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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Changes in force and stiffness were recorded simultaneously during 1 s isometric (fixed ends) tetani of single fibres isolated from the anterior tibialis muscle of Rana temporaria (temperature 1-3 degrees C; sarcomere length, 2.10 micron). Stiffness was measured as the change in force that occurred in response to a 4 kHz sinusoidal length oscillation of the fibre. Some experiments were performed in which stiffness was determined from a fast (0.2 ms) length step that was applied to a 'tendon-free' segment of the muscle fibre during the tetanus plateau. 2. A moderate degree of fatigue was produced by decreasing the time between tetani from 300 s (control) to 15 s. By this treatment the maximum tetanic force (Ftet) was reversibly reduced to 70-75% of the control value. Maximum tetanic stiffness (Stet) was related to Ftet according to the following regression (both variables expressed as percentage of their control values): Stet = 0.369 Ftet + 62.91 (correlation coefficient, 0.95; P less than 0.001). A 25% decrease in isometric force during fatigue was thus associated with merely 9% reduction of fibre stiffness. 3. Whereas the rate of rise of force during tetanus was markedly reduced by fatiguing stimulation, the rate of rise of stiffness was only slightly affected. 4. Intracellular acidification (produced by raised extracellular CO2 concentration) largely reproduced the contractile changes observed during fatigue. However, for a given decrease in tetanic force there was a smaller reduction in fibre stiffness during acidosis than during fatigue. 5. Caffeine (0.5 mM) added to the fibre after development of fatigue and intracellular acidosis greatly potentiated the isometric twitch but did not affect maximum tetanic force. This finding provides evidence that the contractile system was fully activated during the tetanus plateau both in the fatigued state and during acidosis. 6. The results suggest that the decrease in contractile strength after frequent tetanization (intervals between tetani, 15 s) is attributable to altered kinetics of cross-bridge function leading to reduced number of active cross-bridges and, most significantly, to reduced force output of the individual bridge. The possible role of increased intracellular H+ concentration in the development of muscle fatigue is discussed.
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PMID:Changes in force and stiffness induced by fatigue and intracellular acidification in frog muscle fibres. 239 50

Posterior arthrodesis is a preferred treatment for posttraumatic instability of the cervical spine. While most surgical constructs yield predictably high rates of fusion in satisfactory alignment, certain injury patterns involving fractures of the lamina or spinous processes may preclude rigid immobilization by simple wiring techniques. Plate fixation of the posterolateral masses has been advocated for such injuries. The purpose of this biomechanical study was to test the relative stiffness provided by different posterior fusion constructs, including lateral mass plating. All testing was performed on fresh, unembalmed cadaveric spines divided into two vertebral segment units. Muscular tissue was stripped from the specimens, but all discal and ligamentous structures were preserved. Four different posterior fixation constructs were tested. These included 1) Rogers interspinous wiring, 2) Halifax laminar clamps, 3) bilateral 1/3 tubular plates on the lateral masses, using unicortical screws, and 4) bilateral 1/3 tubular plates on the lateral masses, using bicortical screws. Stiffness measurements were taken in both flexion and extension on all specimens. Yield strength and fatigue strength of the spines were not measured. It was found that 1/3 tubular plates secured with bicortical screws to the lateral masses provided the highest mean stiffness. Less stiffness was found in spines stabilized by Halifax clamps, interspinous wiring, and plates secured with unicortical screws. There was, however, no statistically significant difference in stiffness provided by any of these four implants. It was concluded that there is no advantage in plate fixation over standard fusion constructs in augmenting the stiffness of posterior fixation of the cervical spine.
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PMID:Posterior plating of the cervical spine. A biomechanical comparison of different posterior fusion techniques. 319 91

The clinical symptoms of 55 patients with primary fibromyalgia (PF) were studied and compared with 30 patients with rheumatoid arthritis (RA). The PF patients expressed a more intense feeling of illness than did the RA patients. Stiffness occurred just as often in PF as in RA. Trigger points occurred less frequently in RA patients. Muscular fatigue appeared to be one of the most disabling symptoms in PF. Neurophysiological studies indicated that the fatigue was at least partly of central origin. Ischemic forearm exercise test gave no evidence of impaired glycogenolysis. Laboratory investigation revealed normal 25-hydroxyvitamin D, cobalamin, folate, estrogen, testosterone, and myoglobin in the PF patients.
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PMID:Primary fibromyalgia. A clinical and laboratory study of 55 patients. 346 25

