114,536 research outputs found
Impaired Postural Control Reduces Sit-to-Stand-to-Sit Performance in Individuals with Chronic Obstructive Pulmonary Disease
No full textAbstract
Background: Functional activities, such as the sit-to-stand-to-sit (STSTS) task, are often impaired in individuals with chronic
obstructive pulmonary disease (COPD). The STSTS task places a high demand on the postural control system, which has
been shown to be impaired in individuals with COPD. It remains unknown whether postural control deficits contribute to
the decreased STSTS performance in individuals with COPD.
Methods: Center of pressure displacement was determined in 18 individuals with COPD and 18 age/gender-matched
controls during five consecutive STSTS movements with vision occluded. The total duration, as well as the duration of each
sit, sit-to-stand, stand and stand-to-sit phase was recorded.
Results: Individuals with COPD needed significantly more time to perform five consecutive STSTS movements compared to healthy controls (1966 vs. 1364 seconds, respectively; p = 0.001). The COPD group exhibited a significantly longer stand phase (p = 0.028) and stand-to-sit phase (p = 0.001) compared to the control group. In contrast, the duration of the sit phase (p = 0.766) and sit-to-stand phase (p = 0.999) was not different between groups.
Conclusions: Compared to healthy individuals, individuals with COPD needed significantly more time to complete those phases of the STSTS task that require the greatest postural control. These findings support the proposition that suboptimal postural control is an important contributor to the decreased STSTS performance in individuals with COPD
Measuring movement fluency during the sit-to-walk task
No full textRestoring movement fluency is a key focus for physical rehabilitation; it's measurement, however, lacks objectivity. The purpose of this study was to find whether measurable movement fluency variables differed between groups of adults with different movement abilities whilst performing the sit-to-walk (STW) movement. The movement fluency variables were: (1) hesitation during movement (reduction in forward velocity of the centre of mass; CoM), (2) coordination (percentage of temporal overlap of joint rotations) and (3) smoothness (number of inflections in the CoM jerk signal)
Quantification of lower extremity physical exposures in various combinations of sit/stand time duration associated with sit-stand workstation
No full textBackground: Sit-stand workstations are available for office work purposes but there is a dearth of quantitative evidence to state benefits for lower limb outcomes while using them. And there are no guidelines on what constitutes appropriate sit/stand time duration. The primary aim of this study has been to compare muscle activity and perceived discomfort in the lower extremity during various combinations of sit/stand time duration associated with a sit-stand workstation separately and to evaluate the effects of the sit-stand workstation on the lower extremity during the text entry task. Material and Methods: During the 5 days, all participants completed a 2-h text entry task each day for various sit/stand time duration combinations as follows: 5/25 min, 10/20 min, 15/15 min, 20/10 min, 25/5 min. Lower extremity muscular exposure of 12 male and 13 female participants was collected at 8 sites by surface electromyography and body discomfort was calculated by a questionnaire under those 5 conditions. Results: Results have demonstrated that lower extremity muscle activity has been significantly varied among the 5 sit/stand time duration groups. Perceived level of discomfort (PLD) has not differed significantly for 9 out of 10 body parts. Conclusions: The muscle activity of the thigh region was influenced by sit/stand time duration significantly. Ergonomic exposures of lower extremity when using a sit-stand workstation were increased, particularly during the long time standing posture. Results indicate that body mass index (BMI) and gender were not significant factors in this study. Combination of sit/stand time duration 25/5 min appears to show positive effects on relief of muscle exposure of back of thigh in the shifts of sitting and standing work position. Med Pr 2017;68(3):315–32
Realistic quantitative descriptions of electron transfer reactions: Diabatic free-energy surfaces from first-principles molecular dynamics
No full textA general approach to calculate the diabatic surfaces for electron-transfer reactions is presented, based on first-principles molecular dynamics of the active centers and their surrounding medium. The excitation energy corresponding to the transfer of an electron at any given ionic configuration (the Marcus energy gap) is accurately assessed within ground-state density-functional theory via a novel penalty functional for oxidation-reduction reactions that appropriately acts on the electronic degrees of freedom alone. The self-interaction error intrinsic to common exchange-correlation functionals is also corrected by the same penalty functional. The diabatic free-energy surfaces are then constructed from umbrella sampling on large ensembles of configurations. As a paradigmatic case study, the self-exchange reaction between ferrous and ferric ions in water is studied in detail.THEO
The influence of femoral head size following total hip replacement and hip resurfacing on hip biomechanics during walking, stair use and sit-to-stand
No full textDue to geometrical features, it is claimed that larger femoral heads in total hip replacement (THR) are superior in achieving normal biomechanics than smaller ones; and that hip resurfacing (RSF) is superior to THR. This has not been conclusively proven. Most studies have investigated level walking, which may not be demanding enough to highlight what could be small biomechanical differences between implants. Few biomechanical studies have compared more demanding tasks and not with patients with different femoral head sizes or RSF.
This thesis aimed to address these omissions by investigating level walking, stair descent and sit-to-stand (STS) biomechanics between three groups (32mm THR, 36mm THR and RSF). Twenty-six osteoarthritis patients were recruited and tested pre-operatively, then three and twelve months post-operatively. Demographic differences between groups were expected due to patient considerations for different implants, so a study was performed to determine whether level walking biomechanics alter progressively during the aging process with a group of 63 healthy participants. Three matched sub-groups were extracted from this group as controls.
