Search PubMed⌕ Search

Biomedical subjects

H Howald

Publications and source records attributed to H Howald.

At least 73 records · Page 4Linked to original sources
PubMed1985

Influences of endurance training on the ultrastructural composition of the different muscle fiber types in humans.

To investigate changes in the ultrastructure of the different muscle fiber types induced by endurance training ten sedentary subjects (five women and five men) were exercised on bicycle ergometers 5 times a week for 30 min. After 6 weeks of training there were significant changes in VO2max (+14%), in the percentage of type I (+12%) and type IIB fibers (-24%) as well as in the volume densities of mitochondria. The latter increased 35% in type I, 55% in type IIA and 35% in type IIB fibers. The relative increase in subsarcolemmal mitochondria was larger than in interfibrillar mitochondria in all fiber types. There was also a significant increase in the volume density of intracellular lipid in type II fibres. It is concluded that high intensity endurance training leads to an enhancement of the oxidative capacity in all muscle fiber types.

Adult↗
PubMed1985

Transfer effects in endurance exercise. Adaptations in trained and untrained muscles.

The effects of 8 weeks of bicycle endurance training (5 X /week for 30 min) on maximal oxygen uptake capacity (VO2max) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg-VO2max for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (-17%). Despite this decrease of mitochondrial volume arm-VO2max increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm-VO2max/leg-VO2max: 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm-VO2max. However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger VO2max during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm-VO2max found after bicycle endurance training.

Adult↗
PubMed1985

[Incidence of occipital ventriculomegaly in premature infants with peri-intraventricular hemorrhage].

Ventricular dilatation after periventricular/intraventricular hemorrhage (PIVH) is a more common complication than was assumed before the advent of ultrasound. In this prospective study based on 264 ultrasonic head scans, the true incidence of ventriculomegaly was investigated in two groups of preterm infants with PIVH. The major incidence of PIVH in babies with less than 34 weeks of gestation (p less than 0.05) was confirmed. Statistical analysis of the follow-up examinations showed that the degree of ventriculomegaly correlated well with the extent of the cerebral-intraventricular hemorrhage (X2 test, p less than 0.002).

Cerebral Hemorrhage↗
PubMed1985

Oxidation and metabolic effects of fructose or glucose ingested before exercise.

The aim of this study was to compare the effects of fructose (F) and glucose (G) intake before exercise on oxidation of the ingested substrate, glycogen utilization, work output, and metabolic changes. Ten trained subjects ingested F or G (1 g/kg), both of which were naturally enriched in 13C. After 1 h of rest, they exercised on an ergometer at 61% of their maximal oxygen uptake (VO2 max) for 45 min, which was immediately followed by 15 min at their maximal voluntary output. During the resting hour, blood insulin and glucose were lower (p less than 0.05) and respiratory quotient and blood lactate higher (p less than 0.01) after F. During exercise, the differences disappeared, apart from a transient but moderate (4.3 mmol/l) hypoglycemia after G compared to F. No difference between F and G was observed for uric acid, glycerol, FFA, and glucagon. Glycogen decrements in the vastus lateralis muscle were 67 +/- 9 (F) and 97 +/- 15 (G) mmol/kg, values not significantly different from each other (P greater than 0.05). The maximal voluntary work produced during the last 15 min did not differ between treatments. During the 2 h after sugar ingestion, 30 +/- 3 g of F and 26 +/- 3 g of G were oxidized to 13CO2. These findings indicate that fructose ingested before exercise was utilized at least as well as glucose, allowed a more stable glycemia, and did not modify performance.

Adult↗
PubMed1985

Endurance training in humans: aerobic capacity and structure of skeletal muscle.

The adaptation of muscle structure, power output, and mass-specific rate of maximal O2 consumption (VO2max/Mb) with endurance training on bicycle ergometers was studied for five male and five female subjects. Biopsies of vastus lateralis muscle and VO2max determinations were made at the start and end of 6 wk of training. The power output maintained on the ergometer daily for 30 min was adjusted to achieve a heart rate exceeding 85% of the maximum for two-thirds of the training session. It is proposed that the observed preferential proliferation of subsarcolemmal vs. interfibrillar mitochondria and the increase in intracellular lipid deposits are two possible mechanisms by which muscle cells adapt to an increased use of fat as a fuel. The relative increase of VO2max/Mb (14%) with training was found to be smaller by more than twofold than the relative increase in maximal maintained power (33%) and the relative change in the volume density of total mitochondria (+40%). However, the calculated VO2 required at an efficiency of 0.25 to produce the observed mass-specific increase in maximal maintained power matched the actual increase in VO2max/Mb (8.0 and 6.5 ml O2 X min-1 X kg-1, respectively). These results indicate that despite disparate relative changes the absolute change in aerobic capacity at the local level (maintained power) can account for the increase in aerobic capacity observed at the general level (VO2max).

