Changes in blood volume and oxygenation level in a working muscle during a crank cycle

PURPOSE: This study examined circulatory and metabolic changes in a working muscle during a crank cycle in a pedaling exercise with near-infrared spectroscopy (NIRS). METHODS: NIRS measurements sampled under stable metabolic and cadence conditions during incremental pedaling exercise were reordered according to the crank angles whose signals were obtained in eight male subjects. RESULTS: The reordered changes in muscle blood volume during a crank cycle demonstrated a pattern change that corresponded to changes in pedal force and electrical muscle activity for pedal thrust. The top and bottom peaks for muscle blood volume change at work intensities of 180 W and 220 W always preceded (88 +/- 32 and 92 +/- 23 ms, respectively) those for muscle oxygenation changes. Significant differences in the level of NIRS parameters (muscle blood volume and oxygenation level) among work intensities were noted with a common shape in curve changes related to pedal force. In addition, a temporary increase in muscle blood volume following a pedal thrust was detected at work intensities higher than moderate. This temporary increase in muscle blood volume might reflect muscle blood flow restriction caused by pedal thrusts. CONCLUSION: The results suggest that circulatory and metabolic conditions of a working muscle can be easily affected during pedaling exercise by work intensity. The present method, reordering of NIRS parameters against crank angle, serves as a useful measure in providing additional findings of circulatory dynamics and metabolic changes in a working muscle during pedaling exercise.     

基于CT的骨骼肌参数诊断肿瘤病人肌少症

肌少症是一组以骨骼肌质量减少、肌力下降,进而导致机体功能减退为主要特征的临床综合征,与肿瘤病人临床治疗效果和生存时间密切相关。CT不仅是诊断肿瘤的常用方法,而且可以准确评估肌少症,但其测量部位及标准尚未统一。就第一、三腰椎,第三颈椎和第四胸椎的骨骼肌指数以及腰肌指数、体积,骨骼肌密度、度量等常用骨骼肌参数在肿瘤病人中的应用予以综述。     

Changes in muscle fiber size and composition in response to heavy-resistance exercise

Progressive resistance exercise was used to induce hypertrophy in the right palmaris longus muscle (PLM) of 16 cats. The left PLM served as the non-exercised intra-animal control. After an average 150 +/- 26.6 wk of training, left and right PLMs were removed and weighed. Muscle fibers were typed using standard histochemical techniques. Mean fiber cross-sectional area, connective tissue content, and muscle fiber length were determined. The right exercised PLM demonstrated a 24.2 +/- 6.9% increase in muscle mass. Mean muscle fiber cross-sectional area increased 11.0 +/- 7.3% in the exercised muscles. No change in connective tissue content, fiber length, or fiber type composition was observed. The results show that increases in muscle fiber cross-sectional area do not account for all the observed increases in muscle mass, and that other mechanisms, such as muscle fiber hyperplasia, may play a role in contributing to muscle mass increases.     

The paradox of sympathetic vasoconstriction in exercising skeletal muscle.

Is there sympathetic vasoconstriction in exercising skeletal muscle? Although convincing evidence exists that demonstrates vasoconstriction in active muscle, the proposition that the sympathetic nervous system constricts skeletal muscle during exercise poses a paradox, given the robust vasodilation that occurs in muscle during exercise. Ultimately, muscle perfusion is a balance between metabolic vasodilation and sympathetic vasoconstriction.     

Targeting the immune system to improve ventilatory function in muscular dystrophy

