Peak oxygen uptake during running and arm cranking normalized to total and regional skeletal muscle mass measured by magnetic resonance imaging

The purposes of our study were to determine the peak oxygen uptake ( O_2peak) per total or regional skeletal muscle (SM) mass using magnetic resonance imaging (MRI) and to investigate the relationships between SM mass and O_2peak during running and arm cranking. Eight male college swimmers aged 18–22 years [mean (SD) age 20.0 (1.3) years] were recruited to participate in this study. O₂ during running and arm cranking were measured using an automated breath-by-breath mass spectrometry system. Contiguous MRI slices were obtained from the first vertebra cervicale to the malleolus lateralis (1.0-cm slice thickness, 0-cm inter-slice gap), resulting in a total of approximately 156 images for each subject. The absolute O_2peak and the O_2peak per body mass during running and arm cranking were 3.6 (0.6) l.min^-1, 54.4 (5.9) ml.min^-1.kg^-1 and 2.5 (0.5) l.min^-1, 36.9 (5.3) ml.min^-1.kg^-1, respectively. The absolute O_2peak was higher ( P <0.05) during running than during arm cranking, but not the O_2peak per regional area SM mass. The lower body SM mass was correlated to the O_2peak during running ( r =0.95, P <0.001). All measurements and calculated values were expressed as the mean (SD) for the eight subjects. To eliminate the influence of body mass and fat-free mass (FFM), a regression analysis was performed on the mass-residuals of the O_2peak during running and the lower body SM mass. The residuals of lower body SM mass were correlated to the residuals of O_2peak during running, with respect to body mass ( r =0.90, P <0.001) and FFM ( r =0.82, P <0.05). These results suggest that the MRI-measured lower body SM mass was closely associated to the absolute O_2peak during running, independently of body mass or FFM, and that the O_2peak per regional SM mass corresponded, regardless of the type of exercise (upper or lower body).     

Ultrasonographic assessment of human skeletal muscle size

The measurement of human muscle size is essential when assessing the effects of training, disuse and ageing. The considered gold standard for cross-sectional area measurements of muscle size is magnetic resonance imaging (MRI). However, MRI is costly and often inaccessible. The aim of the present study was to test the reproducibility and validity of a more accessible alternative method using ultrasonography (ULT). We examined the cross-sectional areas in the vastus lateralis muscle of six individuals. Axial-plane ULT scans were taken at given levels along the entire muscle length. The ULT scanning was repeated on different days (reliability) and validated against MRI-based measurements. Mean intraclass correlation coefficients were 0.998 for the reliability of ULT and 0.999 for the validity of ULT against MRI. The coefficient of variation values for cross-sectional area measurements assessed by six different experimenters were 2.1% and 0.8% for images obtained with ULT and MRI, respectively. The ULT method is a valid and reliable alternative tool for assessing cross-sectional areas of large individual human muscles. The present findings justify the application of the ULT method for the detection of changes throughout large muscles in response to training, disuse or as a consequence of sarcopenia.     

Fat mass and skeletal muscle mass in hip-fracture women: a cross-sectional study

OBJECTIVES: To investigate the association between appendicular lean mass (aLM) and age, fat mass (FM), serum levels of Vitamin D, parathyroid hormone, three parameters of the protein nutritional status (total lymphocyte count, serum albumin, and insulin-like growth factor I), levels of independence in activities of daily living (assessed by using Barthel index scores), type both of hip fracture and surgical operation, number of medications in use, and number of concomitant diseases in hip-fracture women. METHODS: We investigated 299 of 327 hip-fracture women admitted consecutively to a rehabilitation hospital. Soft tissue body composition was assessed by dual-energy X-ray absorptiometry, 22.1+/-7.5 (mean+/-S.D.) days after fracture occurrence. Appendicular LM was calculated as the sum of LM in arms and legs. Because metal implants (prostheses and nails) affect the regional assessment of body composition, aLM was corrected by substituting LM in unfractured leg for LM in fractured leg: corrected aLM=(LM in unfractured leg x 2)+LM in arms. We divided corrected aLM by height squared (aLM/ht(2)), to adjust it for body size. RESULTS: Four variables were significantly correlated with corrected aLM: age, height, FM, and Barthel index score. FM was the only variable significantly correlated with aLM/ht(2) (r=0.492; p<0.001). This significant correlation was not affected after adjustment for age and Barthel index score. CONCLUSIONS: FM measured after hip fracture was significantly associated with aLM/ht(2) in women.     

