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PubMed1978

A second study of tensile fatigue properties of human articular cartilage.

The tensile fatigue properties of the collagen fibre meshwork in normal human articular cartilage were measured by subjecting isolated specimens of post-mortem femoral head cartilage to cyclic tensile stress. The results of the study showed (1) that the collagen fibre meshwork is fatigue prone and (2) that its fatigue strength decreases rapidly with age. Extrapolation of the data to physiologically possible stress levels suggests that tensile fatigue failure of the collagen meshwork could occur in life.

Adolescent↗

PubMed1979

Fatigue - corrosion of endoprosthesis titanium alloys.

Commercial total hip prostheses often show certain metallurgical faults (porosities, coarse grains, growth dendrites, carbide networks). In order to investigate more accurately the role played by these different parameters in prostheses failure we performed a large number of systematic corrosion, fatigue and fatigue - corrosion tests on these materials and on commercial total hip prostheses. Ultimate strengthes seem to be reached for cast cobalt alloys, whereas titanium alloys, such as Ta 6 V, present very high fatigue limit under corrosion. Thus, rotative bending fatigue - corrosion tests in biological environment provide values about 50 DaN/mm2. This value, is nevertheless appreciably higher than those obtained with stellites and stainless steel. Titanium alloys, because of their mechanical performances, their weak Young's modulus (11000 DaN/mm2) and their relative lightness (4.5. g/cm3), which are associated with a good biocompatibility, seem very promising for permanent implants realisation.

Alloys↗

PubMed1978

Fatigue curves of isokinetic contractions.

Sixteen men and 16 women volunteer college students were tested for elbow flexion fatigue curve production on the Orthotron, an isokinetic testing device. Maximal voluntary contractions were obtained repeatedly, each contraction taking approximately 2 seconds to complete, with minimal (500 msec) intertrial rest, to exhaustion. To provide a basis for plotting the isokinetic fatigue curve, the degradation of torque values from initial to final contractions, was expressed as percentage of contraction time. Results obtained following statistical analysis of the data indicated that the isokinetic fatigue curve is: (1) curvilinear; (2) independent of sex differences; and (3) a function of initial strength. Moreover, it was found that the use of 50% of initial strength to denote fatigue in repetitive rhythmic isokinetic work has merit as a conservative estimate.

Adolescent↗

PubMed1978

Ergonomics. Reducing mental and physical fatigue in the dental operatory.

The work output and the mental and physical fatigue generated by a dental procedure is affected by the length and type of operation, physical facilities, the amount of cooperation given by the patient, operating techniques, and the effective teamwork and rapport of the operatory dental team. Fatigue is also generated by stresses that arise outside of the office and which, when superimposed over the normal operating stresses of the office, can have a cumulative effect of decreasing output and increasing mental and physical fatigue for the dentist, the assistant, and the patient. Probably the three most important means to compensate for both routine and nonroutine physical and mental stresses of any type or origin are: (1) learn to cope with or resolve the origin of the stress; (2) develop a pattern of healthy living; (3) cultivate job satisfaction.

Dental Assistants↗

PubMed1975

[Physical and mental fatigue of probable hyperuricemia origin].

A blood uric acid analysis has been effected on 193 Iranians of the intellectual group aged from 25 to 60, of which the normal average rate for 99 women and 94 men of a normal state are (47.5 +/- 2.73) and (53.62 +/- 2.73) respectively. After having controlled the uricemia of these subjects during a period of three years in the three states of healthiness, fatigue or physical strains and sickness, we have been able to note that during physical fatigue and intellectual strains the uricemia presents an augmentation notable as in the case of the sicknesses. Taking into consideration the hyperuricemia resulting from fatigue and strains, it may be noteworthy to be taken into consideration by the clinical laboratories and the physicians as well.

Adult↗

PubMed1979

EMG frequency spectrum, muscle structure, and fatigue during dynamic contractions in man.

Fatigue of the vastus lateralis muscle was studied in healthy well-conditioned students, who differed considerable regarding their muscle fibre type distribution. Muscle force decline during repeated maximum voluntary knee extensions at a constant angular velocity (180 degree X s-1 or rad X s-1), using isokinetic equipment, was taken as the criterion for the degree of fatigue. In an attempt to study quantitative as well as qualitative changes in the EMG pattern, integrated EMG (IEMG) and the frequency of the mean power (MPF), computed from the power spectral density function (PSDF), were analysed. It was found that individuals with muscles made up of a high proportion of fast twitch (FT) muscle fibres demonstrated higher peak knee extension torque, and a greater susceptibility to fatigue than did individuals with muscles mainly composed of slow twitch (ST) muscle fibres. An IEMG decline (p less than 0.01) was demonstrated during 100 contractions in individuals rich in FT fibres. Only a slight, but not significant, reduction in IEMG occurred in individuals with high percentage of ST fibres. Concomitantly, MPF decreased (p less than 0.001) in individuals with a high percentage of FT fibres, while their opposites demonstrated only a slight decrease (non-significant). It is suggested that muscle conctraction failure might also be related to qualitative changes in the motor unit recruitment pattern, and that these changes occur more rapidly in muscles composed of a high proportion of FT muscle fibres than in muscles composed to a high proportion of ST fibres.

