exercise in humans.

The present study examined the onset and the rate of rise of muscle oxidation during intense exercise in humans and whether oxygen availability limits muscle oxygen uptake in the initial phase of intense exercise. Six subjects performed 3 min of intense one-legged knee-extensor exercise [65.3 +/- 3.7 (means +/- SE) W]. The femoral arteriovenous blood mean transit time (MTT) and time from femoral artery to muscle microcirculation was determined to allow for an examination of the oxygen uptake at capillary level. MTT was 15.3 +/- 1.8 s immediately before exercise, 10.4 +/- 0.7 s after 6 s of exercise, and 4.7 +/- 0.5 s at the end of exercise. Arterial venous O(2) difference (a-v(diff) O(2)) of 18 +/- 5 ml/l before the exercise was unchanged after 2 s, but it increased (P < 0.05) after 6 s of exercise to 43 +/- 10 ml/l and reached 146 +/- 4 ml/l at the end of exercise. Thigh oxygen uptake increased (P < 0.05) from 32 +/- 8 to 102 +/- 28 ml/min after 6 s of exercise and to 789 +/- 88 ml/min at the end of exercise. The time to reach half-peak a-v(diff) O(2) and thigh oxygen uptake was 13 +/- 2 and 25 +/- 3 s, respectively. The difference between thigh oxygen delivery (blood flow x arterial oxygen content) and thigh oxygen uptake increased (P < 0.05) after 6 s and returned to preexercise level after 14 s. The present data suggest that, at the onset of exercise, oxygen uptake of the exercising muscles increases after a delay of only a few seconds, and oxygen extraction peaks after approximately 50 s of exercise. The limited oxygen utilization in the initial phase of intense exercise is not caused by insufficient oxygen availability.

Adult↗
PubMed2000

Endurance training does not alter the level of neuronal nitric oxide synthase in human skeletal muscle.

The effect of endurance training on neuronal nitric oxide synthase (nNOS) content and distribution in muscle was investigated. Seven male subjects performed 6 wk of one-legged knee-extensor endurance training (protocol A). Muscle biopsies, obtained from vastus lateralis muscle in the untrained and the trained leg, were analyzed for nNOS protein and activity as well as immunohistochemical distribution of nNOS and endothelial nitric oxide synthase (eNOS). Muscle biopsies were also obtained from another seven male subjects before and after 6 wk of training by endurance running (protocol B) and analyzed for nNOS protein. No difference was found in the amount of nNOS protein in the untrained and the trained muscle either with protocol A or protocol B (P > 0.05). In protocol A, the activity of nNOS was 4.76 +/- 0.56 pmol. mg protein(-1). min(-1) in the control leg, and the level was not different in the trained leg (P > 0.05). nNOS was present in the sarcolemma and cytosol of type I and type II muscle fibers, and the qualitative distribution was similar in untrained and trained muscle. The number of eNOS immunoreactive structures and the number of capillaries per muscle fiber were higher (P < 0.05) after training than before. The present findings demonstrate that, in contrast to findings on animals, nNOS levels remain unaltered with endurance training in humans. Evidence is also provided that endurance training may increase the amount of eNOS, in parallel with an increase in capillaries in human muscle.

Adult↗
PubMed2000

Total power output generated during dynamic knee extensor exercise at different contraction frequencies.

A novel approach has been developed for the quantification of total mechanical power output produced by an isolated, well-defined muscle group during dynamic exercise in humans at different contraction frequencies. The calculation of total power output comprises the external power delivered to the ergometer (i.e., the external power output setting of the ergometer) and the "internal" power generated to overcome inertial and gravitational forces related to movement of the lower limb. Total power output was determined at contraction frequencies of 60 and 100 rpm. At 60 rpm, the internal power was 18+/- 1 W (range: 16-19 W) at external power outputs that ranged between 0 and 50 W. This was less (P<0.05) than the internal power of 33+/-2 W (27-38 W) at 100 rpm at 0-50 W. Moreover, at 100 rpm, internal power was lower (P<0.05) at the higher external power outputs. Pulmonary oxygen uptake was observed to be greater (P<0.05) at 100 than at 60 rpm at comparable total power outputs, suggesting that mechanical efficiency is lower at 100 rpm. Thus a method was developed that allowed accurate determination of the total power output during exercise generated by an isolated muscle group at different contraction frequencies.

