Induction Of Fatigue Research Articles

Differences in back extensor muscles fatigability for smoking and non-smoking athletes

Background and objective: Empirical research on the influence of smoking on musculoske letal health in athletes is sparse. The objective of this study was to compare back extensor muscles' strength (BEMS) before and after a fatigue indu ction protocol among smoking and non smoking male athletes. A pretest-posttest design was used to determine the difference in BEMS between smoking (N = 52) and non smoking (N = 52) athletes aged 18 and 30. A back and leg dynamometer was used to quantify BEMS while repetitive prone chest raise test was used to induce fatigue of the back extensor muscles. The smoking (23.1± 2.9 years) and non-smoking athletes (23.2± 2.37 years) were comparable in age (p = 0.855). Smoking athletes exhibited a significantly higher rating of perceived exertion ( p = 0.007) and fatigue index (10.76% vs. 5.07%); and significant reduction in BEMS following fatigue induction (p < 0.05) compared with their non smoking counterparts. Smoking athletes have higher rates of muscular fatiguability and decreased back strengt h following back extensors tasks. Smoking is associated with increased muscle fatiguability and impairment of back strength in athletes.

Prevention of scattered light-induced asthenopia and fatigue by a polarized filter

It has been well documented that a long-time irradiation of the eye by a strong light elicits eyestrain and fatigue. To elucidate the mechanism for the induction of light-induced fatigue and asthenopia, changes in the mouse were analyzed after white light-irradiation to the eye. C57BL/6j male mice were irradiated with white light in a specially designed room equipped with four mirrors covering all areas of its four walls to elicit diffused reflected light, and changes in their plasma levels of cortisol, INF-gamma, interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) were analyzed. Irradiation of mice with scattered white light significantly decreased the motional activity of animals, suggesting the occurrence of fatigue. Biochemical analysis and enzyme-immunoassay revealed that the irradiation of mice significantly elevated the plasma levels of cortisol, IFN-gamma, IL-10 and TGF-beta. All these changes were not observed with mice irradiated with the light in a similar room not equipped with mirrors. These changes were successfully inhibited by a polarized glass filter but not by a non-polarized filter with a similar absorbance. These observations suggest that irradiation of the eye by scattered reflected light stimulated a stress response via hypothalamo-pituitary-adrenal axis to enhance the secretion of cortisol from the adrenal grand and increase the plasma levels of cytokines.

Go rinse your mouth: a novel way to improve endurance performance?

Go rinse your mouth: a novel way to improve endurance performance?

Avaliação da ativação neuromuscular em indivíduos com escoliose através da eletromiografia de superfície

OBJECTIVE: The aim of this study was to investigate the potential of surface electromyography (EMG) for assessing neuromuscular efficiency and localized muscle fatigue in the lumbar extensors, in individuals with scoliosis. METHODS: Twenty individuals participated in this study, divided equally into two groups: (1) Scoliosis Group and (2) Control Group. These subjects underwent a fatigue induction test on their lumbar extensor muscles, consisting of one maximum voluntary isometric contraction (MVIC) followed by a test at 80% of the MVIC effort. Force and EMG signals were collected simultaneously. The EMG signal was processed in the frequency domain by means of fast Fourier transforms using the median frequency; and in the time domain by calculating the root mean square value. The data were analyzed by means of one-way analysis of variance to investigate the differences between the two groups. Paired t test was used to investigate the symmetry between the right and left sides. The significance level adopted was 0.05. RESULTS: The results showed that the individuals with scoliosis presented: (1) symmetrical neuromuscular activation between the sides; (2) lower neuromuscular efficiency; (3) greater capacity to resist fatigue; and (4) force values 42.6% lower than those of the individuals in the Control Group. CONCLUSIONS: The results suggest that surface EMG is an effective tool for functional assessments of scoliosis, although the protocol established limited the participation of individuals with scoliosis, from the perspective of neuromuscular efficiency.

