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Biomedical subjects

J Dvorak

Publications and source records attributed to J Dvorak.

At least 19 recordsLinked to original sources
PubMed2001

Active therapy for chronic low back pain part 1. Effects on back muscle activation, fatigability, and strength.

DESIGN: Randomized prospective study of the effects of three types of active therapy on back muscle function in chronic low back pain patients. OBJECTIVES: To quantify the effects of 3 months active therapy on strength, endurance, activation, and fatigability of the back entensor muscles. SUMMARY OF BACKGROUND DATA: Many studies have documented an association between chronic low back pain and diminished muscular performance capacity. Few studies have quantified the changes in these measures following interventions using objective measurement techniques or related them to changes in clinical outcome. METHODS: A total of 148 individuals (57% women) with chronic low back pain (age, 45.0 +/- 10.0 years; duration of low back pain, 10.9 +/- 9.5 years) were randomized to a treatment that they attended for 3 months: active physiotherapy, muscle reconditioning on devices, or low-impact aerobics. Before and after therapy, assessments were made of the following: trunk muscle strength (in flexion, extension, lateral bending, and axial rotation), erector spinae activation (maximal, and during forward bending movements), back extensor endurance (Biering-Sørensen test), and erector spinae fatigability (determined from changes in the median frequency of the surface electromyographic signal) during isometric and dynamic tests. RESULTS: A total of 132 of 148 patients (89%) completed the therapy. Isometric strength in each movement direction increased in all groups post-therapy (P < 0.0008), most notably in the devices group. Activation of the erector spinae during the extension tests also increased significantly in all groups and showed a weak, but significant, relationship with increased maximal strength (P = 0.01). Pretherapy 55% of the subjects showed no relaxation of the back muscles at L5 when in the fully flexed position; no changes were observed in any group post-therapy. Endurance time during the Biering-Sørensen test increased significantly post-therapy in all groups (P = 0.0001), but there were no significant changes in EMG-determined fatigability. Fatigability of the lumbar muscles at L5 (EMG median frequency changes) during the dynamic test increased post-therapy (P = 0.0001) without group differences. CONCLUSION: Significant changes in muscle performance were observed in all three active therapy groups post-therapy, which appeared to be mainly due to changes in neural activation of the lumbar muscles and psychological changes concerning, for example, motivation or pain tolerance.

Adult↗
PubMed2001

Active therapy for chronic low back pain: part 2. Effects on paraspinal muscle cross-sectional area, fiber type size, and distribution.

DESIGN: Randomized prospective study to compare the effects of three types of active therapy on the back muscle structure of chronic low back pain patients. OBJECTIVES: To analyze the effects of 3 months active therapy on gross back muscle size and muscle fiber type characteristics and their relationship to changes in muscle function. SUMMARY OF BACKGROUND DATA: Many studies have documented a diminished muscular performance capacity in cLBP patients, but few have supported this with evidence of alterations in either the macro- or microscopic structure of the paraspinal muscles. Investigations of the changes in muscle structure following active rehabilitation are even rarer. METHODS: Assessments of trunk muscle cross-sectional area (using MRI), erector spinae fiber size/type distribution and pathology (percutaneous biopsy), and muscle function (see Part 1) were made in a group of 59 individuals with cLBP, who were participating in a randomized trial of active therapies for cLBP (physiotherapy, muscle training on devices, aerobics). RESULTS: Fifty-three out of 59 patients (90%) completed the therapy. At baseline, significant correlations were observed between the size of the paraspinal muscles and isometric back extension strength (P=0.0001), and between the proportional area of the muscle occupied by each fiber type and the fatigability of the muscle (P=0.012). Following therapy, there were small (few percent) increases in trunk muscle size in the aerobics and physiotherapy groups and a similarly slight decrease in the devices group. Changes in erector spine size correlated only weakly and nonsignificantly with changes in back extension strength. There were no major changes in fiber type proportion or fiber size in any group following therapy. CONCLUSION: Three months active therapy is not sufficient to reverse the typical "glycolytic" profile of the muscles of cLBP patients or to effect major changes in backmuscle size. The alterations in muscle performance observed (increased strength and endurance; Part 1) werenot explainable on the basis of structural changes within the muscle.

Adult↗
PubMed2001

Active therapy for chronic low back pain: part 3. Factors influencing self-rated disability and its change following therapy.

