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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. In 67 single motor units, the mechanical properties, the recruitment and derecruitment thresholds, and the discharge rates were recorded concurrently in the first dorsal interosseus (FDI) of human subjects during intermittent fatiguing contractions. The task consisted of isometric ramp-and-hold contractions performed at 50 % of the maximal voluntary contraction (MVC). The purpose of this study was to examine the influence of fatigue on the behaviour of motor units with a wide range of activation thresholds. 2. For low-threshold (< 25 % MVC) motor units, the mean twitch force increased with fatigue and the recruitment threshold either did not change or increased. In contrast, the twitch force and the activation threshold decreased for the high-threshold (> 25 % MVC) units. The observation that in low-threshold motor units a quick stretch of the muscle at the end of the test reset the unit force and recruitment threshold to the prefatigue value suggests a significant role for fatigue-related changes in muscle stiffness but not twitch potentiation or motor unit synchronization. 3. Although the central drive intensified during the fatigue test, as indicated by an increase in surface electromyogram (EMG), the discharge rate of the motor units during the hold phase of each contraction decreased progressively over the course of the task for motor units that were recruited at the beginning of the test, especially the low-threshold units. In contrast, the discharge rates of newly activated units first increased and then decreased. 4. Such divergent behaviour of low- and high-threshold motor units could not be individually controlled by the central drive to the motoneurone pool. Rather, the different behaviours must be the consequence of variable contributions from motoneurone adaptation and afferent feedback from the muscle during the fatiguing contraction.
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PMID:Motor unit behaviour and contractile changes during fatigue in the human first dorsal interosseus. 1148 19

We hypothesized that in congestive heart failure (CHF) slow-twitch but not fast-twitch muscles exhibit decreased fatigue resistance in the sense of accelerated reduction of muscle force during activity. Experiments were carried out on anaesthetized rats 6 weeks after induction of myocardial infarction or a sham operation (Sham). Animals with left ventricular end-diastolic pressure (LVEDP) > 15 mmHg under anaesthesia were selected for the CHF group. There was no muscle atrophy in CHF. Force generation by in situ perfused soleus (Sol) or extensor digitorum longus (EDL) muscles was recorded during stimulation (trains at 5 Hz for 6 s (Sol) or 10 Hz for 1.5 s (EDL) at 10 or 2.5 s intervals, respectively) for 1 h in Sol and 10 min in EDL at 37 degrees C. Initial force was almost the same in Sol from CHF and Sham rats, but relaxation was slower in CHF. Relaxation times (95-5 % of peak force) were 177 +/- 55 and 131 +/- 44 ms in CHF and Sham, respectively, following the first stimulation train. After 2 min of stimulation the muscles transiently became slower and maximum relaxation times were 264 +/- 71 and 220 +/- 45 ms in CHF and Sham, respectively (P < 0.05). After 60 min they recovered to 204 +/- 60 and 122 +/- 55 ms in CHF and Sham, respectively (P < 0.05). In CHF but not in Sham rats the force of contraction of Sol declined from the second to the sixtieth minute to 70 % of peak force. The EDL of both CHF and Sham fatigued to 24-28 % of initial force, but no differences in contractility pattern were detected. Thus, slow-twitch muscle is severely affected in CHF by slower than normal relaxation and significantly reduced fatigue resistance, which may explain the sensation of both muscle stiffness and fatigue in CHF patients.
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PMID:Contractile properties of in situ perfused skeletal muscles from rats with congestive heart failure. 1195 44

Primary hypothyroidism is a chronic and insidious disease caused by failure of thyroid hormone production. We observed a 38-year-old woman admitted to our hospital due to progressive proximal weakness, muscle pain and fatigue during mild exercise. Laboratory tests showed features of rhabdomyolysis and hypothyroidism. After examination of the thyroid, we reached a diagnosis of Hashimoto's thyroiditis and hypothyroid myopathy. Hypothyroidism should be considered as a differential diagnosis of creatine kinase elevation; actually, neuromuscular symptoms and signs occur in most newly diagnosed patients with thyroid diseases. Hypothyroidism presenting as muscle stiffness and pseudohypertrophy is called 'Hoffman's syndrome'.
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PMID:Hoffman's syndrome: muscle stiffness, pseudohypertrophy and hypothyroidism. 1258 16

The effects of 10 mM (high) and 70 microM (physiologically relevant) caffeine on force, work output, and power output of isolated mouse extensor digitorum longus (EDL) and soleus muscles were investigated in vitro during recovery from fatigue at 35 degrees C. To monitor muscle performance during recovery from fatigue, we regularly subjected the muscle to a series of cyclical work loops. Force, work, and power output during shortening were significantly higher after treatment with 10 mM caffeine, probably as a result of increased Ca2+ release from the sarcoplasmic reticulum. However, the work required to relengthen the muscle also increased in the presence of 10 mM caffeine. This was due to a slowing of relaxation and an increase in muscle stiffness. The combination of increased work output during shortening and increased work input during lengthening had different effects on the two muscles. Net power output of mouse soleus muscle decreased as a result of 10 mM caffeine exposure, whereas net power output of the EDL muscle showed a transient, significant increase. Treatment with 70 microM caffeine had no significant effect on force, work, or power output of EDL or soleus muscles, suggesting that the plasma concentrations found when caffeine is used to enhance performance in human athletes might not directly affect the contractile performance of fatigued skeletal muscle.
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PMID:Effects of caffeine on mouse skeletal muscle power output during recovery from fatigue. 1450 97

