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Biomedical subjects

R Lorentzon

Publications and source records attributed to R Lorentzon.

At least 73 records · Page 4Linked to original sources
PubMed1996

Total and regional bone mass in female soccer players.

This cross-sectional study investigated bone mass in female athletes participating in an impact-loading sport (soccer), and evaluated whether any changes in bone mass could be related to the type of weight-bearing loading and muscle strength. The group of soccer players consisted of 16 second-division female players (age 20.9 +/- 2.2 years) training for about 6 hours/week. The reference group consisted of 13 nonactive females (age 25.0 +/- 2.4 years) not participating in any kind of regular or organized sport activity. The groups were matched according to weight and height. Areal bone mineral density (BMD) was measured in total body, head, lumbar spine, femoral neck, Ward's triangle, trochanter, the whole femur and humerus, and in specific sites in femur diaphysis, distal femur, proximal tibia, and tibia diaphysis using dual X-ray absorptiometry. Isokinetic concentric peak torque of the quadriceps and hamstring muscles was measured using an isokinetic dynamometer. The soccer players had significantly (P < 0.05-0.01) higher BMD in the lumbar spine (10.7%), femoral neck (13.7%), Ward's triangle (19.6%), nondominant femur and humerus (8.2 and 8.0%, respectively), distal femur (12.6%), and proximal tibia (12.0%) compared with the nonactive women. There was no significant difference in muscle strength of the thigh between the two groups. In the nonactive group, muscle strength in the quadriceps and especially hamstrings, was correlated to BMD of the adjacent bones (whole femur, hip sites) and also to distant sites (humerus). In the soccer group, there were no correlations between muscle strength and BMD of the adjacent and distant bones. Soccer playing and training appears to have a beneficial effect on bone mass in young females, and it seems that there is a site-specific skeletal response to the type of loading subjected to each BMD site. Muscle strength in the thigh is not related to bone mass in female soccer players.

Adult↗
PubMed1996

Site-specific bone mass differences of the lower extremities in 17-year-Old ice hockey players.

The purpose of the present study was to evaluate bone mass in the pelvis and lower extremities in young ice hockey players, and especially to investigate whether any differences are related to the type and magnitude of weight-bearing loading and muscle stress. The ice hockey group consisted of 22 boys (mean age 16.9 +/- 0.3) from three different ice hockey teams training for about 9 hours/week (mean 9.3 +/- 2.0, range 6-15). The reference group consisted of 22 boys (age 16.8 +/- 0.3) not training for more than 4 hours per week (mean 1.5 +/- 1.5, range 0-4). The groups were matched according to age, pubertal stage, weight, and height. Areal bone mineral density (BMD) was measured in total body, head, pelvis, ala ossis ilii, femoral neck, trochanter, femur diaphysis, and tibia diaphysis using dual energy X-ray absorptiometry. Isokinetic muscle strength of the quadriceps and hamstrings muscles was measured using an isokinetic dynamometer. BMDs of the total body, femoral neck, trochanter, and pelvis, but not of the head, ala ossis ilii, femur diaphysis, and tibia diaphysis, were found to be significantly higher (P < 0.05) in the ice hockey group. Muscle strength of the quadriceps muscles was also found to be significantly higher among the ice hockey players, but this greater muscle strength did not predict any BMD site significantly. However, in the reference group, there was a general strong relationship between muscle strength and BMD. This study has demonstrated significantly higher BMD in adolescent ice hockey players than in referents on a low or moderate level of physical activity. The differences seem to be site-specific and may be related to the type and magnitude of loading acting on each site, during off-season training and preferentially during ice hockey. The nonsignificant differences in BMD of the tibia and femur diaphyses may reflect that the compressive forces acting on these sites during ice hockey are not of sufficient magnitude to influence BMD. High muscle stress in itself, without weight-bearing loading, acting on the ala ossis ilii in adolescent boys does not seem to increase BMD, and an increased muscle strength does not predict BMD in highly trained adolescent boys.

Adolescent↗
PubMed1996

The effects of brisk walking on markers of bone and calcium metabolism in postmenopausal women.

Weight-bearing exercise has been shown to maintain or increase bone mass in younger as well as older individuals but the mechanisms by which mechanical loading affects bone metabolism are not known in detail. Twelve postmenopausal women participated in a single bout of brisk walking (50% of VO2 max) for 90 minutes. Calciotropic hormones and markers of type I collagen formation (PICP) and degradation (ICTP) were measured before the exercise, and 1, 24, and 72 hours following the exercise. Total body bone mineral content (BMC) and density (BMD) were measured by dual energy X-ray absorptiometry (DXA). Brisk walking did not induce any significant changes in the concentrations of ionized calcium, parathyroid hormone (PTH), calcitonin, or osteocalcin. A significant increase of PICP was noted 24 and 72 hours (P < 0.01) after exertion and a significant decrease in the concentration of serum ICTP at 1 hour (P < 0.05) was followed by an increase at 72 hours (P < 0.001). There was no significant difference between the increases in the concentrations of PICP and ICTP at 72 hours. Strong inverse correlations between the basal levels of PTH and BMD (r = -0.78; P < 0.01) as well as between osteocalcin and BMD (r = -0.83; P < 0.01) were noticed. The changes in serum levels of bone collagen markers indicate an altered bone collagen turnover due to this moderate endurance exercise. The results also support the fact that serum levels of PTH as well as those of osteocalcin are associated with total body BMD in postmenopausal women.