Skeletal muscle is a unique tissue whose function is dependent in great part on its ultrastructure. Repeated intense muscular contractions, especially those resulting in muscle lengthening, can lead to alterations in muscle structure (i.e., muscle damage) and subsequent decline in contractile force. The damage-induced decline in contractile force can have a significant impact on exercise performance during an athletic performance. In some disease conditions such as Duchenne muscular dystrophy (DMD), the muscles are more vulnerable to contraction-induced damage than normal muscle. In the case of the respiratory muscles, for example, the diaphragm, the consequences of muscle weakness secondary to damage are profound in that respiratory failure leading to premature death often ensues. In normal skeletal muscle, damage is followed by an inflammatory response involving multiple cell types that subsides after several days. This transient inflammatory response is a normal homeostatic reaction to muscle damage. In contrast, a persistent inflammatory response is observed in dystrophic skeletal muscle that leads to an altered extracellular environment, including an increased presence of inflammatory cells (e.g., macrophages) and elevated levels of various inflammatory cytokines (e.g., TNF-alpha, TGF-beta). The signals that lead to successful muscle repair in healthy muscle may promote muscle wasting and fibrosis in dystrophic muscle. Preliminary data indicate that immunosuppression in dystrophic (mdx) mice has beneficial effects on some indices of muscle dysfunction, thereby indicating that targeted immunosuppression may offer some promise in delaying the pathological progression of this insidious muscular disease.     

Sex- and osteoarthritis-related differences in muscle co-activation during weight-bearing tasks

BackgroundIndividuals with knee osteoarthritis (OA) demonstrate impairments in muscle function (i.e. muscle weakness, high muscle co-activation believed to have detrimental effects on joint integrity). Women with knee OA exhibit poorer health outcomes than men. Sex and muscle function are known risk factors for knee OA. It is unclear how these risk factors are associated with muscle function in knee OA and the implications for disease aetiology.Research questionHow does sex and knee osteoarthritis disease status relate to muscle function, specifically strength and muscle co-activation, during walking, stair negotiation and sit-to-walk activities.MethodsA cross-sectional study assessed muscle co-activation in 77 individuals with knee OA (mean[SD], 62.5[8.1] years; 48/29 women/men) and 18 age-matched controls (62.5[10.4] years; 9/9 women/men), during a series of walking, stair ascent and descent and sit-to-walk activities. Muscle strength of the knee extensors and flexors was assessed using maximal voluntary isometric contractions (MVIC). Electromyography was recorded from the vastus lateralis/medalis, rectus femoris, biceps femoris, semitendinosus, medial/lateral gastrocnemius normalised to MVIC. Multiple regression assessed the relationship between sex, disease status, and muscle strength on muscle co-activation.ResultsIndividuals with knee OA were weaker than controls, had higher hamstrings-quadriceps and medial-lateral co-activation for specific phases of gait. Women were weaker than men with higher muscle co-activation across all activities. Sex and muscle weakness, but not age or disease status predicted high muscle co-activation.SignificanceHigh muscle co-activation was associated with female sex and muscle weakness regardless of disease status and age. High muscle co-activation is believed to be a compensatory mechanism for muscle weakness to maintain a certain level of function. High muscle co-activation is also thought to have detrimental effects on cartilage and joint integrity this may explain high muscle co-activation in women with muscle weakness and contribute to increased risk of incidence and progression of knee OA in women.     

Effect of creatine on aerobic and anaerobic metabolism in skeletal muscle in swimmers.

OBJECTIVE: To examine the effect of a relatively low dose of creatine on skeletal muscle metabolism and oxygen supply in a group of training athletes. METHODS: 31P magnetic resonance and near-infrared spectroscopy were used to study calf muscle metabolism in a group of 10 female members of a university swimming team. Studies were performed before and after a six week period of training during which they took either 2 g creatine daily or placebo. Calf muscle metabolism and creatine/choline ratios were studied in resting muscle, during plantar flexion exercise (10-15 min), and during recovery from exercise. RESULTS: There was no effect of creatine on metabolite ratios at rest or on metabolism during exercise and recovery from exercise. Muscle oxygen supply and exercise performance were not improved by creatine if compared to placebo treated subjects. CONCLUSIONS: Oral creatine supplementation at 2 g daily has no effect on muscle creatine concentration, muscle oxygen supply or muscle aerobic or anaerobic metabolism during endurance exercise.     

