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PubMed2000

Muscle fatigue during concentric and eccentric contractions.

We compared the contribution of central and peripheral processes to muscle fatigue induced in the ankle dorsiflexor muscles by tests performed during concentric (CON) and eccentric (ECC) conditions. Each fatigue test consisted of five sets of 30 maximum voluntary contractions at a constant speed of 50 degrees /s for a 30 degrees range of motion of the ankle joint. The torque produced by the dorsiflexors and the surface electromyogram (EMG) of the tibialis anterior muscle were recorded during the fatigue tests. Before, during, and after the tests, the compound muscle action potential (M wave) and the contractile properties in response to single and paired electrical stimuli, as well as the interpolated-twitch method and postactivation potentiation (PAP), were recorded during isometric conditions. Compared with ECC contractions, the CON ones resulted in a greater (P < 0.05) loss of force (-31.6% vs. -23.8%) and a decrease in EMG activity (-26.4% vs. -17.5%). This difference was most pronounced during the first four sets of contractions, but was reduced during the last set. Activation was not altered by the tests because neither the interpolated-twitch response nor the ratio of the voluntary EMG to the amplitude of the M wave was changed in the two fatigue tests. Although there was no significant difference in M-wave amplitude between the two tests, changes in the twitch parameters and in the PAP were found to be greater in the CON than ECC contractions. It is concluded that the greater alterations in the contractile properties observed during the CON contractions indicate that intracellular Ca(2+)-controlled excitation-contraction (E-C) coupling processes, possibly associated with a higher energy requirement, are affected to a much greater degree than during ECC contractions.

Action Potentials↗
PubMed2004

Reversal of muscle fatigue during 16 h of heavy intermittent cycle exercise.

This study examined the effects of extended sessions of heavy intermittent exercise on quadriceps muscle fatigue and weakness. Twelve untrained volunteers (10 men and 2 women), with a peak oxygen consumption of 44.3 +/- 2.3 ml.kg(-1).min(-1), exercised at approximately 91% peak oxygen consumption for 6 min once per hour for 16 h. Muscle isometric properties assessed before and after selected repetitions (R1, R2, R4, R7, R12, and R15) were used to quantitate fatigue (before vs. after repetitions) and weakness (before vs. before repetitions). Muscle fatigue at R1 was indicated by reductions (P < 0.05) in peak twitch force (135 +/- 13 vs. 106 +/- 11 N) and by a reduction (P < 0.05) in the force-frequency response, which ranged between approximately 53% at 10 Hz (113 +/- 12 vs. 52.6 +/- 7.4 N) and approximately 17% at 50 Hz (324 +/- 27 vs. 270 +/- 30 N). No recovery of force, regardless of stimulation frequency, was observed during the 54 min between R1 and R2. At R2 and for all subsequent repetitions, no reduction in force, regardless of stimulation frequency, was generally found after the exercise. The only exception was for R2, where, at 20 Hz, force was reduced (P < 0.05) by 18%. At R15, force before repetitions for high frequencies (i.e., 100 Hz) returned to R1 (333 +/- 29 vs. 324 +/- 27 N), whereas force at low frequency (i.e., 10 Hz) was only partially (P < 0.05) recovered (113 +/- 12 vs. 70 +/- 6.6 N). It is concluded that multiple sessions of heavy exercise can reverse the fatigue noted early and reduce or eliminate weakness depending on the frequency of stimulation.

Adult↗
PubMed1992

Human muscle fatigue after glycogen depletion: a 31P magnetic resonance study.