Adult↗
PubMed1999

AMP deamination and purine exchange in human skeletal muscle during and after intense exercise.

1. The present study examined the regulation of human skeletal muscle AMP deamination during intense exercise and quantified muscle accumulation and release of purines during and after intense exercise. 2. Seven healthy males performed knee extensor exercise at 64.3 W (range: 50-70 W) to exhaustion (234 s; 191-259 s). In addition, on two separate days the subjects performed exercise at the same intensity for 30 s and 80 % of exhaustion time (mean, 186 s; range, 153-207 s), respectively. Muscle biopsies were obtained from m.v. lateralis before and after each of the exercise bouts. For the exhaustive bout femoral arterio-venous concentration differences and blood flow were also determined. 3. During the first 30 s of exercise there was no change in muscle adenosine triphosphate (ATP), inosine monophosphate (IMP) and ammonia (NH3), although estimated free ADP and AMP increased 5- and 45-fold, respectively, during this period. After 186 s and at exhaustion muscle ATP had decreased (P < 0.05) by 15 and 19 %, respectively, muscle IMP was elevated (P < 0. 05) from 0.20 to 3.65 and 5.67 mmol (kg dry weight)-1, respectively, and muscle NH3 had increased (P < 0.05) from 0.47 to 2.55 and 2.33 mmol (kg d.w.)-1, respectively. The concentration of H+ did not change during the first 30 s of exercise, but increased (P < 0.05) to 245.9 nmol l-1 (pH 6.61) after 186 s and to 374.5 nmol l-1 (pH 6. 43) at exhaustion. 4. Muscle inosine and hypoxanthine did not change during exercise. In the first 10 min after exercise the muscle IMP concentration decreased (P < 0.05) by 2.96 mmol (kg d.w.)-1 of which inosine and hypoxanthine formation could account for 30 %. The total release of inosine and hypoxanthine during exercise and 90 min of recovery amounted to 1.07 mmol corresponding to 46 % of the net ATP decrease during exercise or 9 % of ATP at rest. 5. The present data suggest that AMP deamination is inhibited during the initial phase of intense exercise, probably due to accumulation of orthophosphate, and that lowered pH is an important positive modulator of AMP deaminase in contracting human skeletal muscle in vivo. Furthermore, formation and release of purines occurs mainly after intense exercise and leads to a considerable loss of nucleotides.

Adenosine Monophosphate↗
PubMed1999

Vasoactive substances in the interstitium of contracting skeletal muscle examined by microdialysis.

In the study of the regulation of skeletal muscle blood flow during exercise it is useful to obtain information regarding the concentrations of vasoactive substances in the muscle interstitium, a site where the compounds act on the vascular and skeletal muscle cells. The microdialysis technique is a useful tool for measuring interstitial substances in the muscle at rest and during exercise in human subjects, and the technique can also be used to study the effect of both systemic and local interventions in a specific area of an exercising muscle. Probe recovery, which represents the relative amount of a substance that is diffusing to the dialysis membrane, changes from rest to exercise and can be determined by the internal-standard technique which allows for a relatively high time resolution (min). Furthermore, the use of electrodes at the microdialysis outlet makes it possible to perform continuous measurements of interstitial substances. The present review gives examples of how the microdialysis technique has been applied to study potentially important vasodilators such as adenosine, NO and K+ in human skeletal muscles and highlights areas for future research to establish the functional importance of these compounds.

Adenosine↗
PubMed1999

Effect of high-intensity exercise training on lactate/H+ transport capacity in human skeletal muscle.

The present study examined the effect of high-intensity exercise training on muscle sarcolemmal lactate/H+ transport and the monocarboxylate transporters (MCT1 and MCT4) as well as lactate and H+ release during intense exercise in humans. One-legged knee-extensor exercise training was performed for 8 wk, and biopsies were obtained from untrained and trained vastus lateralis muscle. The rate of lactate/H+ transport determined in sarcolemmal giant vesicles was 12% higher (P < 0.05) in the trained than in untrained muscle (n = 7). The content of MCT1 and MCT4 protein was also higher (76 and 32%, respectively; n = 4) in trained muscle. Release of lactate and H+ from the quadriceps muscle at the end of intense exhaustive knee-extensor exercise was similar in the trained and untrained leg, although the estimated muscle intracellular-to-interstitial gradients of lactate and H+ were lower (P < 0.05) in the trained than in the untrained muscle. The present data show that intense exercise training can increase lactate/H+ transport capacity in human skeletal muscle as well as improve the ability of the muscle to release lactate and H+ during contractions.