Aged↗
PubMed1996

Local bone mineral density, muscle strength, and exercise in adolescent boys: a comparative study of two groups with different muscle strength and exercise levels.

The primary objective of the present study was to evaluate the impact of physical activity and muscle strength on bone mineral density (BMD) of the tuberositas tibiae in adolescent boys. Two groups with different exercise levels were compared. The high activity group consisted of 20 subjects (age 15.9 +/- 0.3) from a junior ice hockey team. The reference group consisted of 24 volunteers (age 15.9 +/- 0.3) not training for more than 3 hours per week. The groups were matched for age, weight, and pubertal stage. BMDs (g/cm2) of the tuberositas tibiae and proximal tibia were measured using dual energy X-ray absorptiometry. Quadriceps strength was significantly higher in the high activity group (P < 0.01). Univariate correlations were measured between tuberositas tibiae BMD and pubertal stage, weight, height, BMI, fat mass, lean body mass, quadriceps strength, and hamstrings strength in the high activity group and the reference group, respectively. Quadriceps strength was estimated to be the best significant predictor of BMD of the tuberositas tibiae in the reference group. A multivariate analysis confirmed this result. In the high activity group, there was no significant predictor of BMD of the tuberositas tibiae. There was no significant difference in BMD at this site when comparing the two groups. However, five of the boys in the high activity group had a former history of Mb Osgood-Schlatter with a significantly lower BMD of the tuberositas tibiae than the rest of the boys in that group. After exclusion of these boys, the remaining 15 boys were matched against 20 boys from the reference group using the previous criteria. These 15 boys then showed a significantly higher BMD of the tuberositas tibiae (P < 0.05) but not of the proximal tibia than the 20 boys in the reference group. In conclusion, this study demonstrates site-specific increments of tuberositas tibiae BMD in adolescent ice hockey players unless they are affected by the negative effects on BMD by Mb Osgood-Schlatter. These increments seem primarily to be associated with forceful muscle contractions related to high quadriceps strength and not greater weight-bearing loading. Muscle strength seems to positively affect BMD of the tuberositas tibiae in adolescents, but only up to a certain level, above which additional muscle strength has no effect.

Adolescent↗
PubMed1996

High bone mass and altered relationships between bone mass, muscle strength, and body constitution in adolescent boys on a high level of physical activity.

We have recently demonstrated a general relationship between bone mass, muscle strength, and several body constitutional parameters in adolescent boys with a moderate exercise level. The present study was conducted to evaluate these previously described relationships in adolescent boys subjected to high physical activity and also to compare the bone mass of the same group with that of adolescents on a moderate level of physical activity. The reference group consisted of 24 boys, age 15.9 +/- 0.3 years, not training for more than 3 h per week. The ice hockey players consisted of 20 boys, age 15.9 +/- 0.3 years, from an ice hockey junior team training for about 10 h per week. The groups were matched according to age, pubertal stage, and weight. Areal bone mineral density (BMD) was measured in total body, head, humerus, spine, femur, and proximal femur using dual energy X-ray absorptiometry. BMD was significantly higher in the humerus (p < 0.01), femur (p < 0.05), and proximal femur (p < 0.05) in the high activity group. Furthermore, physical activity (h/week) was an independent predictor of humerus BMD (p < 0.01) and proximal femur BMD (p < 0.05), among all subjects investigated (n = 44). Isokinetic muscle strength of the quadriceps and hamstrings muscles was significantly higher in the high activity group (p < 0.05). In the reference group, there was a general strong independent relationship between BMD, muscle strength, and different body constitutional parameters. In the high activity group, muscle strength of the thigh independently predicted BMD of humerus and spine. Furthermore, in the same group, weight, BMI, and fat mass independently predicted only spine BMD. In conclusion, the higher BMD demonstrated in the ice hockey players seems to be site-specific and may well be associated with the type and magnitude of loading from predominantly ice hockey. High physical activity seems to weaken the relationship between BMD, muscle strength, and body constitution demonstrated in adolescent boys on a low or moderate level of physical activity.

Adolescent↗
PubMed1996

Concussion among Swedish elite ice hockey players.

