[The role of inorganic phosphate in the development of muscle fatigue].
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Animals↗
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Results for “Muscle Fatigue”
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Reducing muscle fatigue in FES applications by stimulating with N-let pulse trains.
Applications of electrical stimulation for restoration of functional movements such as standing, gait, and grasp have always been hindered by the rapid fatigue of stimulated muscle. This paper describes an experimental investigation of stimulation with N-lets (a set of N closely spaced stimulation pulses) as a means of producing contractions with improved fatigue characteristics. Experiments were conducted on 27 able-bodied and four SCI human subjects using surface stimulation of the quadriceps muscle to produce isometric knee joint torque. Based upon evidence from the literature on muscle fatigue, parameters of the N-let trains for N = 1-6 were optimized to produce the most force per pulse. The results demonstrated that: 1) nonlinear summation of the twitch response occurs in human subjects with N-let surface stimulation; 2) for most subjects, doublet stimulation (N = 2) with a pulse interval of about 5 ms produced the maximum torque-time integral per pulse of the resulting twitch; and 3) on average, optimal N-let stimulation resulted in a 36% increase in isometric torque tracking when compared to traditional singlet stimulation. The results have immediate implications for alleviating the problem of premature fatigue during functional electrical stimulation.
Adult↗
Patterns of electromyographic shoulder muscle fatigue during MTM-paced repetitive arm work with and without pauses.
Surface electromyographic recordings from the lateral and the cervical portions of the descending trapezius muscle and from the infraspinatus muscle were assessed for 12 female subjects during performance of a standardized repetitive work simulation task involving 1 h of continuous work and 1 h with introduced pause activities. Discomfort ratings and ratings of perceived exertion were also assessed. Work pace was determined according to MTM-110 (Methods-Time Measurement) as 2466 cycles for both working hours. Muscle fatigue with a decrease in the mean power frequency and an increase in root mean square amplitudes was found both during continuous work and during work with pause activities. The muscle fatigue was less pronounced when pause activities were introduced into the work. Five-minute fatigue patterns were lower during the second hour, indicating adaptation to the work task and work pace. The ratings of perceived exertion and discomfort were similar during work with and without pauses and were higher during the second hour of work. Both work pace and a varied muscle activity pattern are of importance for prevention of muscle fatigue.
Adult↗
Effects of shoulder muscle fatigue caused by repetitive overhead activities on scapulothoracic and glenohumeral kinematics.
The purpose of this study was to determine the effects of shoulder muscle fatigue on three dimensional scapulothoracic and glenohumeral kinematics. Twenty healthy subjects participated in this study. Three-dimensional scapulothoracic and glenohumeral kinematics were determined from electromagnetic sensors attached to the scapula, humerus, and thorax. Surface electromyographic (EMG) data were collected from the upper and lower trapezius, serratus anterior, anterior and posterior deltoid, and infraspinatus muscles. Median power frequency (MPF) values were derived from the raw EMG data and were used to indicate the degree of local muscle fatigue. Kinematic and EMG measures were collected prior to and immediately following the performance of a shoulder elevation fatigue protocol. Following the performance of the fatigue protocol subjects demonstrated more upward and external rotation of the scapula, more clavicular retraction, and less humeral external rotation during arm elevation. All muscles with the exception of the lower trapezius showed EMG signs of fatigue, the most notable being the infraspinatus and deltoid muscles. In general, greater scapulothoracic motion and less glenohumeral motion was observed following muscle fatigue. Further studies are needed to determine what effects these changes have on the soft tissues and mechanics of the shoulder complex.
Adolescent↗
Electromyographic analysis of muscle fatigue in anterior cruciate ligament deficient knees.