Acid-Base Equilibrium↗
PubMed1999

Potassium fluxes in contracting human skeletal muscle and red blood cells.

The present study examined K+ fluxes in red blood cells and muscle during muscle contractions. Seven subjects performed two-legged submaximal knee-extensor exercise for 30 min. After 10 min of leg exercise (L1), intense arm exercise was also performed for 10 min (L2+A). Plasma epinephrine and norepinephrine concentrations were higher (P < 0.05) in L2+A compared with L1. Arterial plasma K+ at the end of L2+A was higher than in L1 (5.6 vs. 4.4 mM, P < 0.05) and returned to the L1 level on cessation of arm exercise. A net K+ release of 0.16 mmol/min from the active legs during L1 was turned to a net K+ uptake of 0.79 mmol/min during L2+A. Both arterial and venous red blood cell K+-to-hemoglobin ratios were constant during exercise. The present data suggest that contracting muscle can take up K+ probably by a combination of K+ and hormone activation of the Na+-K+ pump. Furthermore, changes in red blood cell K+ concentrations during muscle activity appear to be due to water movements and not transmembrane fluxes of K+.

Adult↗
PubMed1999

Development of muscle strength in relation to training level and testosterone in young male soccer players.

Isometric and functional strength of ninety-eight 11-yr-old male soccer players at an elite (E) and nonelite (NE) level were determined (3-4 times) through a 2-yr period, and the changes were related to growth and maturation. The initial isometric strength for extension with dominant leg [1,502 +/- 35 (E) vs. 1,309 +/- 39 (NE) N], extension with nondominant leg (1,438 +/- 37 vs. 1,267 +/- 45 N), extension with both legs (2,113 +/- 76 vs. 1,915 +/- 72 N), back muscles (487 +/- 11 vs. 414 +/- 10 N), abdominal muscles (320 +/- 9 vs. 294 +/- 8 N), and handgrip (304 +/- 10 vs. 259 +/- 8 N) increased by 15-40% during the period. Broad jump increased (P < 0. 05) by 15 (E) and 10% (NE). The E players had higher (P < 0.05) initial isometric strength and broad jump performance compared with NE players, and differences were maintained throughout the period (multiple ANOVA for repeated measures) also when adjustment was made for age, dimensions, testosterone, and insulin-like growth factor I (generalized estimating equations analyses). The development of strength for both E and NE players together was significantly (P < 0. 001) related to changes in serum testosterone concentrations. The present data indicate that testosterone is important for development of strength in young boys and that, independent of serum testosterone concentration, E players have developed greater muscle strength compared with NE players.

Adolescent↗
PubMed1999

Muscle interstitial glucose and lactate levels during dynamic exercise in humans determined by microdialysis.

The purpose of the present study was to use the microdialysis technique to determine skeletal muscle interstitial glucose and lactate concentrations during dynamic incremental exercise in humans. Microdialysis probes were inserted into the vastus lateralis muscle, and subjects performed knee extensor exercise at workloads of 10, 20, 30, 40, and 50 W. The in vivo probe recoveries determined at rest by the internal reference method for glucose and lactate were 28.7 +/- 2.5 and 32.0 +/- 2.7%, respectively. As exercise intensity increased, probe recovery also increased, and at the highest workload probe recovery for glucose (61.0 +/- 3.9%) and lactate (66. 3 +/- 3.6%) had more than doubled. At rest the interstitial glucose concentration (3.5 +/- 0.2 mM) was lower than both the arterial (5.6 +/- 0.2 mM) and venous (5.3 +/- 0.3 mM) plasma water glucose levels. The interstitial glucose levels remained lower (P < 0.05) than the arterial and venous plasma water glucose concentrations during exercise at all intensities and at 10, 20, 30, and 50 W, respectively. At rest the interstitial lactate concentration (2.5 +/- 0.2 mM) was higher (P < 0.05) than both the arterial (0.9 +/- 0. 2 mM) and venous (1.1 +/- 0.2 mM) plasma water lactate levels. This relationship was maintained (P < 0.05) during exercise at workloads of 10, 20, and 30 W. These data suggest that interstitial glucose delivery at rest is flow limited and that during exercise changes in the interstitial concentrations of glucose and lactate mirror the changes observed in the venous plasma water compartments. Furthermore, skeletal muscle contraction results in an increase in the diffusion coefficient of glucose and lactate within the interstitial space as reflected by an elevation in probe recovery during exercise.