To differentiate the effects of high energy phosphates, pH, and [H2PO4-] on skeletal muscle fatigue, intracellular acidosis during handgrip exercise was attenuated by prolonged submaximal exercise. Healthy human subjects (n = 6) performed 5-min bouts of maximal rhythmic handgrip (RHG) before (CONTROL) and after prolonged (60-min) handgrip exercise (ATTEN-EX) designed to attenuate lactic acidosis in active muscle by partially depleting muscle glycogen. Concentrations of free intracellular phosphocreatine ([PCr]), adenosine triphosphate ([ATP]), and orthophosphate ([P(i)]) and pH were measured by 31P nuclear magnetic resonance spectroscopy and used to calculate adenosine diphosphate [ADP], [H2PO4-], and [HPO4(2-)]. Handgrip force output was measured with a dynamometer, and fatigue was determined by loss of maximal contractile force. After ATTEN-EX, the normal exercise-induced muscle acidosis was reduced. At peak CONTROL RHG, pH fell to 6.3 +/- 0.1 (SE) and muscle fatigue was correlated with [PCr] (r = 0.83), [P(i)] (r = 0.82), and [H2PO4-] (r = 0.81); [ADP] was 22.0 +/- 5.7 mumol/kg. At peak RHG after ATTEN-EX, pH was 6.9 +/- 0.1 and [ADP] was 116.1 +/- 18.2 mumol/kg, although [PCr] and [P(i)] were not different from CONTROL RHG (P greater than 0.05). After ATTEN-EX, fatigue correlated most closely with [ADP] (r = 0.84). The data indicate that skeletal muscle fatigue 1) is multifactorial, 2) can occur without decreased pH or increased [H2PO4-], and 3) is correlated with [ADP] after exercise-induced glycogen depletion.

Acidosis, Lactic↗
PubMed1989

Respiratory muscle fatigue research: implications for clinical practice.

Research into respiratory muscle fatigue and failure has centered around three issues: the factors that place individuals at risk for fatigue; the physiologic manifestations of fatigue development; and the various treatment alternatives available to prevent and respond to respiratory muscle failure. Selected studies in this field of investigation are discussed, and applications to clinical practice are proposed.

Aged↗
PubMed1996

Muscle fatigue, lactate, and pyruvate in mitochondrial myopathy with progressive external ophthalmoplegia.

We studied muscle fatigue and serum lactate and pyruvate levels in 20 patients with mitochondrial myopathy with progressive external ophthalmoplegia (PEO). Fatigue was assessed in the adductor pollicis muscle (AP) using a low-intensity exercise protocol (20 min). Forces (TFs) and relaxation times of ulnar nerve evoked twitches, compound muscle action potentials (CMAPs), and maximal voluntary contractions (MVCs) were monitored. Serum lactate and pyruvate levels were independently measured at rest and after exercise on a bicycle (15 min, 30 W). Most patients showed abnormal fatigue of the AP with a reduction of TFs and MVCs and normal CMAPs. The reduced TFs were significantly correlated with lactate levels at rest (r= - 0.60, P<0.05) and less so with those after exercise (r=- 0.47,P<0.05). Pyruvate levels revealed a similar correlation although they were widely scattered. We conclude that abnormal fatigue in PEO is metabolic, is localized beyond the muscle fiber membrane, and involves the electrome-chanical coupling and the contractile apparatus. Serum lactate levels at rest are good predictors of fatigue in PEO.

Action Potentials↗
PubMed1998

Is spectral analysis of the surface electromyographic signal a clinically useful tool for evaluation of skeletal muscle fatigue?

Normal values for initial median frequency (IMF) of the electromyographic (EMG) power-density spectrum must be determined before EMG spectral analysis can be used to evaluate clinically muscle fatigue. This study attempts to establish normal values in four muscles. Thirty-one healthy subjects performed isometric contractions of the biceps brachii, triceps, deltoid, and tibialis anterior muscles at 50% maximum voluntary contraction. Linear regression analysis was used to compute the IMF and the slope of the median frequency as it decayed with fatigue over 45 seconds. The IMF of the tibialis anterior (mean +/- standard deviation, 116 +/- 20 Hz) was significantly higher (p < 0.001) than that of the biceps (90 +/- 18 Hz), triceps (85 +/- 18 Hz), and deltoid (87 +/- 15 Hz). The deltoid and tibialis anterior had the steepest slopes. The IMF of all muscles was greater in men than in women, but gender did not affect the slope. This study attempted to establish normal values for IMF and slope in specific muscles. However, the range of normal values is so broad that it may preclude the clinical use of spectral analysis to evaluate muscle fatigue.

Adult↗
PubMed2006

Performance of soccer passing skills under moderate and high-intensity localized muscle fatigue.