The aim of this study was to detect possible differences in muscle fatigue and recovery of knee flexor and extensor muscles in patients with a deficient anterior cruciate ligament compared with patients with a normal anterior cruciate ligament. Surface electromyography of 15 patients with anterior cruciate ligament deficiency was performed while the muscles were under 80% of maximum isometric contraction, and after 1, 2, 3, and 5 minutes of rest. During the first 60 seconds of contraction, all muscles recorded significantly decreased mean power frequency and increased amplitude. The rate of decrease of mean power frequency was significantly greater in the injured quadriceps and normal hamstrings. All muscles except two recovered to the initial mean power frequency level after 1 minute of rest. All but two muscles in the injured and normal limb recorded an overshoot of mean power frequency during the recovery phase. This overshoot phenomenon also was seen for some muscles in the amplitude analysis. The findings confirm the fatigue state in all the muscles, suggest recruitment of more Type II fibers as the muscle fatigues, and show the physiologic adaptation of the quadriceps and hamstrings to anterior cruciate ligament insufficiency. The current study indirectly shows a dissociation between low intramuscular pH and mean power frequency during the recovery phase. It also indirectly suggests that the atrophied thigh muscles have fiber type composition similar to that of the normal side.
Adaptation, Physiological↗
[Initial masseter muscle fatigue in maximal voluntary teeth clenching].
Fatigue of striated muscles is defined as the impossibility to generate the expected or required force during the repeated contraction. During the maximal voluntary teeth contraction in the position of central occlusion the initial fatigue in masticatory muscles during the isometric contraction occurs. If a person can clench its teeth continuously and voluntarily it has a diagnostic significance since the peripheral fatigue is that important factor in the masticatory muscles activity, which is in direct correlation with the function of the masticatory system. The aim was to compare the obtained results of the initial fatigue of masseter muscles during the maximal voluntary teeth contraction in subjects with naturally healthy intact dentition and subjects with a pair of new full dentures. The investigation comprised 20 subjects with healthy stomatognathic system of the skeletal class I by Angle. Comparison of the values of the obtained results was performed electromyographically by synchronous registration of action potentials of masseter muscles. Results of the investigation of the onset of initial fatigue of masseter muscles in the subjects with natural healthy intact dentions showed lower values, i.e., faster development of the muscular fatigue (31.5 s) compared to the subjects with a pair of new full dentures (44.5 s).
Adult↗
The effect of muscle fatigue on instep kicking kinetics and kinematics in association football.
The aim of this study was to examine the effect of leg muscle fatigue on the kinetics and kinematics of the instep football kick. Fatigue was induced by repeated, loaded knee extension (40% body weight) and flexion (50% body weight) motions on a weight-training machine until exhaustion. The kicking motions of seven male players were captured three-dimensionally at 500 Hz before and immediately after the fatigue protocol. The significantly slower ball velocity observed in the fatigue condition was due to both reduced lower leg swing speed and poorer ball contact. The reduced leg swing speed, represented by a slower toe linear velocity immediately before ball impact and slower peak lower leg angular velocity, was most likely due to a significantly reduced resultant joint moment and motion-dependent interactive moment during kicking. These results suggest that the specific muscle fatigue induced in the present study not only diminished the ability to generate force, but also disturbed the effective action of the interactive moment leading to poorer inter-segmental coordination during kicking. Moreover, fatigue obscured the eccentric action of the knee flexors immediately before ball impact. This might increase the susceptibility to injury.
Adult↗
Assessment of lower-back muscle fatigue using electromyography, mechanomyography, and near-infrared spectroscopy.
We have investigated the etiology of lower-back muscle fatigue using simultaneous recordings of electromyography (EMG), mechanomyography (MMG), and near-infrared spectroscopy (NIRS) in an attempt to shed some light on the electrophysiological, mechanical, and metabolic characteristics, respectively. Eight male subjects performed isometric back extensions at an angle of 15 degrees with reference to the horizontal plane, for a period of 60 s. Surface EMG, MMG and NIRS signals were recorded simultaneously from the center of the erector spinae at the level of L3. NIRS was measured to determine the level of muscle blood volume (BV) and oxygenation (Oxy-Hb). The root mean square amplitude value (RMS) of the EMG signal was significantly increased at the initial phase of contraction and then fell significantly, while mean power frequency (MPF) of the EMG signal decreased significantly and progressively as a function of time. There were also significant initial increases in RMS-MMG that were followed by progressive decreases at the end of fatiguing contractions. MPF-MMG remained unchanged. Muscle BV and Oxy-Hb decreased dramatically at the onset of the contraction and then remained almost constant throughout the rest of the contraction. These results, obtained by simultaneous recordings of EMG, MMG, and NIRS, demonstrate that the restriction of blood flow due to high intramuscular mechanical pressure is one of the most important factors in muscle fatigue in the lower-back muscles. In addition, the simultaneous recording system described here can be used to obtain more reliable information regarding the mechanism(s) of lower-back muscle fatigue.
