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PubMed2006

Electromyographic and neuromuscular fatigue thresholds as concepts of fatigue.

The aim of this study was to investigate the concepts of electromyographic (EMG) threshold (EMGT) by integrated EMG (iEMG) signals and neuromuscular fatigue threshold (NMFT) concepts in trained male athletes. Nine competitive national-level male rowers (21.8 +/- 4.4 years; 186.2 +/- 4.6 cm; 79.6 +/- 8.4 kg) took part in this investigation. Subjects were asked to participate in the graded exercise test to volitional exhaustion and 500-, 1,000-, and 2,000-m all-out rowing ergometer tests on a rowing ergometer. During all tests, oxygen consumption parameters, average power, and iEMG of the musculus vastus lateralis were recorded. The second ventilatory threshold (248.9 +/- 26.67 W) and EMGT (258.89 +/- 27.13 W) were not significantly different but were significantly lower than the NMFT (302.25 +/- 45.10 W). During 1,000- and 2,000-m all-out distances, VO(2) increased during the first minute and then leveled on a plateau with a slight decrease at the end of the exercise. Vastus lateralis activity showed a slight increase during all distances that was accompanied by a remarkable increase towards the end of the distance. All measured threshold values were significantly correlated (r > 0.70; p < 0.05) to the rowing ergometer performance characteristics. It was concluded that EMGT is closely related to the aerobic-anaerobic transition phase, because NMFT represents the local fatigue accumulation in the muscle. NMFT indicates the performance capacity of the muscles; therefore, it helps coaches to better predict top athletes' performance.

Adult↗
PubMed2004

Fatigue and performance models: general background and commentary on the circadian alertness simulator for fatigue risk assessment in transportation.

Mathematical models of fatigue and performance are potentially powerful tools to predict the effects of duty-rest schedules in many situations. Most current models, including the Circadian Alertness Simulator (CAS), derive from the two-process theory of sleep regulation. In these models, performance and fatigue are determined by a homeostatic process that depends solely on sleep/wake history, and a circadian process, driven by the biological clock. These models assume: 1) performance capability recovers in an exponential manner during sleep; 2) the homeostatic and circadian processes are additive. Current evidence suggests that both assumptions require modification. An attractive feature of the CAS is that it computes alertness curves for individuals, based on individual sleep/wake histories and other data. However, statistical evaluation is usually based on group data, with few performance metrics. As in other models, there is no substantive theory to connect the alertness computation with specific cognitive or psychomotor functions.

Circadian Rhythm↗
PubMed2003

The effect of tryptophan deficiency in the brain on rat fatigue levels: a rat model of fatigue reduction.

The level of tryptophan and 5-hydroxyindoleacetic acid were measured in the brain (striatum) of rats on tryptophan-deficient diet and tryptophan-enriched diet. We measured concentrations of tryptophan and 5-hydroxyindoleacetic acid in striatum by using microdialysis and HPLC methods. The extracellular level of tryptophan and 5-hydroxyindoleacetic acid concentration in the striatum of a tryptophan-reduced rats was decreased by about 50% compared with a tryptophan-enriched diet. In the tryptophan-reduced condition, the rats an increased the running time of more than 100 min, compared with those on a tryptophan-enriched diet. These results suggest the tryptophan and 5-hydroxytryptamine in the central nervous system are involved in fatigue.

Animals↗
PubMed1998

Chronic fatigue syndrome differs from fibromyalgia. No evidence for elevated substance P levels in cerebrospinal fluid of patients with chronic fatigue syndrome.

Levels of substance P were determined in the cerebrospinal fluid (CSF) in 15 patients with chronic fatigue syndrome (CFS). All values were within normal range. This is in contrast to fibromyalgia (FM). The majority of patients with FM have increased substance P values in the CSF. The results support the notion that FM and CFS are different disorders in spite of overlapping symptomatology.

Adult↗
PubMed2002

Psychosocial characteristics and immunological functions in patients with postinfectious chronic fatigue syndrome and noninfectious chronic fatigue syndrome.

Differences between patients with postinfectious chronic fatigue syndrome (CFS, n = 16) and noninfectious CFS (n = 20) were clarified. The noninfectious CFS group had problems in family and developmental history, and had chronic stresses. Members of the postinfectious CFS group were social extroverts while those in the noninfectious CFS group was neurotic and introspective. Natural killer cell activity was suppressed in both groups. These findings suggest that the postinfectious CFS group and the noninfectious CFS group differed in their pathogenesis until the onset of CFS. The latter group should be considered as a variant of psychiatric disorder and treated accordingly.

Adult↗
PubMed2002

The prognosis after multidisciplinary treatment for patients with postinfectious chronic fatigue syndrome and noninfectious chronic fatigue syndrome.