Exercise↗
PubMed1998

Adenosine concentrations in the interstitium of resting and contracting human skeletal muscle.

BACKGROUND: Adenosine has been proposed to be a locally produced regulator of blood flow in skeletal muscle. However, the fundamental questions of to what extent adenosine is formed in skeletal muscle tissue of humans, whether it is present in the interstitium, and where it exerts its vasodilatory effect remain unanswered. METHODS AND RESULTS: The interstitial adenosine concentration was determined in the vastus lateralis muscle of healthy humans via dialysis probes inserted in the muscle. The probes were perfused with buffer, and the dialysate samples were collected at rest and during graded knee extensor exercise. At rest, the interstitial concentration of adenosine was 220+/-100 nmol/L and femoral arterial blood flow (FaBF) was 0.19+/-0.02 L/min. When the subjects exercised lightly, at a work rate of 10 W, there was a markedly higher (1140+/-540 nmol/L; P<0.05) interstitial adenosine concentration and a higher FaBF (2.22+/-0.18 L/min; P<0.05) compared with at rest. When exercise was performed at 20, 30, 40, or 50 W, the concentration of adenosine was moderately greater for each increment, as was the level of leg blood flow. The interstitial concentrations of ATP, ADP, and AMP increased from rest (0.13+/-0.03, 0.07+/-0.03, and 0.07+/-0.02 micromol/L, respectively) to exercise (10 W; 2.00+/-1.32, 2.08+/-1.23, and 1.65+/-0.50 micromol/L, respectively; P<0.05). CONCLUSIONS: The present study provides, for the first time, interstitial adenosine concentrations in human skeletal muscle and demonstrates that adenosine and its precursors increase in the exercising muscle interstitium, at a rate associated with intensity of muscle contraction and the magnitude of muscle blood flow.

Adenosine↗
PubMed1998

Optimal preparation for the World Cup in soccer.

In preparing for the World Cup in soccer, the players should recover in the first period after their club season. It is, however, important that they try to maintain their endurance capacity by frequently performing aerobic low-intensity exercise in order to be prepared for the rebuilding period starting about 5 weeks before the World Cup. During the rebuilding period, mainly aerobic high-intensity exercise, but also various types of anaerobic training, should be performed. At the onset of the tournament, the amount of fitness training can be reduced for the players who regularly play on the team; however, frequent sessions with aerobic high-intensity training are recommended. The training plan should take into account the need of each individual player. Players who do not regularly play on the team should follow an extensive fitness training program throughout all periods.

Humans↗
PubMed1998

Muscle blood flow and oxygen uptake in recovery from exercise.

The metabolic and muscle blood flow response in recovery from exercise is dependent on the type and the duration of the exercise. Immediately after both intense static and dynamical exercise blood flow to the exercised muscles increases suggesting that blood flow is mechanically hindered by muscle contraction. After the initial rise (seconds) muscle blood flow decreases at a moderate rate and the time to reach resting flow levels varies from seconds to more than 30 min. It is unclear as to what causes the elevated blood flow during recovery. A mismatch between the time course of changes in blood flow and oxygen uptake suggests that the blood flow is not directly regulated by the need of oxygen in the exercised muscles. The hyperaemic response may be linked to locally released factors, such as ions and metabolites. However, the signal by which the blood flow is elevated remains unknown. After exercise both pulmonary and muscle oxygen uptake decrease rapidly, but can remain above resting levels for several hours. Resynthesis of substrates such as CP, ATP and glycogen cannot account for the entire excessive post-exercise oxygen uptake (EPOC) in the exercised muscles and the cause of the elevated muscle oxygen uptake in recovery from exercise remains to be assessed.

Energy Metabolism↗
PubMed1998

Quantification of anaerobic energy production during intense exercise.

