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Biomedical subjects

R Lorentzon

Publications and source records attributed to R Lorentzon.

At least 91 records · Page 5Linked to original sources
PubMed1989

Knee extensor muscle function before and after reconstruction of anterior cruciate ligament tear.

Knee extensor performance, in 17 subjects with chronic anterior cruciate ligament (ACL) tear, was investigated preoperatively and on four different occasions postoperatively, using isokinetic measurements and electromyography of single maximum and repetitive manoeuvres. Preoperatively maximum mechanical output was comparatively low (injured leg), deteriorating further by 50% at fourteen weeks postoperatively. Endurance also falls markedly. Thereafter knee-extensor performance improved successively, mostly during intensive training (14-20 weeks postoperatively) irrespective of the training programme used. After one year, maximum performance was still unequal but the injured leg had achieved the "normal" preoperative noninjured value. Fatiguability/endurance level improved over preoperative values. Muscular work/integrated EMG was stable while EMG/t increased. Twenty weeks postoperatively quadriceps area was decreased to 69%, cf. noninjured control. The early postoperative loss of performance was evidently caused by loss of muscle mass. Neuromuscular relearning appears to be a sizable factor in later recovery. Isokinetic training does not offer any specific advantage in the early muscular rehabilitation after ACL reconstruction.

Adolescent↗
PubMed1988

Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers.

Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad.s-1) and knee extensions (1.57 rad.s-1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70 +/- 17%) than for the knee extensors (56 +/- 12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71-72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.

Adult↗
PubMed1988

Does a torn anterior cruciate ligament lead to change in the central nervous drive of the knee extensors?

Integrated surface electromyograms of the three superficial parts of the quadriceps and isokinetic knee extensor maximum torque and power production were recorded simultaneously and at different angular velocities in both legs in 11 male subjects with unilateral tear of the anterior cruciate ligament. The cross-sectional area (CSA) of the thigh and its muscular components were measured by computerized tomography. The principal findings were a small but significant decrease in quadriceps CSA on the affected side; a decreased active, but not passive, range of movement; decreased mechanical output, whether or not corrected for differences in CSA; and decreased electromyographic activity--particularly in rectus femoris. These findings suggest that the reason for the decreased maximum and total knee extensor performance seen in these patients is a change in knee joint receptor afferent inflow.

Adult↗
PubMed1988

Peak torque and OBLA running capacity in male orienteers.

The isokinetic (30, 60, 120 and 180 degrees s-1) peak torque of m. quadriceps femoris and m. triceps surae, and the running velocity at the onset of blood lactate accumulation (VOBLA) were determined at three different occasions (November, April and September) during a year in 15 male élite orienteers. The amount and type of training for each individual was also registered. At the first test (November) there was no significant intra-individual correlation between peak torque of m. quadriceps and m. triceps surae. A negative correlation was found between VOBLA and peak torque of m. quadriceps at the lower velocities of angular motion, but not at the higher. The peak torque of m. triceps surae increased during the training period and decreased during the competition period back to the original level. Over the whole year the peak torque of m. quadriceps increased while no changes could be demonstrated within the two periods of the study. The running velocity at the onset of blood lactate accumulation increased during both training and competition periods. The changes in VOBLA were negatively associated with the changes in peak torque of m. quadriceps at 180 degrees s-1 during the training period. During the competition period the changes in VOBLA were, for the majority of the orienteers, negatively correlated to the ratio of quality:quantity running, i.e. to a high content of forest running.

Adult↗
PubMed1988

Fatigue during dynamic muscle contractions in male sprinters and marathon runners: relationships between performance, electromyographic activity, muscle cross-sectional area and morphology.

Knee extensor fatigue and endurance during repeated maximum isokinetic manoeuvres were studied in five sprinters and five marathon runners, all males. Fatigue and endurance were expressed in terms of output (contractional work, CW) and input (integrated electromyograms, iEMG), and was related to muscle fibre composition of m. vastus lateralis and to cross-sectional area (CSA) of m. quadriceps. The initially performed contractional work was positively related to the calculated absolute type II fibre area of m. vastus lateralis, but not to the cross-sectional area of m. quadriceps. During the first 25 contractions, sprinters fatigued, with a slope of decline in contractional work that was correlated to the absolute type II fibre area, also after correction of performed work for CSA of m. quadriceps. As the electromyographic activity decreased less than the contractional work, a drastic fall in the CW/iEMG ratio was found in the sprinter group. Three out of five sprinters could perform less than 50 knee extensions, due to subjective discomfort in tested thighs. In contrast, all marathon runners could, after a minor similar decline in electromyographic activity and contractional work during the first part of the experiment, maintain a steady-state endurance level of CW and iEMG throughout the test (200 knee extensions). In conclusion, fatigue during isokinetic maximal knee extensions is closely related to the muscle structure of m. vastus lateralis.