Development of nonexercise prediction models of maximal oxygen uptake in healthy Japanese young men

The present study developed nonexercise models for predicting maximal oxygen uptake using skeletal muscle (SM) mass and cardiac dimensions and to investigate the validity of these equations in healthy Japanese young men. Sixty healthy Japanese men were randomly separated into two groups: 40 in the development group and 20 in the validation group. during treadmill running was measured using an automated breath-by-breath mass spectrometry system. Left ventricular internal dimensions at end-diastole (LVIDD) and at end-systole (LVIDS) were measured using M-mode ultrasound with a 2.5 MHz transducer. Stroke volume (SV) was calculated based on the Pombo rule. SM mass was predicted by B-mode ultrasound muscle thickness. Correlations were observed between and predicted thigh (r = 0.74, P < 0.001) and lower leg SM mass (r = 0.55, P < 0.001). Furthermore, there were correlations between and LVIDD (r = 0.74, P < 0.001) and SV (r = 0.72, P < 0.001). Stepwise regression analysis was applied to thigh SM mass and SV for prediction of in the development group, and these parameters were closely correlated with absolute measured by multiple regression analysis. When the prediction equations were applied to the validation group, significant correlations were also observed between the measured and predicted These results suggested that nonexercise prediction of using thigh SM mass and cardiac dimension is a valid method to predict in young Japanese adults.     

CDMNP-PEG-CD磁纳米颗粒诱导的骨骼肌反应性分析

目的　探讨SOMNP、CDMNP及CDMNP-PEG-CD磁性纳米颗粒置入小鼠骨骼肌所诱发的免疫反应性。 方法　以磁性Fe3O4与SiO2复合制备SOMNP, 将聚乙二醇（PEG）、环糊精（β-CD）分子链接SOMNP合成CDMNP,进一步添加聚假单胞烷（polypseudorotaxanes）合成CDMNP-PEG-CD磁性纳米颗粒。分别将3种纳米颗粒置入B6小鼠腓肠肌。组化染色、免疫荧光及FACS分析,分别评估不同置入时段SOMNP、CDMNP和CDMNP-PEG-CD纳米颗粒所诱发的肌毒性及肌内炎性渗出特征。 结果　SOMNP链接β-CD、PEG/β-CD及polypseudorotaxanes将限制纳米颗粒的肌内扩散,导致CDMNP和CDMNP-PEG-CD在肌内的滞留时间延长、材料邻近区肌细胞坏死、肌内单核/巨噬细胞聚集。较之CDMNP-PEG-CD, CDMNP纳米颗粒吸引更多T细胞进入肌组织。 结论　SOMNP、CDMNP及CDMNP-PEG-CD纳米颗粒均为潜在的体内免疫诱导物。polypseudorotaxanes修饰赋予CDMNP-PEG-CD纳米颗粒较好的体内相容性。     

Changes in phosphorus compounds and water content in skeletal muscle due to eccentric exercise