DESIGN: Cross-sectional analysis of the factors influencing self-rated disability associated with chronic low back pain and prospective study of the relationship between changes in each of these factors and in disability following active therapy. OBJECTIVES: To examine the relative influences of pain, psychological factors, and physiological factors on self-rated disability. SUMMARY OF BACKGROUND DATA: In chronic LBP, the interrelationship between physical impairment, pain, and disability is particularly complicated, due to the influence of various psychological factors and the lack of unequivocal methods for assessing impairment. Investigations using new "belief" questionnaires and "sophisticated" performance tests, which have shown promise as discriminating measures of impairment, may assist in clarifying the situation. Previous studies have rarely investigated all these factors simultaneously. METHODS: One hundred forty-eight patients with cLBP completed questionnaires and underwent tests of mobility, strength, muscle activation, and fatigability, and (in a subgroup) erector spinae size and fiber size/type distribution. All measures were repeated after 3 months active therapy. Relationships between each factor and self-rated disability (Roland and Morris questionnaire) at baseline, and between the changes in each factor and changes in disability following therapy, were examined. RESULTS: Stepwise linear regression showed that the most significant predictors of disability at baseline were, in decreasing order of importance: pain; psychological distress; fear-avoidance beliefs; muscle activation levels; lumbar range of motion; gender. Only changes in pain, psychological distress, and fear-avoidance beliefs significantly accounted for the changes in disability following therapy. CONCLUSION: A combination of pain, psychological and physiological factors was best able to predict baseline disability, although its decrease following therapy was determined only by reductions in pain and psychological variables. The active therapy program-in addition to improving physical function-appeared capable of modifying important psychological factors, possibly as a result of the positive experience of completing the prescribed exercises without undue harm.

Adaptation, Psychological↗
PubMed2001

Trapped in the neutral zone: another symptom of whiplash-associated disorder?

Instability of the cervical spine following whiplash trauma has been demonstrated in a number of studies. We hypothesized that, in patients with whiplash-associated disorder, rotation of the head would be accompanied by an earlier onset of neck muscle activity to compensate for intrinsic instability. The aim of the study was to examine the range of motion (RoM) of the cervical spine and the onset and activity of the sternocleidomastoid (SCM) muscles during axial rotation, in healthy control subjects and in patients with chronic whiplash-associated disorder. Forty-eight control subjects (42% male) and 46 patients (33% male) with chronic whiplash-associated disorder (symptoms lasting longer than 3 months) were examined. Cervical axial RoM differed significantly (P = 0.0001) between the groups, with the whiplash patients showing lower values (83 degrees +/- 30 degrees) than the healthy controls (137 degrees +/- 19 degrees). The whiplash patient group showed no evidence of the predicted earlier activation of SCM muscles. Many patients never reached the point in the RoM where SCM muscle activity rises steeply, as it does in the healthy controls (the 'elastic zone'), and their movements remained mostly within the region of low muscle activity (the 'neutral zone'). The whiplash patients appeared either unable or unwilling to drive the cervical spine into this region of high muscle activity, possibly because they were restricted by existing pain or fear of pain.

Adult↗
PubMed2000

Centromere association is an unlikely mechanism by which the wheat Ph1 locus regulates metaphase I chromosome pairing between homoeologous chromosomes.

Chiasmate pairing between homoeologous chromosomes at metaphase I (MI) of meiosis in wheat is prevented by the activity of the Ph1 locus on chromosome 5B. Several hypotheses have been proposed sharing the assumption that Ph1 regulates MI chromosome pairing by regulating centromere-mediated chromosome alignment before the onset of meiosis. To test the relevance of the putative predetermination of chromosome pairing at MI by the centromere-mediated chromosome association prior to meiosis, a 2BL.2RL homoeoisochromosome was constructed and its MI pairing was assessed in the presence and absence of the Ph1 locus. Although the 2BL and 2RL arms of the homoeoisochromosome paired with each other at MI in the absence of Ph1, they never paired with each other at MI in the presence of Ph1. Since the two arms were permanently associated in the homoeoisochromosome via a common centromere, it is unlikely that Ph1 predetermines MI pairing between homoeologous chromosomes solely by controlling premeiotic association of centromeres. These findings are consistent with the idea that Ph1 determines the chromosome pairing pattern at MI by scrutinizing homology across the entire chromosome.

Centromere↗
PubMed2000

Range of global motion of the cervical spine: intraindividual reliability and the influence of measurement device.

