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Biomedical subjects

J Karlsson

Publications and source records attributed to J Karlsson.

At least 271 records · Page 15Linked to original sources
PubMed1979

Muscle strength and muscle characteristics in monozygous and dizygous twins.

Muscle strength and electrical activity were investigated on 31 pairs of young male and female monozygous (MZ) and dizygous (DZ) twins. The measurements included leg forces, force-time, running velocity, muscular power, maximal integrated electromyographic activity (IEMG) and chronaximetry of the quadriceps muscle group. In each parameter the intrapair variance was computed and the differences were tested between the MZ and DZ twins. The variance ratio (MZ vs. DZ) was statistically significant only for muscular power confirming an earlier finding which has demonstrated a genetic component for the variable. In addition to the various performance variables several key enzymes involved in ATP turnover during muscle contraction and in glucose residue metabolism were analyzed from the muscle biopsy samples (m. vastus lateralis). A genetic component could not be observed in any of their activities or their relationships to performance variables.

Adolescent↗
PubMed1979

Changes in lipoprotein-lipase activity and lipid stores in human skeletal muscle with prolonged heavy exercise.

Lipoprotein-lipase (LPL) activity and intracellularly stored triglycerides were determined in muscle biopsies taken before and after an 85 km skiing race from 7 volunteers. The triglyceride stores were larger in slow twitch than in fast twitch fibres (proportions 5:1 before the race). The LPL activity increased and the triglyceride stores in slow twitch fibres decreased during the race. The best trained subjects had the largest TG stores before the race and their TG stores also decreased most during the race. These subjects also had very small increase of LPL activity. The least trained subject on the other hand showed a 6-fold increase of LPL activity. The high post-race LPL activity in less trained subjects indicates a higher capacity for uptake of fatty acids from serum TG as compared to the more trained subjects.

Adult↗
PubMed1979

Muscle strength and speed of movement in relation to age and muscle morphology.

Maximum values for isometric strength, dynamic strength, and speed of movement (MEV) in the quadriceps muscle were measured in 114 male subjects who were between 11 and 70 yr. Biopsy samples were taken from the quadriceps muscle in 51 of the subjects (22-65 yr. old). Isometric and dynamic strength increased up to the third decade, remained almost constant to the fifth decade, and then decreased with increasing age. However, no measurable external atrophy of the quadriceps muscle, explaining the decline in strength, could be seen in old age. Histochemical changes in the muscle tissue such as decreased proportion of type II fibers and a selective atrophy of type II fibers, were seen with increasing age. The strength decline in old age was also observed to correlate significantly with the type II fiber area. Multiple regression analyses indicated, however, that mechanisms other than the type II fiber atrophy might be responsible for the decline in strength performance during aging. The implications of these findings are discussed.

Adolescent↗
PubMed1979

Some features of glycogen metabolism in human skeletal muscle.

The higher the exercise intensity, the greater the relative proportion of energy output derived from carbohydrate metabolism. Muscle glycogen stores are the most important source of carbohydrate during heavy exercise and in normal dietary conditions. At the same relative energy output, a muscle rich in type II fibers obtains a relatively larger energy contribution from carbohydrates, in terms of local muscle glycogen utilization, than one rich in type I fibers. This pattern can be modified by different dietary means.

Dietary Carbohydrates↗
PubMed1978

Histochemical and biochemical changes in human skeletal muscle with age in sedentary males, age 22--65 years.

Biopsies for histochemical and biochemical analyses were taken from the vastus lateralis muscle of 55 untrained, healthy male subjects from 22 to 65 years of age. Fibre type distribution changed towards a decrease in the percentage of type II fibres, both in type IIA and type IIB fibres, whereas type IIB/IIA fibre ratio and type IIC percentage did not change with increasing age. It was found that the type IIB/IIA fibre ratio was inversely related to type I fibres, i.e. subjects rich in type I fibres had a relatively smaller proportion of type IIB fibres. Fibre area determinations revealed a selective decrease in type II fibre area. Consequently, the type II/I fibre area ratio and relative type II fibre area decreased. No changes in the specific activities of Mg2+ stimulated ATPase and myokinase were observed, while the activity of lactate dehydrogenase (LDH) was higher in the youngest groups than in the oldest. LDH isozyme pattern shifted towards a decrease in percentage distribution of the muscle specific isozymes and a corresponding decrease in muscle specific activity while the activity of the heart specific isozymes did not change.