달리기시 맞춤형 발보조기 사용이 피로물질변화에 미치는 영향

The purpose of this study is to examine the changes in blood fatigue induction factors and the comfort when the orthotics was put on during running. There were ten subjects, who participated in absolute intensity exercise(6mile/hr, 5%). They ran on the treadmill with and without the custom foot orthotics. Lactate, ammonia, and phosphorous were analyzed after blood sampling was taken three times(before exercise, after finishing exercise performance, and 30min after recovery). The data concerning the overall comfort was collected by a questionairre. Experimental data were analysed using SPSS program. The level of blood lactate, ammonia, and phosphorous with custom foot orthotics were the lower than that of without custom foot orthotics. During running the overall comfort was higher for the foot orthotic condition than the nonorthotic conditions.

Expiratory muscle fatigue impairs exercise performance

High-intensity, exhaustive exercise may lead to inspiratory as well as expiratory muscle fatigue (EMF). Induction of inspiratory muscle fatigue (IMF) before exercise has been shown to impair subsequent exercise performance. The purpose of the present study was to determine whether induction of EMF also affects subsequent exercise performance. Twelve healthy young men performed five 12-min running tests on a 400-m track on separate days: a preliminary trial, two trials after induction of EMF, and two trials without prior muscle fatigue. Tests with and without prior EMF were performed in an alternate order, randomly starting with either type. EMF was defined as a >or=20% drop in maximal expiratory mouth pressure achieved during expiratory resistive breathing against 50% maximal expiratory mouth pressure. The average distance covered in 12 min was significantly smaller during exercise with prior EMF compared to control exercise (2872+/-256 vs. 2957+/-325 m; P=0.002). Running speed was consistently lower (0.13 m s(-1)) throughout the entire 12 min of exercise with prior EMF. A significant correlation was observed between the level of EMF (decrement in maximal expiratory mouth pressure after resistive breathing) and the reduction in running distance (r2=0.528, P=0.007). Perceived respiratory exertion was higher during the first 800 m and heart rate was lower throughout the entire test of running with prior EMF compared to control exercise (5.3+/-1.6 vs. 4.5+/-1.7 points, P=0.002; 173+/-10 vs. 178+/-7 beats min(-1), P=0.005). We conclude that EMF impairs exercise performance as previously reported for IMF.

목질진흙(상황)버섯과 동충하초 투여가 운동 시 혈중 피로요인 변화와 항산화체계에 미치는 영향

The purpose of this study was to investigate the effects of p. Linteus and C. militaris supplement on lactate, phosphorous, ammonia, MDA(malondialdehyde), GPX(glutathione peroxidase) and TAS(total antioxidant status) following , and 85% exercise. The 15 male college students were divided into three groups: 5 P. liteus supplied(PL), 5 C. militaris supplied(CM), and 5 placebos supplied(PB) and compared the differences between supplement before and after. Obtained results were as follows: In the exercise performance time, there were no differences in PL, CM and PB groups. Regular supplement of P. linteus or C. militaris partially reduces fatigue induction factors. Also, P. linteus or C. militaris supplement decreases MDA, increases GPX and TAS. Therefore, it can be concluded that P. linteus or C. militaris supplement not only have a pharmacological effect for clinical treatment, but also have a maintenance effects on the tissue oxidant-antioxidant system after exercise.

Role of TGF-beta in the brain in induction of central fatigue and fever by Poly I:C

Role of TGF-beta in the brain in induction of central fatigue and fever by Poly I:C

The effects of the myosin‐II inhibitor N‐benzyl‐p‐toluene sulphonamide on fatigue in mouse single intact toe muscle fibres

This study determined whether fatigue in skeletal muscle is primarily due to the repeated elevations of myoplasmic free calcium concentration ([Ca(2+)](i)) or to metabolite accumulation. We examined the effects of N-benzyl-p-toluene sulphonamide (BTS) which is a potent and specific inhibitor of fast muscle myosin-II on the development of fatigue in mouse flexor digitorum brevis (FDB) muscle fibres. Single intact FDB fibres were micro-injected with indo-1 to monitor changes in [Ca(2+)](i) and stimulated repeatedly for a maximum of 150 tetani or until force declined to 40%. BTS markedly reduced tetanic force but had no effect on the tetanic [Ca(2+)](i) transients. When fatigue was induced in the presence of BTS, the reduction in [Ca(2+)](i) and force transients occurred much more slowly than in the absence of BTS. The extent of force depression was similar after induction of fatigue in fibres exposed to Tyrode only or to BTS and force recovered to the same extent. The results suggest that the decrease in tetanic [Ca(2+)](i) and force caused during fatigue are due mainly to accumulated metabolic changes.

