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

Many problems of the lumbar spine that cause pain are attributed to instability. The ligamentous spine (without muscles) is unstable at very low compressive loads. This study examined the hypothesis that instability of the lumbar spine is prevented under normal circumstances by the stiffness of spinal musculature, without active responses from the neuromuscular control system. The effect of muscle activity (force and stiffness) on the stability of the lumbar spine was analyzed for maximum voluntary extension efforts with different spinal postures in the sagittal plane. The analysis included realistic three-dimensional representation of the muscular anatomy with muscles crossing several motion segments. The stiffness of motion segments was represented using in vitro measured properties. Under a range of conditions with maximum extension effort, active muscle stiffness was required to prevent the lumbar spine from buckling. The dimensionless value of the muscle stiffness parameter q as a function of activation and length had to be greater than a critical value in the range of 3.7-4.7 in order to stabilize the spine. Experimentally determined values of q ranged from 0.5 to 42. These analyses demonstrate how changes in motion segment stiffness, muscle activation strategy, or muscle stiffness (due to degenerative changes, injuries, fatigue, and so on) might lead to spinal instability and "self-injury."
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PMID:Role of muscles in lumbar spine stability in maximum extension efforts. 747 60

1. The initiation of exercise-induced muscle injury is thought to be the result of high tensile stresses produced in the muscle during eccentric contractions. Materials science theory suggests that high tensile stresses could initiate the injury during the first eccentric contraction (normal stress theory) or after multiple eccentric contractions (materials fatigue). It was the objective of this study to investigate the two possibilities. 2. Rat soleus muscles (n = 66; 11 protocols with 6 muscles per protocol) were isolated, placed in an oxygenated Krebs-Ringer buffer at 37 degrees C, and baseline measurements were made. The muscle then performed an injury protocol which consisted of between zero and ten eccentric contractions (muscle starting length = 0.90 soleus muscle length, L0; length change = 0.25 L0; velocity = 1.5 L0/s; peak force = 180% maximal isometric tetanic tension (P0); time between contractions = 4 min; total duration of the injury protocol = 40 min). At the end of the injury protocol, the muscle was incubated in buffer for 1 h; every 15 min, an isometric twitch and tetanus were performed and lactate dehydrogenase (LDH) release was measured. Total muscle [Ca2+] was measured at the end of the incubation. 3. Change-point regression analysis indicates that at 0 min into the incubation, declines in P0, maximal rate of tension development (+dP/dt), maximal rate of relaxation (-dP/dt), and muscle stiffness (dP/dx) became significantly greater after eight eccentric contractions (p < or = 0.05). No relation was found between the number of eccentric contractions performed and the LDH activity at 0 min into the incubation, although after 60 min of incubation, LDH activity in the buffer was linearly related to eccentric contraction number (p = 0.01). There was no relationship between total muscle [Ca2+] and eccentric contraction number. These findings support the materials fatigue hypothesis of exercise-induced muscle injury.
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PMID:Materials fatigue initiates eccentric contraction-induced injury in rat soleus muscle. 822 14

This study examined the catchlike property of skeletal muscle during eccentric and concentric isovelocity contractions of fresh and fatigued quadriceps femoris muscles of 10 healthy subjects. During concentric contractions of fresh muscles, stimulation trains that elicited a catchlike response (CITs) produced greater force outputs and rates of rise force than comparable constant-frequency trains. These enhancements became more pronounced during fatigue. CITs were less effective in enhancing forces during eccentric contractions but did improve the rates of rise of force. Overall, the CIT that produced the greatest augmentation had a 5-ms initial interpulse interval. Proposed mechanisms for the catchlike property involve enhanced muscle stiffness for more efficient transmission of tension and increased calcium release. These results suggest that stimulation trains that take advantage of the catchlike property of skeletal muscle may be helpful during clinical applications where neuromuscular electrical stimulation is used to restore function in patients with damaged central nervous systems.
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PMID:Catchlike property of human muscle during isovelocity movements. 880 13

