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PubMed2000

Measures of postural stability are not predictors of recovery from large postural disturbances in healthy older adults.

OBJECTIVES: To determine, in healthy older adults, the relationship between postural steadiness, stability limits, and the ability to recover balance from three postural disturbances requiring anteriorly directed stepping responses. DESIGN: Analysis of multiple motor tasks in a cross-sectional sample of healthy older adults. SETTING: A biomechanics research laboratory. PARTICIPANTS: Fifty women and 29 men aged 65 or older, all healthy, living in the community, participated in this study. Subjects were examined by a geriatrician to identify the presence of exclusionary factors. MEASUREMENTS: Anterior-posterior and medial-lateral excursion distances of the center of pressure during quiet standing (postural steadiness), static leaning (static stability limits), and dynamic swaying (dynamic stability limits) were determined from ground reaction forces measured by a strain gauge forceplate. Within the same group of subjects, the maximum angle of forward lean from which a subject could recover with a single step, the ability to recover balance in response to an accelerated support surface, and the ability to recover balance after being tripped were determined. RESULTS: Recovery from the three types of postural disturbances were found to be statistically independent. The postural steadiness and the stability limit variables were only weakly correlated. Postural steadiness and stability limits were not related to the maximum recoverable angle of lean. The average medial-lateral center of pressure speed during the postural steadiness test was significantly slower for those who failed to recover after tripping than for the subjects who recovered successfully. However, a logistic regression model failed to achieve statistical significance, suggesting that the difference may not be functionally important. The anterior-posterior static stability limits were significantly larger for subjects who recovered successfully than for those who failed to recover during the accelerated support surface test. Although logistic regression suggested that a reduced anterior-posterior stability limit represents a risk factor for failure to recover during this task, only nine of 28 failures could be properly classified, thus diminishing the functional importance of this finding. CONCLUSIONS: Because recovery following postural disturbances could not generally be predicted from measures of postural stability, these findings suggest that these measures of postural stability are of limited utility in identifying potential anteriorly directed fallers in healthy older adults.

Aged↗
PubMed1990

Genetic characterization of the stabilizing functions of a region of broad-host-range plasmid RK2.

One of the regions responsible for the stable inheritance of the broad-host-range plasmid RK2 is contained within the PstI C fragment, located from coordinates 30.8 to 37.0 kb (P.N. Saurugger, O. Hrabak, H. Schwab, and R.M. Lafferty, J. Biotechnol. 4:333-343, 1986). Genetic analysis of this 6.2-kb region demonstrated that no function was present that stabilized by selectively killing plasmid-free segregants. The sequence from 36.0 to 37.0 kb mediated a twofold increase in plasmid copy number, but this region was not required for stabilization activity. The PstI C fragment was shown to encode a multimer resolution system from 33.1 to 35.3 kb. The resolution cis-acting site was mapped to 140 bp, sequenced, and observed to contain two directly repeated sequences of 6 and 7 bases and two perfect inverted repeats of 6 and 8 bases. The trans-acting factor(s) was mapped and functionally determined to encode a resolvase capable of catalyzing recombination at high frequency between cis-acting sites in either direct or inverted orientation. Multimer resolution alone did not account for complete plasmid stabilization by the PstI C fragment, since removal of regions adjacent to the 35.3-kb border of the minimal mrs locus dramatically reduced stabilization. The minimal region required for complete stabilization, from 32.8 to 35.9 kb, was capable of fully stabilizing plasmids independently of the replicon or the recA proficiency of the host. Stabilization activity was also fully expressed in several diverse gram-negative bacteria, whereas the F plasmid par locus functioned only in Escherichia coli. On the basis of these observations, we conclude that under the growth conditions used, the minimal stabilization locus encodes both an mrs activity and a stabilization activity that has the properties of a par locus.

Azotobacter↗
PubMed2003

Role of feedforward control of movement stability in reducing slip-related balance loss and falls among older adults.