Anaerobic energy production during supramaximal exercise has been estimated from muscle metabolic changes. Based on such measurements the anaerobic energy production was determined to be 63 and 189 mmol ATP x kg(-1) d.w. for 60 and 142 s of exhaustive cycling exercise, respectively. These estimations do not, however, include release of lactate from the exercising muscles. Furthermore, the anaerobic production cannot be related to the work performed since the muscle biopsy sample may not be representative for the muscles involved in the exercise, and the total anaerobic energy production during whole body exercise cannot be determined because the mass of the muscles used is unknown. When a single muscle is exercised, the problems are minimized. With a one-legged knee-extensor exercise model, which uses a defined muscle mass, the anaerobic energy production has been estimated to be 370 mmol ATP x kg(-1) d.w. for a 192-s exhaustive exercise period. Estimated pulmonary oxygen deficit based on an energy demand extrapolated from a linear relationship between exercise intensity and oxygen uptake at submaximal exercise does not appear to represent the anaerobic energy production during whole body exercise.

Adenosine Triphosphate↗
PubMed1998

Urate uptake and lowered ATP levels in human muscle after high-intensity intermittent exercise.

The exchange of purines in exercised and rested muscle and their relation to muscle ATP levels after intense intermittent exercise were investigated. Seven subjects performed one-legged knee extensor exercise on the following two occasions: without (control; C) and with (high purines; HP) additional arm exercise. There was a greater net release of hypoxanthine by the exercised muscle during the recovery period in HP compared with C [185 +/- 44 vs. 101 +/- 30 (SE) mumol/kg muscle; P < 0.05]. During recovery, the arterial urate concentration was higher in HP compared with C (peak: 585 +/- 48 vs. 355 +/- 20 mumol/l; P < 0.05). The exercised but not the rested muscle extracted a marked amount of urate (330 mumol/kg muscle) from plasma in the HP trial. Muscle ATP levels after 90 min of recovery in HP were lower than at rest (24.3 +/- 0.6 vs. 20.1 +/- 1.1 mmol/kg dry wt). The present data suggest that a single session of long-term high-intensity intermittent exercise causes a significant release of purines from the muscle into blood, which contributes to a sustained lowered level of the muscle ATP concentration. Furthermore, intensely exercised muscle extracts urate when plasma urate is elevated, an event that may be of importance for the replenishment of oxidized muscle urate stores.

Adenosine Triphosphate↗
PubMed1998

Microdialysis ethanol removal reflects probe recovery rather than local blood flow in skeletal muscle.

The present study compared the microdialysis ethanol outflow-inflow technique for estimating blood flow (BF) in skeletal muscle of humans with measurements by Doppler ultrasound of femoral artery inflow to the limb (BFFA). The microdialysis probes were inserted in the vastus lateralis muscle and perfused with a Ringer acetate solution containing ethanol, [2-3H]adenosine (Ado), and D-[14C(U)]glucose. BFFA at rest increased from 0.16 +/- 0.02 to 1.80 +/- 0.26 and 4.86 +/- 0.53 l/min with femoral artery infusion of Ado (AdoFA,i) at 125 and 1,000 microg . min-1 . l-1 thigh volume (low dose and high dose, respectively; P < 0.05) and to 3.79 +/- 0.37 and 6.13 +/- 0.65 l/min during one-legged, dynamic, thigh muscle exercise without and with high AdoFA,i, respectively (P < 0.05). The ethanol outflow-to-inflow ratio (38.3 +/- 2.3%) and the probe recoveries (PR) for [2-3H]Ado (35.4 +/- 1.6%) and for D-[14C(U)]glucose (15.9 +/- 1.1%) did not change with AdoFA,i at rest (P = not significant). During exercise without and with AdoFA,i, the ethanol outflow-to-inflow ratio decreased (P < 0.05) to a similar level of 17.5 +/- 3.4 and 20.6 +/- 3.2%, respectively (P = not significant), respectively, while the PR increased (P < 0.05) to a similar level (P = not significant) of 55.8 +/- 2.8 and 61.2 +/- 2. 5% for [2-3H]Ado and to 42.8 +/- 3.9 and 45.2 +/- 5.1% for D-[14C(U)]glucose. Whereas the ethanol outflow-to-inflow ratio and PR correlated inversely and positively, respectively, to the changes in BF during muscular contractions, neither of the ratio nor PR correlated to the AdoFA,i-induced BF increase. Thus the ethanol outflow-to-inflow ratio does not represent skeletal muscle BF but rather contraction-induced changes in molecular transport in the interstitium or over the microdialysis membrane.

Adenosine↗