Adult↗
Neurophysiological assessment of skeletal muscle fatigue in patients with congestive heart failure.
BACKGROUND: Recent research has demonstrated that patients with congestive heart failure (CHF) exhibit significant functional impairment of skeletal muscle and that these changes may be important determinants of exercise capacity. Although muscle strength may be mildly reduced, the most significant abnormality is markedly enhanced muscle fatigue. The goal of the present study is to determine whether accelerated fatigue is caused by impaired muscle activation, as a result of inadequate central motor drive or neuromuscular transmission, or by a change in the muscle itself. METHODS AND RESULTS: The study population consisted of nine patients with New York Heart Association class I-III CHF and eight sedentary, age- and sex-matched control subjects. Maximal voluntary contraction force of the foot dorsiflexors (primarily the tibialis anterior) was quantified as a measure of muscle strength, isometric endurance was quantified by the time required for force to decline to 60% of maximal during a sustained maximal contraction, and dynamic endurance was defined as the number of maximal contractions required for force to decline to 60% of maximal under a protocol of six repetitions per minute with an incremental duty cycle. The degree of central motor drive failure was quantified by the degree of force augmentation produced by a superimposed tetanic stimulus delivered to the peroneal nerve during the initial maximal voluntary contraction and at the time when force during the sustained isometric contraction declined to 60% of maximal. Neuromuscular junction transmission was examined by quantifying the amplitude of the compound muscle action potential (M wave) in response to a single nerve stimulus during fatiguing exercise. Muscle strength was relatively preserved in the CHF patients versus the control subjects (93 +/- 41 versus 105 +/- 34 lb; p = NS), but isometric endurance (time to decline to 60%, 34 +/- 15 versus 54 +/- 19 seconds; p less than 0.02) and dynamic endurance (number of repetitions before decline to 60%, 30 +/- 6 versus 43 +/- 7 contractions; p less than 0.001) were both impaired. Tetanic nerve stimulation increased force by similar degrees in the two groups, and the amplitude of the M wave did not decline in either group during exercise. CONCLUSIONS: These findings indicate that enhanced muscle fatigue in patients with CHF is not caused by impaired central motor drive or an abnormality of neuromuscular junction transmission but rather by an abnormality in the muscle itself.
Action Potentials↗
Cardiac and muscle fatigue due to relative functional overload induced by excessive stimulation, hypersensitive excitation-contraction coupling, or diminished performance capacity correlates with sarcoplasmic reticulum failure.
The development of muscle fatigue due to exhaustive exercise is associated with impaired sarcoplasmic reticulum (SR) Ca-transport activity. This study tested the hypothesis that SR failure is a consistent feature of cardiac and skeletal muscle fatigue owing to relative functional overload regardless of the method of induction: excessive stimulation, diminished performance capacity, or excessive excitation-contraction coupling. The Ca-transport activity was determined using three unique models of muscle fatigue: chronic and rapid ventricular pacing in dogs; metabolic inhibition caused by global cardiac ischemia in swine; and the hypermetabolic syndrome of porcine malignant hyperthermia (MH). Both pacing- and ischemia-induced fatigue resulted in reduction of SR Ca-transport ATPase activity: from 275 +/- 58 to 159 +/- 57 nmol.min-1.mg-1 (mU/mg) and from 577 +/- 82 to 177 +/- 133 mU/mg, respectively. Both pacing-induced fatigue and halothane-induced MH resulted in reduction of Ca-sequestration activity of muscle homogenates from 5.95 +/- 2.4 to 3.11 +/- 0.67 nM/s at 300 nM Ca and 38.7 +/- 10.5 to 16.3 +/- 8.0 nM/s at 1500 nM Ca, respectively (all p less than 0.01). The isolated SR Ca-ATPase activity correlated with Ca-sequestration activity of myocardial homogenates (r = 0.76; p less than 0.005). Different models were used to study the relationship of Ca-transport activity with relaxation function, degree of acidosis, and ionized Ca concentration.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
[Relationship between surface electromyographic signal (sEMG) changes and subjective assessment of muscle fatigue during isometric contractions].