Human upright posture is inherently unstable. To counter the mechanical effect of a large-scale perturbation such as a slip, the CNS can make adaptive adjustments in advance to improve the stability of the body center-of-mass (COM) state (i.e., its velocity and position). Such feedforward control relies on an accurate internal representation of stability limits, which must be a function of anatomical, physiological, and environmental constraints and thus should be computationally deducible based on physical laws of motion. We combined an empirical approach with mathematical modeling to verify the hypothesis that an adaptive improvement in feedforward control of COM stability correlated with a subsequent reduction in balance loss. Forty-one older adults experienced a slip during a sit-to-stand task in a block of slip trials, followed by a block of nonslip trials and a re-slip trial. Their feedforward control of COM stability was quantified as the shortest distance between its state measured at seat-off (slip onset) and the mathematically predicted feasible stability region boundary. With adaptation to repeated slips, older adults were able to exponentially reduce their incidence of falls and backward balance loss, attributable significantly to their improvement in feedforward control of stability. With exposure to slip and nonslip conditions, subjects began to select "optimal" movements that improved stability under both conditions, reducing the reliance on prior knowledge of forthcoming perturbations. These results can be fully accounted for when we assume that an internal representation of the COM stability limits guides the adaptive improvements in the feedforward control of stability.

Adaptation, Physiological↗
PubMed2007

The ability of the Biodex Stability System to distinguish level of function in subjects with a second-degree ankle sprain.

OBJECTIVE: To assess the capacity of the Biodex Stability System using a one-leg stance protocol to differentiate between injured and non-injured limbs and between level of disabilities. DESIGN: Cross-sectional study. SETTING: Military and civilian clinic. SUBJECTS: Thirty-four individuals with a second-degree lateral ankle sprain and 36 healthy subjects. METHODS AND MEASURES: Subjects were tested on the Stability System 30 days after injury using a one-leg stance protocol in the dynamic limit-of-stability mode. All subjects also filled out a disability questionnaire (Lower Extremity Functional Scale). The groups were compared based on the overall dynamic limit-of-stability score and its relationship with the score on the disability questionnaire was also examined. RESULTS: The overall dynamic limit-of-stability scores (subjects with a lateral ankle sprain: 13.0% (5.5)-26.0% (9.2); healthy subjects: 16.9% (7.9)-27.9% (9.6)) clustered in the lower end of the theoretical range of 0-100%. Statistically significant differences in the overall dynamic limit-of-stability scores were found between the injured and non-injured limbs but group differences were small and clinically not relevant. No significant relationships were found between the overall dynamic limit-of-stability scores and the Lower Extremity Functional Scale scores (58.2 (11.8)) of the subjects with a lateral ankle sprain. CONCLUSIONS: The one-leg stance protocol carried out in the dynamic limit-of-stability mode is very challenging and offers a very limited capacity to differentiate between injured and non-injured limbs. The main outcome of the Stability System does not appear to be a good indicator of the functional capacity of people with a lateral ankle sprain.

Adult↗
PubMed2005

Functional determination of plasmin in arginine-stabilized plasma.

Reliable data on plasmin activities in blood of patients during fibrinolytic treatment are lacking. This is due to continuing plasminogen activation by plasminogen activators after blood withdrawal. The purpose of this study was to establish a new method for stabilization of blood and to detect plasmin activity in stabilized plasma. For optimization of plasma stabilization by arginine, 50 microL pooled normal citrated plasma was incubated with 50 microL of 0 to 1500 mM arginine, pH 8.7, and 25 microL 100 IU/mL u-PA, 1250 IU/mL t-PA, 10000 U/mL reteplase, 400 U/mL plasminogen-streptokinase-activator complex, 10 microg/mL tenecteplase in 6% BSA-PBS or 25 microL 25 microg/mL plasmin in 20% glycerol. Twenty-five microliters 3 mM HD-Val-Leu-Lys-pNA were added immediately (1 step) or after 90 minutes (room temperature [RT]). The same experiment was performed with pooled normal citrated plasma supplemented with 3.2 mg/mL EDTA, preoxidized with 0 mM or 20 mM chloramine-T for 10 minutes (37 degrees C). For optimization of plasmin activity, the oxidation time of the arginine-stabilized plasma sample containing 0.5 U/mL active plasmin and the chloramine-T amount was varied. Citrated plasma is stabilized against the in vitro action of all six plasminogen activators tested if the final arginine concentration is greater than 500 mM. Neither the addition of EDTA nor the addition of chloramine-T changes this plasma-stabilizing power of arginine. The optimized functional plasmin assay consists of incubation of 10 microL arginine-stabilized plasma with 10 microL 1.5 M arginine, pH 8.7, and 10 microL 100 mM CT in PBS. After 30 minutes (37 degrees C), 75 microL 1.2 M KCl, 1.6 M Arg, 0.75 mM Val-Leu-Lys-pNA (Stop-CS Reagent), and 175 microL 6% BSA-PBS are added and the absorbance increase (DeltaA) at 405 nm is determined. With the present arginine stabilization procedure of plasma and the determination of plasmin activity in arginine-stabilized plasma as described, it is feasible to determine the activity of plasmin in blood of patients receiving fibrinolytic treatment without artefactual in vitro changes in the samples.

