Biomedical subjects

Klaus Völker

Publications and source records attributed to Klaus Völker.

11 recordsLinked to original sources

PubMed2006

Passive stability characteristics of ankle braces and tape in simulated barefoot and shoe conditions.

BACKGROUND: Ankle sprains are among the most common injuries in barefoot sport activities such as dance, gymnastics, or trampoline. At present, the use of external ankle devices for prevention of ligament injuries for barefoot activities remains unclear. HYPOTHESIS: External ankle devices have a significant loss of passive stability when used without a shoe in barefoot activities. STUDY DESIGN: Controlled laboratory study. METHODS: Twenty-five healthy subjects participated in the project (mean age, 26.2 +/- 3.3 years; mean body mass, 71.2 +/- 10.3 kg; mean height, 178 +/- 7 cm). Passive range of motion measurements were performed with 3 different ankle stabilizers (a stirrup brace, a lace-up brace, and tape), as well as 2 different shoe conditions (cutout shoe [simulated barefoot] and normal shoe). RESULTS: In the simulated barefoot condition, a significantly reduced stabilizing effect for inversion and eversion (19% and 29%, respectively) was found for the stirrup ankle brace. Small decreases were noted with the soft brace and tape, but these were not statistically significant. CONCLUSION: The passive stability characteristics of ankle braces depend to a great extent on being used in combination with a shoe. This is especially true for semirigid braces with stirrup design. Therefore, it is recommended that soft braces (like the one tested in the present investigation) be used in barefoot sports for restricting passive range of motion of the foot and ankle complex. CLINICAL RELEVANCE: This study provides useful information for clinicians to select or recommend an external ankle stabilizing device in barefoot sports to restrict passive range of motion of the foot-ankle complex most effectively.

Adult↗

PubMed2006

[Physical activity, hypertension, and cardiac and circulatory system].

Because of its increasing incidence hypertension is--as one of the most important risk factor of diseases of the cardiac and circulatory system--a challenge for prevention and rehabilitation. Besides the established pharmacological therapy regular physical activity is one of the effective nonpharmacological therapies; particularly, there are also effects on other risk factors. Meta-analyses show a decreasing effect of physical activity both on the systolic and diastolic value. With a nonresponder rate of 25% the effects are similar to pharmacological therapy. Modulators can be found in the pathology of the disease itself, in the age, and in genetic polymorphisms. The mechanisms for blood pressure reduction might be the diuretic effect of physical activity, the reorganization of the vegetative reaction toward a sympathicolysis, the humeral modifications like changes in glucose metabolism and the improvement of endothelial function. Recommendations concerning the nature, the intensity and duration of physical activity refer more to consent statements than to evidence-based studies. Nevertheless, the following recommendations can be given. Endurance events with cyclic movements should be performed at a moderate intensity between 40% and 60% VO2(max). Though a duration of 60-90 min has the highest effect on blood pressure reduction, a duration of only 30 min per unit is favored to reach a higher compliance. No influence has yet been verified concerning the frequency of physical activity. Because of its effects on risk factors other than hypertension physical activity represents an all-embracing treatment concept. Therefore it is desirable to integrate physical activity in the treatment routine, especially in the therapy of patients with different risk factors.

Blood Pressure↗

PubMed2006

[Physical activity and prevention of cardiovascular diseases].

Physical inactivity is one of the major risk factors for cardiovascular diseases. Regular physical activity, conversely, is effective in reducing all-cause mortality, cardiovascular morbidity and mortality. Older and recent meta-analyses confirm the reduction of all-cause mortality and cardiovascular mortality by regular physical activity. So far, there is a dose-effect relationship especially from low to moderate training intensity; the steepness of this curve is more curvilinear with a decrease at higher categories of activity intensity. Regular physical activity even at low level of intensity should be a part of daily life and of lifestyle. The risks and side effects of physical activity can be neglected, preparticipation examination before training is strongly recommended. Counseling healthy persons and patients at any age for physical activity, and training prescription should be an essential part of physicians' work in general practice.

Adult↗

PubMed2005

Phase diagram and critical exponents of a dissipative Ising spin chain in a transverse magnetic field.

We consider a one-dimensional Ising model in a transverse magnetic field coupled to a dissipative heat bath. The phase diagram and the critical exponents are determined from extensive Monte Carlo simulations. It is shown that the character of the quantum phase transition is radically altered from the corresponding nondissipative model and the double well coupled to a dissipative heat bath with linear friction. Spatial couplings and the dissipative dynamics combine to form a new quantum criticality which is independent of dissipation strength.

Journal Article↗

PubMed2005

The influence of external ankle braces on subjective and objective parameters of performance in a sports-related agility course.