Action Potentials↗

PubMed1978

A central nervous component in local muscular fatigue.

It has been shown previously (this journal) that any activity, physical or mental, performed as "diverting activity" in the pauses between bouts of exhaustive musclar work has a positive effect on the recuperation after fatigue. It was concluded that this effect was primarily of central nervous origin (Setchenov, 1903) and not a circulatory effect (Weber, 1914). In the present experiments it is shown that the amount of work that can be performed before exhaustion is larger when the subjects work with their eyes open than when they work with closed eyes. Further, when complete exhaustion has been reached with closed eyes, opening of the eyes results in an immediate return of a working capacity amounting to 15-30% of that already performed. It is demonstrated, that patellar reflexes are brisker when the eyes are open than when they are closed. The same is the case during the diverse forms of "diverting activity" used in this and the previous article. The brisker myotatic reflexes are taken to mean an enhanced central nervous arousal, and the recuperative effect of "diverting activity" is consequently explained as being due to an increased facilitation of the neuro-motor system, which in fatigue is inhibited centrally through afferents from receptors in the fatigued muscles.

Adolescent↗

PubMed1977

Fatigue of airway obstruction during long-term exposure to allergen aerosol.

The response to prolonged antigen exposure and the potentiation of airway resistance increase to ACH challenge, after this exposure, were studied on sixteen boxer dogs. One group of animals presented fatigue to A.E. after 3 hours of exposure. This group developed an increased response to ACH aerosol after fatigue to antigen was present. In a second group of dogs, absence of fatigue during prolonged exposure to allergen was observed. A growing tendency of Edyn (as an index of airway resistance) was observed after 5 hours of exposure. The therapeutical influence of bilateral vagus blockade was tested in these last animals. Blockade of nervus vagus released airway obstruction during prolonged allergen exposure and no bronchoconstriction was observed after ACH challenge during blockade.

Acetylcholine↗

PubMed1979

The consequences of diaphragmatic muscle fatigue in the newborn infant.

We have previously demonstrated that diaphragmatic muscle fatigue can be diagnosed in infants from spectral frequency analysis of the surface diaphragmatic electromyogram. This requires a digital computer, but the analysis takes several days. Spectral frequency changes, however, can be accurately reflected by band pass filtering and expressing the ratio of high-frequency power to low-frequency power. A fall in this ratio of greater than 20% indicates muscle fatigue. Using a simple analog device to obtain this ratio permits the results to be immediately available; we have used this method to study weaning from mechanical ventilators in ten infants. With a successful weaning step there is no significant change in the ratio, whereas an unsuccessful weaning step invariably leads to a decrease in the ratio of greater than 20%, which precedes CO2 retention and clinical deterioration. These data indicate that diaphragmatic muscle fatigue plays an important role in the infant's response to lung disease. Monitoring of the high/low frequency ratio may be helpful in weaning infants from assisted ventilation.

Computers, Analog↗

PubMed1978

Composition of vacuoles and sarcoplasmic reticulum in fatigued muscle: electron probe analysis.

Electron probe analysis, cryo-ultramicrotomy, and freeze-substitution were used to determine the nature of vacuolation and the subcellular composition in fatigued frog skeletal muscle fibers. The vacuoles caused by fatigue were part of the T-tubule system and contained high concentrations of NaCl. The calcium concentration in the terminal cisternae was higher than previously measured normal resting values. Mitochondrial calcium content was relatively low (mean +/- SEM, 2 +/- 2 mmol/kg dry weight). Fiber NaCl was increased. It is concluded that fatigue is not due to the depletion of calcium stores from the terminal cisternae or to uncoupling of mitochondria due to calcium loading but may be caused by multiple mechanisms including failure of the T-tubule action potential.

Animals↗

PubMed1977

Fatigue of long duration in human skeletal muscle after exercise.

1. After severe muscular contraction in man recovery of force is largely complete in a few minutes, but is not wholly so for many hours. The long-lasting element of fatigue is found to occur primarily for low frequencies of stimulation (e.g. 20/sec), and is much less pronounced, or absent, at high frequencies (80/sec). The twitch force is an unreliable measure of the state of fatigue. 2. The long-lasting element of fatigue is not due to depletion of high-energy phosphate nor is it due to failure of electrical activity as recorded from surface electrodes. It is probably the result of an impairment of the process of excitation-contraction coupling. Its practical importance for man could be significant as an explanation of the subjective feelings of weakness following exercise.