Arginine↗
PubMed1980

Contrast sensitivity measures and accuracy of image stabilization systems.

Recently, it has been argued that the precision of image stabilization is reflected in the magnitude of the differences in contrast sensitivity measures obtained with and without image stabilization. Here we present two sets of data, one showing large and the other small differences in contrast sensitivity to sinusoidal gratings viewed under stabilized and unstabilized, normal conditions. Both sets of data were obtained by the use of the same apparatus optimized for image stabilization. Large differences occur between unstabilized and stabilized measures of sensitivity only when the observer is allowed to scan the unstabilized test grating, or to prolong inspection of the stabilized target thus allowing for disappearance of the stabilized image. On the other hand, when the target is presented for a few seconds and the observer fixates on it, normal image motion, which results from eye movements of fixation, is found to enhance contrast sensitivity by only a small amount. It would appear, therefore, that the extent of reduction of sensitivity for a stabilized grating cannot be used as an index of the precision of image stabilization.

Adult↗
PubMed2004

Influence of fatigue in neuromuscular control of spinal stability.

Lifting-induced fatigue may influence neuromuscular control of spinal stability. Stability is primarily controlled by muscle recruitment, active muscle stiffness, and reflex response. Fatigue has been observed to affect each of these neuromuscular parameters and may therefore affect spinal stability. A biomechanical model of spinal stability was implemented to evaluate the effects of fatigue on spinal stability. The model included a 6-degree-of-freedom representation of the spine controlled by 12 deformable muscles from which muscle recruitment was determined to simultaneously achieve equilibrium and stability. Fatigue-induced reduction in active muscle stiffness necessitated increased antagonistic cocontraction to maintain stability resulting in increased spinal compression with fatigue. Fatigue-induced reduction in force-generating capacity limited the feasible set of muscle recruitment patterns, thereby restricting the estimated stability of the spine. Electromyographic and trunk kinematics from 21 healthy participants were recorded during sudden-load trials in fatigued and unfatigued states. Empirical data supported the model predictions, demonstrating increased antagonistic cocontraction during fatigued exertions. Results suggest that biomechanical factors including spinal load and stability should be considered when performing ergonomic assessments of fatiguing lifting tasks. Potential applications of this research include a biomechanical tool for the design of administrative ergonomic controls in manual materials handling industries.

Adult↗
PubMed2006

Salting the charged surface: pH and salt dependence of protein G B1 stability.

This study shows significant effects of protein surface charges on stability and these effects are not eliminated by salt screening. The stability for a variant of protein G B1 domain was studied in the pH-range of 1.5-11 at low, 0.15 M, and 2 M salt. The variant has three mutations, T2Q, N8D, and N37D, to guarantee an intact covalent chain at all pH values. The stability of the protein shows distinct pH dependence with the highest stability close to the isoelectric point. The stability is pH-dependent at all three NaCl concentrations, indicating that interactions involving charged residues are important at all three conditions. We find that 2 M salt stabilizes the protein at low pH (protein net charge is +6 and total number of charges is 6) but not at high pH (net charge is or=18). Furthermore, 0.15 M salt slightly decreases the stability of the protein over the pH range. The results show that a net charge of the protein is destabilizing and indicate that proteins contain charges for reasons other than improved stability. Salt seems to reduce the electrostatic contributions to stability under conditions with few total charges, but cannot eliminate electrostatic effects in highly charged systems.