Range of motion tests are often employed in the quantification of musculoskeletal impairment and in the assessment of the efficacy of therapeutic interventions. The aim of the present study was to compare the absolute values for, and the day-to-day reliability of, measures of cervical spinal mobility made with two computerised motion analysis devices. The ranges of cervical flexion, extension, lateral bending, axial rotation, and axial rotation in flexion and extension were determined for 19 volunteers using both the CA6000 Spine Motion Analyser and the Zebris CMS system; all measures were repeated on a second occasion 1-3 days later. The test-retest reliability was good for each instrument: there was no significant difference between the mean values derived on the two separate days (P>0.05), and the corresponding intraclass correlation coefficients were 0.75-0.93 for all pri-O mary movements and 0.57-0.93 for axial rotation in flexion or in extension. For each primary movement, a small but significant difference (1-10%; P<0.05) between the values derived from the two instruments was observed, the systematic nature of which was revealed by the excellent correlation coefficients between them. For the measures of axial rotation in flexion or in extension, however, there was not only a poor correlation between the data obtained from the two devices, but the mean values also differed significantly. Each device is highly reliable in itself and can be used with confidence in longitudinal studies. The establishment of 'normal' values for the primary motions should take account of the slight differences observed between devices. Normal values for rotation in flexion or extension cannot be established until the source of the device-dependent difference is identified.

Adult↗
PubMed2000

Influence of age and duration of symptoms on fibre type distribution and size of the back muscles in chronic low back pain patients.

Many studies have documented an association between chronic low back pain (LBP) and deficits in back muscle strength and endurance. The sub-optimal performance is believed to be the result of alterations in the size and structure of the muscle, although the long-standing issue of whether the observed changes precede or are a consequence of the pain remains unresolved. If consequent to the problem, and predominantly related to disuse of the muscles, then it may be expected that a relationship between muscle structure and symptom duration would exist. Lumbar paraspinal muscle samples were obtained from 59 chronic LBP patients using the percutaneous biopsy technique. The samples were subject to routine histochemical analysis for the examination of muscle fibre type characteristics and cytochemical architectural changes. In 55 of the patients, the gross cross-sectional areas of magnetic resonance images of the trunk muscles were also measured. Multivariate analysis showed that symptom duration was the strongest predictor of the individual proportions of the fast-fatigable type IIX fibres; with age and gender included in the model, nearly 30% of the variance in fibre type distribution could be accounted for. Duration of pain had no influence on fibre size. Gross muscle cross-sectional area correlated directly with lean body mass and inversely with age, but showed no relationship with symptom duration. Pathological changes in the internal fibre structure were more frequently encountered in older patients, and were independent of symptom duration. The results suggest that, over the long term, fibre type transformations rather than alterations in fibre size are the predominant changes to be found in the muscles of chronic LBP patients. The direction of change supports the results of many previous studies that have demonstrated corresponding differences in the fatigability of the muscles. There is a strong case for the early implementation of active measures to attempt to offset the development of these changes in back pain patients.

Adult↗
PubMed2000

Positional MR imaging of the lumbar spine: does it demonstrate nerve root compromise not visible at conventional MR imaging?

PURPOSE: To evaluate whether positional magnetic resonance (MR) images of the lumbar spine demonstrate nerve root compromise not visible on MR images obtained with the patient in a supine position (conventional MR images). MATERIALS AND METHODS: Thirty patients with chronic low back pain unresponsive to nonsurgical treatment and with disk abnormalities but without compression of neural structures were included. Positional MR images were obtained by using an open-configuration, 0.5-T MR imager with the patients seated and with flexion and extension of their backs. The disk and nerve root were related to the body position. Nerve root compression and foraminal size were correlated with the patient's symptoms, as assessed with a visual analogue scale. RESULTS: Nerve root contact without deviation was present in 34 of 152 instances in the supine position, in 62 instances in the seated flexion position, and in 45 instances in the seated extension position. As compared with the supine position, in the seated flexion position nerve root deviation decreased from 10 to eight instances; in the seated extension position, it increased from 10 to 13 instances. Nerve root compression was seen in one patient in the seated extension position. Positional pain score differences were significantly related to changes in foraminal size (P =.046) but not to differences in nerve root compromise. CONCLUSION: Positional MR imaging more frequently demonstrates minor neural compromise than does conventional MR imaging. Positional pain differences are related to position-dependent changes in foraminal size.

Adult↗
PubMed2000

Psychological and sport-specific characteristics of football players.