There was no suggestion that gait deteriorates progressively with age. Hip reconstruction, irrespective of head size, can allow patients to return to the biomechanical levels of controls during level walking. Stair descent differences remained 12 months post-operatively in cadence (p=0.042) and peak hip power generated (p<0.001) compared to controls. The 32mm group exhibited vertical ground reaction force (vGRF) asymmetry pre-operatively (p<0.001) and 3 months post-operatively (p=0.013); and impulse asymmetry (p<0.001) pre-operatively during STS. The 36mm group exhibited impulse asymmetry (p=0.05)three months post-operatively.
This thesis is the first biomechanical analysis of stair descent and STS of two THR groups and a RSF group. It has demonstrated stair descent differences at 12 months post-operatively and overloading of the healthy limb in some THR patients. The latter could be problematic for the healthy limb
Pilot implementation and evaluation of the Sit-Stand e-Guide: an e-training program on the use of sit-stand workstations
No full textThe ‘Sit-Stand e-Guide’ e-training program, designed to promote appropriate use of sit-stand workstations (SSWs), was evaluated for usability, acceptability and impact on various outcomes among SSW users. Participants from a large municipal organisation (25% male; mean age 45 [SD = 10.6] years) completed questionnaires pre-training (T0, n = 57), immediately post-training (T1, n = 50), and four weeks (T2, n = 46: primary endpoint) and twelve months later (T3, n = 30). High usability, acceptability and usefulness scores were reported at T1. Median [IQR] knowledge (4.4/5 [0.9]) and confidence (4.6/5 [1.0]) significantly increased at T1 compared to baseline (2.8 [1.2]; 3.3 [1.4]) and maintained at T2 and T3. At T2, mean [SD] sitting time (5.3 [1.2] h/workday) and low back discomfort (2.4 [2.3]) significantly decreased compared to baseline (6.1 [1.3] h; 3.4 [2.5] discomfort), SSW usage increased (1.4 [1.4]–2.8 [1.7] transitions), with no significant changes in work performance. Some behavioural changes were sustained at T3. The Sit-Stand e-Guide was acceptable and effective; evaluation across diverse workplaces and workers is now needed
Car-Parrinello molecular dynamics in the DFT + U formalism: Structure and energetics of solvated ferrous and ferric ions
No full textWe implemented a rotationally-invariant Hubbard U extension to density-functional theory in the Car-Parrinello molecular dynamics framework. with the goal of bringing the accuracy of the DFT + U approach to finite-temperature simulations, especially for liquids or solids containing transition-metal ions. First, we studied the effects on the Hubbard U on the static equilibrium structure of the hexaaqua ferrous and ferric ions, and the inner-sphere reorganization energy for the elect ron-tran sfer reaction between aqueous ferrous and ferric ions. It is found that the reorganization energy is increased, mostly as a result of the Fe-O distance elongation in the hexa-aqua ferrous ion. Second, we performed a first-principles molecular dynamics study of the solvation structure of the two aqueous ferrous and ferric ions. The Hubbard term is found to change the Fe-O radial distribution function for the ferrous ion, while having a negligible effect on the aqueous ferric ion. Moreover, the frequencies of vibrations between Fe and oxygen atoms in the first-solvation shell are shown to be unaffected by the Hubbard corrections for both ferrous and ferric ions
COMP 127-Ab Initio density-functional theory approach to evaluating electronic couplings in transition-metal systems: Application to the hexa-aquo Fe2+/3+ redox couple
No full textEvaluation of Electronic Coupling in Transition-Metal Systems Using DFT: Application to the Hexa-Aquo Ferric-Ferrous Redox Couple
No full textWe present a density-functional theory (DFT) approach, with fractionally occupied orbitals, for studying the prototypical ferric-ferrous electron-transfer (ET) process in liquid water. We use a recently developed ab initio method to calculate the transfer integral (also named electronic-coupling or ET matrix element) between the solvated ions. The computed transferBelgium integral is combined with pRevious ab initio values of the reorganization energy, within the framework of Marcus' theory, to estimate the rate of the electron self-exchange reaction. The self-interaction correction incorporated (through an appropriate treatment of the electronic correlation effects) into a Hubbard U extension to the DFT scheme leads to a theoretical value of the ET rate relatively close to an experimental estimate from kinetic measurements. The use of fractional occupation numbers (FON) turned out to be crucial for achieving convergence in most self-consistent calculations because of the open-shell d-multiplet electronic structure of each iron ion and the near degeneracy of the redox groups involved. We provide a theoretical justification for the FON approach, which allows a description of the chemical potential and orbital relaxation, and possible extension to other transition-metal redox systems. Accordingly, the methodology developed in this paper, which rests on a suitable combination of Hubbard U correction and a FON approach to DFT, seems to offer a fruitful approach for the quantitative description of ET reactions in biochemical systems. © 2009 American Chemical Society
Saaz / Entw u. gez. v. F. Handke, Berge unter dessen Leitung v. A. Pohl ; Sit. u. Schrift gest. v. H. Herzberg, Berge v. H. Petters in Hildburghausen
No full textSAAZ / ENTW U. GEZ. V. F. HANDKE, BERGE UNTER DESSEN LEITUNG V. A. POHL ; SIT. U. SCHRIFT GEST. V. H. HERZBERG, BERGE V. H. PETTERS IN HILDBURGHAUSEN
G. D. Reymann's topographische Special-Karte von Central-Europa (-)
Saaz / Entw u. gez. v. F. Handke, Berge unter dessen Leitung v. A. Pohl ; Sit. u. Schrift gest. v. H. Herzberg, Berge v. H. Petters in Hildburghausen (186) ( -
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