Bacterial Proteins↗
PubMed2005

Anteroinferior bone-grafting can restore stability in osseous glenoid defects.

BACKGROUND: Glenohumeral instability associated with a large osseous defect of the glenoid can be treated with bone graft to restore the glenoid concavity. The shape and positioning of the graft is critical: a graft that encroaches on the extrapolated glenoid curvature can prevent the head from seating completely in the glenoid, whereas a graft that is too far from the curvature does not restore the glenoid concavity. The purpose of the present study was to investigate how the intrinsic stability that is provided by the glenoid is affected by (1) a standardized anteroinferior glenoid defect and (2) different configurations of anteroinferior glenoid bone graft. METHODS: The anteroinferior stability provided by the glenoid was quantitated by measuring the balance stability angle in that direction. The balance stability angle is the maximal angle that the direction of the net humeral joint-reaction force can make with the glenoid centerline before dislocation takes place. The anteroinferior stability was assessed in each of four fresh-frozen, grossly normal cadaveric glenoids in (1) the unaltered state, (2) after the creation of a standardized defect of a magnitude that has been reported by other investigators to be sufficient to require a bone graft, and (3) after each step of a series of bone-grafting procedures involving grafts of varying height and contour. RESULTS: The anteroinferior glenoid defect significantly diminished the anteroinferior stability by almost 50% (p = 0.006). Bone-grafting significantly increased the stability provided by the glenoid. The increase in stability as compared with that of the glenoid with the standardized defect was particularly marked for contoured graft heights of 6 and 8 mm, for which the increases were 150% (p = 0.0001) and 229% (p < 0.00025), respectively. Contouring of the graft minimized the potential for unwanted contact between the ball and the graft. CONCLUSIONS: Anteroinferior shoulder instability caused by an osseous defect in the glenoid can be corrected with bone-grafting. The effectiveness of the graft in restoring the lost stability is related both to its height and to the extent to which it is contoured as long as the graft is not so prominent that it forces the ball posteriorly from the center of the glenoid.

Aged↗
PubMed2006

Contribution of articular surface geometry to ankle stabilization.

BACKGROUND: Passive ankle stability under weight-bearing conditions has been found to depend substantially on the role of the articular surface geometry. In the present study, it was hypothesized that, in the ankle under axial loading, contact-stress changes in response to alterations of external load involve reproducible and specific patterns to maintain ankle stability. METHODS: Six cadaver ankles with the peri-ankle ligaments intact were tested. Each specimen, held at several predetermined ankle positions under a primary one-body-weight axial force, was subjected to an additional secondary load. The secondary load-specifically, anterior/posterior shear force, inversion/eversion torque, or internal/external rotation torque-was applied independently, while motion associated with the two other secondary loading directions was unconstrained. Contact stress in the tibiotalar articulation was monitored by a real-time contact-stress sensor. Site-specific stress changes solely due to secondary loading at each load/position were identified by subtraction of the corresponding axial-force-only baseline distribution. The role of these stress changes in ankle stabilization was studied for each specimen by analyzing the data with a computer model of ankle geometry. RESULTS: In the cadaver experiment, anterior and posterior shear forces caused reproducible positive changes in articular contact stresses on the anterior and posterior regions, respectively. Similar changes with version torques occurred on the medial and lateral regions. Positive changes with internal/external rotation torques occurred at two diagonal locations: anterolateral and posteromedial, or anteromedial and posterolateral. In the model analysis, these stress-change patterns were found to be effective in ankle stabilization, and the levels of contribution by the articular surface were calculated as accounting for approximately 70% of anterior/posterior stability, 50% of version stability, and 30% of internal/external rotation stability. CONCLUSIONS: The documented changes in contact stress illustrate the major role of articular geometry in passive ankle stabilization. The levels of contribution by the articular surface that we calculated are consistent with those reported in the literature. These findings support the conceptual mechanism of ankle stabilization by redistribution of articular contact stress.