The interrelationship of the time courses of soreness and oedema, and of force and phosphorus metabolites after eccentric exercise was studied. Eight male subjects performed 120 maximal eccentric contractions with their left forearm flexors. Soreness, maximal force, flexion and extension elbow angle, and creatine kinase and myoglobin efflux were followed for 96 h after exercise. For equal periods T1 and T2 relaxation times and muscle cross-sectional area were calculated from magnetic resonance images as indications of oedema, and inorganic phosphate (P_i) and phosphocreatine (PCr) were measured with magnetic resonance spectroscopy. Soreness on extension increased at 1 h (P = 0.043), T1 and T2 (both P = 0.01) and soreness when the arm was pressed (P = 0.028) at 24 h, and muscle cross-sectional area increased at 48 h (P = 0.01) after exercise. Soreness on extension reached a maximum at 48 h, the other four parameters at 72 h. All parameters related to oedema, and soreness, showed an increasing pattern for the period after exercise as a whole, but the largest increase between two points of measurement occurred earlier for soreness than for oedema. Creatine kinase increased significantly from baseline from 24 h onwards (P = 0.017) and myoglobin from 1 h onwards (P = 0.012). The P_i: PCr ratio differed from baseline for the first time 24 h after exercise (P = 0.018), increased to 225%, and then remained on a plateau until 72 h. Maximal isotonic force decreased to 53% at 1 h (P = 0.012), and recovered from then on. It was concluded firstly that the largest increase in soreness precedes that of oedema, and secondly that the decrease in force after eccentric exercise is not related to an altered metabolic state. The combined imaging and spectroscopy results gave the impression that changes in phosphorus metabolites were homogeneously distributed over the flexor muscles whereas oedema was not.Parts of this study have already been presented during a conference as preliminary results (Rodenburg et al. 1992)     

Visualization of capillaries in skeletal muscle by the ATPase reaction

Summary A simple and reliable technique for the visualization of capillaries in skeletal muscle of dogs, guinea pigs and rats is described. 10–20 μm frozen sections were incubated in a medium containing Ca²⁺ and ATP following acid preincubation (pH 3.8–4.2). The capillaries stained in black and were readily seen surrounding the muscle fibers. Serial sections were also treated for alkaline phosphatase. Values for capillary density using both methods were not different. Supported by USPHS NIH Grant HL 12679-HL 18145 Supported by a fellowship from the Rockefeller Fndn     

Supplemental oxygen and muscle metabolism in mitochondrial myopathy patients

Patients with mitochondrial myopathy (MM) have a reduced capacity to perform exercise due to a reduced oxidative capacity. We undertook this study to determine whether skeletal muscle metabolism could be improved with oxygen therapy in patients with MM. Six patients with MM and six controls, matched for age, gender and physical activity, underwent ³¹P-magnetic resonance spectroscopy (³¹P-MRS) examination. ³¹P-MR spectra were collected at rest and in series during exercise and recovery whilst breathing normoxic (0.21 O₂) or hyperoxic (1.0 O₂) air. At rest, MM showed an elevated [ADP] (18 ± 3 μmol/l) and pH (7.03 ± 0.01) in comparison to the control group (12 ± 1 μmol/l, 7.01 ± 0.01) (P < 0.05) consistent with mitochondrial dysfunction. Oxygen supplementation did not change resting metabolites in either MM or the control group (P > 0.05). Inferred maximal ATP synthesis rate improved by 33% with oxygen in MM (21 ± 3 vs. 28 ± 5 mmol/(l min), P < 0.05) but only improved by 5% in controls (40 ± 3 vs. 42 ± 3 mmol/(l min), P > 0.05). We conclude that oxygen therapy is associated with significant improvements in muscle metabolism in patients with MM. These data suggest that patients with MM could benefit from therapies which improve the provision of oxygen.     