Despite the acknowledged importance of fatigue on performance, ecologically sound studies investigating fatigue and its effects on sport-specific skills are surprisingly limited. The aim of this study was to investigate the effects of moderate and high-intensity localized muscle fatigue on passing performance in soccer. Twenty physically active male college students (age, 22.9 +/- 5.3 years) participated in this study. Subjects performed the modified Loughborough Soccer Passing Test under the following three conditions: rest, moderate fatigue, and high-intensity fatigue. Fatigue intensity was established using a percentage of the maximal number of alternate split squats performed by the subject in 1 minute. Results revealed a significant difference between performance at rest and performance following high-intensity, localized muscle fatigue. The results suggest the need for trainers and coaches to incorporate high-intensity exercise drills into training plans to help players better cope with the demands of the game on the pitch.

Adult↗
PubMed2006

Assessment of skeletal muscle fatigue of road maintenance workers based on heart rate monitoring and myotonometry.

OBJECTIVE: This research work is dedicated to occupational health problems caused by ergonomic risks. The research object was road building industry, where workers have to work very intensively, have long work hours, are working in forced/constrained work postures and overstrain during the work specific parts of their bodies. The aim of this study was to evaluate the work heaviness degree and to estimate the muscle fatigue of workers after one week work cycle. The study group consisted of 10 road construction and maintenance workers and 10 pavers aged between 20 and 60 years. METHODS: Physical load were analyzed by measuring heart rate (HR), work postures (OWAS) and perceived exertion (RPE). Assessments of the muscles strain and functional state (tone) were carried out using myotonometric (MYO) measurements. The reliability of the statistical processing of heart rate monitoring and myotonometry data was determined using correlating analysis. RESULTS: This study showed that that road construction and repairing works should be considered as a hard work according to average metabolic energy consumption 8.1 +/- 1.5 kcal/min; paving, in its turn, was a moderately hard work according to 7.2 +/- 1.1 kcal/min. Several muscle tone levels were identified allowing subdivision of workers into three conditional categories basing on muscle tone and fatigue: I--absolute muscle relaxation and ability to relax; II--a state of equilibrium, when muscles are able to adapt to the work load and are partly able to relax; and III--muscle fatigue and increased tone. It was also found out that the increase of muscle tone and fatigue mainly depend on workers physical preparedness and length of service, and less on their age. CONCLUSION: We have concluded that a complex ergonomic analysis consisting of heart rate monitoring, assessment of compulsive working postures and myotonometry is appropriate to assess the work heaviness degree and can provide prognosis of occupational pathology or work-related musculoskeletal disorders for the workers under different workload conditions. These results can also be used when deciding on necessary rest time and its periodicity.

Journal Article↗
PubMed2007

Does motoneuron adaptation contribute to muscle fatigue?

To help reduce the gap between the cellular physiology of motoneurons (MNs) as studied "bottom-up" in animal preparations and the "top-down" study of the firing patterns of human motor units (MUs), this article addresses the question of whether motoneuron adaptation contributes to muscle fatigue. Findings are reviewed on the intracellularly recorded electrophysiology of spinal MNs as studied in vivo and in vitro using animal preparations, and the extracellularly recorded discharge of MUs as studied in conscious humans. The latter "top-down" approach, combined with kinetic measurements, has provided most of what is currently known about the neurobiology of muscle fatigue, including its task and context dependencies. It is argued that although the question addressed is still open, it should now be possible to design new "bottom-up" research paradigms using animal preparations that take advantage of what has been learned with the use of relatively noninvasive quantitative procedures in conscious humans.

Action Potentials↗
PubMed2002

Ergonomics: muscle fatigue, posture, magnification, and illumination.

Chronic low-level trauma very often goes unnoticed until symptoms prompt sufferers to seek medical help. Many combined risk factors, rather than a single event or practice, lead to cumulative trauma disorders. Muscle fatigue leads to muscle trauma as well as a cascade of other injuries. With preemptive ergonomic strategies, such as the use of magnification and illumination, many of the common disabilities associated with dental careers can be avoided or reduced. The information in this article is of particular interest to not only the practicing dentist, but the entire dental team.

Age Factors↗
PubMed2003

[sEMG Time-frequency analysis techniques for evaluation of muscle fatigue and it's application in ergonomic studies].

As a non-invasive on-line measurement, sEMG can reflect the status of muscle activity and muscle function accurately and objectively. Some sEMG Time-frequency analysis techniques, especially the JASA (joint analysis of EMG spectrum and amplitude) analysis, for evaluation of muscle fatigue in ergonomics and occupational field studies are introduced and evaluated in this paper. The sEMG signal analysis and the necessity for developing sEMG analysis techniques for field use in ergonomics are also briefly discussed.