Establishment of a protocol to test fatigue of the trunk muscles

Background: Muscle fatigue has high relevance in human performance yet little research has evaluated how it should be assessed. Objective: To perform a pilot study to identify suitable methods of...

Task-induced fatigue states and simulated driving performance.

States of fatigue are implicated in driver impairment and motor vehicle accidents. This article reports two studies investigating two possible mechanisms for performance impairment: (1) loss of attentional resources; and (2) active regulation of matching effort to task demands. The first hypothesis predicts that fatigue effects will be accentuated by high task demands, but the second hypothesis predicts that fatigue effects will be strongest in "underload" conditions. In two studies, drivers performed a stimulated driving task, in which task demands were manipulated by varying road curvature. In a "fatigue induction" condition, the early part of the drive was occupied by performance of a demanding secondary task concurrently with driving, after which the concurrent task ceased. Post-induction driving performance was compared with a control condition in which drivers were not exposed to the induction. In both studies, the fatigue induction elicited various subjective fatigue and stress symptoms, and also raised reported workload. Fatigue effects on vehicle control and signal detection were assessed during and after the fatigue induction. The fatigue induction increased heading error, reduced steering activity, and, in the second study, reduced perceptual sensitivity on a secondary detection task. These effects were confined to driving on straight rather than on curved road sections, consistent with the effort regulation hypothesis. The second study showed that fatigue effects were moderated by a motivational manipulation. Results are interpreted within a control model, such that task-induced fatigue may reduce awareness of performance impairment, rather than reluctance or inability to mobilize compensatory effort following detection of impairment.

Increased production of interleukin-6 by adherent and non-adherent mononuclear cells during 'natural fatigue' but not following 'experimental fatigue' in patients with chronic fatigue syndrome.

In an investigator-blinded study, adherent (monocytes) and non-adherent cells (lymphocytes) from patients with chronic fatigue syndrome (CFS) were examined on two separate occasions (when feeling 'fatigued' and when feeling 'rested') for in vitro spontaneous, phytohemagglutinin- (PHA, for lymphocytes), and lipopolysaccharide- (LPS, for monocytes) induced production of IL-6 by ELISA assay. A group of CFS patients and controls were also subjected to exercise-induced fatigue ('experimental fatigue') and IL-6 production was compared, in a double-blinded manner, prior to and following induction of fatigue. A significant increase in spontaneous, PHA- and LPS-induced IL-6 secretion by both lymphocytes and monocytes was observed in CFS patients during 'natural fatigue' as compared to during state. However, no such changes in IL-6 production were observed during 'experimental fatigue'. These data suggest a role of IL-6 in natural symptomatology and perhaps in the pathogenesis of CFS. In addition, the data demonstrate that laboratory-induced fatigue (experimental fatigue) may not be a good model to study immunological changes in CFS; immunological parameters should be studied in a longitudinal manner during the natural course of the disease.

Recovery of PdiTwitch following the induction of diaphragm fatigue in normal subjects.