BOLD MRI mapping of transient hyperemia in skeletal muscle after single contractions

Transient increases in signal intensity (DeltaSI, peak 2.6 +/- 0.6 %, mean +/- SE, n = 14) were observed in axial, gradient-echo, echo-planar magnetic resonance images acquired at 1.5 T from human anterior tibialis muscle following single, 1 s duration, isometric ankle dorsiflexion contractions. The magnitude of the MRI-measured DeltaSI was not significantly different using TR of 2000 vs 500 ms, or using spin-echo vs gradient-echo echo-planar pulse sequences. However, DeltaSI measured by gradient-echo sequences was significantly greater at 3 vs 1.5 T (3.8 +/- 0.8 vs 1.6 +/- 0.2 %, n = 5). The time course of the transient DeltaSI (peak at 7.9 +/- 0.4 s after each contraction, decay with half-time of 4.6 +/- 0.6 s) was comparable to the time course of the transient increase in relative heme saturation (13 +/- 2 %, n = 5) measured after single contractions in another group of subjects by near-infrared spectroscopy (peak at 9.3 +/- 0.5 s, decay with half-time 6.2 +/- 0.8 s, n = 8). Simulations of intravascular and extravascular blood-oxygenation level-dependent (BOLD) effects in muscle suggested that intravascular BOLD makes a major contribution to the transient changes, although other factors such as increased vascular volume or increased muscle cell T2 may also contribute. The transients can be exploited for muscle functional imaging analogous to BOLD-based brain functional imaging, and might provide an index of peripheral vascular function.     

Measurement of anterior tibial muscle size using real-time ultrasound imaging

Summary Cross-sectional images of the anterior tibial muscle group were obtained using real-time ultrasound scanning in 17 normal women. From photographs taken of the images, the cross-sectional area (CSA) and two linear measurements of muscle cross-section were determined. A measurement of the shortest distance of the muscle depth was termed DS, and a measurement of the longest distance through the muscle group was termed DL. Both linear dimensions showed a positive correlation with CSA and the best correlations were obtained when the dimensions were squared or combined (DS × DL). The correlation values were: CSA vs DS², r=0.9; CSA vs DL², r=0.75 and CSA vs DS × DL, r=0.88. An approximate value for CSA could be calculated from DS² by the equation 2 × DS² + 1. A shape ratio, obtained by dividing DL by DS, was consistent within the group [mean 2.1 (SD 0.2)] and characterised the muscle geometrically. The CSA of repeated scans was assessed for repeatability between-days and between-scans by analysis of variance and the coefficient of variation (CV) calculated. Areas were repeatable between-days (CV 6.5%) and between-scans (CV 3.6%). Linear dimensions of the anterior tibial muscle group reflected CSA and their potential for assessing changes in muscle size with atrophy and hypertrophy have yet to be established.     

Functional organization of the human masseter muscle

The authors carried out an anatomic and magnetic resonance imaging study of the architecture of the elevator muscles of the mandible in 169 cadavers. The aim of this study was to define the architectural organization of the human masseter muscle, temporalis and pterygoid muscles. Layered dissections and anatomic sections in different spatial planes showed that the masseter muscle exhibited a typical pennate structure consisting of a succession of alternating musculoaponeurotic layers. The muscle had three well-differentiated parts the superficial, intermediate and deep masseter muscles. The same pattern was constantly found 1) for the superficial masseter, two alternate musculoaponeurotic layers oriented at 60∘ in relation to the plane of occlusion, 2) for the intermediate masseter, a single musculo-aponeurotic layer oriented at 90∘ in relation to the occlusal plane, 3) for the deep masseter, three musculoaponeurotic layers whose general orientation was at 90∘ for the bounding layers and 110∘ for the intermediate layer. The MRI study confirmed the reality of this architectural arrangement.     