Aged↗
PubMed2002

In vitro biomechanical study of rotational stabilizers of the canine elbow joint.

OBJECTIVE: To develop a model for measuring rotary stability of the canine elbow joint and to evaluate the relative contribution of the anconeal process (AN), lateral collateral ligament (LCL), and medial collateral ligament (MCL). SAMPLE POPULATION: 18 forelimbs from 12 canine cadavers. PROCEDURE: Forelimbs were allocated to 3 experimental groups (6 forelimbs/group). Each intact forelimb was placed in extension at an angle of 135 degrees and cycled 50 times from -16 degrees (pronation) to +28 degrees (supination) in a continuous manner at 2.0 Hz. Cycling was repeated following sectioning of the structure of interest (group 1, AN; group 2, LCL; and group 3, MCL). Torque at -12 degrees (pronation) and +18 degrees (supination) was measured for each intact and experimentally sectioned limb. A Student t test was performed to compare torque values obtained from intact verses experimentally sectioned limbs and for comparison with established criteria for differentiation of primary (> or = 33%), secondary (10 to 33%), and tertiary rotational stabilizers (< 10%). RESULTS: In pronation, the AN was the only primary stabilizer (65%). For supination, the LCL was a primary stabilizer (48%), AN was a secondary stabilizer (24%), and MCL was a tertiary stabilizer (7%). CONCLUSIONS AND CLINICAL RELEVANCE: With the elbow joint in extension at an angle of 135 degrees, the AN is a primary rotational stabilizer in pronation, and the LCL is a primary stabilizer in supination. Disruption of the AN or LCL may affect rotary range of motion or compromise stability of the elbow joint in dogs.

Animals↗
PubMed1999

Effects of practice on the ability to perform lumbar stabilization exercises.

STUDY DESIGN: Randomized pretest-posttest control group design. OBJECTIVES: To determine the intratester and intertester reliability of a modified isometric stability test and to use this test to evaluate the effects of practice following a 4-week stabilization exercise program with weekly reinstruction. BACKGROUND: Although "stabilization" exercise programs are commonplace in the clinic, the reliability to a tool capable of measuring changes in the ability to perform increasingly difficult stabilization exercises has not, to our knowledge, been reported. In addition, it is not clear if practice improves the ability to perform stabilization exercises. METHODS AND MEASURES: A convenience sample of 44 asymptomatic subjects was pretested using a pressure transducer placed beneath the lumbar spine to detect motion (+/- 4 mm Hg). A series of 7 exercises was attempted, which required increasing levels of muscular control of the lumbar spine for stability. Subjects received a pass or fail for each exercise level based on the pressure gauge readings and the absence of movement compensations. Subjects were assigned randomly to exercise and nonexercise groups, and posttest measurements were taken after 4 weeks. The control group did not receive additional instruction. RESULTS: The weighted kappa coefficient of 0.61 for intratester and 0.62 for intertester represents good agreement. The median level of exercise attainment increased for the exercise group but not for the nonexercise group. CONCLUSION: These results suggest that the modified isometric stability test was reliable and that a 4-week lumbar stabilization exercise program, with weekly intervals of reinstruction and testing, improves the ability to perform progressively difficult lumbar stabilization exercises.

Adult↗
PubMed2003

Evaluation of hemodynamics: comparison of vacuum and mechanical stabilization in the beating heart.