Adipose Tissue↗
PubMed1985

Malleability of the motor system: training for maximizing power output.

The training programmes used to improve the strength and/or endurance capacities of athletes are described. Specific stimuli are either high tension in contracting myofibrils or high turnover rates in the oxidative metabolism of the muscle cell. Structural adaptations consist of the synthesis of additional myofibrillar material or increased volume density of both interfibrillar and subsarcolemmal mitochondria. Transformation of fibre types at the level of the molecular structure of myosin seems possible with high-intensity training of long duration. Functional adaptations consist of higher activities of important enzymes in either anaerobic or aerobic energy metabolism and of larger intracellular stores of the respective substrates. All adaptations are highly specific and reversible through detraining or immobilization of the muscle.

Adaptation, Physiological↗
PubMed1985

Interruption of breast-feeding versus phototherapy as treatment of hyperbilirubinemia in full-term infants.

Since 1963 there are reports in the literature about the syndrome of breast milk jaundice. The factors that may contribute to this phenomenon are still unclear. In our study the effect of interruption of breast-feeding in 25 jaundiced full-term infants was compared to the effect of phototherapy in 25 jaundiced otherwise healthy full-term infants. The results show that this treatment has the same therapeutic effect as phototherapy (p greater than 0.05) without its stressful complications and can be recommended as alternative treatment of this type of hyperbilirubinemia.

Bilirubin↗
PubMed1985

[Ergometric validation of a questionnaire on the physical activity in 2 Swiss towns].

A questionnaire concerning physical activity used in the National Research Program No. 1A (PNR 1A) was evaluated by using a physical fitness test on an ergometric bicycle. The values of maximum oxygen consumption correspond to different classes of physical activity set up according to the questionnaire (comparison of groups statistically significant). In addition, it appears that maximal oxygen consumption is in direct relation to the intensity of physical activity during leisure hours, whilst the degree of activity connected with professional or household duties is of very little importance.

Adult↗
PubMed1984

[Cardiovascular risk factors: an intervention program for general practice].

A new multiple risk factor intervention program, combining a comprehensive, stepwise and health education-based approach, was tested in an outpatient setting. In the first 47 patients (aged 17-55, referred by their physicians) total cardiovascular risk (estimated by Framingham index) was reduced within the first 12 months by an average of 32.5%. This improvement derived from significant reductions in all major risk factors. These findings demonstrate the feasibility and potential, yet unexploited, benefit of a more comprehensive risk factor, approach in general medical practice.

Adolescent↗
PubMed1984

[Sports and coronary heart disease].

Vigorous leisure-time exercise induces protection against the risks of coronary heart disease, thus contributing to a lower rate of both morbidity and mortality. The protection is due to a higher HDL/LDL ratio, improved oxygen utilisation capacity of skeletal muscle, enhanced performance capacity of the myocardium, decreased blood pressure and an increase in fibrinolytic activity. A significant training effect can be obtained by running, cycling, rowing, swimming or cross-country skiing 3 times 20-30 minutes per week at an intensity eliciting a heart rate of 180 beats per minute minus the age of the subject in years.

Adult↗
PubMed1984

Improved resolution with one-dimensional polyacrylamide gel electrophoresis: myofibrillar proteins from typed single fibers of human muscle.

Standard procedures for one-dimensional discontinuous sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and silver staining were modified to give more effective separation and an improved resolution of human skeletal muscle proteins. In this system, an electrophoresis buffer composed of 100 mM L-isoleucine, 25 mM Tris base, and 0.1% SDS was used. The separating gel consisted of 16% acrylamide with N,N'-methylenebisacrylamide as a crosslinker (1:23), 0.4% SDS, 1.5 M Tris-HCl, pH 8.8. By the present procedure, the slow and the fast forms of myosin light chains (LCs, LCf) and other contractile proteins from human muscle could be better separated. The silver stain is based on a combination of methods previously described. The modified method requires a small fragment of a single fiber to observe as few as 10 ng of myofibrillar muscle proteins. The described simplifications made it possible to assay and compare up to 40 single fibers in the same electrophoretic run. Improved separation of other proteins migrating at basic pH could be achieved by a similar approach.