OBJECTIVE: To evaluate the frequency of concussion in Swedish ice hockey and to establish a uniform grading and treatment model for concussions of different severity. METHODS: Frequency of concussion was investigated in two studies, one retrospective and one prospective. In the retrospective study, all Swedish elite ice hockey players (n = 265) were asked to answer a questionnaire on the number and treatment of previous concussions. Only concussions diagnosed by a doctor were recorded. The questionnaire was completed by 227 players (86%). In the prospective study, all injuries including concussions occurring during game and practice in the Swedish Elite League (n = 12 teams) were recorded during four years. The causes of injury, referees judgements, diagnosis, treatment, and time absent from ice hockey were registered on special cards. RESULTS: In the retrospective study, 51 out of 227 players (22%) in the Swedish Elite League reported at least one concussion. In the prospective study, 52 concussions were reported. The incidence of a concussion is at least one concussion every year/team or a yearly risk of about 5% for a player to sustain a concussion. Most concussions occurred during league play (81%). Body contact (checking or boarding) was the most common cause of concussions. The players were absent from full training and play on a mean of 6 d. CONCLUSIONS: As this injury is potentially dangerous it must be treated seriously according to a simple treatment model presented. In cases of repeated concussions during the same season, a longer period of time away from play is suggested. In players who have sustained several concussions over the years a thorough medical examination including EEG, CT/MRI, and neuropsychological tests should be performed. If any of these is pathological the player should be advised to give up ice hockey.

Absenteeism↗
PubMed1995

Bone mass, muscle strength, and different body constitutional parameters in adolescent boys with a low or moderate exercise level.

This study was conducted to evaluate the association between muscle strength of the thigh, different body constitutional parameters, and bone mineral density (BMD) in adolescents. The subjects were 26 healthy adolescent boys, age 15.9 +/- 0.3 years, not training for more than 3 h per week. BMD was measured in total body, head, humerus, spine, femur, and tibia/fibula. Univariate correlations were measured between the explanatory parameters height, weight, body mass index (BMI), fat mass, lean body mass, quadriceps strength, hamstrings strength, and each BMD site using Pearson's coefficient of correlation. The explanatory variables were also used in a multivariate analysis to explain each BMD site. There was a high degree of concordance when comparing the two methods of analysis. Using the multivariate analysis, quadriceps strength and lean body mass showed significant independent correlations to all BMD sites measured, the correlations being stronger for the adjacent femur and tibia/fibula than for the distant humerus and head. Hamstrings strength correlated significantly and independently with tibia/fibula BMD and spine BMD. Fat mass, BMI, and weight correlated significantly and independently to all BMD sites except femur. This study demonstrates a general relationship between BMD and different body constitutional parameters and muscle strength of the thigh.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

Effects of short-term maximal work on plasma calcium, parathyroid hormone, osteocalcin and biochemical markers of collagen metabolism.

Physical activity is most probably an important factor to increase bone mass. The exact mechanisms by which this takes place are not completely understood. During the last years methods have become available making it possible to study the metabolism of type I collagen in bone in more detail. In this study seven male athletes were studied before and after a short-term maximal work (a modified Wingate test at a retardation of 7.5% of body weight) during 30 seconds. Blood samples were drawn before the test and 5 and 60 minutes after. Serum concentrations of type I procollagen carboxyterminal propeptide (PICP) and carboxyterminal telopeptide of type I collagen (ICTP) were measured, as were serum calcium, parathyroid hormone and osteocalcin. Serum PICP and ICTP reflect synthesis and degradation of type I collagen, respectively and mainly bone collagen metabolism. A significant increase of ionized calcium and lactate was noted while PTH and total serum calcium did not change. No significant alterations of either ICTP, PICP or osteocalcin were registered. We conclude from this study that the short-term maximal work performed by means of the modified Wingate test failed to show any significant changes in bone metabolism (osteocalcin and metabolites of type I collagen). A short experimental period and lactacidosis might contribute to the unaltered bone metabolism. The results mainly indicate that there is no pool of bone biochemical markers in young athletic males that is washed out by short bursts of intense exercise.

Acidosis, Lactic↗
PubMed1993

Ice hockey injuries: a 4-year prospective study of a Swedish élite ice hockey team.

In this prospective study, we have investigated the incidence of injuries of different severity, types of injury, and mechanisms of injury during ice hockey practice and games. One Swedish élite hockey team was closely observed during four seasons (1986-1990). There were 376 injuries, of which 148 resulted in absence from practice or games. The incidence of injury (injuries associated with later absence) during practice was 2.6 per 1000 player-practice hours and 74.1 per 1000 player-game hours. Nuisance injuries (without any later absence) and minor injuries (absence < 1 week) constituted the vast majority (95.2%) and only 4.8% (18 cases) were classified as moderate or major injuries (absence > 1 week). Of the injuries 85% were caused by trauma and 15% by overuse. Injuries were most often localized to the lower limb (37.8%) and head/face (31.4%). The commonest injuries were contusions, lacerations/wounds, strains and sprains. Most injuries resulted from stick or player contact (predominantly checking). The results are in close agreement with those of a previous investigation of another Swedish élite hockey team covering the years 1982-1985. It should be possible to reduce the number of injuries by stricter enforcement of the hockey rules, especially against stick violations, and a more widespread use of visors.

Adult↗
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↗