OBJECTIVE: To investigate the numerical relationship between the changes of surface electromyographic (sEMG) signal indexes and subjective assessment of muscle fatigue during isometric contractions. METHOD: Eleven healthy subjects participated in the experiment. The sEMG signals of biceps were recorded during their sustained isometric contractions at 50% maximum voluntary contraction (MVC). Fatigue was subjectively rated using a Borg CR-10 scale. Correlations between Borg ratings and a series of fatigue-related indexes such as MPF, MF and Lempel-ziv complexity were analyzed, and curve estimation was also explored. RESULT: A strong positive correlation was found between Borg ratings and endurance time, and negative correlations at different degrees were found between Borg ratings and each of sEMG signal indexes. Curve estimation (Logarithmic curve and Power curve) was also significant. CONCLUSION: The significant correlation between the Borg scale, sEMG signal indexes and endurance time indicates a close relationship between subjective and objective assessment of muscle fatigue. The numerical relationship between them accord with the power law of Stevens in psychophysics relatively.
Adult↗
Role of central respiratory muscle fatigue in endurance exercise in normal subjects.
The role of central respiratory muscle fatigue in determining endurance time (ET) of steady-state ergometry, ventilation (VE), and breathing pattern during exhaustive submaximal exercise is not known. Six normal subjects exercised on a cycle ergometer to exhaustion at 72-82% of maximal power output on three occasions. During the second test, inspiratory muscle load was reduced (approximately 50% of baseline load) for all but the last 3 min of exercise. ET was determined, and VE, tidal volume (VT), respiratory rate (f), and sense of breathing effort (Borg scale) were assessed at different points during the assisted exercise and compared with the values obtained at the same time in identical tests without assist, carried out before and after the assisted test (different days). Borg scale rating was less and there was a nonsignificant trend for VT and VE to be higher and for f to be lower when the assist was in place than at the same time during the unassisted runs. In the last 3 min of exercise, when the respiratory load was comparable (assist removed) but ventilatory work history was different, there were no significant differences in sense of respiratory effort, VE, VT, or f between the experimental and control tests, and ET was also similar. We conclude that central respiratory muscle fatigue plays no role in determining ET, sense of respiratory effort, or breathing pattern in normal subjects during exhaustive submaximal exercise.
Adult↗
Muscle fatigue and lactic acid accumulation.
Lactic acid is formed and accumulated in the muscle under conditions of high energy demand, rapid fluctuations of the energy requirement and insufficient supply of O2. During intense exercise sustained to fatigue muscle pH decreases to about 6.4-6.6. Force generation does not appear to be limited by the high H+ ion concentration per se but is more related to the PCr level. Phosphofructokinase may be inhibited by high H+ concentration but the inhibition is adequately overcome by increases in the activators AMP and ADP. A high concentration of H+ will decrease PCr by a direct effect on the creatine kinase equilibrium and indirectly by an increase in ADP. The effect of acidosis on glycolysis and on the PCr level will result in a decreased rate of ADP rephosphorylation, and it is suggested that ADP increases transiently above the steady-state level in the contracting muscle fibre. It is further suggested that the function of Na-K-ATPase is impaired by the increase of ADP resulting in an altered ionic balance over the muscle cell membrane. Muscle fatigue is thus considered to be due to an insufficient rate of ADP rephosphorylation resulting in a block in the activation process or in the excitation/contraction coupling.
Adenosine Triphosphate↗
Respiratory muscle fatigue and breathing pattern.