Adenosine Triphosphate↗

PubMed1978

Effect of fatigue and alcohol on observer perception.

A test series of chest radiographs containing pseudonodules was used to establish baseline sensitivity, specificity, and accuracy rates for individual observers. This experiment studies the effect of fatigue (as subjectively measured) and alcohol (as measured by blood alcohol levels) on observer perception and performance. The results indicate that the fatigue encountered in the course of ordinary professional activities has no significant effect on diagnostic accuracy. Modest quantities of alcohol may adversely influence diagnostic sensitivity, but the effect is unpredictable. Subjective estimates of the influence of fatigue or alcohol on performance by individual observers are frequently erroneous.

Ethanol↗

PubMed1979

[Fatigue fracture of the patella in cerebral palsy (author's transl)].

Amongst approximately 1 500 spastic children under treatment, the authors have seen three cases of fatigue fracture of the patella. One patient was spastic and two others were athetotic. The fatigue fractures can be explained by a flexed knee gait aggravated by a contracture of the hamstring tendons. No fracture was seen in patients treated by Egger's operation. It is concluded that this procedure both prevents and cures fatigue fracture of the patella.

Adolescent↗

PubMed1977

Fatigue characteristics of posterior elements of vertebrae.

The fatigue strength of vertebral posterior elements was determined by applying repetitive forces to the inferior joints between the articular processes of human rhesus-monkey vertebrae. The results indicate that in vivo stresses resulting from unusual activities for sustained periods can induce fatigue fracture of the lumbar vertebrae. Comparison of these data with those of other investigators suggests the use of ultimate strength as a normalizing factor to correlate fatigue-strength data obtained under different test conditions.

Animals↗

PubMed1979

[Stress and fatigue].

Investigations into fatigue are very important for development of labour and sports physiology. Many occupations in modern industry do not often show apparent fatigue. This is the reason for the interest shown for occupational strain sgudies. Occupational strain has proved to have laws of optimum. In some occupational situations work is performed at a different than the optimum, level. It is important to take into consideration general and local strain as well as specific and unspecific components of strain. The fatigue level is a significant sign characterizing the occupational strain.

Fatigue↗

PubMed1978

Workload and operational fatigue in helicopter pilots.

In light of the modern aetiopathogenic views, a brief review was made concerning possible causes of operational fatigue to which flying personnel in general are exposed in the exercise of flying activity. The author then describes and analyzes the meaning and importance of the various stressing factors that constitute the physical and psychic workload to which the helicopter pilot is subjected in performing his professional activities. Also analyzed are the influences exercised, both separately and jointly, on the genesis of flight fatigue in helicopter pilots by stressing and fatiguing effects of vibrations, noise, and psycho-emotional and psycho-sensorial factors related to the variety and danger of utilization of this modern aircraft. Such an analytical investigation enables the author to conclude that one must admit that helicopter piloting involves a psycho-physical workload certainly no less than that required by more powerful and faster aircraft.

Aerospace Medicine↗

PubMed1979

The influence of grain size on the fatigue behavior of annealed 316 LVM stainless steel.

Experimental tests demonstrate that there is a sharp drop in resistance to fatigue fracture when the grain size is increased from 75 to 150 micrometers. This is at least a partial explanation for fatigue fractures of the stems of total hip-joint prostheses reported in the literature. It is also shown that plastic strains associated with fatigue stressing increase with increasing grain size so that loosening of the bone cement embedment may also be part of the premature failure process.

Hip Joint↗

PubMed1976

Action potential fatigue in nonmyelinated nerve fibers: garfish olfactory and rabbit vagus nerve.

A decrease in amplitude and conduction speed in the compound action potential is observed with time in gar olfactory and rabbit vagus nerve when it is stimulated between 4 and 15 Hz at 26 degrees C in vitro. The amplitude decays exponentially for 1-3 min before reaching a steady state. Recs 15 s for gar olfactory nerve and 50 s for rabbit vagus nerve. The steady state values are 14% and 36% of the original amplitude, respectively, and conduction speeds are reduced by 25 % in both nerves. The effect results from completion between ion flow during the action potential and active transport. The accumulation of K+ions and depletion of Na+ ions in the restricted extracellular space contributes to the amplitude fatigue while the depletion of Na+ ions alone causes the decrease in conduction speed. Ouabain increases the fatigue rate in both preparations, but more so for gar. The fatigue and recovery measurements may provide a useful method to investigate active pumping, including both the total pumping rate and the electrogenic component.

Action Potentials↗