Lifting-induced fatigue may influence neuromuscular control of spinal stability. Stability is primarily controlled by muscle recruitment, active muscle stiffness, and reflex response. Fatigue has been observed to affect each of these neuromuscular parameters and may therefore affect spinal stability. A biomechanical model of spinal stability was implemented to evaluate the effects of fatigue on spinal stability. The model included a 6-degree-of-freedom representation of the spine controlled by 12 deformable muscles from which muscle recruitment was determined to simultaneously achieve equilibrium and stability. Fatigue-induced reduction in active muscle stiffness necessitated increased antagonistic cocontraction to maintain stability resulting in increased spinal compression with fatigue. Fatigue-induced reduction in force-generating capacity limited the feasible set of muscle recruitment patterns, thereby restricting the estimated stability of the spine. Electromyographic and trunk kinematics from 21 healthy participants were recorded during sudden-load trials in fatigued and unfatigued states. Empirical data supported the model predictions, demonstrating increased antagonistic cocontraction during fatigued exertions. Results suggest that biomechanical factors including spinal load and stability should be considered when performing ergonomic assessments of fatiguing lifting tasks. Potential applications of this research include a biomechanical tool for the design of administrative ergonomic controls in manual materials handling industries.
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PMID:Influence of fatigue in neuromuscular control of spinal stability. 1515 Nov 56

Rippling muscle disease (RMD) is a rare muscle disorder characterised by muscle stiffness, exercise induced myalgia, and cramp-like sensations. It is genetically heterogeneous and can be acquired, but most cases show autosomal dominant inheritance due to mutations in the caveolin-3 (CAV3) gene. We report a novel heterozygous missense mutation in CAV3 in a Belgian family with autosomal dominant RMD. A 40 year old woman complained of fatigue, exercise induced muscle pain, and muscle cramps since the age of 35. Neurological examination revealed percussion induced rapid muscle contractions (PIRCs) and localised muscle mounding on percussion; muscle rippling was not observed. Creatine kinase (CK) was elevated but electromyography and nerve conduction studies were normal. Fluorescence immunohistochemistry revealed reduced caveolin-3 and dysferlin staining in a quadriceps muscle biopsy. Western blot analysis confirmed severely reduced caveolin-3 levels, whereas dysferlin was normal. Sequence analysis of the two coding exons of CAV3 revealed a hitherto unreported heterozygous C82A transversion in the first exon, predicting a Pro28Thr amino acid exchange. Thr patient's first degree relatives did not present with neuromuscular complaints, but PIRCs, muscle mounding, and muscle rippling were found in the mother, who also carried the CAV3 mutation.
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PMID:Novel missense mutation in the caveolin-3 gene in a Belgian family with rippling muscle disease. 1531 33

This double-blind, placebo-controlled, crossover study investigated the effect of blackcurrant anthocyanin (BCA) intake on peripheral circulation during rest and during typing work by using near-infrared spectroscopy (NIRS), and it also assessed improvement in shoulder stiffness caused by poor local circulation. In a resting circulation study, nine healthy male subjects took capsules of BCA at a dosage of 17 mg kg(-1) or placebo (isoenergetic sugar). NIRS was used to measure left forearm blood flow (FBF) following venous occlusion and muscle oxygen consumption following arterial occlusion prior to and hourly for 4 h after ingestion of BCA. Plasma anthocyanin concentration was measured prior to ingestion and 1, 2, and 4 h later. FBF increased significantly 2 h after BCA ingestion [BCA 1.22 (0.13)-fold increase relative to pre-values vs placebo 0.83 (0.06) of pre-values; P < 0.05] and then tended to increase for a further 3 h after ingestion [BCA 1.26 (0.15)-fold increase relative to pre-values vs placebo 0.82 (0.07) of pre-values; P = 0.078]. There was, however, no significant difference in muscle oxygen consumption between BCA and placebo intake at any time point. In a typing work study, 11 healthy subjects took capsules of BCA (7.7 mg kg(-1)) or placebo (isoenergetic sugar) daily for 2 weeks. The subjects then performed intermittent typing workload for 30 min in order to induce acute shoulder stiffness. During the workload, total hemoglobin and oxygenated hemoglobin (oxy-Hb) were determined using NIRS and myoelectric signals measured in the right trapezius muscle using electromyography (EMG). The viscoelasticity of the trapezius muscle was also evaluated using a muscle stiffness meter before and after the typing workload. BCA intake prevented the decrease in oxy-Hb significantly (P < 0.05), and also tended to alleviate the increase in root mean square (RMS) of the EMG during the typing workload, and also muscle stiffness after the workload. There was no improvement in typing performance with BCA intake. The results of this study suggest that intake of BCA may improve shoulder stiffness caused by typing work by increasing peripheral blood flow and reducing muscle fatigue.
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PMID:Effects of blackcurrant anthocyanin intake on peripheral muscle circulation during typing work in humans. 1560 79