With lateral ankle sprains being the most frequent sports-related injury, there is an evident demand for the preventive measures in active individuals with chronic ankle instability. Braces are commonly used for prevention and treatment of ankle injuries. Various investigations-mostly performed with healthy subjects-focused on this problem, yet they often compared only a few models or used only limited testing procedures. However, controversy exists whether braces affect sports performance. The purpose of the present study was to compare the effects of ten different ankle braces-one rigid, five semirigid, four soft models-in a comprehensive evaluation with multiple testing procedures in 34 subjects with self-reported chronic ankle instability. The multiple testing procedures evaluated objective performance-related parameters and subjective parameters related to comfort and stability. The subjects performed an agility course with maximal effort. The course included a vertical jump and a cutting maneuver, both on a force platform, a single leg hopping test on level and inclined plates, a combined straight and curve sprint and sidesteps. Three valid trials were measured and averaged for each brace and every subject. Subjective aspects were evaluated with a questionnaire about handling, perceived restrictions, support and comfort; it was completed after each brace was worn and tried. With regard to the objective parameters, no significant differences were found between the braces except for the rigid brace which showed decreased values for the vertical jump and longer times for the other tests compared to all other braces. The subjective evaluation of the braces revealed significant differences with respect to comfort and handling and therefore, permitted a distinction between semirigid and soft braces. Although significant differences between braces were found in subjective performance restriction, no significant differences were revealed in the objective evaluation. From that point of view, patients could choose a brace model according to their individual needs. A comfortable brace might have a positive influence on the athlete's state of mind although other aspects like the brace's stabilizing effect play an additional role and should also be taken into account for recommendation of braces.

Adolescent↗

PubMed2004

An explanation for a universality of transition temperatures in families of copper oxide superconductors.

A remarkable mystery of the copper oxide high-transition-temperature (T(c)) superconductors is the dependence of T(c) on the number of CuO2 layers, n, in the unit cell of a crystal. In a given family of these superconductors, T(c) rises with the number of layers, reaching a peak at n = 3, and then declines: the result is a bell-shaped curve. Despite the ubiquity of this phenomenon, it is still poorly understood and attention has instead been mainly focused on the properties of a single CuO2 plane. Here we show that the quantum tunnelling of Cooper pairs between the layers simply and naturally explains the experimental results, when combined with the recently quantified charge imbalance of the layers and the latest notion of a competing order nucleated by this charge imbalance that suppresses superconductivity. We calculate the bell-shaped curve and show that, if materials can be engineered so as to minimize the charge imbalance as n increases, T(c) can be raised further.

Journal Article↗

PubMed2004

Reduced plantar sensation causes a cautious walking pattern.

The aim of this study was to investigate the influence of reduced plantar sensation on gait patterns during walking in 20 healthy subjects (25.9 +/- years, 61.6 +/- 11.5 kg, 178 +/- 9.5 cm) with no history of sensory disorders. Force plate measurements, electromyography (EMG) measurements and a three-dimensional movement analysis were performed simultaneously during barefoot walking before and after reduction of plantar sensation using an ice immersion technique. The results show that reduced plantar sensation leads to significant changes in gait patterns that are present at the ankle, knee and hip joint and indicate a more cautious ground contact and push-off with modified EMG and motion patterns.

Adult↗

PubMed2004

Exercise-induced apoptosis of lymphocytes depends on training status.

PURPOSE: To investigate the effect of training status on lymphocyte apoptosis as well as the expression of cell death receptors and ligands after a marathon run, and to compare these data with the alterations after treadmill exercise tests. METHODS: Sixteen volunteers successfully finished the 2002 Münster marathon. Venous blood samples were drawn before and 0, 3, and 24 h after the race. After cell isolation, cell-based apoptosis markers annexin V, Fas receptor, and Fas ligand were measured by flow cytometry. The same parameters were investigated in a group of 10 subjects before, and 0 and 1 h after both an exhaustive (ExT) and a low-intensity (LoT) treadmill test. RESULTS: The percentage of apoptotic cells after the marathon changed in a biphasic manner. An early increase 3 h after the run was followed by a significant decrease 1 d later. Interestingly, the increase in apoptotic cells was not observed in highly trained athletes, whereas it was significantly more pronounced in badly trained athletes. ExT induced a lymphocyte apoptosis similar to the marathon, whereas no change in apoptosis was observed after the LoT. Both Fas receptor and ligand were increased after the marathon with different kinetics. Whereas the Fas receptor peaked at 1 h, Fas ligand was increased 3 h after the run. After the treadmill tests Fas receptor expression was enhanced in both groups, whereas Fas ligand increased only after the ExT. CONCLUSIONS: Endurance exercise like a marathon is able to induce apoptosis in lymphocytes. Thereby, apoptosis sensitivity seems to be related to training status in an inverse relationship. The increased expression levels of death receptors and ligands might indicate the high apoptosis inducing potential of this type of exercise.

