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Force Levels (force + level)
Selected AbstractsTask-related electromyographic spectral changes in the human jaw musclesJOURNAL OF ORAL REHABILITATION, Issue 9 2002M. FARELLA The masticatory muscles differ in their fibre type composition. It can therefore be expected that their electromyographic (EMG) power spectra will differ during the performance of different bite force tasks. In the present study surface EMG activity was picked up from the masseter, and anterior and posterior temporalis muscles of nine adult subjects. Direction and magnitude of bite force were recorded using a three-component force transducer. Bite forces were exerted in five different directions: vertical, forward, backward, to the right and to the left of the subject. Non-vertical forces were kept at an angle of 15° from the vertical. Force levels of 25, 50, 100 and 200 N were exerted in each of the investigated directions. Data collected were analysed by means of a regression model for repeated measurements. It appeared that the mean power frequency (MPF) values of the posterior temporalis were significantly lower (P < 0·01) than those of the masseter and anterior temporalis. The MPF values of the masseter muscles decreased with an increase of bite force magnitude (P < 0·001) whereas the MPF values of the anterior and posterior temporalis did not change significantly (P > 0·05). The MPF values were significantly influenced by the direction of bite force (P < 0·01). The observed changes of MPF are possibly related to the recruitment of different fibre types and support the concept that the masticatory muscles behave heterogeneously. [source] Gated dynamic 31P MRS shows reduced contractile phosphocreatine breakdown in mice deficient in cytosolic creatine kinase and adenylate kinaseNMR IN BIOMEDICINE, Issue 5 2009Hermien E. Kan Abstract We developed a new dedicated measurement protocol for dynamic 31P MRS analysis in contracting calf muscles of the mouse, using minimally invasive assessment of the contractile force combined with the acquisition of spectroscopic data gated to muscle contraction and determination of phosphocreatine (PCr) recovery rate and ATP contractile cost. This protocol was applied in a comparative study of six wild type (WT) mice and six mice deficient in cytosolic creatine kinase and adenylate kinase isoform 1 (MAK,/, mice) using 70 repeated tetanic contractions at two contractions per minute. Force levels during single contractions, and metabolite levels and tissue pH during resting conditions were similar in muscles of MAK,/, and WT mice. Strikingly, muscle relaxation after contraction was significantly delayed in MAK,/, mice, but during repeated contractions, the decrease in the force was similar in both mouse types. Gated data acquisition showed a negligible PCr breakdown in MAK,/, immediately after contraction, without a concomitant decrease in ATP or tissue pH. This protocol enabled the determination of rapid PCr changes that would otherwise go unnoticed due to intrinsic low signal-to-noise ratio (SNR) in mouse skeletal muscles combined with an assessment of the PCr recovery rate. Our results suggest that MAK,/, mice use alternative energy sources to maintain force during repeated contractions when PCr breakdown is reduced. Furthermore, the absence of large increases in adenosine diphosphate (ADP) or differences in force compared to WT mice in our low-intensity protocol indicate that creatine kinase (CK) and adenylate kinase (AK) are especially important in facilitating energy metabolism during very high energy demands. Copyright © 2009 John Wiley & Sons, Ltd. [source] Task-related electromyographic spectral changes in the human masseter and temporalis musclesEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 1 2002Mauro Farella The masticatory muscles differ in their fiber type composition. It can therefore be expected that their electromyographic (EMG) power spectra will differ during the performance of different bite force tasks. In the present study, surface EMG activity was picked up from the masseter and from the anterior and posterior temporalis muscles of nine adult subjects. At a bite force level as low as 25 N, the mean power frequency (MPF) values of the posterior temporalis were significantly lower than those of the masseter and anterior temporalis. The MPF values of the masseter muscles decreased with an increase of bite force magnitude, whereas the MPF values of the anterior and posterior temporalis did not change significantly. The MPF values were significantly influenced by the direction of bite force. The observed changes of MPF are possibly related to the recruitment of different fiber types, and support the concept that the masticatory muscles behave heterogeneously. [source] Identification of the maximum acceptable frequencies of upper-extremity motions in the sagittal planeHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 3 2009Ochae Kwon The present study examined the maximum acceptable frequencies (MAFs; motions/min) of upper-extremity motions in the sagittal plane at different forces. A dumbbell of 9.8 or 39.2 N was rotated by the arm about the shoulder, the forearm about the elbow, and the hand about the wrist; a dynamometer was pressed to 2.45 or 9.8 N by the index finger. Seventeen right-handed Korean men in their 20s without any history of musculoskeletal disorders received 1 hour of individual training and conducted