Electrophoresis, Polyacrylamide Gel↗
PubMed1984

The relationship of oxygen uptake to superoxide dismutase and catalase activity in human skeletal muscle.

A considerable amount of evidence now makes it clear that aerobic tissues require an elaborate enzyme system to remove the harmful reaction products of oxygen reduction. A portion of this protective system has been studied in human muscle and rat tissues. The VO2 max as well as the superoxide dismutase and catalase activity of vastus lateralis muscle of 12 healthy, male subjects was measured. The subjects with a high aerobic capacity (VO2 max greater than 60 ml . kg-1 . min-1) had significantly greater levels of both superoxide dismutase and catalase. There was also a linear relationship between both superoxide dismutase and catalase and VO2 max. The tissue oxygen consumption, and enzyme activity of the liver, heart, lung, and gastrocnemius from 24 rats was also studied. There VO2 and tissue enzyme activity of both superoxide dismutase and catalase.

Adolescent↗
PubMed1983

Morphometric analysis of the capillary supply in skeletal muscles of trained and untrained subjects--its limitations in muscle biopsies.

Muscle fiber area, capillary density, and capillary to fiber ratio were determined in needle biopsy samples of M. vastus lateralis processed for electron microscopy from 9 untrained men (average VO2 max = 43.7 ml/min kg) and 5 well trained orienteers (VO2 max = 76.1 ml/min kg). The volume density of mitochondria was previously reported to be significantly higher in orienteers (7.32%) than in untrained men (5.19%) and in untrained women (4.08%) in the same material (Hoppeler et al. 1973). The mean fiber area was found to be somewhat larger in orienteers (6,410 microns 2) than in untrained men (5,350 microns 2, not significant), but significantly smaller values were found in untrained women (3,390 microns 2). The capillary density was almost identical in the three experimental groups, it ranged from 416 to 431 mm-2. The absolute values reported for both of the above variables are subjected to a bias due to fiber shrinkage, fiber shortening and fiber kinking occurring during the needle biopsy procedure and the subsequent steps of tissue preparation. The capillary to fiber ratio is much less affected by tissue handling and significantly higher values were found in orienteers (2.70) than in untrained men (2.07) and in untrained women (1.37). There was a significant linear relationship between the capillary to fiber ratio and both VO2 max and the volume density of mitochondria for all subjects analysed, suggesting an adjustment of the capillary supply to the maximal aerobic capacity as well as to the mitochondrial content in M. vastus lateralis.

Adult↗
PubMed1983

Nutrient intake and energy regulation in physical exercise.

Rates of energy expenditure as well as total daily energy cost can be considerable during periods of exercise. In trained athletes, expenditure can be as high as 380 kJ/min during short-term maximal exercise. Training programmes of several hours' duration lead to a daily nutrient intake of 25-35 MJ in most Olympic sports. The mobilization of the energetic fuels of the body is modulated by the nature of the exercise. ATP and creatine phosphate stores in muscle cells are depleted within seconds during maximal work. Glycogen is the main fuel for heavy exercise of a few minutes' duration where performance capacity is limited by the degree of lactate accumulation and intracellular acidosis. Oxidation of both glucose and free fatty acids supplies the energy needed for exercise lasting more than two minutes, the relative contribution of lipids increasing with a longer duration or a lower intensity of the muscular work. Intramuscular stores of glycogen and triglycerides may be almost completely depleted in long-lasting exercise, e.g. a 100 km run. Under these conditions, glycogen stores in the liver and triglycerides in adipose tissue contribute approximately 70% of the energy need whereas 5-10% of the supply comes from oxidation of amino acids. Although adequate nutrition for exercise could be achieved through the intake of a well-balanced diet, the regulation of energy utilization can be influenced by the sources of food energy, by dietary modifications before exercise or by nutrient supplements during exercise. Intake before exercise of fructose or medium-chain triglycerides, both only weakly insulinogenic compared to glucose, leads to changes in blood substrates and metabolites. However, neither glycogen depletion in the working muscles nor performance capacity was influenced by a single meal containing this particular carbohydrate or lipid. Mobilization of free fatty acids in adipose tissue can be enhanced by caffeine or depressed by nicotinic acid. Since the rate of free fatty acid oxidation in skeletal muscle depends on the blood concentration of this substrate, energy regulation during exercise and work output are considerably influenced by the ingestion of such substances.

Adipose Tissue↗