Electromyography↗
PubMed2004

The influence of celecoxib on muscle fatigue resistance and mobility in elderly patients with inflammation.

BACKGROUND: Acute inflammation has a negative effect on the muscular system in elderly patients, compromising the outcome of the underlying disease. OBJECTIVE: The aim of this study was to evaluate the effect of cyclooxygenase-2 (COX-2) inhibition on muscle performance and mobility in hospitalized elderly patients with acute inflammation of infectious origin. METHODS: In this single-blind, controlled trial, consecutively hospitalized elderly patients (age > or = 70 years) with inflammation (C-reactive protein [CRP] levels > or =10 mg/L) due to acute infection were randomly assigned to receive 2 weeks of treatment with the COX-2-selective inhibitor celecoxib, acetaminophen, or no supplementary medication (control). The following variables were assessed at baseline and at 1 and 2 weeks' follow-up: muscle fatigue resistance (primary outcome measure); grip strength and mobility (secondary outcome measures); and levels of the acute-phase markers CRP, interleukin (IL)-1beta, IL-6, IL-10, tumor necrosis factor-alpha (TNF-alpha), and transforming growth factor-beta (TGF-beta) as explanatory variables. RESULTS: Forty-three consecutively hospitalized elderly patients (31 women, 12 men; mean [SD] age, 84 [6] years) were enrolled. Fourteen patients received celecoxib, 14 received acetaminophen, and 15 received no supplementary medication. The change in fatigue resistance was significantly different between groups (P = 0.021, Kruskal-Wallis chi-square test), with significantly greater improvement in patients receiving celecoxib compared with the acetaminophen and control groups (63% increase from baseline; P < 0.05). There were no significant between-group differences in changes in grip strength, mobility, IL-1beta, IL-6, TNF-alpha, or TGF-beta. The changes in levels of IL-10 differed significantly between groups (P = 0.020, Kruskal-Wallis chi-square test), with greater improvement in the celecoxib group compared with the acetaminophen group (P = 0.032). CONCLUSION: The results of this study suggest that COX-2-selective inhibition has a beneficial effect on muscle fatigue resistance in hospitalized elderly patients with acute inflammation of infectious origin. However, until further trials are conducted, the use of COX-2-selective inhibitors for this indication is not recommended.

Acute Disease↗
PubMed1991

[Cardiac assist device with skeletal muscle ventricle--alternate-drive twin pump system as a countermeasure to prevent skeletal muscle fatigue].

Many studies on cardiac assist devices using skeletal muscle ventricle (SMV) require preconditioning for 6-9 weeks as a countermeasure to prevent skeletal muscle fatigue. Therefore this method does not seem to be indicated in cases of acute heart failure. However we performed experiments to develop Alternate-Drive Twin SMVs as a cardiac assist device without preconditioning. Adult mongrel dogs were used. In order to obtain adequate alternating SMV during pattern, fundamental experiments were performed. The function of SMVs prepared by rolled pedunculated sartial muscle was studied hydrodynamically in three groups; continuous driving for one hour in group a (n = 3): intermittent driving for 3 hours in group b (n = 15): intermittent driving for 12 hours in group c (n = 3). Group b was divided into three subgroups with interval for 10 minutes in subgroup I (n = 5), for 20 minutes in subgroup II (n = 5), for 30 minutes in subgroup III (n = 5). In group b and c, the recess interval between driving was set the same as the driving interval in each subgroup. All SMVs were stimulated by electrical bursts. In every experiment pump pressure, pump max dp/dt and pump stroke work index/10 kg body weight were measured for 3 hours. In subgroups I and II, pump function decreased gradually, however, the parameters did not show any change for up to 3 hours in subgroup III. We defined the reduction ratio as the difference of parameters before and after driving divided by the value at the start of driving.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

[Dependence of skeletal muscle fatigue on the membrane polarization of the different types of muscle fibers in tourniquet shock].

Fatigue, polarization level and excitability of striated muscle fibers from ischemia zone were studied on experimental rats under the tourniquet shock. It was established that violation-mediated contraction and fatigue of skeletal muscle was associated with a decrease in a number of muscle fibers with high level of MPP. The article discussed the mechanisms of fatigue and depolarization of muscle fibres in tourniquet shock.