Dynamic and static stretch responses in muscle spindle receptors in fatigued muscle

Dynamic and static stretch responses in muscle spindles were investigated in fatigued muscle to determine if acute adaptations do occur in receptor discharge as has been shown after contractions of short duration. Fatigue to 60-50% maximum tetanic tension was induced in the isolated gastrocnemius muscle in 16 cats by sustained, 7 X threshold electrical stimulation (100 Hz) of the cut L7 ventral root and S1 ventral root. Group Ia and II afferent fiber responses to slow ramp stretches (5 mm X s-1) and vibration (100 Hz) applied to the Achilles tendon were monitored before and immediately after muscle tetany to fatigue. Changes in firing characteristics were similar when results from faster (25-30 mm X s-1) ramp stretches were contrasted. During muscle fatigue, decreases in response latency to displacement and increases in resting discharge, mean frequency during stretch, and frequency of firing to vibration were predominant in both afferent fiber types. Static responses were generally lower, indicating a decrease in position sensitivity. Resting muscle force and passive peak muscle stiffness were consistently higher following contraction. The sum effects of these proprioceptive afferent and mechanical muscle responses would be to increase muscle stiffness and thus resist yield in muscle length to perturbations at lower muscle forces. The magnitude of these adaptations in proprioceptive discharge appears dependent on intrafusal muscle fiber activation.     

Magnetic resonance findings in skeletal muscle tears

Magnetic resonance (MR) images of skeletal muscle tears can clearly delineate the severity of muscle injury. Although MR imaging is seldom necessary in patients with acute muscle trauma, it can be helpful in deciding on clinical management. The two major MR findings in acute muscle tears are deformity of the muscle and the presence of abnormal signal reflecting hemorrhage and edema. In acute tears, methemoglobin within the extravascular blood causes high-signal areas on both T1-and T2-weighted images. With partial tears, the blood may dissect in a distinctive linear pattern along the muscle bundles and fibers. As healing begins, the muscle signal diminishes, first on the T1-weighted images and then on the T2-weighted images. When there is residual abnormal signal on images obtained more than several months after the injury, it is presumed to represent hemorrhage from recurrent tears. In patients with a questionable history of a remote injury, the clinical presentation may be that of persistent pain or a soft tissue mass. In these cases MR imaging may identify the cause of the pain and can exclude a neoplasm by proving that the mass is a hypertrophied or retracted muscle. Thus, MR imaging has a limited, but occasionally important role in selected patients with skeletal muscle tears.     

Indium-111 monoclonal anti-myosin antibody in assessing skeletal muscle damage in trauma

Accurate assessment of the severity of soft tissue damage particularly skeletal muscle associated with fractures in trauma patients is important in determining the plan of management and prognosis. We used Indium-111 labelled anti-myosin to determine the extent of skeletal muscle injury in five patients involved in traumatic accidents. We found abnormal uptake in all 20 sites of muscle injury in four patients, 13 at the sites of fractures and seven away from fracture sites. There was good correlation between the degree of uptake and the extent of muscle injury. No uptake was seen in a case with no fracture and no muscle injury. At surgery this case proved to be haemarthrosis of the left knee. Indium-111 anti-myosin scanning is a potentially sensitive and useful technique in assessing extent of acute muscle injury in trauma patients.     

Intrinsic and extrinsic risk factors for muscle strains in Australian football

Muscle strains are common injuries in Australian football and other sports involving sprinting. Between 1992 and 1999, 83,503 player-matches in the Australian Football League were analyzed for risk of muscle strain injuries using logistic regression analysis. There were 672 hamstring, 163 quadriceps, and 140 calf muscle strain injuries. All three types of muscle strains were associated with significant risk factors. For all injuries, the strongest risk factor was a recent history of that same injury and the next strongest risk factor was a past history of the same injury. History of one type of muscle strain increased the risk for certain types of other muscle strains. Age was a risk factor for hamstring and calf muscle strains (even when adjusted for injury history) but was not a risk factor for quadriceps muscle strains. Quadriceps muscle injuries were more common in shorter players and were more likely when there had been less rainfall at the match venue in the previous week. Quadriceps muscle injuries were significantly more common in the dominant kicking leg, whereas hamstring and calf muscle injuries showed no difference in frequency between the dominant and nondominant legs.     