1. Intact frog single fibres were investigated under control conditions (1 s tetanus every 2, 3 or 5 min) and during moderate fatigue (interval between tetani 15 or 30 s). 2. Fatigue reduced isometric force (P0) by 25.8 +/- 1.6% (S.E.M.; n = 13) and depressed the maximum velocity of shortening (Vmax) by 10.2 +/- 2.2% (n = 13). The force-velocity relation became less curved, a/P0* (see Methods) being increased by 29.5 +/- 8.8% (n = 13). Thus, power was less affected than isometric force or Vmax. 3. The velocity of unloaded shortening (V0), from slack test measurements, was reduced proportionally more than Vmax during fatigue. Under control conditions V0 was larger than Vmax, but during fatigue their values were not significantly different. 4. Stiffness during shortening was reduced during fatigue indicating fewer attached cross-bridges in fatigue. Force was reduced more than stiffness indicating that, on average, there is less force per attached cross-bridge. 5. The force-lengthening velocity relation showed that the ability to resist forces greater than isometric was well preserved in fatigue. 6. Compared with fatigue, intracellular acidification with CO2 produced a smaller reduction in isometric force. However, reduction in Vmax was not significantly different from that in fatigue. These results are consistent with both inorganic phosphate and H+ increasing in fatigue, but only H+ increasing during acidification, and isometric force being reduced by both, Vmax being sensitive only to H+.
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PMID:Force-velocity relation for frog muscle fibres: effects of moderate fatigue and of intracellular acidification. 800 30

The injection of bone cement by minimally invasive techniques for the treatment of vertebral body fractures or for stabilization of an osteoporotic vertebral body is regarded as promising in spinal surgery. The purpose of this study was to develop a novel injectable bioactive bone cement to address such concerns. The cement was composed mainly of strontium-containing hydroxyapatite (Sr-HA) filler and Bisphenol A Diglycidylether Dimethacrylate (D-GMA) resin. The Sr-HA filler was prepared by precipitation and calcination, then analyzed with Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns. Samples of strontium-containing hydroxyapatite cement (SrHAC) were formed by a combination of powder filler and resin matrix, with the setting time and peak temperature recorded. Cell relative growth rate (RGR), Tetrazolium bromide (MTT), and haemolysis tests were used to detect initial in vitro biocompatibility of the new cement. In vitro spinal biomechanical testing and morphological observation after bone cement injection were performed on pig spines. Results indicate that the setting time and peak temperature of the cement was 15 min and 55 degrees C, respectively. Cytotoxicity of the cement was class 1 (no cytotoxicity) and haemolysis was 1% (no haemolysis). Stiffness after cement injection and fatigue loading were 112% and 95% of the intact bone, respectively, which is similar to that of natural bone. Radiopacity of SrHAC allowed easy radiographic imaging. The use of SrHAC cement is, thus, promising in spinal surgery.
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PMID:A novel injectable bioactive bone cement for spinal surgery: a developmental and preclinical study. 1090 88

Muscle fatigue reflects alterations of both activation and cross-bridge function, which will have markedly different affects on steady-state vs. dynamic performance. Such differences offer insight into the specific origins of fatigue, its mechanical manifestation, and its consequences for animal movement. These were inferred using dynamic contractions (twitches and cyclic work as might occur during locomotion) and steady-state performance with maximal, sustained activation (tetani, stiffness, and isokinetic force) during fatigue and then recovery of frog (Rana pipiens) anterior tibialis muscle. Stiffness remained unaltered during early fatigue of force and then declined only 25% as force dropped 50%, suggesting a decline with fatigue in first the force-generating ability and then the number of cross bridges. The relationship between stiffness and force was different during fatigue and recovery; thus the number of cross bridges and force per cross bridge are not intimately linked. Twitch duration increased with fatigue and then recovered, with trajectories that were remarkably similar to and linear with changes in tetanic force, perhaps belying a common mechanism. Twitch force increased and then returned to resting levels during fatigue, reflecting a slowing of activation kinetics and a decline in cross-bridge number and force. Net cyclic work fatigued to the degree of becoming negative when tetanic force had declined only 15%. Steady-state isokinetic force (i.e., shortening work) declined by 75%, while cyclic shortening work declined only 30%. Slowed activation kinetics were again responsible, augmenting cyclic shortening work but greatly augmenting lengthening work (reducing net work). Steady-state measures can thus seriously mislead regarding muscle performance in an animal during fatigue.
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PMID:Fatigue and recovery of dynamic and steady-state performance in frog skeletal muscle. 1472 26

Adhesive/abrasive wear in ultra-high molecular weight polyethylene (UHMWPE) has been minimized by radiation cross-linking. Irradiation is typically followed by melting to eliminate residual free radicals that cause oxidative embrittlement. Irradiation and subsequent melting reduce the strength and fatigue resistance of the polymer. We determined the radiation dose dependence and decoupled the effects of post-irradiation melting on the crystallinity, mechanical properties and fatigue crack propagation resistance of room temperature irradiated UHMWPE from those of irradiation alone. Stiffness and yield strength, were largely not affected by increasing radiation dose but were affected by changes in crystallinity, whereas plastic properties, ultimate tensile strength and elongation at break, were dominated at different radiation dose ranges by changes in radiation dose or crystallinity. Fatigue crack propagation resistance was shown to decrease with increase in radiation dose and with decrease in crystalline content. Morphology of fracture surfaces revealed loss of ductility with increase in radiation dose and more detrimental effects on ductility at lower radiation doses after post-irradiation melting.
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PMID:Mechanisms of decrease in fatigue crack propagation resistance in irradiated and melted UHMWPE. 1610 82

