Search PubMed⌕ Search

Biomedical subjects

H Howald

Publications and source records attributed to H Howald.

At least 91 records · Page 5Linked to original sources
PubMed1983

Energy metabolism of medium-chain triglycerides versus carbohydrates during exercise.

Medium-chain triglycerides (MCT) are known to be rapidly digested and oxidized. Their potential value as a source of dietary energy during exercise was compared with that of maltodextrins (MD). Twelve subjects exercised for 1 h on a bicycle ergometer (60% VO2 max), 1 h after the test meal (1MJ). The metabolism of MCT was followed using 1-13C-octanoate (Oc) as tracer and U-13C-glucose (G) was added to the 13C-naturally enriched MD. After MCT ingestion no insulin peak was observed with some accumulation of ketone bodies (KB), blood levels not exceeding 1 mM. Total losses of KB during exercise in urine, sweat and as breath acetone were small (less than 0.2 mmol X h-1). Hence, the influence of KB loss and storage on gas exchange data was negligible. The partition of fat and carbohydrate utilization during exercise as obtained by indirect calorimetry was practically the same after the MCT and the CHO meals. Oxidation over the 2-h period was 30% of dose for Oc and 45% for G. Glycogen decrements in the Vastus lateralis muscle were equal. It appears that with normal carbohydrate stores, a single meal of MCT or CHO did not alter the contribution of carbohydrates during 1 h of high submaximal exercise. The moderate ketonemia after MCT, despite substantial oxidation of this fat, led to no difference in muscle glycogen sparing between the diets.

Adolescent↗
PubMed1983

Human muscle adaptations to chronic hypoxia.

Maximal aerobic power (V02max) decreases with increasing altitude, the drop being about the same in acute and chronic hypoxia. To elucidate this well established but still rather inexplicable finding, experiments were carried out on a group of participants before and immediately after return from a mountaineering expedition to Mount Lhotse Shar (8398 m). The results of a typical subject exposed over a period of 5 weeks to an altitude of at least 5200 m indicate that: A) In the vastus lateralis muscle the number of capillaries to the number of fibers ratio was unchanged, the mean fiber diameter was reduced from 77.3 to 67.9 mu while the mitochondrial to fiber volume ratio increased from 6.7 to 7.9%; in addition, muscle protein concentration diminished by 37% and succinate dehydrogenase activity (SDH) was 48% less than in control conditions; B) Cardiac output and muscular (vastus lateralis) blood flow at submaximal work loads were reduced by 21% and 53%, respectively; C) The V02 on-response kinetics at the mouth upon rectangular submaximal work loads was delayed (t 1/2 = 37.5 vs. 27.0 s). From the above results it is concluded that the apparent lack of beneficial effects of acclimatization on maximal aerobic power is likely the consequence of the interaction of a number of positive (increased hematocrit, rightward shift of the 02 dissociation curve) and negative (reduced thoracic and peripheral blood flow, decreased muscle mass and oxidative enzymes activity) changes induced by hypoxia.

Adaptation, Physiological↗
PubMed1982

Training-induced morphological and functional changes in skeletal muscle.

In addition to the histochemical ATPase staining techniques, immunohistochemistry and two-dimensional gel electrophoresis lead to a better understanding of the molecular structure of the contractile proteins actin, myosin, tropomyosin, and troponin in the different fiber types of human skeletal muscle. A great plasticity enables muscle fibers to adapt to different genetic and environmental influences not only on the level of cellular ultrastructure and metabolic function, but also on the molecular level of the contractile proteins. Fiber type transformation is possible with cross-innervation and specific electrical stimulation. Prolonged and intense endurance training probably also transforms type II fibers into type I fibers, whereas with spring or strength training changes in the different fiber types are restricted to ultrastructure (e.g., myofibrillar to mitochondrial volume ration) and metabolic function. The fiber type distribution pattern in top athletes seems to be determined by both hereditary and environmental factors.

Animals↗
PubMed1982

Anaerobic muscle enzyme changes after interval training.

In contrast to endurance training, little evidence is available concerning the effects of sprint-type training programs on the anaerobic metabolism of skeletal muscle. Four male subjects completed a mean of 16 training sessions consisting of eight 200-m runs at 90% of maximal speed, which were separated by 2-min rest periods. Before and after the 5-week training period, muscle biopsies were taken out of the lateral head of m. gastrocnemius and analyzed for the activities of phosphorylase, phosphofructokinase (PFK), glyceraldehyde phosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and malate dehydrogenase (MDH). Following training there was a significant increase in the subjects' performance time in a treadmill test at a speed of 16 km/h speed and 15% grade. Significant increases were observed in the activities of phosphorylase, PFK, GAPDH, LDH, and MDH, whereas the 17.5% increase in SDH was not statistically significant. It is concluded that interval training with high intensity and a 1:4 work-rest ratio leads to increased activities of key enzymes involved in glycogenolysis and anaerobic glycolysis of skeletal muscle.