Low frequency diaphragm fatigue (LFF) may play a major role in the pathogenesis of ventilatory failure; however, recovery from LFF is not well studied. We measured transdiaphragmatic twitch pressure (PdiT) at FRC (using a reduction of PdiT as an index of LFF) and maximum transdiaphragmatic pressure (Pdimax) before and after the induction of diaphragm fatigue in seven normal subjects, age 31 +/- 3 yr (mean +/- SD). Fatigue was induced by breathing through an inspiratory resistive load. PdiT produced by bilateral transcutaneous supramaximal electrophrenic stimulation was measured at baseline, 15, 30 min, 1, 2, 3, 4 h, and then 1 to 3 times between hour 20-25 post-fatigue. Pdimax estimated by twitch occlusion was measured at baseline, 30 min, 2-3, and 20-25 h post-fatigue. Pre-fatigue values (mean +/- SE) were: PdiT 23.6 +/- 2.5 cm H2O. The mean +/- SD time to fatigue was 25.3 +/- 12.3 min. Post-fatigue PdiT was reduced to 50%, and by 3 h was 72% of the initial value; 100% by 25 h. Pdimax was reduced to 75% post-fatigue, but recovered to 87% by 3 h, and 100% by 25 h. We concluded that recovery of PdiT and Pdimax in normal subjects starts to occur within the first few hours following diaphragm fatigue, and is complete by 25 h.

Compartmental analysis of Ca2+ kinetics in long-lasting diaphragm fatigue: loss of t-tubular membrane Ca2+.

An analytic method based on simulation and modeling of long-term 45Ca2+ efflux data was used to estimate Ca2+ contents (nmol Ca2+/g tissue wet wt) and exchange fluxes (nmol Ca2+.min-1.g-1) for extracellular and intracellular compartments in in vitro hamster diaphragm. Three physiological states were studied: control (n = 5), acute fatigue (after repeated tetany; n = 5), and long-lasting fatigue (1-h recovery; n = 5). Experimental muscles were loaded with 45Ca2+ for 1 h, and efflux data were collected for 8 h by use of a flow-through tissue chamber. Induction of acute diaphragm fatigue led to a uniform 200% elevation of the 8-h efflux curve (expressed as dpm.min-1.mg-1) relative to control. Conversely, in long-lasting fatigue the early component of the efflux curve was depressed compared with control, whereas the balance of the curve was restored to baseline. Analysis of control efflux data revealed that the early curve (0-2 h) contained data on two rapidly exchanging extracellular Ca2+ compartments, whereas the late curve (2-8 h) reflected information on two slowly exchanging intracellular compartments. Modeling of acute fatigue efflux data estimated a 239% increase in one extracellular Ca2+ compartment (putative t-tubular membrane) and a 546% increase in one intracellular Ca2+ compartment (putative terminal cisternae). These increase accounted for the model prediction of a twofold rise in total diaphragm Ca2+. The kinetic data were quantitatively consistent with the hypothesis that diaphragm Ca2+ overload in acute fatigue required sarcolemmal Ca2+ permeability to double and Ca2+ diffusion into the t-tubular and terminal cisternal compartments to escalate nearly threefold. Fitting of long-lasting fatigue efflux data was associated with the sole prediction that t-tubular membrane Ca2+ was reduced to less than one-half of the control value.

Comparison of magnetic and electrical phrenic nerve stimulation in assessment of diaphragmatic contractility

Unlike the standard electrical approach, cervical magnetic stimulation of the phrenic nerves is less painful and achieves a constant degree of diaphragmatic recruitment, features that should enhance its applicability in a clinical setting. An unexplained phenomenon is the greater transdiaphragmatic twitch pressure (Pditw) with magnetic vs. electrical stimulation. We hypothesized that this greater Pditw is due to coactivation of extradiaphragmatic muscles. Because impedance to rib cage expansion is increased at high lung volumes and efficiency of extradiaphragmatic muscles is less than that of the diaphragm, we reasoned that the difference between electrical Pditw and magnetic Pditw would be less evident at high volumes than at end-expiratory lung volume. In human volunteers, magnetic Pditw and electrical Pditw were 37.7 +/- 1.9 (SE) and 32.3 +/- 2.2 cmH2O, respectively, at end-expiratory lung volume (P < 0.005) and 24.0 +/- 2.9 and 27.2 +/- 2.8 cmH2O, respectively, at one-half inspiratory capacity (not significant); at total lung capacity, magnetic Pditw was less than electrical Pditw (10.6 +/- 0.8 and 16.2 +/- 2.9 cmH2O, respectively; P < 0.05). Magnetic stimulation caused significant extradiaphragmatic muscle depolarization and rib cage expansion, whereas electrical stimulation caused virtually no extradiaphragmatic muscle depolarization and rib cage deflation. Despite these differences, the induction of respiratory muscle fatigue produced reductions in both electrical and magnetic Pditw values (P < 0.01), which were of similar magnitude and closely correlated (r = 0.96). In conclusion, magnetic stimulation recruits both extradiaphragmatic and diaphragmatic muscles, and it is equally as effective as electrical stimulation in detecting diaphragmatic fatigue.