The prognosis after multidisciplinary treatment for patients with postinfectious chronic fatigue syndrome (CFS, n = 9) and noninfectious CFS (n = 9) was clarified. After treatment, natural killer (NK) cell activity increased in the postinfectious CFS group but did not recover to within normal range in the noninfectious CFS group. In the postinfectious CFS group, physical and mental symptoms improved, and 8 patients returned to work. In the noninfectious CFS group, symptoms did not improve, and only 3 patients returned to work. The prognosis of postinfectious CFS group was better than that of noninfectious CFS group. Classification of CFS patients into postinfectious and noninfectious groups is useful for choosing the appropriate treatment in order to obtain better prognosis.

Adult↗
PubMed2002

High prevalence of Mycoplasma infections among European chronic fatigue syndrome patients. Examination of four Mycoplasma species in blood of chronic fatigue syndrome patients.

Prevalence of Mycoplasma species infections in chronic fatigue syndrome (CFS) has been extensively reported in the scientific literature. However, all previous reports highlighted the presence of Mycoplasmas in American patients. In this prospective study, the presence of Mycoplasma fermentans, M. penetrans, M. pneumoniae and M. hominis in the blood of 261 European CFS patients and 36 healthy volunteers was examined using forensic polymerase chain reaction. One hundred and seventy-nine (68.6%) patients were infected by at least one species of Mycoplasma, compared to two out of 36 (5.6%) in the control sample (P<0.001). Among Mycoplasma-infected patients, M. hominis was the most frequently observed infection (n=96; 36.8% of the overall sample), followed by M. pneumoniae and M. fermentans infections (equal frequencies; n=67; 25.7%). M. penetrans infections were not found. Multiple mycoplasmal infections were detected in 45 patients (17.2%). Compared to American CFS patients (M. pneumoniae>M. hominis>M. penetrans), a slightly different pattern of mycoplasmal infections was found in European CFS patients (M. hominis>M. pneumoniae, M. fermentansz.Gt;M. penetrans).

Adolescent↗
PubMed2001

[International consensus meeting on fatigue and the risk of traffic accidents. The significance of fatigue for transportation safety is underestimated].

Recently there has been a sizeable increase in research on fatigue and accidents in transportation. Therefore a meeting was convened last year to discuss prevalence, mechanisms and countermeasures, with the intention to produce an international consensus document. It was concluded that official statistics strongly underestimate prevalence, and that a reasonable estimate, based on research, lies between 10 and 20% for accidents on the road, in the air and at sea. The main causes are disturbed sleep and work at the circadian low, caused by night work, morning work, sleep/wake disorders (including sleep apnea) or social obstacles to sleep. Suggested countermeasures include information/education of the public and of transportation companies, as well as enforcement of existing work hour regulation. Additional countermeasures include strategic use of napping and caffeine, as well as implementation of rumble strips and--possibly--electronic devices for drowsiness detection.

Accidents, Occupational↗
PubMed1995

Muscle fatigue in old animals. Unique aspects of fatigue in elderly humans.

Muscle atrophy, weakness, injury, and fatigue are inevitable and immutable concomitants of old age. Atrophy results from a gradual process of fiber denervation with loss of some fibers and atrophy of others. Fast fibers show more denervation and atrophy than slow fibers. Some fast fibers are reinnervated by axonal sprouting from slow fibers resulting in remodeling of motor units. With aging, the decreases in strength and power are greater than expected from the loss in muscle mass. Contraction-induced injury is proposed as a mechanism of the fast fiber denervation. With atrophy and weakness, human beings show a dramatic decrease in endurance and increase in fatigability with aging, but strength and endurance training slows the process.

Aging↗
PubMed1997

Material optimisation of the femoral component of a hip prosthesis based on the fatigue notch fatigue approach.

Previous studies have optimised the shape of a cemented stainless steel stem in order to minimise the fatigue notch factor Kf in the cement whilst at the same time maximising Kt in the proximal medial bone to prevent bone resorption [1]. The present study firstly describes the effect of changes in the modulus of elasticity of the stem material for both the original Charnley stem and the optimised shape on Kf as predicted by a 2D finite element (FE) model of the implanted prosthesis. The paper further describes a method for parametric optimisation to determine the best material properties of a layered composite femoral stem consisting of a core material (stainless steel) and an outer layer of a different material, the elastic modulus of which is used as a design variable. The overall objective of the optimisation was to maximise Kf in the proximal bone whilst at the same time constraining Kf at all cement interfaces to be no greater than its initial value. The results of the first study suggest that Young's moduli of about 145 and 210 GPa are optimal for the monolithic Charnley and optimised stems, respectively. A composite prosthesis with a layer of modulus 31 GPa added to the optimised stainless steel stem in the proximal region only was found to significantly increase the stresses in the proximal bone and reduce Kf in the cement whilst retaining the advantages of an outer stem profile very similar to that of the original Charnley prosthesis.

Bone Cements↗