It is hypothesized that players of different levels of play might differ not only in their football skills but also in their way of playing football and with respect to psychological factors such as concentration, reaction time, or competitive anxiety. The psychological characteristics of a player might influence his way of playing football (in particular with respect to fair play) and also his risk of injury. A group of 588 football players were studied by questionnaire; additionally, reaction time tests were performed. Psychological characteristics were assessed by three established self-evaluation questionnaires: the Athletic Coping Skills Inventory, the State Competitive Anxiety Test, and the State-Trait-Anger-Expression-Inventory. Football-specific characteristics that were investigated included playing experience and positions played, style of play, number of training hours and games, as well as aspects of fair play. Reaction time was tested twice: without the influence of physical exercise and immediately after a 12-minute run. A significant reduction in reaction time was observed after physical exercise. In high-level players, the reaction time immediately after the 12-minute run was significantly shorter than it was in low-level players. The questionnaire answers given regarding fair play clearly indicated that fair play is not paid sufficient respect. The relationship between psychological characteristics and attitudes toward fair play was analyzed and discussed.

Adolescent↗
PubMed2000

Assessment and evaluation of football performance.

The most important variables for measuring performance in team sports such as football are physical condition and technical and tactical performance. However, because of the complexity of the game of football it is difficult to ascertain the relative importance of each of these variables. The aim of the present study was to develop a standardized test battery to evaluate physical performance in football players. The F-MARC test battery was designed to closely relate to the football player's normal activity and comprised a functional, structured training session of approximately 2.5 hours. It included a "quality rating" of the warm-up procedure, tests of flexibility, football skills, power, speed, and endurance. The players finished with a cool-down. A total of 588 football players underwent the F-MARC test battery. Mean values for performance on each test are presented for groups of differing age and skill levels. The test battery proved to be a feasible instrument to assess both physical performance and football skills. This study supports the proposal by Balsom (1994) that analysis of an individual player's physical profile, in relation to mean values for a similar age group and skill level, might be of assistance to the coach in objectively evaluating the effects of a specific training program. It may also be of use to the physician and physical therapist responsible for monitoring progress during rehabilitation after football injuries.

Adolescent↗
PubMed2000

Football injuries and physical symptoms. A review of the literature.

Football is one of the most popular sports worldwide. The frequency of football injuries is estimated to be approximately 10 to 35 per 1000 playing hours. The majority of injuries occur in the lower extremities, mainly in the knees and ankles; the number of head injuries is probably underestimated. The average cost for medical treatment per football injury is estimated to be $150 (U.S. dollars). Considering the number of active football players worldwide, the socioeconomic and financial consequences of injury are of such a proportion that a prevention program to reduce the incidence of injuries is urgently required. For this reason, an analysis of intrinsic (person-related) and extrinsic (environment-related) risk factors was undertaken based on a review of the current literature. It was concluded that the epidemiologic information regarding the sports medicine aspects of football injuries is inconsistent and far from complete because of the employment of heterogeneous methods, various definitions of injury, and different characteristics of the assessed teams. The aim of this study was to analyze the literature on the incidence of injuries and symptoms in football players, as well as to identify risk factors for injury and to demonstrate possibilities for injury prevention.

Adolescent↗
PubMed2000

Influence of definition and data collection on the incidence of injuries in football.

Studies on the incidence of football injuries vary in the definition of injury, study design, methods of data collection, and observation periods. The aim of this study was to review the different methodologies applied in the evaluation of football injuries as well as to analyze the influence of data collection methods on the incidence of football injuries. In this study, injury data obtained weekly by a physician during 1 year of follow-up in 264 football players were compared with the results of retrospective questionnaires completed by the players at the end of the observation period. In the retrospective questionnaire, the incidence of injuries as well as of complaints was significantly lower than that found in the weekly follow-up examinations. Approximately every third moderate injury and less than 10% of the mild injuries were remembered retrospectively. The shorter the period of symptoms and the longer ago the injury occurred, the more frequently it was forgotten. However, even severe injuries, such as fractures, were not reported in the retrospective investigation. Based on the review of the literature and the data presented, recommendations in relation to study design, the definition of injury, and the calculation of incidence are proposed.

Adolescent↗
PubMed2000

Incidence of football injuries in youth players. Comparison of players from two European regions.