RETRACTED ARTICLE: Dobutamine increases contractility of fatigued diaphragm in dogs: The relationship between dose and diaphragmatic contractility

The dose-related effects of dobutamine (DOB) on the contractility of fatigued diaphragm were studied in 16 anesthetized, mechanically ventilated dogs. The animals were divided into two groups of eight: the control (group C) and the DOB (group D). Diaphragmatic fatigue was induced by intermittent supramaximal electrophrenic stimulation at a frequency of 20 Hz applied for 30 min. Diaphragmatic contractility was assessed from changes in transdiaphragmatic pressure (Pdi). After the induction of diaphragmatic fatigue, Pdi at low-frequency (20-Hz) stimulation decreased significantly compared with the prefatigue values (P<0.05), whereas no change in Pdi was observed at high-frequency (100-Hz) stimulation. In group D, after producing fatigue, Pdi at 20-Hz stimulation increased significantly with a continuous infusion of DOB (5 and 10 μg·kg(-1)·min(-1)) i.v. (P<0.05). The Pdi at 100-Hz stimulation increased significantly with administration of DOB 10 μg·kg(-1)·min(-1) i.v. (P<0.05). There was a significant correlation between dose of DOB and Pdi at both stimuli (P<0.05). In group C, the speed of Pdi recovery at 20-Hz stimulation was relatively slower. The integrated diaphragmatic electric activity (Edi) in each group did not change at any frequency of stimulation throughout the study. It is concluded that DOB increases the contractility of fatigued diaphragm in a dose-dependent manner.

Dobutamine increases contractility of fatigued diaphragm in dogs: the relationship between dose and diaphragmatic contractility

The dose-related effects of dobutamine (DOB) on the contractility of fatigued diaphragm were studied in 16 anesthetized, mechanically ventilated dogs. The animals were divided into two groups of eight: the control (group C) and the DOB (group D). Diaphragmatic fatigue was induced by intermittent supramaximal electrophrenic stimulation at a frequency of 20Hz applied for 30min. Diaphragmatic con- tractility was assessed from changes in transdiaphragmatic pressure (Pdi). After the induction of diaphragmatic fatigue, Pd~ at low-frequency (20-Hz) stimulation decreased signifi- cantly compared with the prefatigue values (P < 0.05), whereas no change in Pdi was observed at high-frequency (100-Hz) stimulation. In group D, after producing fatigue, Pd~ at 20-Hz stimulation increased significantly with a continuous infusion of DOB (5 and 10 ~tg.kg z-rain-l) i.v. (P < 0.05). The P~ at 100-Hz stimulation increased significantly with adminis- tration of DOB 10~tg.kg-l.min -1 i.v. (P < 0.05). There was a significant correlation between dose of DOB and Pd~ at both stimuli (P < 0.05). In group C, the speed of Pa~ recovery at 20- Hz stimulation was relatively slower. The integrated diaphrag- matic electric activity (Edi) in each group did not change at any frequency of stimulation throughout the study. It is concluded that DOB increases the contractility of fatigued diaphragm in a dose-dependent manner.