The metal stem of the totally replaced hip carries load and resists fatigue, but it is electrochemically corroded. Metallic atoms act as haptens, induce type 1 T-helper cells/Th1-type immune responses and enhance periprosthetic osteolysis. Stiff metal implants, which do not have the same elasticity as the surrounding bone, cause stress shielding. Cyclic loading and lack of ligamentous support lead to mechanical and ischemia reperfusion injury and particle formation from bone, polymethylmethacrylate, and porous implant surfaces, which accelerate third-body polyethylene wear. Surgical injury and micromotion induce the formation of a fibrous capsule interface. Type-B lining cells produce lubricin and surface-active phospholipids to promote solid-to-solid lubrication but may loosen the implant from bone. The pumping action of the cyclically loaded joint and synovial fluid pressure waves dissect the implant-host interface and transports polyethylene particles and pro-inflammatory mediators to the interface. Hyaluronan induces formation of a synovial lining like layer. Because of its localization close to bone, foreign body inflammation at the interface stimulates osteoclastogenesis and peri-implant bone loss. Metal-on-metal and ceramic-on-ceramic pairs might minimize third body wear, but can lead to high-impact load of the acetabulum. Diamond coating of a metal-on-polyethylene couple might solve both of these problems. The basic biomaterial solutions allow good mechanical performance and relatively long life in-service, but surface modifications (porous coating, hydroxyapatite, diamond, bioglass, and others) may facilitate performance of the implant and improve the biomaterial and body interfaces.
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PMID:The microenvironment around total hip replacement prostheses. 1566 1

Knowledge of the muscle activation and the development of muscle fatigue may provide more inside in the effects of long-term driving in the occurrence of health problems in the neck/shoulder/back area. The basic assumption behind fatigue detection with electromyography (EMG) is an increase in the EMG amplitude and a decrease of the mean frequency (MF). This study aimed at checking this assumption in monotonous task performance with low level activity during car driving. Surface electromyography was captured from left and right trapezius and deltoid muscles, during a repetitive, non-continuous, driving task (gearing and steering) and the active parts were separated from the non-active parts. Muscle stiffness was reported by more than half of the subjects after a 1 h drive. Only for the active parts a significant decrease of the MF was seen. But also the EMG amplitude decreased significantly. Two possible mechanisms are posted in literature for this finding: no extra recruitment of motor units (MU) and potentiation of muscle fibers. Literature also hypothesizes that low-force occupational work engages only a fraction of the MU available for recruitment and that these units are selectively type I muscle fibers (Cinderella fibers). Initiators of this phenomenon are probably the time lag between activations and the stress from driving and vibration exposure.
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PMID:Assessment of muscle fatigue in low level monotonous task performance during car driving. 1576 73

To resolve the trunk redundancy to determine muscle forces, spinal loads, and stability margin in isometric forward flexion tasks, combined in vivo-numerical model studies was undertaken. It was hypothesized that the passive resistance of both the ligamentous spine and the trunk musculature plays a crucial role in equilibrium and stability of the system. Fifteen healthy males performed free isometric trunk flexions of approximately 40 degrees and approximately 65 degrees +/- loads in hands while kinematics by skin markers and EMG activity of trunk muscles by surface electrodes were measured. A novel kinematics-based approach along with a nonlinear finite element model were iteratively used to calculate muscle forces and internal loads under prescribed measured postures and loads considered in vivo. Stability margin was investigated using nonlinear, linear buckling, and perturbation analyses under various postures, loads and alterations in ligamentous stiffness. Flexion postures significantly increased activity in extensor muscles when compared with standing postures while no significant change was detected in between flexed postures. Compression at the L5-S1 substantially increased from 570 and 771 N in upright posture, respectively, for +/-180 N, to 1912 and 3308 N at approximately 40 degrees flexion, and furthermore to 2332 and 3850 N at approximately 65 degrees flexion. Passive ligamentous/muscle components resisted up to 77% of the net moment. In flexion postures, the spinal stability substantially improved due both to greater passive stiffness and extensor muscle activities so that, under 180 N, no muscle stiffness was required to maintain stability. The co-activity of abdominal muscles and the muscle stiffness were of lesser concern to maintain stability in forward flexion tasks as compared with upright tasks. An injury to the passive system, on one hand, required a substantial compensatory increase in active muscle forces which further increased passive loads and, hence, the risk of injury and fatigue. On the other hand, it deteriorated the system stability which in turn could require greater additional muscle activation. This chain of events would place the entire trunk active-passive system at higher risks of injury, fatigue and instability.
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PMID:Model and in vivo studies on human trunk load partitioning and stability in isometric forward flexions. 1638 91


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