The short latency stretch-reflex component (M1) and its interactions with muscle stiffness and with muscle performance were investigated before and after long-term stretch-shortening cycle (SSC) exercise. Dramatic fatigue induced reduction in maximal SSC performance capability, and electromyographic activity was accompanied by a consistent decrease in the M1 reflex component and eccentric peak stiffness of the muscle. It can be suggested, therefore, that the decreased muscle performance is not simply a direct effect of central or peripheral fatigue, but is partly due to impairment of the ability to utilize stiffness-related elastic energy.
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PMID:Interaction between muscle stiffness and stretch reflex sensitivity after long-term stretch-shortening cycle exercise. 970 54

A 43-year-old woman presented at the age of 38 with joint pains and muscle stiffness. Tender points were found fulfilling ACR criteria (1) for fibromyalgia. She had well developed muscles and decreasing muscle power since the age of 35. Muscle pains increased after exercise. Her 10-year-old son had similar symptoms and one paralytic attack. Muscle pain and fatigue increasing with age were found by history in three close relatives. Forearm cold water test produced myotonia in both mother and son. Electromyography was normal and muscle biopsy showed minor unspecific changes. Biochemical investigation of muscle mitochondrial function was normal. Peroral potassium load test produced complete muscle paralysis at a potassium serum level of 5.0 mmol/l. Autosomal dominant hyperkalemic periodic paralysis was diagnosed. Frequent carbohydrate enriched meals, peroral bendroflumethiazide and restriction to submaximal exercise improved muscle and joint pain. Salbutamol peroral spray relieved the periodic weakness.
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PMID:Fibromyalgia in hyperkalemic periodic paralysis. 980 5

It has been suggested that during repeated long-term stretch-shortening cycle (SSC) exercise the decreased neuromuscular function may result partly from alterations in stiffness regulation. Therefore, interaction between the short latency stretch-reflex component (M1) and muscle stiffness and their influences on muscle performance were investigated before and after long lasting SSC exercise. The test protocol included various jumps on a sledge ergometer. The interpretation of the sensitivity of the reflex was based on the measurements of the patellar reflexes and the M1 reflex components. The peak muscle stiffness was measured indirectly and calculated as a coefficient of the changes in the Achilles tendon force and the muscle length. The fatigue protocol induced a marked impairment of the neuromuscular function in maximal SSC jumps. This was demonstrated by a 14.1%-17.7% (n.s. - P < 0.001) reduction in the mean eccentric forces and a 17.3%-31.8% (n.s. - P < 0.05) reduction in the corresponding M1 area under the electromyograms. Both of these methods of assessing the short latency reflex response showed a clear deterioration in the sensitivity of the reflex after fatigue (P < 0.05-0.001). This was also the case for the eccentric peak stiffness of the soleus muscle which declined immediately after fatigue by 5.4% to 7.1% (n.s. - P < 0.05) depending on the jump condition. The results observed would suggest that the modulation of neural input to the muscle was at least partly of reflex origin from the contracting muscle, and furthermore, that the reduced muscle stiffness which accompanied the decreased reflex sensitivity could have been partly responsible for the weakened muscle performance due to impaired utilization of elastic energy.
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PMID:Reduced stretch reflex sensitivity and muscle stiffness after long-lasting stretch-shortening cycle exercise in humans. 980 40