each upper-extremity task for 30 minutes a day, assuming they were on an incentive basis. The participants determined their MAFs for 8 hours of work by the self-adjustment method, and work pulse (change in heart rate; beats per minute [bpm]) and rating of perceived exertion (RPE) were measured. For a limited set of conditions, the reproducibility of the MAF experimental protocol was found satisfactory (r = 0.97; interclass correlation coefficient > 0.95). The average MAFs of arm, forearm, hand, and index finger motions were 24, 45, 56, and 128 at their low force level and 9, 20, 30, and 66 at their high force level. The average work pulses of arm, forearm, and hand motions were 3.0, 2.1, and 1.5 times that of index finger motion (4.2 bpm at their low force level and 5.7 bpm at their high force level). The maximum average RPEs at the upper-extremity regions ranged from 2.1 (weak) to 3.1 (moderate) in Borg's CR-10 scale. © 2009 Wiley Periodicals, Inc. [source] MECHANICAL CHARACTERIZATION OF SHREDDED WHEATJOURNAL OF TEXTURE STUDIES, Issue 5 2008J.B. LAURINDO ABSTRACT The purpose of the study was to evaluate a methodology for mechanical characterization of brittle foods with strong anisotropy. Spoon-sized pieces of three commercial brands of dry shredded wheat were chosen for the demonstration. They were compressed along their three principal axes, individually and grouped in the same orientation. The force-displacement curves in the three directions were all irregular and irreproducible but had discernible features characteristic of the specimen's orientation. When tested as constrained groups, these features could change, depending on the compression direction, reflecting on the contribution of the broken structure's remnants to the specimen's mechanical resistance. The assemblies' force-displacement curves were all smoother than those of the individual particles, a result of the "averaging effect." The overall force level could not be predicted from the number of pieces because of differences in the specimens' post-failure response to added deformation. The jaggedness of the normalized (dimensionless) force oscillations record was quantified in terms of an apparent Kolmogorov (fractal) dimension, determined with the box counting algorithm. Its value strongly depended on the smoothing model's goodness fit if the fit was too close, but not if it only captured the general shape of the force-displacement curve. PRACTICAL APPLICATIONS Despite the irregular and irreproducible mechanical signature of shredded wheat and the dependence on the specimens' orientation, it is still possible to characterize the products' mechanical properties in a way that distinguishes between their overall strength and brittleness. The described method could help to quantify textural differences between these and other brittle food products, and probably identify the conditions under which crunchiness would be maintained or lost. [source] Police Pay and Bargaining in the UK, 1978,2000BRITISH JOURNAL OF INDUSTRIAL RELATIONS, Issue 1 2003Laurie Hunter Police pay and conditions in the UK are governed by a unique mechanism, the Police Negotiating Board. This paper reviews the circumstances in which it was set up and examines the outcomes, relative to other public service workers, over the first twenty years of its operation. Recent developments highlight the role of ministerial intervention and raise questions about the relationship between the PNB negotiating system and working practice at police force level. [source] Spectral analysis and design approach for high force-to-volume extrusion damper-based structural energy dissipationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2008Geoffrey W. Rodgers Abstract High force-to-volume extrusion damping devices can offer significant energy dissipation directly in structural connections and significantly reduce seismic response. Realistic force levels up to 400,kN have been obtained experimentally validating this overall concept. This paper develops spectral-based design equations for their application. Response spectra analysis for multiple, probabilistically scaled earthquake suites are used to delineate the response reductions due to added extrusion damping. Representative statistics and damping reduction factors are utilized to characterize the modified response in a form suitable for current performance-based design methods. Multiple equation regression analysis is used to characterize reduction factors in the constant acceleration, constant velocity, and constant displacement regions of the response spectra. With peak device forces of 10% of structural weight, peak damping reduction factors in the constant displacement region of the spectra are approximately 6.5,×, 4.0,×, and 2.8,× for the low, medium, and high suites, respectively. At T,=,1,s, these values are approximately 3.6,×, 1.8,×, and 1.4,×, respectively. The maximum systematic bias introduced by using empirical equations to approximate damping reduction factors in design analyses is within the range of +10 to ,20%. The seismic demand spectrum approach is shown to be conservative across a majority of the spectrum, except for large added damping between T,=,0.8 and 3.5,s, where it slightly underestimates the demand up to a maximum of approximately 10%. Overall, the analysis shows that these devices have significant potential to reduce seismic response and damage at validated prototype device force levels. Copyright © 2007 