BACKGROUND: Hemodynamic instability remains a prominent concern for surgeons performing coronary surgery without cardiopulmonary bypass. The purpose of this study was to further elucidate the mechanism of hemodynamic instability by comparing vacuum stabilization to mechanical stabilization. METHODS: Four 60-kg swine were placed under general anesthesia. A median sternotomy incision was made, and baseline hemodynamic measurements were recorded. Mechanical and vacuum stabilization of the circumflex distribution were alternately compared with repeated baseline measurements in a counterbalanced method, and 32 experiments were conducted. RESULTS: There were significant differences between baseline hemodynamics and stabilized hemodynamics for mechanical stabilization versus vacuum stabilization, respectively, for the following parameters: blood pressure (mean decrement), -32.18% (P =.0028) versus -31.3% (P =.0006); cardiac output, -31.03% (P =.0046) versus -35.2% (P =.03); and mixed venous oxygen saturation, -29.8% (P =.008) versus -27.4% (P =.0004). There were no statistical differences between mechanical and vacuum stabilization when their decremental effects on baseline hemodynamics were compared with each other for any of the measured variables. CONCLUSIONS: The mechanisms of hemodynamic compromise during coronary stabilization remain to be fully elucidated. Our study demonstrates no statistical difference between vacuum and mechanical stabilization on the measured hemodynamic values. More sophisticated studies involving detailed analysis of motion and geometry are required so that technical solutions to hemodynamic instability can be developed.

Animals↗
PubMedDate not supplied

Resonance frequency measurement of implant stability in vivo on implants with a sandblasted and acid-etched surface.

PURPOSE: To determine the changes in stability as a reflection of early healing around single-stage, roughened-surface implants in humans utilizing resonance frequency analysis (RFA). RFA makes use of a transducer, attached to an implant, which is excited over a range of sound frequencies with subsequent response analysis. MATERIALS AND METHODS: Twenty patients had 1 to 4 implants placed in the posterior maxilla or mandible. Bone type was classified into 1 of 4 groups according to the Lekholm and Zarb index (1985). RFA was used for direct measurement of implant stability on the day of implant placement and consecutively once per week for 6 weeks and at weeks 8 and 10. RESULTS: Twenty-seven ITI SLA implants placed in the premolar and molar regions of the maxilla and mandible were evaluated. Early failure occurred with 1 implant related to parafunction. The remaining 26 implants were distributed as follows: 29.6% in Type 1 bone, 37% in Type 2 or 3 bone, and 33.3% in Type 4 bone. The lowest mean stability measurement was at 3 weeks for all bone types. The percentage decrease in stability from baseline to 3 weeks was highest for Type 4 bone (8.6%), as was the percentage increase in stability from 3 to 10 weeks (26.9%). A Bonferroni adjusted Student t test comparison of bone groups at each time point revealed highly significant differences between implant stability in Types 1 and 4 bone at 3 weeks (P = .004) and a moderately significant difference between Types 2, 3, and 4 bone (P = .08) at 3 weeks. Implant stability did not change significantly during the 10-week period in Type 1 bone (P > .10). With the same test, by 5 weeks, no bone groups showed any difference in implant RFA measurements (P = 1.0). DISCUSSION: This study demonstrated the lowest values for implant stability at 3 weeks after placement for all bone types. This effect was statistically significant and most pronounced in Type 4 bone. CONCLUSION: There was no significant difference in the pattern of stability changes among different bone types after 5 weeks of healing.

Acid Etching, Dental↗
PubMed1992

[Comparative biomechanical studies of internal stabilization of trans-foraminal sacrum fractures].

A new method of internal stabilization of transforaminal sacrum fractures in unstable pelvic ring fractures was developed by modification of standard AO small-fragment implants. The rationale of this type of stabilization is the use of an unilateral dorsal approach and avoidance of transfixation of the uninvolved SI joints. In a comparative biomechanical study on 8 human cadaver pelvises two types of the new type of stabilization were compared to stabilization with Harrington sacral bars and transiliosacral screw fixation. The fracture model represented a Tile C1 type injury (symphysis disruption and transforaminal sacral osteotomy) on a complete pelvic ring. The anterior stabilization was performed with a 4-hole AO 4.5 mm DC plate in all cases. The load simulation used a one-leg standing model in an upright position with abductor muscle simulation. The pelvises were loaded in 4 load stages of 50%, 80%, 100% and 130% body weight. In each load stage 4 load-unload cycles were completed. With a three-dimensional measurement system (Polhemus 3 Space Motion Tracker) translations an rotations in the fracture plane could be analyzed. Typical behavior in the load-displacement curve was seen in all implants, with settling during the first cycles and permanent displacement after exceeding a specific failure load. The failure load showed no significant differences between implants (99.6-113.6% body weight). The analyses of the persistent displacement, the elasticity and the direction of displacement and rotation showed a typical behavior in the implants, but no differences, which can be interpreted as a significant difference in the stability of the fixation methods. In an additional test the new fixation method showed no loosening in 10,000 cycle loading with 60% body weight. The new stabilization method showed biomechanical results comparable to clinically successful methods of stabilization in the chosen fracture model. Thus, clinical applications of this type of stabilization may be successful.