Metabolic cost of submaximal running at constant speed is influenced by various factors including fatigue and kinematic characteristics. Metabolic costs typically drift upwards during extended running while stride characteristics often shift away from initial. When non-fatigued, experienced runners naturally optimize stride frequency in a manner that minimizes oxygen uptake. An initial objective was to determine whether runners demonstrate a similar self-optimizing capability when fatigued where stride characteristics have perhaps shifted away from the initial state. A secondary objective involved measurement of vertical and leg stiffness characteristics as a potential explanation for frequency changes with fatigue. We hypothesized that runners decrease stride frequency and stiffness with fatigue while optimizing these characteristics to minimize metabolic cost. Sixteen experienced runners completed a near maximal effort 1-h treadmill run at a constant speed. Preferred and optimal stride frequencies (PSF and OSF) were measured near the beginning and end of the hour run using frequencies +/-4 and +/-8% around PSF. From vertical force data recorded throughout the run, leg and vertical stiffness were determined. As expected, oxygen uptake significantly increased during the run from 45.9 to 47.4 ml kg(-1) min(-1) (P = 0.004). There was no difference between preferred and optimal stride frequencies at the beginning or the end of running (P = 0.978), however both PSF and OSF significantly decreased from 1.45 to 1.43 Hz (P = 0.026). All runners self-optimized stride frequency at the beginning and end of one-hour of running despite changes of optimal stride frequency. Stiffness and stride frequency changes were subject specific with some runners exhibiting little to no change. No clear relationship of frequency or stiffness changes to economy was found.
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PMID:Preferred and optimal stride frequency, stiffness and economy: changes with fatigue during a 1-h high-intensity run. 1760 39

Purpose. The aims of this study were to describe the symptoms experienced by patients in the first year following treatment for lower extremity sarcoma by limb conservation and to describe the relationship between symptoms and physical disability.Subjects. Eighty consecutive patients treated for primary bone or soft tissue sarcoma (STS) of the lower limb who were treated with limb preservation surgery.Methods. Subjects were evaluated by questionnaire at 6 weeks, and 3, 6, and 12 months post surgery. They identified whether they experienced any of the following symptoms: pain, stiffness, fatigue, weakness, limited range of motion, or swelling.The Toronto Extremity Salvage Score (TESS), a measure of physical disability, was also completed. Frequency of symptoms over time was calculated and change was evaluated using the Cochrane test. The relationship of symptoms to disability was analyzed with regression methods.Results. The mean age was 43.0, SD=20.4 with a gender ratio of 1:1. There were 38 bone tumours and 42 STS.The most frequently reported symptoms were: stiffness 48 (60%), weakness 41 (51%), fatigue 26 (33%), and pain 25 (31%) at 6 weeks. Stiffness and fatigue decreased and plateaued by 3 months. Complaints of weakness and pain continued to decrease over time. At 6 weeks, pain, stiffness, weakness and limited motion predicted disability in both univariate and multivariate analyses. At 12 months, pain, stiffness, fatigue, weakness and limited motion were significant predictors of the TESS in univariate analysis with only pain, stiffness and limited motion significant predictors in the multivariate model.Discussion. Pain, stiffness, fatigue, weakness and limited motion are common symptoms with stiffness and weakness decreasing significantly over time. The symptoms predictive of disability differ between the acute and late phases of recovery.
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PMID:Symptoms and their Relationship to Disability Following Treatment for Lower Extremity Tumours. 1852 Dec 66

The mechanical and microstructural bases of tendon fatigue, by which damage accumulates and contributes to degradation, are poorly understood. To investigate the tendon fatigue process, rat flexor digitorum longus tendons were cyclically loaded (1-16 N) until reaching one of three levels of fatigue damage, defined as peak clamp-to-clamp strain magnitudes representing key intervals in the fatigue life: i) Low (6.0%-7.0%); ii) Moderate (8.5%-9.5%); and iii) High (11.0%-12.0%). Stiffness, hysteresis, and clamp-to-clamp strain were assessed diagnostically (by cyclic loading at 1-8 N) before and after fatigue loading and following an unloaded recovery period to identify mechanical parameters as measures of damage. Results showed that tendon clamp-to-clamp strain increased from pre- to post-fatigue loading significantly and progressively with the fatigue damage level (p <or= 0.010). In contrast, changes in both stiffness and hysteresis were significant only at the High fatigue level (p <or= 0.043). Correlative microstructural analyses showed that Low level of fatigue was characterized by isolated, transverse patterns of kinked fiber deformations. At higher fatigue levels, tendons exhibited fiber dissociation and localized ruptures of the fibers. Histomorphometric analysis showed that damage area fraction increased significantly with fatigue level (p <or= 0.048). The current findings characterized the sequential, microstructural events that underlie the tendon fatigue process and indicate that tendon deformation can be used to accurately assess the progression of damage accumulation in tendons.
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PMID:Subrupture tendon fatigue damage. 1868 81


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