Effect of Inspiratory Muscle Fatigue on Inspiratory Muscle Relaxation Rates in Healthy Subjects

Simple methods to diagnose inspiratory muscle fatigue in the clinical setting would be of considerable benefit. Inspiratory muscle relaxation rates are known to slow following induction of fatigue. Inspiratory muscle relaxation rates have been measured following a short sharp inspiratory effort against an occluded airway (sniffmouth) or through the unoccluded nostrils (sniffnostrils). Relaxation rates in the absence of fatigue are faster when sniffs are performed through the unoccluded nostrils. While both methods have been shown to be capable of detecting inspiratory muscle fatigue, there may be quantitative or qualitative differences between the two techniques in their ability to detect fatigue similar to the differences observed in the fresh state. Accordingly, we measured relaxation rates with the two sniff techniques in five healthy naive male subjects before and after induction of fatigue. Inspiratory muscle fatigue was induced by threshold loading at 80 percent of Pesmax until the subjects were unable to generate the target pressure. For those trials in which sniffnostrils were performed, the maximum relaxation rate from the esophageal pressure curve (MRRes) was significantly decreased following induction of fatigue in nine of ten trials, while the exponential time constant (taues) was significantly increased in all ten trials. In contrast, for those trials in which sniffmouth were performed, the MRRes was significantly decreased following induction of fatigue in only six of ten trials. Similarly, taues was significantly increased following induction of fatigue in only six of ten trials. In addition, the magnitude of change in the MRR or tau following induction of fatigue was quantitatively greater with sniffnostrils compared with sniffmouth. Similar findings were obtained when relaxation rates were measured from the diaphragmatic pressure tracing. In conclusion, changes in relaxation rate following induction of fatigue were quantitatively greater and more consistently observed when sniffs were performed through the unoccluded nostrils rather than against an occluded airway.

The effect of inspiratory muscle fatigue on breathing pattern and ventilatory response to CO2.

1. The effects of inducing inspiratory muscle fatigue on the subsequent breathing pattern were examined during resting unstimulated breathing and during CO2 rebreathing. In addition, we examined whether induction of inspiratory muscle fatigue alters CO2 responsiveness. 2. Global inspiratory muscle fatigue and diaphragmatic fatigue were achieved by having subjects breathe against an inspiratory resistive load while generating a predetermined fraction of either their maximal mouth pressure or maximal transdiaphragmatic pressure until they were unable to generate the target pressure. 3. Induction of inspiratory muscle fatigue had no effect on the subsequent breathing pattern during either unstimulated breathing or during CO2 rebreathing. 4. Following induction of inspiratory muscle fatigue, the slope of the ventilatory response to CO2 was significantly decreased from 18.8 +/- 3.3 during control to 13.8 +/- 2.1 l min-1 (% end-tidal CO2 concentration)-1 with fatigue (P < 0.02).

Effect of respiratory muscle fatigue on subsequent exercise performance

The purpose of this study was to determine whether induction of inspiratory muscle fatigue might impair subsequent exercise performance. Ten healthy subjects cycled to volitional exhaustion at 90% of their maximal capacity. Oxygen consumption, breathing pattern, and a visual analogue scale for respiratory effort were measured. Exercise was performed on three separate occasions, once immediately after induction of fatigue, whereas the other two episodes served as controls. Fatigue was achieved by having the subjects breathe against an inspiratory threshold load while generating 80% of their predetermined maximal mouth pressure until they could no longer reach the target pressure. After induction of fatigue, exercise time was reduced compared with control, 238 +/- 69 vs. 311 +/- 96 (SD) s (P less than 0.001). During the last minute of exercise, oxygen consumption and heart rate were lower after induction of fatigue than during control, 2,234 +/- 472 vs. 2,533 +/- 548 ml/min (P less than 0.002) and 167 +/- 15 vs. 177 +/- 12 beats/min (P less than 0.002). At exercise isotime, minutes ventilation and the visual analogue scale for respiratory effort were larger after induction of fatigue than during control. In addition, at exercise isotime, relative tachypnea was observed after induction of fatigue. We conclude that induction of inspiratory muscle fatigue can impair subsequent performance of high-intensity exercise and alter the pattern of breathing during such exercise.