Adult↗
PubMed2004

Adaptations in horizontal head stabilization in response to altered vision and gaze during natural walking.

The purpose of this study was to determine adaptations in head stability resulting from altered gaze control and vision during over-ground walking. Using over-ground walking permitted adaptations in walking velocity and cadence that are otherwise not possible during treadmill walking or walking-in-place. Gaze control and vision were manipulated by having 20 young adult subjects 1) walk naturally, 2) view a distant, earth-fixed target to enhance the vestibulo-ocular reflex (VOR), 3) view a head-fixed target to suppress the VOR, and 4) walk in darkness. Horizontal head and trunk angular velocities in space, walking velocity and cadence were measured. Root-mean-square head and trunk angular velocities were calculated and frequency analyses determined head-trunk movement patterns. Results demonstrated that when given the opportunity, subjects slowed down and decreased cadence in response to challenging tasks. Despite strongly reduced walking velocity and cadence, walking in darkness proved most challenging for head stabilization, indicating the importance of vision during this process. Viewing the earth-fixed target demonstrated the greatest head stability thereby, facilitating gaze stabilization. However, comparisons between the earth-fixed and head-fixed target conditions suggest a reciprocal relationship where gaze stability also facilitates head stability. This contribution of gaze stability to head stability is more important than vision alone as the head stabilization response was diminished during the VOR suppressed condition.

Adaptation, Physiological↗
PubMed2005

[Studies on the spectrum and frequency repetition of double-mode He-Ne laser with frequency stabilization].

Theoretical analysis of spectrum and frequency repetition of the double-model frequency stabilization He-Ne laser has been done, and the beat frequency experiment using 632 nm I2 frequency stabilization He-Ne laser has been carried out. The authors used the intercavity laser, and the double mode frequency stabilization to get the laser stabilized output through adjusting the two neighbor vertically polarized modes to the equal power reference point. Through the experiment, the authors analyzed the factors which affect the laser frequency repetition and stabilization, and measured the stabilized laser power and the frequency stabilization. The beat frequency experiment has shown that the frequency repetition can reach (1-2) x 10(-8) by frequency difference, and the laser stabilization can reach 10(-10) by Allan variances. The experiments show that the stabilized laser can work well and can be used as frequency reference point.

Algorithms↗
PubMed1993

[The structure of distracting-compressing stabilizers Dynastab DK intended for functional treatment of articular fractures].

The structure of the distracting-compressing stabilizers Dynastab DK intended for functional treatment of transarticular fractures is described. The stabilizers realize the idea of functional treatment of fractures outside the hospital bed making possible free moving around of the patient during the treatment. This has been made possible owing to building-in of a mechanical articulation imitating the physiological movement in the injured joint. The articulation in the stabilizer reduces also the load on the joint. In the stabilizers for the treatment of such fractures of the elbow joint and ankle joint the articulations are monoaxial (hinge-like). In the stabilizer for the treatment of the radiocarpal joint this is a hinge articulation making possible flexion in sagittal plane. In the stabilizer for knee fractures the movements in the injured joint are taken over by a mechanical articulation of special structure. The distracting-compressing action of the Dynastab DK stabilizers for the treatment of transarticular fractures is realized by the tension screw mechanism e.g. in the stabilizer for the treatment of knee joint fractures. In the case of stabilizers for ankle joint, radiocarpal joint and elbow joint this tension is provided by calibrated compressing springs.

Biomechanical Phenomena↗