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Biomedical subjects

R Lorentzon

Publications and source records attributed to R Lorentzon.

At least 19 recordsLinked to original sources
PubMed1992

Do muscle fibre size and fibre angulation correlate in pennated human muscles?

Several studies have reported estimations of the total number of fibres in a muscle, e.g. before and after training or before and after inactivity. In those investigations a combination of computed tomographic estimations of muscle size and morphological studies of fibre size has most often been used. There have been doubts about the reliability of those studies on pennate muscles, since changes in muscle fibre size have been said to alter fibre angulation and thus the number of fibres that will cross a section. If such an alteration in fibre angulation takes place with an increase in fibre size, there ought to be some correlation between fibre size and fibre angulation. The present study was designed to test whether repetitive estimations of muscle fibre angulation could be performed in vivo and if any such correlation could be found between fibre size and fibre angulation. A group of 15 women volunteered to take part in the study. Repeated ultrasonographic recordings were made on five subjects on 3 consecutive days to test the repeatability of ultrasonographic measurement of fibre angulation. Both muscle morphological analyses and ultrasonographic measurements of fibre angulation were performed on the other 10 subjects. Ultrasonographic measurement of fibre angulation was found to be reproducible since no variation between measurements made on different days was found. When trying to correlate muscle fibre size to the muscle fibre angulation, measured ultrasonographically, no significant correlation was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Muscle performance, electromyography and fibre type composition in fibromyalgia and work-related myalgia.

Muscle performance and fibre type composition were investigated in women with fibromyalgia, work-related trapezius myalgia and healthy volunteers. Each subject performed 100 repetitive shoulder flexions using an isokinetic dynamometer during simultaneous registration of surface electromyography. A biopsy from the trapezius muscle was obtained. The groups differed neither in mechanical performance nor in fibre type proportions. An inability to relax between contractions was found in all registered muscles in patients with fibromyalgia. The patients with work-related myalgia displayed an inability to relax only in the myalgic trapezius muscle. An inability to relax during repetitive movements might play an important role both in initiating and upholding muscle pain.

Adult↗
PubMed1991

Dependence of the mean power frequency of the electromyogram on muscle force and fibre type.

The aim of this study was to investigate whether the mean power frequency of the electromyogram of the knee extensors was force and/or muscle fibre-type dependent. Ten female subjects performed a gradually increasing static knee extension (5 seconds duration) using an isokinetic dynamometer. Electromyogram-signals were obtained from the vastus lateralis, vastus medialis and the rectus femoris muscles. The torque signal and the three electromyogram signals were recorded on a tape recorder. From the electromyogram recordings the mean power frequency and the signal amplitude were determined. Muscle biopsies were later obtained from the right vastus lateralis and stained for alkaline and acid mATPase for the determination of fibre-type proportion and areas. Both the mean power frequencies and the signal amplitudes of the three knee extensors were positively torque dependent. Furthermore it was found that the fibre type proportion and the regression coefficient of the torque (%)-mean power frequency relationship were positively correlated. Also a negative correlation existed between the type-1 (%) proportion and the intercept of the individual torque (%)-mean power frequency relationships. In contrast to proposed models of the electromyogram signal no correlation was found between the mean power frequency and the fibre area.

Action Potentials↗
PubMed1991

Ice hockey injuries: incidence, nature and causes.

In this prospective study, we have investigated incidence of injuries of different severity, types of injury, and mechanisms of injury during ice hockey games. All twelve Swedish elite hockey teams were observed during the season 1988-1989 when a total number of 664 games were played. There was a total number of 285 injuries, of which the majority were minor (61%) and only 9% were classified as major. Seventy-four per cent of the injuries occurred during games and 26% during practice. The overall incidence of injury was 53.0 per 1000 player-game hours. Eighty-five per cent of injuries were caused by trauma and 15% by over-use. Injuries were most often localized to the head/face (39%) or the lower limb (32%). Most injuries resulted from stick contact or player contact including checking. A reduction of minor and moderate injuries should be possible by stricter enforcement of the hockey rules, and more widespread use of visors.