Adult↗
PubMed1981

Analysis of myosin light and heavy chain types in single human skeletal muscle fibers.

In this study, myosin types in human skeletal muscle fibers were investigated with electrophoretic techniques. Single fibers were dissected out of lyophilized surgical biopsies and typed by staining for myofibrillar ATPase after preincubation in acid or alkaline buffers. After 14C-labelling of the fiber proteins in vitro by reductive methylation, the myosin light chain pattern was analysed on two-dimensional gels and the myosin heavy chains were investigated by one-dimensional peptide mapping. Surprisingly, human type I fibers, which contained only the slow heavy chain, were found to contain variable amounts of fast myosin light chains in addition to the two slow light chains LC1s and LC2s. The majority of the type I fibers in normal human muscle showed the pattern LC1s, LC2s and LC1f. Further evidence for the existence in human muscle of a hybrid myosin composed of a slow heavy chain with fast and slow light chains comes from the analysis of purified human myosin in the native state by pyrophosphate gel electrophoresis. With this method, a single band corresponding to slow myosin was obtained; this slow myosin had the light chain composition LC1s, LC2s and LC1f. Type IIA and IIB fibers, on the other hand, revealed identical light chain patterns consisting of only the fast light chains LC1f, LC2f and LC3f but were found to have different myosin havy chains. On the basis of the results presented, we suggest that the histochemical ATPase normally used for fibre typing is determined by the myosin heavy chain type (and not by the light chains). Thus, in normal human muscle a number of 'hybrid' myosins were found to occur, namely two extreme forms of fast myosins which have the same light chains but different heavy chains (IIA and IIB) and a continuum of slow forms consisting of the same heavy chain and slow light chains with a variable fast light chain composition. This is consistent with the different physiological roles these fibers are thought to have in muscle contraction.

Adenosine Triphosphatases↗
PubMed1981

Biochemical changes in a 100 km run: carbohydrates, lipids, and hormones in serum.

During the 100 km race in Biel, Switzerland, seven-well trained men (age 33.3 +/- 3.5 years; V02 max. 59.9 +/- ml/kg) have been investigated. Their mean running time over the 100 km distance averaged 10.41 +/- 1.25 h. In contrast to almost unchanged blood glucose and lactate concentrations, blood lipids showed significant changes. Triglycerides decreased about two-fold, whereas glycerol and free fatty acids increased to extremely high concentrations (0.628 and 2.44 mmol/l respectively). Plasma insulin after the run was unaffected, whereas growth hormone, aldosterone and cortisol concentrations were significantly increased. With the exceptions of a still significantly elevated aldosterone and lactate concentration as well as a decreased triglyceride concentration all other values in the blood are restored to normal 24 h after completion of the run.

Adult↗
PubMed1981

[Physical activity and capacity in 4 Swiss cities].

As part of the Swiss National Research Program for the Prevention of Cardiovascular Disease, the degree of physical activity at work and during leisure time ws investigated in 3614 men and 4221 women living in four Swiss cities. Some 50% of the men and more than 60% of the women were considered insufficiently active. Since their jobs involve little physical activity, the quantity and quality of exercise needed for prevention of coronary heart disease can only be obtained from sports during leisure time. Of the men and women investigated in Aarau, 65 and 61% respectively volunteered for a bicycle ergometer test while in Nyon the participation in this part of the study was considerably lower (29 and 24% of the men and women). In both sexes and all age groups the mean values for the extrapolated maximum oxygen uptake were comparable to those reported from other highly industrialized countries.

Adolescent↗
PubMed1980

Myosin types in human skeletal muscle fibers.