Adenosine Triphosphatases↗
PubMed1978

Relationship between lactate accumulation, LDH activity, LDH isozyme and fibre type distribution in human skeletal muscle.

Lactate concentration, total LDH activity and muscle-specific LDH isozymes were determined in pools of the two main types of human skeletal muscle fibres. Analyses were made from biopsy specimens obtained after intense dynamic exercise lasting approximately 30 s. Lactate concentration, total LDH activity and muscle-specific LDH activity displayed higher average values for FT (fast twitch) fibres than for ST (slow twitch) fibres. In addition, positive correlations were found both between the individual percentage of FT fibres and muscle lactate concentration and between lactate concentration and total LDH activity and muscle-specific LDH activity respectively.

Adult↗
PubMed1978

Isometric strength performance and muscle fibre type distribution in man.

Maximal isometric one-leg strength (MIS) was determined in 31 physical education students displaying a wide range in muscle fibre type distribution (21-79% fast twitch (FT) muscle fibres) in their vastus lateralis muscles. A linear positive correlation was found between MIS and the relative distribution of FT fibres (p less than 0.001). This should mean that not only muscle mass involved but also the quality of muscle will be decisive for the ability to develop high isometric strength.

Adult↗
PubMed1978

Skeletal muscle fibre types, enzyme activities and physical performance in young males and females.

Differences in skeletal muscle characteristics, metabolic profiles and functional performance between males and females were investigated using young (15--24 yrs) male and female twins as subjects. The comparison included such variables as anthropometry, muscle strength, mechanical power, maximum oxygen uptake, electrical activation of muscle, muscle fibre composition (m. vastus lateralis), and activities of several skeletal muscle enzymes. The results disclosed the following primary differences between males and females: In the various functional tests the performance of females was from 61.1 to 84.6% of that in males; distribution of slow twitch fibres in m. vastus lateralis of the females (49.1 +/- 7.7%) was lower (p less than .05) than that of the males (55.9 +/- 11.9); activities of enzymes Ca2+ stimulated ATPase, CPK, phosphorylase and LDH1a leads to py were higher (p less than .05--0.1) in the males, whereas the distribution pattern of LDH-1 isozyme was higher (p less than .05) in the females. A pronounced difference between the two groups was a almost 100% longer rise time of isometric force in females. It is concluded that the males as compared to the females demonstrate higher aerobic and strength performance capacity, more efficient neuromotoric output during contraction, more slow twitch muscle fibres and more pronounced contractile and glycolytic profiles in the skeletal muscles.

Adenosine Triphosphatases↗
PubMed1978

Muscle fatigue and its relation to lactate accumulation and LDH activity in man.

The lactate concentration in different muscle fibre types was determined in biopsy specimens from human vastus lateralis muscle after 30 and 60 s of maximal dynamic leg exercise. In addition, muscle fibre type distribution, total lactate dehydrogenase (LDH) activity, and isozymes of LDH were determined. In accordance with previous studies (Thorstensson and Karlsson 1976, Nilsson et al. 1977) it was found that an increasing proportion of slow twitch (ST) fibres corresponded to better sustained muscle force. Lactate was found preferentially in fast twitch (FT) fibres after 30 s, but after 60 s this difference was abolished. Differences between the two main muscle fibre types in muscle lactate, total LDH activity, and M-LDH activity were correlated to muscle fatigue. It was concluded that lactate or associated pH changes primarily in FT fibres could be one factor responsible for the impaired muscle function.

Adult↗
PubMed1978

Isometric and dynamic endurance as a function of age and skeletal muscle characteristics.