The major determinants of VO2 resp and, thus, diaphragmatic endurance are the tension-time index, work rate and lung volume. Changes in breathing pattern that adversely affect any of these factors can impair diaphragmatic endurance. A TTdi above 0.15-0.18 indicates a potentially fatiguing pattern of contraction. However, fatigue may occur at a TTdi below 0.15 if the work rate is sufficiently high or the Pdimax is not measured at the prevailing lung volume. Inspiratory muscle fatigue usually elicits an increase in minute ventilation and respiratory rate and to a lesser degree a reduction in tidal volume. However, fatigue may not always be accompanied by changes in breathing pattern. Furthermore, fatigue may sometimes result in a reduction rather than an increase in motor outflow to the respiratory muscles. Finally, abdominal paradox initially considered to be characteristic clinical sign of inspiratory muscle fatigue appears to be due to increases in respiratory load rather than to muscle fatigue.
Animals↗
Effect of inspiratory muscle fatigue on perception of effort during loaded breathing.
The present study examined the relationship between the intensity of the sense of effort during inspiratory threshold loading and the severity of inspiratory muscle fatigue. Studies were performed on normal subjects in whom the magnitude of airway pressure developed (Pm) and the duty cycle of breathing (TI/TT) were constrained to achieve a pressure-time integral (i.e., Pm/Pmax X TI/TT) 24% of maximum. In separate trials, the same pressure-time index (24%) was achieved using two widely different patterns of pressure magnitude and duty cycle to allow the effects of changes in the pattern of inspiratory muscle contraction on sensation and fatigue to be assessed. The intensity of the sense of effort was assessed using a category (Borg) scale. The severity of inspiratory muscle fatigue was assessed both from changes in the centroid frequency of the diaphragm electromyogram and from changes in the maximum static inspiratory pressure. Loaded breathing produced inspiratory muscle fatigue and a progressive increase in the sense of effort over time in all subjects. The rate at which the inspiratory muscles fatigued was the same with the two patterns of loading. In contrast, the rate of growth in the intensity of the sense of effort varied significantly as a function of the pattern of loaded breathing. The sense of effort increased at a faster rate with the high pressure-short duty cycle pattern of contraction as compared with the low pressure-long duty cycle pattern. As a result, the intensity of the sense of effort was not uniquely related to the severity of inspiratory muscle fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Between-days reliability of subjective and objective assessments of back extensor muscle fatigue in subjects without lower-back pain.
BACKGROUND: It is important to evaluate the reliability of common used methods of examining muscle fatigue from the lower back since the methods are used in patient evaluation. METHODS: To establish between-days reliability, ten subjects without lower-back pain performed a Sorensen test, a prone test for back extensor muscles against gravity, on three separate days. EMG was recorded from the L1 and L5 of the back extensor muscles. Fatigue was subjectively rated using a Borg CR-10 scale. Intraclass correlation coefficient, standard error of measurement and coefficient of variation were calculated from a one-way ANOVA. Percent agreement was also calculated. RESULTS: The study revealed good reliability for the slope for the total time (ICC 0.65-0.90), the initial and end median frequency (ICC 0.75-0.89), median frequencies at Borg ratings of three (ICC 0.63-0.88), five (ICC 0.62-0.84) and seven (ICC 0.67-0. 87), endurance time (ICC 0.89). The Borg ratings of the first minute agreed better than those of the second and the third. The Borg ratings at the second and the third test agreed to 40-80%, indicating a need for a practice session. CONCLUSION: The protocol used for assessing fatigue in the back extensor muscles proved to be reliable and is recommended for further use.
Adult↗
Endotoxins modify muscle fatigue characteristics.
To test the hypothesis that endotoxins can directly modify muscle fatigue characteristics, in vitro experiments were performed on rat muscles 48 hours after injection of lipopolysaccharides (LPS) from Klebsiella pneumoniae. Resistance to fatigue was quantified by measuring tension production during repetitive electrical stimulation of the isolated epitrochlearis muscle. LPS treatment did not significantly modify initial force production whereas fatigability of the muscle was increased. This in vitro preparation should be used for testing antifatigue drugs.
Animals↗
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.
Adult↗