By combining enzyme histochemistry for fiber typing with immunohistochemistry for slow and fast myosin a correlation between fiber type and myosin type was sought in human skeletal muscle. Fiber typing was done by staining for myofibrillar ATPases after preincubation at discriminating pH values. Myosin types were discriminated using type specific anti-rabbit myosin antibodies shown to cross-react with human myosin and were visualized by a protein A-peroxidase method. Type I fibers were shown to contain slow myosin only, type IIA and IIB fibers fast myosin only, and type IIC fibers both myosins in various proportions. When muscle biopsies from well-trained athletes were investigated essentially the same staining pattern was observed. However, rarely occurring type I fibers with high glycolytic activity were detected containing additional small amounts of fast myosin and occasional type IIA fibers had small amounts of slow myosin. Based on the observation of various fiber types in which slow and fast myosin coexist we propose a dynamic continuum of fibers encompassing all fiber types.

Adenosine Triphosphatases↗
PubMed1980

[Doping control].

Explore the source record for details and available documents.

Doping in Sports↗
PubMed1980

Muscle fiber types and morphometric analysis of skeletal msucle in six-year-old children.

Needle biopsies from the vastus lateralis of 13 six-year-old Swiss children were analyzed for muscle fiber type populations and morphometrical characteristics. No significant differences existed between the males and females for fiber type distribution, maximum oxygen consumption, or any of the ultra-structural parameters investigated. The vastus lateralis muscle consisted of 19.7% fast twitch glycolytic (FG) fibers, 21.5% fast twitch oxidative glycolytic (FOG) fibers, and 5,9,% slow twitch oxidative (SO) fibers. Maximum oxygen consumption averaged 45.2 ml/kg min-1 when the subjects were considered as a single group. Morphometrically, it was found that the mean volume density of the central mitochondria was 5.54%, the mitochondrial/myofibrillar volume ratio was 6.68%, and the intracellular lipid volume was 0.46%. There was a significant correlation (r=0.69) between the mitochondrial volume density and the distribution of SO fibers as determined histochemically. It was concluded that the fiber type distribution pattern and ultrastructure of skeletal muscle in six-year-old children was not different from normal adult tissue.

Age Factors↗
PubMed1979

[Prevention of arteriosclerosis. Current basis].

Despite the advances in therapy, the high incidence, high mortality, and prematurity of coronary heart disease demonstrate the need for prevention. Measurement of a series of easily determined risk factors permits the early recognition of subjects at risk with remarkable reliability. However, reduction of risk factors affords protection against the illness only if they are causally connected with the disease mechanisms. The major evidence for linking atherosclerosis and its consequences with risk factors is reviewed. Particular attention is focused on serum lipids and the "lipid theory", smoking, elevated blood pressure, and physical inactivity, which are, on the basis of current knowledge, not only the most important factors but those most readily influenced by changes in daily living habits. Among the multiple risk factors mention is also made of obesity, diabetes, psychosocial stress, and hereditary predisposition. The probability of a causal relationship between risk factors and disease mechanisms justifies every effort to prevent the development of these precursors, or to treat them prophylactically if already present.

Arteriosclerosis↗
PubMed1979

Liver function in physically trained subjects: galactose elimination capacity, plasma disappearance of indocyanine green, and aminopyrine metabolism in long-distance runners.

Physical exercise and physical training are known to affect several aspects of hepatic metabolism. To assess whether adaptation to long-lasting exercise modifies microsomal drug metabolism, 8 long-distance runners were compared with a group of medical students having significantly lower maximal rates of oxygen consumption. At rest the hepatic galactose elimination capacity and the indocyanine green plasma disappearance rate used as reference methods were the same in both groups. The plasma clearance of ([14C]dimethylamine) aminopyrine and the kinetics of 14CO2 in breath did not differ either. It is concluded that adaptation to long-lasting exercise can occur without evidence for changes in hepatic galactokinase activity, liver blood flow, or microsomal metabolism of aminopyrine.

Adaptation, Physiological↗
PubMed1979

Mitochondrial volume density in human skeletal muscle following heavy resistance training.

Needle biopsies were taken from triceps brachii of 6 healthy males before and after a 6 month intensive weight training programme. The tissue was sectioned, photographed under a Philips EM200 and subjected to stereological analysis. Cross sectional fibre areas were also calculated from cryostat sections stained for ATPase activity. Morphometric analysis indicated that training resulted in a significant 26% reduction in mitochondrial volume density and a 25% reduction in the mitochondrial volume to myofibrillar volume ratio. These changes were accompanied by significant increases in fibre area for both FT (33%) and ST (27%) fibres as determined from the light microscope. There was a significant correlation between the reduction in mitochondrial volume density and the increase in FT fibre area following training (r=0.845). It was concluded that heavy resistance training leads to a dilution of the mitochondrial volume density through an increase in myofibrillar size with hypertrophy.

Adenosine Triphosphatases↗