彩色多普勒超声在高龄人群小腿肌静脉丛病变中的诊断价值

目的探讨彩色多普勒超声对高龄人群小腿肌静脉丛病变诊断价值。方法分析78例小腿肌静脉丛病变患者超声图像特征,其中,53例小腿肌静脉丛扩张并静脉瓣功能不全,25例小腿肌静脉丛血栓。结果彩色多普勒超声不仅能清楚显示病变的大小和位置,而且能准确反映病变的特征及与周边组织的关系。结论彩色多普勒超声诊断小腿肌静脉丛病变简单、无创、方便,可以作为首选的普检方法。     

Suturing versus immobilization of a muscle laceration. A morphological and functional study in a mouse model

Muscle laceration remains a difficult problem for orthopaedic surgeons. Despite many studies related to the muscle's ability to regenerate after muscle degeneration, very few reports are available regarding structural and functional recovery after skeletal muscle laceration. We developed an animal model of muscle laceration in mice, where the gastrocnemius muscles were reproducibly transected. We compared the effect of a surgical repair versus a short period of immobilization (5 days) on the muscle healing. The natural course of muscle recovery was monitored at several points after injury using histologic, immunohistochemical, and functional testing. In the injured muscle, we observed a high number of regenerating myofibers and development of fibrotic scar tissue. Suturing the lacerated muscle immediately after injury promoted better healing of the injured muscle and prevented the development of deep scar tissue in the lacerated muscle; conversely, immobilization resulted in slower muscle regeneration and the development of a large area of scar tissue. Tetanus strength 1 month after injury was 81% of control muscles for the sutured muscles, 35% for the lacerated muscles with no treatment, and 18% for the immobilized muscles. Based on this study, suturing a muscle laceration with a modified Kessler stitch results in the best morphologic and functional healing.     

Fiber-type discrimination in disuse and glucocorticoid-induced atrophy

Data are presented which demonstrate that phasic/glycolytic muscles atrophy more than tonic/oxidative muscles in response to exogenously introduced glucocorticoids. Data are also presented demonstrating that immobilization makes a muscle unusually sensitive to glucocorticoid-induced atrophy and that remobilization of a previously immobilized muscle protects a muscle from glucocorticoid-induced atrophy. These observations are discussed within the context of the role of mechanical activity in the acquisition and maintenance of fiber-type characteristics. In addition, the available data on the glucocorticoid receptor population in skeletal muscles of various types and circumstance are reviewed within the context of the recent observations concerning the glucocorticoid induction of the enzyme glutamine synthetase in skeletal muscle. It is proposed here that atrophy is not necessarily the response of skeletal muscle to glucocorticoids. Rather, atrophy is a possible consequence of the glucocorticoid-induced increase in export of amino acid carbon from the muscle. Whether such export causes a muscle to atrophy or perhaps even hypertrophy will depend on the capacity of the muscle to sustain its free amino acid pools. Mechanical activity greatly promotes the uptake of free amino acids in skeletal muscle. Such promotion takes the form of both contraction-induced uptake and increased insulin sensitivity. Within this perspective, it is suggested that tonic muscles and remobilized muscles are protected from atrophy by exogenous glucocorticoids because their high level of mechanical activity allows them to maintain their free amino acid pools.     

Satellite cells and training in the elderly

In the present review, we describe the effects of ageing on human muscle fibres, underlining that each human muscle is unique, meaning that the phenotype becomes specifically changed upon ageing in different muscles, and that the satellite cells are key cells in the regeneration and growth of muscle fibres. Satellite cells are closely associated with muscle fibres, located outside the muscle fibre sarcolemma but beneath the basement lamina. They are quiescent cells, which become activated by stimulation, like muscle fibre injury or increased muscle tension, start replicating and are responsible for the repair of injured muscle fibres and the growth of muscle fibres. The degree of replication is governed by the telomeric clock, which is affected upon excessive bouts of degeneration and regeneration as in muscular dystrophies. The telomeric clock, as in dystrophies, does not seem to be a limiting factor in ageing of human muscle. The number of satellite cells, although reduced in number in aged human muscles, has enough number of cell divisions left to ensure repair throughout the human life span. We propose that an active life, with sufficient general muscular activity, should be recommended to reduce the impairment of skeletal muscle function upon ageing.     