Adult↗

PubMed2002

Modified pressure distribution patterns in walking following reduction of plantar sensation.

The aim of the present study was to investigate the influence of reduced plantar sensation on pressure distribution patterns during gait of 40 healthy subjects (25.3+/-3.3 yr, 70.8+/-10.6 kg and 176.5+/-7.8 cm) with no history of sensory disorders. Plantar sensation in the subjects was reduced by using an ice immersion approach, and reduced sensitivity was tested with Semmes-Weinstein monofilaments. All subjects performed six trials of barefoot walking over a pressure distribution platform under normal as well as iced conditions. Plantar cutaneous sensation was significantly reduced after the cooling procedure (p<0.0001). Pressure distribution analysis showed substantially modified plantar pressure distribution patterns during the roll-over process (ROP) under iced conditions. Analysis of peak pressures revealed significant reductions under the toes and under the heel (p<0.001). The contact time and the relative impulse for the whole foot did not change significantly between the two conditions. For the different areas, a significant load shift from the heel and toes towards the central and lateral forefoot and the lateral midfoot was observed. The results indicate the strong influence of reduced afferent information of the sole of the foot on the ROP in walking.

Adult↗

PubMed2002

Comprehensive testing of 10 different ankle braces. Evaluation of passive and rapidly induced stability in subjects with chronic ankle instability.

OBJECTIVE: The aim of the present investigation was to test the stability of 10 different ankle braces under passive and rapidly induced loading conditions in a population suffering from chronic ankle instability in order to provide objective information to choose or recommend an appropriate model for specific needs. In addition, the relationship between passive and rapidly induced testing of the stabilizing effect against inversion was evaluated to identify if passive support characteristics of braces are reflected under rapidly induced conditions. DESIGN: An experimental in vivo study with a repeated-measures design was used. BACKGROUND: Ankle braces are commonly used for treatment, rehabilitation, and prevention of ankle injuries. A variety of products exists but there is few information available to assist clinicians, physiotherapists and coaches as well as consumers in choosing a brace on a basis of objective information. Furthermore, there is a lack of studies that provide data for both passively and rapidly induced movement of the ankle joint when using different ankle braces. METHODS: Twenty-four subjects with chronic ankle instability participated in the project. Passive ankle range of motion measurements were performed in a custom-built fixture and simulated inversion sprains were elicited on a tilting platform. RESULTS: The tested braces restrict range of motion significantly compared to the no-brace condition for both the passively and rapidly induced inversion and marked differences between braces were revealed. A close relationship between passive and rapidly induced test results for inversion was found. CONCLUSIONS: Passive as well as rapidly induced stability tests provide a basis of objective information to describe the characteristics of different ankle braces. Combined results of passive and rapidly induced inversion as well as correlation between results demonstrate that passive support characteristics of braces are reflected under rapidly induced conditions but the amount of restriction is reduced. Therefore, caution should be taken when recommending braces for applications under dynamic circumstances only on the basis of passive support characteristics. RELEVANCE: A basis of information regarding the stability characteristics of different ankle braces under passive and rapidly induced conditions will help the clinician and consumer in choosing the most appropriate brace model for specific use. The results also provide more insights into factors that influence stability characteristics of ankle braces.

Adult↗

PubMedDate not supplied

Characteristic plantar pressure distribution patterns during soccer-specific movements.

PURPOSE: To characterize in-shoe pressure measurements during different soccer-specific maneuvers on two playing surfaces to identify the main loading areas of the foot. METHODS: Twenty-one experienced male soccer players participated in the study (25.5 +/- 1.8 years, 78.7 +/- 5.4 kg, and 182.9 +/- 5.7 cm). The Pedar Mobile system was used to collect plantar pressure information inside the soccer shoe. Four soccer-specific movements were performed (normal run, cutting maneuver, sprint, and goal shot) on both a grass and a red cinder surface. RESULTS: Results showed characteristic pressure distribution patterns with specific loading areas of the foot that correspond to the evaluated movements. In addition, loading patterns with higher pressure values than those observed during normal run were found. In cutting, the medial part of the foot; in sprinting, the first and second ray; and in kicking, the lateral part of the foot are predominantly loaded. No global effect of the two surfaces on pressure parameters was found. CONCLUSION: The results of the present investigation suggest that the high load in soccer in combination with a high repetition may have an important influence in the development of overuse injuries.

Adult↗