Adult↗
PubMed1988

Muscle pathomorphology in m. quadriceps of marathon runners. Early signs of strain disease or functional adaptation?

Muscle biopsies were obtained from m. vastus lateralis of five male marathon runners and five sprinters. The athletes performed their last competition at least 2 weeks prior to the investigation. No clinical signs of discomfort or injury were observed in the runners. The biopsy specimens from the sprinters showed an ordinary overall morphology, although fibre sizes varied considerably within and between the individuals. In contrast, in the marathon runners, structural deviations of pathologic value appeared in four out of five subjects. The fibre shapes were irregular, irrespective of fibre type, and internal architectural changes were common. An increased amount of connective tissue was found. A majority of fibres showed one or more central nuclei. A few fibres were flat and there were also evidence of fibre type grouping. The divergent picture might be an expression of repeated fibre injury with subsequent processes. If so, a peripheral, relative, arterial insufficiency is suggested as a possible aetiology. However, it cannot be ruled out that the deviations express a functional adaptation to the extreme endurance demands.

Adaptation, Physiological↗
PubMed1988

Sonography of popliteal masses.

Sonography of the popliteal space was performed in 28 patients with a history of a popliteal mass, verified by physical examination in all but 7 patients. The final diagnosis was established by needle biopsy or surgery. Three main types of lesions were found sonographically. A thin-walled echo-free cyst was present in 16 patients. The diagnosis in all of these cases was Baker's cyst. Two patients had a mixed cystic and solid lesion, which was found to be a Baker's cyst, with a loose body in 1 case and a soft-tissue sarcoma with hematoma in the other. Three patients showed solid lesions subsequently diagnosed as an old rupture of the semimembranosus muscle, lipoma, and soft tissue sarcoma. Sonography was normal in the 7 patients without clinical evidence of a popliteal mass. Sonography of popliteal masses is useful to distinguish benign cysts from other lesions.

Adolescent↗
PubMed1987

Sprinters and marathon runners. Does isokinetic knee extensor performance reflect muscle size and structure?

In order to evaluate relationships between structure and concentric function of the quadriceps muscle, isokinetic maximum knee extensor output at different velocities of angular motion (30-180 degrees s-1), integrated electromyographic activity (iEMG), cross-sectional area (CSA) of m. quadriceps and fibre composition of m. vastus lateralis were analysed in five sprinters and five marathon runners (all males). Both output and input parameters, concerning peak torque (PT), instantaneous power (IP), contractional work (CW) and the summed iEMG were closely correlated to the m. quadriceps CSA, as well as to the calculated absolute type II (A + B), IIA and IIB fibre areas of m. vastus lateralis. When PT, IP, CW and the summed iEMG were corrected for CSA, such relationships were found only at 180 degrees s-1 and only for type IIA fibre area. The electromyographic findings indicate that m. vastus lateralis was representative for the total mechanical output. The calculated mean power output (CW s-1) and output/input balance (CW/iEMG) describe similar relationships with the velocity of angular motion and were not related to the CSA or to the absolute area of any fibre type. The calculated optimal CW per second and CW/iEMG occur for sprinters at about 450 degrees s-1 and for marathon runners at about 270 degrees s-1, that is, velocities well above the capacity of the isokinetic dynamometer. Our observations indicate that the peak torque or instantaneous power, during single maximum knee extensions, at least at 180 degrees s-1, express characteristics of the muscle structure.

Adult↗
PubMed1987

Fatigue and endurance of lower extremity muscles in relation to running velocity at OBLA in male orienteers.

At three occasions during a year, the ratio of contractional work (output)/integrated electromyographic activity (input), that is, CW/iEMG, was measured during repetitive maximum isokinetic manoeuvres for m. quadriceps and m. triceps surae in male elite orienteers. Running velocity at the onset of blood lactate accumulation (VOBLA), which was considered as a measure of running performance, and maximal oxygen uptake (VO2max) were analysed at each test. Type and amount of training were continuously registered. For m. quadriceps there was a decline in CW/iEMG during the first 30 manoeuvres, followed by an unchanged plateau level. In contrast, m. triceps surae showed a plateau level of virtually unaltered CW/iEMG ratio from the start to the end of the experiment. The differences might be explained by structural causes, but also by local muscle adaptation to training. The plateau level of CW/iEMG of m. quadriceps was positively correlated to VO2max. An increase in the plateau level of CW/iEMG was found for both tested muscle groups after the winter training period (mainly low intensity road running) when both VOBLA and VO2OBLA increased. During the competition period (mainly high intensity forest running), the whole group increased while some orienteers lowered their VOBLA. During this period, no changes in the plateau level of CW/iEMG of any muscle group or in VO2OBLA occurred. The changes in the plateau level of CW/iEMG might express local muscle adaptations to changes in running technique and aerobic/anaerobic demands during low intensity road running versus high intensity forest running.