The aim of the study was to investigate the influence of age on endurance of human skeletal muscle. An attempt was made to correlate muscular performance at various ages with some morphological and enzymatic characteristics of the muscle. Fifty healthy men, 22-65 years of age, with low daily physical activity (clerks) volunteered for the study. Isometric and dynamic endurance were determined under standardized conditions and measured in relation to maximum strength, thereby correcting for individual as well as age differences in maximum strength. Biopsies taken from the quadriceps muscle were used for muscle fibre classification, fibre area determinations, and measurements of some enzyme activities (Mg2+ stimulated ATPase, myokinase (MK), lactate dehydrogenase (LDH),LDH isozymes). Maximum isometric and dynamic strength decreased in the older groups while no significant change was seen in isometric or dynamic endurance. Significant correlations were observed between endurance and fibre type distribution, fibre areas, and LDH isozyme activities.

Adenosine Triphosphatases↗
PubMed1978

Skeletal muscle metabolism and ultrastructure in relation to age in sedentary men.

In order to find out if there are age-related changes in human skeletal muscle metabolism or ultrastructure, biopsy material from 56 sedentary men aged 22-65 years was studied by means of enzyme activity determinations, histochemistry and quantitative electron microscopy. For comparison, a younger (16-18 years) and an older (66-76 years) group were included. These subjects were relatively more active. There was an increase in percentage of slow twitch fibres with age. Mitochondrial volume fraction decreased with age, primarily due to diminished mean mitochondrial volume. In spite of this, no overall decrease in the activities of five enzymes, representative of the major pathways in energy metabolism, was observed. Thus, increased amounts of enzymes per unit mitochondrial volume are implicated. Lipofuscin was more frequently found in the older groups. Correlations were present between fibre type distribution and oxidative enzymes, as well as between different enzymes. It was concluded, that the decrease in maximal oxygen uptake and muscular strength in aging humans probably may not be explained in terms of a deteriorating skeletal muscle energy metabolism.

Adolescent↗
PubMed1978

Lactate release in relation to tissue lactate in human skeletal muscle during exercise.

In four healthy volunteers, muscle lactate concentration and the release of lactate from the leg were determined at rest and at 4 and 12 min of sitting bicycle exercise at four intensities (30, 50, 70, and 90% of maximal oxygen uptake). The muscle biopsies were obtained by needle biopsy technique from m. vastus lateralis. The rate of lactate release was calculated from the femoral venous-arterial differences of lactate and the leg blood flow was determined by constant rate dye infusion. Both leg blood flow and leg oxygen consumption increased linearly with work intensity. The release of lactate rose approximately linearly with the muscle lactate concentration up to about 4-5 mmol/min but then the relationship revealed a clear leveling off. These results indicate a maximal level for the lactate release from the exercising muscles with a translocation hindrance for lactate within the muscles.

Adult↗
PubMed1978

Phosphorylase a in human skeletal muscle during exercise and electrical stimulation.

Experiments were conducted to examine the conversions of phosphorylase b to phosphorylase a in human skeletal muscle during bicycle exercise or isometric contractions. Muscle biopsies were obtained from the vastus lateralis with the needle technique at rest and either during or immediately after activity and frozen in liquid nitrogen within 2--4 s. Total phosphorylase and phosphorylase a activities were differentiated by measurement in the presence and absence of AMP, respectively. At rest 8.5% of the total phosphorylase activity existed in the a form. Little or no change in the percent of phosphorylase in the a form occurred during voluntary dynamic or static muscular activity that produced muscle lactate concentrations in excess of 18 mmol.kg-1 wet muscle. Electrical stimulation of the vastus lateralis muscle also failed to produce an increase in the percentage of phosphorylase a. These data suggest that during exercise the conversion of phosphorylase to the a form is of minor importance. An increased activity of phosphorylase b due to changes in muscle concentrations of ATP, AMP, and inorganic phosphate may regulate glycogenolysis during voluntary exercise in man.

Adenosine Monophosphate↗