Several authors have investigated the frequency of football injuries in youth players. However, the results of these studies are inconsistent because of the different age groups investigated and the different methods applied. The aim of the present study was to compare the incidence and characteristics of football injuries in youth players of two European regions. A total of 444 youth players from the Czech Republic and the Alsace region of France and Germany were followed weekly for 1 year. In 311 players (70%), complete weekly follow-ups over the 1-year period were available. The comparison of injury data revealed no substantial differences between players from the Alsace region and the Czech Republic in injury incidence per 1000 hours of exposure, degree of injury severity, or the circumstances in which the injuries occurred. However, players from the Czech Republic spent more time in training and playing football than did players from the Alsace region, and in the Czech Republic a higher proportion of injuries was caused by foul play. With only a few exceptions, the statistics were similar in the amount of football played as well as in the incidence of injury between different age and skill levels in both European regions.

Adolescent↗
PubMed2000

Incidence of football injuries and complaints in different age groups and skill-level groups.

In this study, the incidence of football injuries and complaints as related to different age groups and skill levels was studied over the period of 1 year. All injuries and complaints as well as the amount of time players spent in training and games were recorded. All injured players were examined weekly by physicians, and all injuries were assessed according to the International Classification of Diseases (ICD-10), which describes them in terms of injury type and location, the treatment required, and the duration of subsequent performance limitations. A total of 264 players of different age groups and skill levels was observed for 1 year. Five hundred fifty-eight injuries were documented. Two hundred sixteen players had one or more injuries. Only 48 players (18%) had no injury. The average number of injuries per player per year was 2.1. Injuries were classified as mild (52%), moderate (33%), or severe (15%). Almost 50% of all injuries were contact injuries; half of all the contact injuries were associated with foul play. The majority of injuries were strains and sprains involving the ankle, knee, and lumbar spine. Nearly all players (91%) suffered from complaints related to football. Only 23 players reported no injuries and no complaints. Prevention programs, fair play, and continuing education in techniques and skills may reduce the incidence of injuries over time.

Adolescent↗
PubMed2000

Severe injuries in football players. Influencing factors.

The aims of this prospective study were to analyze factors related to the occurrence of severe football injuries in players of different ages (14 to 42 years) and different skill levels (local teams to first league teams). In the Czech Republic, 398 players were followed up for 1 year, during which time they sustained 686 injuries. Of these, 113 (16.5%) were severe injuries. Ninety-seven severe injuries (86%) were able to be documented in detail. Trauma was the cause of 81.5% of the injuries and overuse was the cause of 18.5%. Joint sprains predominated (30%), followed by fractures (16%), muscle strains (15%), ligament ruptures (12%), meniscal tears and contusions (8%), and other injuries. Injuries to the knee were most prevalent (29%), followed by injuries to the ankle (19%) and spine (9%). More injuries occurred during games (59%) than in practice. Twenty-four percent of the injured players had suffered a previous injury of the same body part. Forty-six percent of injuries were caused by contact and 54% involved no body contact. Thirty-one percent of severe injuries were caused by foul play. From these results and the analysis of injuries in specific body parts, the following factors were determined to influence the occurrence of severe injuries: 1) personal factors (intrinsic): age of player, previous injuries, joint instability, abnormality of the spine, poor physical condition, poor football skills, or inadequate treatment and rehabilitation of injuries; 2) environmental factors (extrinsic): subjective exercise overload during practices and games, amount and quality of training, playing field conditions, equipment (wearing of shin guards and taping) and violations of existing rules (foul play).

Adolescent↗
PubMed2000

Risk factor analysis for injuries in football players. Possibilities for a prevention program.

Review of the literature shows that information concerning risk factors for football injuries is incomplete and partly contradictory. The aim of this study was to analyze the influence of medical history, physical findings, football skills, and football performance, as well as psychosocial characteristics on the occurrence and severity of football injuries. The prospective outline of the study was as follows: after a baseline examination was performed to ascertain possible predictors of injury, all players were followed up weekly for 1 year to register subsequent injuries and complaints. Two hundred sixty-four of 398 players (67%) had complete weekly follow-ups over 1 year. A majority of the players (N = 216; 82%) were injured during the observation period. In comparing injured and uninjured players, several differences were observed. To create a multidimensional predictor score for football injuries, 17 risk factors were selected. These risk factors covered a wide spectrum, such as previous injuries, acute complaints, inadequate rehabilitation, poor health awareness, high life-event stress, playing characteristics, poor reaction time, poor endurance, and insufficient preparation for games. By summing up the individual risk factors, a predictive sum was calculated for each player. The more risk factors present at the baseline examination, the higher the probability of that player incurring an injury in the ensuing year. Using two risk factors as the cut-off score, more than 80% of the players were correctly classified as to whether they went on to incur an injury. Based on these findings, knowledge from the literature, and practical experience, possibilities for a prevention program are suggested.

Adolescent↗