The distribution of intracellular calcium concentration in isolated single fibres of mouse skeletal muscle during fatiguing stimulation

Fluorescence microscopy has been used to examine the distribution of intracellular calcium concentration ([Ca²⁺]_i) in isolated single fibres from the mouse flexor brevis muscle during fatiguing stimulation. Under control conditions there was a virtually uniform distribution of [Ca²⁺]_i in fura-2 loaded fibres either at rest or during short (0.35 s, 100 Hz) tetani. Fatigue produced by repeated short tetani was accompanied by an early rise, followed by a marked fall, in tetanic [Ca²⁺]_i. Throughout the period of fatiguing stimulation the distribution of [Ca²⁺]_i remained uniform with no detectable gradients observed. In contrast, when fatigue was produced by continuous 100 Hz stimulation, a small gradient of [Ca²⁺]_i developed across the fibre with the [Ca²⁺]_i in the centre of the fibre lower than that at the edge of the fibre. This gradient was apparent after 1.7 s, persisted for at least 11 s and was superimposed on a rise followed by a fall in spatially averaged [Ca²⁺]_i. Reduction of the extracellular Na⁺ to 50% caused reduced force production and a reduced [Ca²⁺]_i in the centre of the fibre. To assess the contribution of reduced response of the myofibrillar proteins to [Ca²⁺]_i during continuous tetani, the relation between [Ca²⁺]_i and force throughout the long tetanus was compared with that obtained in short, unfatigued tetani. These results show that in long tetani, reduced tetanic [Ca²⁺]_i and reduced responsiveness of the myofibrillar proteins to [Ca²⁺]_i each make important contributions to the decline of force, whereas the gradients of [Ca²⁺]_i make only a small contribution.     

微小RNA调节骨骼肌发育与损伤修复的作用及其机制

microRNAs是一类非编码小RNAs分子,新近发现其具有重要的调节基因表达的功能,它能通过抑制翻译和降解靶mRNA来负性调控转录后水平的基因表达,miRNAs已经被证实在肌肉发育和肌细胞增殖和分化的调节中具有重要作用。最近研究发现,肌肉特异性转录因子控制一些microRNAs的表达,通过多种机制调节肌肉发育和功能。结合信息学、生物化学和遗传基因学方法,不仅将阐明骨骼肌microRNAs调控网络,更好地理解肌肉组织的调节,还将通过鉴定候选microRNAs的潜在临床应用靶点,增加肌肉营养不良的治疗干预的新机会。     

Regulation of dihydropyridine receptor levels in skeletal and cardiac muscle by exercise training

To examine the influence of exercise training on the expression of dihydropyridine (DHP)-sensitive Ca²⁺ channels in skeletal and cardiac muscle, we have determined DHP receptor levels by [³H]PN200-110-binding and immunoblot analysis in homogenates and microsomal fractions of slow- and fast-twitch muscles and heart from rats subjected to a 12-week programme of moderate endurance training. We found that exercise increases the amount of DHP receptor in homogenates of the slow-twitch soleus (42%) and the fast-twitch extensor digitorum longus (60%). Comparable increases in DHP receptor density with training were also observed in the microsomal fractions isolated from both skeletal muscles; these increases were not due to differences in the membrane composition of the microsomal fractions, since the relative proportion of specific enzyme markers was not affected by exercise training. Levels of DHP receptor were not modified in cardiac muscle as a result of the exercise programme. These data suggest an up-regulation of the DHP receptor in the skeletal muscle as a consequence of exercise training, which may play a role in the adaptation of skeletal muscle to increased contractile activity.     

Validity of ultrasonograph muscle thickness measurements for estimating muscle volume of knee extensors in humans

This study aimed to investigate the suitability of using ultrasonograph muscle thickness (MT) measurements to estimate the muscle volume (MV) of the quadriceps femoris as an alternative approach to magnetic resonance imaging (MRI). The subjects were 46 men aged from 20 to 70 years who were randomly allocated to either a validation or a cross-validation group. In the validation group, multiple and simple regression equations, which used a set of MT values determined at mid-thigh and thigh length (l) and the product of π, (MT/2)², and l [π·(MT/2)²·l], respectively, as independent variables, were derived to estimate the MV measured by MRI. Because the two equations were cross-validated, the data from the two groups were pooled to generate the final prediction equations: MV (cm³)=(MT×311.732)+(l×53.346) –2058.529 as the multiple regression equation and MV (cm³)=[π·(MT/2)²·l]×1.1176+663.040 as the simple regression equation. In the multiple regression equation, MT explained 75% of the variation in the MV measured by MRI. The r ² and the standard error of the estimate (SEE) of the equations were 0.824 and 175.6 cm³ (10.6%), respectively, for the multiple regression equation and 0.829 and 173.7 cm³ (10.5%), respectively, for the simple regression equation. Thus, the present results indicate that ultrasonograph MT measurements at mid-thigh are useful for estimating the MV of knee extensors. However, the observed SEE values suggest that the prediction equation obtained in this study may be limited to population studies rather than individual assessments in longitudinal studies. Electronic Publication     