John Wiley & Sons, Ltd. [source] Seismic performance evaluation of steel arch bridges against major earthquakes.EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2004Part 1: dynamic analysis approach Abstract In this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three-dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper-deck steel arch bridge having a reinforced concrete (RC) deck, steel I-section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken-Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time-history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effects of Aging on Hand FunctionJOURNAL OF AMERICAN GERIATRICS SOCIETY, Issue 11 2001Vinoth K. Ranganathan MSE OBJECTIVES: The purpose of this study was to quantify age-induced changes in handgrip and finger-pinch strength, ability to maintain a steady submaximal finger pinch force and pinch posture, speed in relocating small objects with finger grip, and ability to discriminate two identical mechanical stimuli applied to the finger tip. DESIGN: A cross-sectional study. SETTINGS: Greater Cleveland area of Ohio. PARTICIPANTS: Healthy, independent, young (n = 27, range 20,35 years) and older (n = 28, range 65,79 years) subjects. MEASUREMENTS: Handgrip strength, maximum pinch force (MPF), ability to maintain a steady pinch force at three relative force levels (5%, 10%, and 20% MPF) and three absolute force levels (2.5 Newtons (N), 4 N, and 8 N), ability to maintain a precision pinch posture, speed in relocating pegs from a nearby location onto the pegboard, and the shortest distance for discriminating two stimuli were measured in both young and older groups. RESULTS: Compared with young subjects, the older group's handgrip force was 30% weaker (P < .001), MPF was 26% lower (P < .05), and ability to maintain steady submaximal pinch force and a precision pinch posture was significantly less (P < .05). The time taken to relocate the pegs and the distance needed to discriminate two identical stimuli increased significantly with age (P < .01). The decrease in the ability to maintain steady submaximal pinch force was more pronounced in women than men. CONCLUSION: Aging has a degenerative effect on hand function, including declines in hand and finger strength and ability to control submaximal pinch force and maintain a steady precision pinch posture, manual speed, and hand sensation. [source] Sensory-motor function of human periodontal mechanoreceptors,JOURNAL OF ORAL REHABILITATION, Issue 4 2006M. TRULSSON summary, Natural teeth are equipped with periodontal mechanoreceptors that signal information about tooth loads. In the present review, the basic force-encoding properties of human periodontal receptors will be presented along with a discussion about their likely functional role in the control of human mastication. Microneurographic recordings from single nerve fibres reveal that human periodontal receptors adapt slowly to maintained tooth loads. Most receptors are broadly tuned to the direction of force application, and about half respond to forces applied to more than one tooth. Populations of periodontal receptors, nevertheless, reliably encode information about both the teeth stimulated, and the direction of forces applied to the individual teeth. Information about the magnitude of tooth loads is made available in the mean firing rate response of periodontal receptors. Most receptors exhibit a markedly curved relationship between discharge rate and force amplitude, featuring the highest sensitivity to changes in tooth load at very low force levels (below 1 N for anterior teeth and 4 N for posterior teeth). Thus, periodontal receptors efficiently encode tooth load when subjects contact and gently manipulate food using the teeth. It is demonstrated that signals from periodontal receptors are used in the fine motor control of the jaw and it is clear from studies of various patient groups (e.g. patients with dental implants) that important sensory-motor functions are lost or impaired when these receptors are removed during the extraction of teeth. [source] Titanium-niobium, a new finishing wire alloyORTHODONTICS & CRANIOFACIAL RESEARCH, Issue 1 2000Michel Dalstra The mechanical properties of the newly introduced titanium-niobium finishing wires were investigated. Both in bending and torsional loading mode, the stiffness, yield point, post-yield behavior, and springback of titanium-niobium wires were experimentally determined and compared to those of equally sized stainless steel wires. The experimentally obtained values were also validated with theoretical values from engineering formulas of cantilever deformations. The ratios for these parameters for the two materials proved to be different in bending and torsion. The stiffness of titanium-niobium in bending is roughly half of that of stainless steel, whereas in torsion it is roughly one-third. These characteristics enable the clinician to use titanium-niobium for creative bends without the excessive force levels of steel wires. The springback of titanium-niobium in bending is 14% lower than that of steel, whereas in torsion it is about the same or even slightly higher than that of steel, thus making it possible to utilize the wire for even major third-order corrections. Finally, the weldability of titanium-niobium wires was found to be good, so it is possible to weld wires of different dimensions together for the generation of differentiated force systems. [source] | |||||||||||||