Athletic Injuries↗
PubMed1991

Evaluation of knee braces in Swedish ice hockey players.

In this retrospective investigation we have determined the rate and types of knee injuries among Swedish ice hockey players, and related these data to the use of knee braces. Thirty-seven of the originally selected 50 hockey teams (74%) of elite or first division calibre took part in the study, and 600 players answered a questionnaire. A total of 254 previous knee injuries sustained while playing hockey were reported by 243 players; tears of the medical collateral ligament (60%), meniscus (15%) or anterior cruciate ligament (12%) were the most commonly reported injuries. Prophylactic knee braces were worn by 138 (23%) of the players. Of these, 122 (88%) had earlier sustained a knee injury, and 16 had not. A total of 17 knee injuries had occurred while the players were wearing a brace. Six of these players had previously uninjured knees while 11 had repeat injury in a brace despite earlier successful rehabilitation or operation. The most common injury in braced knees was a tear of the medial collateral ligament. We conclude that the number of knee injuries is high among Swedish ice hockey players, and that the efficacy of functional knee braces to reduce knee injuries is questionable.

Braces↗
PubMed1990

Chronic achilles paratenonitis with tendinosis: an experimental model in the rabbit.

An experimental model for inducing chronic Achilles paratenonitis with tendinosis in the rabbit is presented. Thirteen rabbits were exercised in a kicking machine producing passive flexions and extensions of the ankle joint. Active contractions of the triceps surae muscles were induced by electric stimulation via surface electrodes. The animals were exercised for 5 to 6 weeks, with a rate of 150 flexions and extensions per minute for 2 h, three times a week. Light microscopic examination showed degenerative changes of the tendon, and increased number of capillaries, infiltrates of inflammatory cells, edema, and fibrosis in the paratenon. We conclude that chronic Achilles paratenonitis with tendinosis can be experimentally induced in a standardized manner in rabbits.

Achilles Tendon↗
PubMed1990

Kinetics of proteoglycans and cells in growth plate of normal, diabetic, and malnourished rats.

The metabolism of proteoglycans in normal growth plate and the changes in growth plate morphology induced by diabetes and malnutrition were studied in rats. The proteoglycans had a significantly faster turnover (half-life measured with [35S]sulfate labeling: 25-30 h) than the cells in the growth plate. Morphometric studies showed significant reductions of cell number, zone height, and [3H]thymidine incorporation in growth plates from rats with untreated streptozotocin-induced diabetes compared to normal rats. Similar, although less pronounced alterations were observed in malnourished, nondiabetic rats. Disaggregation and degradation of proteoglycans are probably necessary prerequisites for calcification. Our data indicate that the proteoglycans are in a dynamic state of rapid biosynthesis and degradation throughout the growth plate with a shift in the balance at the calcification front toward less synthesis and more degradation.

Animals↗
PubMed1989

Fusimotor neurones can be reflexly influenced by activity in receptor afferents from the posterior cruciate ligament.

Recordings were made simultaneously from 2-4 primary muscle spindle afferents from triceps surae and/or posterior biceps and semitendinosus muscles in cats anaesthetized with alpha-chloralose. It was demonstrated that stretch of the posterior cruciate ligament of the ipsilateral knee could cause changes in dynamic and/or static sensitivity of these afferents to sinusoidal stretching. The changes were due to reflex actions of stretch/tension-sensitive receptors in the cruciate ligaments onto fusimotor neurones. It is concluded that the cruciate ligaments may play an important 'sensory' role and that they may participate, via reflex actions on the gamma-motor-muscle spindle system, in the regulation of muscular stiffness of the knee joint, and thereby of the knee joint stability.

Action Potentials↗
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↗
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↗