Animals↗
PubMed1992

Simultaneous electromyography and 31P nuclear magnetic resonance spectroscopy--with application to muscle fatigue.

The electromyogram (EMG) is often used to study human muscle fatigue, but the changes in the electromyographic signals during muscle contraction are not well understood in relation to muscle metabolism. The 31P NMR spectroscopy is a semi-quantitative non-invasive method for studying the metabolic changes in human muscle. The aim of this study was to develop a method by which EMG and NMR spectroscopy measurements could be performed simultaneously. All measurements were performed in a whole body 1.5 Tesla NMR scanner. A calf muscle ergometer, designed for use in a whole body NMR scanner, was used. The subject had the left foot strapped to the ergometer. The anterior tibial EMG was recorded by bipolar surface electrodes. A surface coil was strapped to the anterior tibial muscle next to the EMG electrodes. Simultaneous measurements of surface EMG and surface coil 31P NMR spectroscopy were performed in the scanner during an isometric submaximal voluntary contraction until exhaustion, in 6 normal volunteers. Concentrations of phosphocreatine (PCr), inorganic phosphate (P(i)) and pH were analysed together with root mean square (RMS) and median frequency of the EMG. The fatiguing contractions (endured 5-13 min) produced a rapid decline in PCr and pH accompanied by a rapid rise in P(i). The RMS was approximately constant until the normalized PCr concentration declined below 0.6-0.7 and the pH declined below 6.75-6.85; exceeding these metabolic limits was associated with a rapidly increasing RMS value (2-3 times the previous level by exhaustion). The median frequency declined linearly with time and was found to be highly linearly correlated with the pH value (r = 0.82).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Effect of massage on blood flow and muscle fatigue following isometric lumbar exercise.

BACKGROUND: This study attempted to investigate the influence of massage on the skin and the intramuscular circulatory changes associated with localized muscle fatigue. MATERIAL/METHODS: Twenty-nine healthy male subjects participated in two experimental sessions (massage and rest conditions). Subjects lay prone on the table and were instructed to extend their trunks until the inferior portion of their rib cage no longer rested on the table. Subjects held this position for 90 seconds (Load I). Subjects then either received massage on the lumbar region or rested for 5 minutes, then repeated the same load (Load II). Skin blood flow (SBF), muscle blood volume (MBV), skin temperature (ST), and subjects' subjective feelings of fatigue were evaluated using Visual Analogue Scale (VAS). RESULTS: An increase of MBV between pre- and post-load II periods was higher after massage than after rest (p<0.05). An increase of SBF at pre- and post-load II was observed only under massage condition. An increase of SBF between post-load I and pre-load II periods was higher after massage than after rest (p<0.05). An increase of ST between post-load I and post-load II periods was greater after massage than after rest (p<0.05). The VAS score was lower with massage than with rest in the post-treatment period (p<0.01). CONCLUSIONS: A significant difference was observed between massage and rest condition on VAS for muscle fatigue. Lumbar massage administration also appeared to have some effect on increasing skin temperature and enhancement of blood flow in local regions.

Adolescent↗
PubMed2001

Relaxation rate in the assessment of masseter muscle fatigue.

The aim of this study was to assess a simple method of measuring relaxation rate in the jaw-closing system for the purpose of quantifying jaw muscle fatigue. A summary of the various different methods of measuring relaxation rate is also provided. The rates of twitch contraction and relaxation were measured in 30 symptom-free subjects following bilateral direct electrical stimulation of the masseter muscles. The resulting twitch force was recorded via a force transducer placed between the anterior teeth. The transducer was held between the teeth with as little force as possible while four single stimuli were delivered at 5-s intervals. The stimulating electrodes were then removed and replaced and the experiment was repeated. The force records of the resulting twitches were averaged and the half-contraction time, twitch amplitude and half-relaxation time were measured. There was a significant difference in half-relaxation time between males and females, being faster in females (P=0.0045, independent t-test). No significant difference was found in twitch amplitude and half-contraction time between males and females. Half-relaxation time and half-contraction time were independent of twitch amplitude. This method of measuring the relaxation rate of the masseter muscles was found to be practical and the results were reproducible between sessions.

Adult↗