Adult↗
PubMed1986

Osteopenia in mice with genetic diabetes.

Bone mass and growth were studied in mice with genetic diabetes (db/db) characterized by obesity, hyperinsulinemia and hyperglycemia, in their lean litter mates (db/+) and in non-diabetic mice of the same strain (+/+). No significant difference was observed between db/+ and +/+ mice. The length, bone mass, bone mineral mass, bone mineral density and content of moisture of the tibia of the db/db mice were significantly decreased compared with the db/+ and +/+ mice. Microradiographs of the distal femur diaphysis of the db/db mice showed a significant reduction of the spongious bone area and of the number and thickness of bone trabeculae with a normal mineralization. The amount of osteoid was significantly increased in the db/db mice. The area of cortical bone of the tibia epiphysis of the db/db mice was significantly decreased compared with the db/+ and +/+ mice. The data suggest the occurrence of osteopenia due to decreased mineralization in mice with genetic diabetes.

Animals↗
PubMed1986

Factors affecting Ca2+ transport in mouse islet and kidney mitochondria.

The transport of Ca2+ in islet and kidney mitochondria respiring on succinate was inhibited by atractylate and fluorocitrate, and stimulated by pyruvate, isocitrate, alpha-ketoglutarate, dibutyryl cAMP, oligomycin and bongkrekate, and by in vivo administration of glucagon, glyceraldehyde or glucose. The kidney [beta-hydroxybutyrate]/[acetoacetate] ratio was increased in glyceraldehyde treated mice. The data suggest a relationship, which might be influenced by cAMP, between activity of pyruvate, isocitrate and alpha-ketoglutarate dehydrogenases and transport of Ca2+ in islet and kidney mitochondria. A contributory role of reductive carboxylation for Ca2+ uptake, and a role of citrate for Ca2+ retention are discussed.

Animals↗
PubMed1985

Alterations in mitochondrial aconitase activity and respiration, and in concentration of citrate in some organs of mice with experimental or genetic diabetes.

Mouse islets (not used for respiration), kidneys and liver were studied in early and manifest alloxan diabetes, and in genetic diabetes. In these organs the mitochondrial aconitase activity was lower, state 3 respiration with citrate or pyruvate plus malate (but not with succinate) was decreased, and the concentration of citrate was increased, compared with non-diabetic control mice. The alterations suggest a role of lowered activity of mitochondrial aconitase in alloxan diabetes, and probably also in genetic diabetes.

Aconitate Hydratase↗
PubMed1985

Quantitative morphological assessment of parathyroid activity in response to variations in calcium concentration in vitro.

Isolated parathyroid glands from gerbils incubated at low (0.5 mM), normal (1.25 mM) or high (3 mM) calcium concentration for 1 or 6 h were studied with regard to the following stereological parameters: the volume densities of the nucleus, mitochondria, endoplasmic reticulum, Golgi zone, lipid bodies, lysosomes, secretory granules and storage granules, and the surface densities of the cell membrane and endoplasmic reticulum. In glands incubated for 1 h no significant differences were seen between the experimental groups in any of the parameters investigated, however, the volume density of the Golgi zone and the surface density of the cell membrane were significantly increased in glands incubated for 6 h at low calcium concentration, compared with those incubated at high calcium concentration. The enlargement of the Golgi zone in stimulated glands was also evident when the two glands from the same animal incubated at different calcium concentrations were compared. The data suggest that the early response of parathyroid glands to altered concentration of extracellular calcium includes functional activities associated with the Golgi zone.

Animals↗
PubMed1985

The effects of different vitamin D-states on intestinal absorption of vitamin D3 and its metabolites in rats.

Rats were kept on a diet deficient in vitamin D for 2 months and were then randomly assigned to one of three groups with different supplies of vitamin D for 9 days. At the end of this period [3H]-cholecalciferol (5 microCi) was administered intragastrically and the serum radioactivity was recorded after various periods of time. The animals were kept in metabolic cages and urine and faeces were collected. After 3 days the animals were killed and the liver, kidney and fat tissue were investigated for radioactivity. The radioactivity was separated into different fractions of vitamin D by means of chromatography. The animals with vitamin D deficiency displayed higher levels of serum radioactivity, which were to a great extent confined to the fractions of the more polar metabolites (25(OH)D3 and 1,25(OH)2D3). There was significantly less radioactivity in the 3-day faecal collection from these animals. In general, there was a low urinary excretion of radioactivity. In the rats with sufficient vitamin D, most of the radioactivity remained as the parent substance and was also detected in increased amounts in the liver, kidney and fat tissue. The results suggest a discriminatory enterohepatic cycling of vitamin D and its more polar metabolites leading to an increased faecal loss of the pro-hormone in animals with a vitamin D surplus. It is proposed that the selectively effective enterohepatic reabsorption of the different metabolites may serve as a protective mechanism when body stores of vitamin D are overloaded.

Adipose Tissue↗