Myofascial pain syndrome (MPS) is a common illness, characterised by acute or chronic focal pain, muscle stiffness and fatigue. The pathophysiology of MPS remains unclear. Previous preliminary studies have demonstrated therapeutic efficacy of the muscle relaxant botulinum toxin type A (BTX-A) in the treatment of MPS. A single-centre, randomised trial compared the effects of BTX-A with the steroid methylprednisolone (both administered intramuscularly with 0.5% bupivacaine), in 40 patients suffering from chronic myofascial pain in the piriformis, iliopsoas or scalenus anterior muscles. Thirty days after receiving an injection of either BTX-A or steroid followed by post-injection physiotherapy, pain severity had decreased significantly from baseline in both treatment groups, with no significant difference between the two treatment groups. However, the baseline pain score was significantly higher in the BTX-A treatment group compared with the steroid group (7.9 vs. 7.3), and the reduction in pain score between baseline and 30 days post-injection was greater in the BTX-A group compared with the steroid group (-3.9 vs. -3.5; P=0.06). At 60 days post-injection, the pain severity score for the BTX-A-treated patients was statistically significantly lower than the pain score for the steroid-treated population (2.3 vs. 4.9). Furthermore, the reduction in pain score in the BTX-A group at 60 days post-injection was greater than at 30 days (-5.5 vs. -3.9), whereas the effect of the steroid had begun to wane. These results indicate the superior efficacy of BTX-A over conventional steroid treatment in patients suffering from MPS, when combined with appropriate physiotherapy.
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PMID:A comparative trial of botulinum toxin type A and methylprednisolone for the treatment of myofascial pain syndrome and pain from chronic muscle spasm. 1069 8

Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) phase in SSC action such as hopping and running. The amplitude of the stretch reflex component - and the subsequent force enhancement - may vary according to the increased stretch-load but also to the level of fatigue. While moderate SSC fatigue may result in slight potentiation, the exhaustive SSC fatigue can dramatically reduce the same reflex contribution. SSC fatigue is a useful model to study the processes of reversible muscle damage and how they interact with muscle mechanics, joint and muscle stiffness. All these parameters and their reduction during SSC fatigue changes stiffness regulation through direct influences on muscle spindle (disfacilitation), and by activating III and IV afferent nerve endings (proprioseptic inhibition). The resulting reduced stretch reflex sensitivity and muscle stiffness deteriorate the force potentiation mechanisms. Recovery of these processes is long lasting and follows the bimodal trend of recovery. Direct mechanical disturbances in the sarcomere structural proteins, such as titin, may also occur as a result of an exhaustive SSC exercise bout.
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PMID:Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. 1089 28

The objective of this study was to investigate muscle and tendon stiffness in the triceps surae muscles in patients who had previously had a stroke. The participants were 12 men showing slight to moderate degrees of muscle tonus in the affected leg. All patients showed minimal or no overt clinical motor symptoms, and all walked without mechanical aid. Muscle strengths in isometric and isokinetic activities were measured, as was passive resistance during plantarflexion in each leg. Walking speed was also measured. Evaluations of physical performance and muscle tone were made. Muscle and tendon stiffness was calculated from measurements whilst passively stretching during electrical stimulation, separately for each leg. Muscle strength was significantly higher in the non-affected than in the affected leg. Muscle stiffness was significantly higher in the affected leg than in the non-affected leg. Tendon stiffness was significantly higher in the non-affected than in the affected leg. The higher muscle stiffness in the affected leg might enhance the possibility for storing elastic energy during preactivation. Lower tendon stiffness in the affected leg might reduce the development of fatigue in movements at low velocities.
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PMID:Muscle and tendon stiffness in patients with upper motor neuron lesion following a stroke. 1095 69

In clinical settings, no method has been established to examine the fatigue of a latissimus dorsi muscle (LDM) preconditioned for cardiomyoplasty. We examined the feasibility of measuring muscle stiffness (tactile stiffness) to evaluate muscle fatigue in situ using our tactile sensor. We stimulated canine LDM with burst pacing and monitored both stiffness and tension to determine their relationship. In both dissected LDM and LDM in situ, the decrements of these parameters during burst pacing were compared between preconditioned and unconditioned LDM. In measurement in situ, the sensor probe was placed on the LDM through a small incision. Strong statistical correlation was shown between stiffness and tension (r = 0.935). In decrements of stiffness in situ, there were statistically significant differences between preconditioned and unconditioned LDM. Our tactile sensor system can provide an efficient method for evaluating fatigue of muscles in situ without measuring muscle tension.
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PMID:Use of tactile stiffness to detect fatigue in the latissimus dorsi muscle. 1109 Nov 70


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