Acute Retropharyngeal Calcific Tendinitis in an Unusual Location: a Case Report in a Patient with Rheumatoid Arthritis and Atlantoaxial Subluxation

Retropharyngeal calcific tendinitis is defined as inflammation of the longus colli muscle and is caused by the deposition of calcium hydroxyapatite crystals, which usually involves the superior oblique fibers of the longus colli muscle from C1-3. Diagnosis is usually made by detecting amorphous calcification and prevertebral soft tissue swelling on radiograph, CT or MRI. In this report, we introduce a case of this disease which was misdiagnosed as a retropharyngeal tuberculous abscess, or a muscle strain of the ongus colli muscle. No calcifications were visible along the vertical fibers of the longus colli muscle. The lesion was located anterior to the C4-5 disc, in a rheumatoid arthritis patient with atlantoaxial subluxation. Calcific tendinitis of the longus colli muscle at this location in a rheumatoid arthritis patient has not been reported in the English literature.     

Muscle fibre type adaptation in the elderly human muscle

This short review discusses changes in the fibre type distribution, myosin heavy chain isoform composition and histological appearance of the very elderly human skeletal muscle. Point of origin of the discussion comes from data that we have obtained from muscle biopsies from the vastus lateralis muscle of a group of frail very elderly subjects (age: 88 +/- 3 years, range 85-97). Myosin heavy chain composition of muscle homogenates and single fibres, fibre type distribution, fibre size and capillary density were examined and compared with muscle biopsies from the young vastus lateralis muscle. Histological preparations of the muscle biopsies from our elderly subjects showed extended "grouping" (Nygaard & Sanchez, Anat Rec 1992: 202: 451-459) of the fibre types as well as significant changes in the appearance and size of the individual muscle fibres. On average, the fibre type composition of our very elderly subjects do not seem to be different to what is observed in a corresponding young group when examined with ATPase histochemistry. Likewise, the MHC composition of the muscle homogenates is comparable to what is observed in young subjects. Nevertheless, a detailed examination of the MHC composition of single fibres from the old subjects revealed that the most prominent phenotype was fibres co-expressing MHC I and MHC IIA. This is very different from what is observed in the young muscle. Detailed investigation of longitudinally cut fibres indicated that some fibres in the very old muscle, in contrast to the young muscle, switch fibre type along the length of the fibre or contain areas or nuclear domains in which the MHC expression is different from the remaining part of the fibre.     

Closed proximal muscle rupture of the biceps brachii in wakeboarders

Closed proximal muscle rupture of the biceps brachii is a rare injury. In this report, two cases of closed proximal muscle rupture of the biceps brachii after wakeboard traumas are described. Both patients presented with a swollen arm, weakness during flexion, and a mass in the affected forearm. Magnetic resonance imaging showed displacement of the biceps brachii into the forearm. The rupture was successfully treated with muscle removal in one case and muscle repair in the other. In patients with a wakeboard trauma and similar presentations, closed proximal muscle rupture of the biceps brachii should be suspected.     

Regional variations in intramyocellular lipid concentration correlate with muscle fiber type distribution in rat tibialis anterior muscle.

1H MR spectroscopy (MRS) has proved to be a valuable noninvasive tool to measure intramyocellular lipids (IMCL) in research focused on insulin resistance and type II diabetes in both humans and rodents. An important determinant of IMCL is the muscle fiber type, since oxidative type I fibers can contain up to three times more IMCL than glycolytic type II muscle fibers. Because these different muscle fiber types are inhomogeneously distributed in rodent muscle, in the present study we investigated the distribution of IMCL within the rat tibialis anterior muscle (TA) in vivo using single-voxel 1H MRS along with the muscle fiber distribution in the TA ex vivo determined from immunohistological assays. IMCL levels in the TA differed by up to a factor of 3 depending on the position of the voxel. The distribution of IMCL over the TA cross section was not random, but emerged in a pattern similar to the distribution of the predominantly oxidative muscle fiber types. Dietary interventions, such as high-fat feeding and 15 hr of fasting, did not significantly change this typical fiber type-dependent pattern of IMCL content. These results stress the importance of voxel positioning when single-voxel 1H MRS is used to study IMCL in rodent muscle.