Paralysis of skeletal muscle by butanedione monoxime,a chemical phosphatase

The chemical phosphatase butanedione monoxime (BDM) reversibly inhibited twitches and tetanic contractions in bundles of rat soleus fibres in a dose-dependent manner (2–20 mM) but had no effect on the amplitude or time course of action potentials. In addition, BDM reversibly reduced the amplitude of potassium contractures demonstrating a depressant effect on contraction not mediated by action potentials. BDM had no effect on asymmetric charge movement but depressed calcium currents across the surface membrane in voltage-clamped fibres. The most significant effect of BDM on excitation-contraction coupling was a reduction in the amplitude of the calcium transient associated with contraction in aequorin-injected fibres. While these experiments do not eliminate the possibility of a direct effect of BDM on contractile filaments, reduction of calcium release from the sarcoplasmic reticulum, at least at low concentrations of BDM (below 2 mM), would seem to be the main mechanism for the inhibition of contractions in rat skeletal muscle.     

Functional anatomy of the human lateral pterygoid muscle

The authors studied the lateral pterygoid muscle of 179 fresh cadavers by both anatomical dissection and magnetic resonance imaging. The aim was to define the general morphology and the architectural organisation of the lateral pterygoid muscle. Dissection plane by plane, anatomical sections in different planes of space and dissections via multiple approaches on harvested blocks allowed the demonstration that the lateral pterygoid shows an architectural arrangement different from that which is usually described but similar to that, from its typically penniform structure of the masseter and the medial pterygoid. The anatomical situation of this muscle gives rise to numerous differences in opinion much to its morphology as to its functional examination. This study has shown that one part of the muscle has a typical penniform structure made up of alternating musculo-aponeurotic layers and by the absence of individual muscle bellies. In addition the particular shape of this muscle makes it useless to insert intramuscular electrodes in its only accessible portion, which makes the results of electromyographic studies debatable.     

Lactate oxidation by skeletal muscle during sustained contraction in vivo

Summary Estimation of lactate oxidation in vivo was carried out by a tracer technique in the muscles of the lower hindleg of the dog during tetani of different duration. The fractional (%) rate of lactate oxidation increased markedly, compared with that of the resting muscle, after the first 2 min of stimulation. Lactate oxidation afforded a large contribution to the total oxygen consumption. Fatigue appeared to play a role in limiting lactate oxidation in the later phase of sustained contraction.     

Experimental induction of ring fibers in regenerating skeletal muscle

Light microscopy and electron microscopy were used to study the formation of ring fibers induced experimentally in regenerating muscle subjected to tenotomy-induced tension deficiency. Anterior tibial rat muscles were injured by intramuscular injection of mepivacain, tenotomized at varying stages of the regenerative process, and analyzed 30 days after sectioning the tendon. The combination of regeneration and tenotomy led to the appearance of ring fibers at different developmental stages. Ring fibers were not observed in regenerating control muscles and were scarce in tenotomized controls. Our results showed that the regenerative phase in which tension deficiency was established had a significant influence on the number of developing ring fibers; the number increased when tenotomy was performed during subsarcolemmic myofibrillogenesis in regenerating fibers. As a consequence, one might hypothesize that tension deficiency during muscle fiber repair plays a critical role in ring fiber formation.