Comparing human skeletal muscle architectural parameters of cadavers with in vivo ultrasonographic measurements

The purpose of this study was to document and compare the architectural parameters (fibre bundle length, angle of pennation) of human skeletal muscle in cadaveric specimens and live subjects. The medial (MG) and lateral (LG) gastrocnemius, and posterior (PS) and anterior (AS) soleus were examined bilaterally in 5 cadavers (mean age 72.6, range 65–83 y) and 9 live subjects (mean age 76.3, range 70–92 y). Data were obtained from direct measurement of cadaveric specimens and from ultrasonographic scans of the live subjects. In cadaveric muscle, fibre bundles were isolated; their length was measured in millimetres and pennation angles were recorded in degrees. In live muscle, similar measurements were taken from ultrasonographic scans of relaxed and contracted muscle. For the scans of relaxed muscle, subjects were positioned prone with the foot at a 90° angle to the leg, and for scans of contracted muscle, subjects were asked to sustain full plantarflexion during the scanning process. Fibre bundle length and angle of pennation were compared at matched locations in both groups. It was found that the relationship between cadaveric and in vivo values for fibre length and angle of pennation varied between muscle parts. The cadaveric architectural parameters did not tend to lie consistently towards either extreme of relaxation or contraction. Rather, within MG, PS and AS, cadaveric fibre bundle lengths lay between those for relaxed and contracted in vivo muscle. Similarly both the anterior and posterior cadaveric fibre angles of pennation lay between the in vivo values within LG and PS. In summary, architectural characteristics of cadaveric muscle differ from both relaxed and contracted in vivo muscle. Therefore, when developing models of skeletal muscle based on cadaveric studies, the architectural differences between live and cadaveric tissue should be taken into consideration.     

Three‐dimensional study of pectoralis major muscle and tendon architecture

A thorough understanding of the normal structural anatomy of the pectoralis major (PM) is of paramount importance in the planning of PM tendon transfers or repairs following traumatic PM tears. However, there is little consensus regarding the complex musculotendinous architecture of the PM in the anatomic or surgical literature. The purpose of this study is to model and quantify the three‐dimensional architecture of the pectoralis muscle and tendon. Eleven formalin embalmed cadaveric specimens were examined: five (2M/3F) were serially dissected, digitized, and modeled in 3D using Autodesk® Maya®; six (4M/2F) were dissected and photographed. The PM tendon consisted of longer anterior and shorter posterior layers that were continuous inferiorly. The muscle belly consisted of an architecturally uniform clavicular head (CH) and a segmented sternal head (SH) with 6–7 segments. The most inferior SH segment in all specimens was found to fold anteriorly forming a trough that cradled the inferior aspect of the adjacent superior segment. No twisting of either the PM muscle or tendon was noted. Within the CH, the fiber bundle lengths (FBL) were found to increase from superior to inferior, whereas the mean FBLs of SH were greatest in segments 3–5 found centrally. The mean lateral pennation angle was greater in the CH (29.4 ± 6.9°) than in the SH (20.6 ± 2.7°). The application of these findings could form the basis of future studies to optimize surgical planning and functional recovery of repair/reconstruction procedures. Clin. Anat. 22:500–508, 2009. © 2009 Wiley‐Liss, Inc.     

DTI of human skeletal muscle: the effects of diffusion encoding parameters,signal‐to‐noise ratio and T2 on tensor indices and fiber tracts

In this study, we have performed simulations to address the effects of diffusion encoding parameters, signal‐to‐noise ratio (SNR) and T₂ on skeletal muscle diffusion tensor indices and fiber tracts. Where appropriate, simulations were corroborated and validated by in vivo diffusion tensor imaging (DTI) of human skeletal muscle. Specifically, we have addressed: (i) the accuracy and precision of the diffusion parameters and eigenvectors at different SNR levels; (ii) the effects of the diffusion gradient direction encoding scheme; (iii) the optimal b value for diffusion tensor estimation; (iv) the effects of changes in skeletal muscle T₂; and, finally, the influence of SNR on fiber tractography and derived (v) fiber lengths, (vi) pennation angles and (vii) fiber curvatures. We conclude that accurate DTI of skeletal muscle requires an SNR of at least 25, a b value of between 400 and 500 s/mm², and data acquired with at least 12 diffusion gradient directions homogeneously distributed on half a sphere. Furthermore, for DTI studies focusing on skeletal muscle injury or pathology, apparent changes in the diffusion parameters need to be interpreted with great care in view of the confounding effects of T₂, particularly for moderate to low SNR values. Copyright © 2013 John Wiley & Sons, Ltd.     

Human skeletal muscle fiber type alteration with high-intensity intermittent training

Summary The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical charactertics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.     

Relationship of primary mitochondrial respiratory chain dysfunction to fiber type abnormalities in skeletal muscle

Variation in the size and relative proportion of type 1 and type 2 muscle fibers can occur in a number of conditions, including structural myopathies, neuropathies, and various syndromes. In most cases, the pathogenesis of such fiber type changes is unknown and the etiology is heterogeneous. Skeletal muscle mitochondrial respiratory chain analysis was performed in 10 children aged 3 weeks to 5 years with abnormalities in muscle fiber type, size, and proportion. Five children were classified as having definite, four as probable, and one as possible mitochondrial disease. Type 1 fiber predominance was the most common histological finding (six of 10). On light microscopy, four cases had subtle concomitants of a mitochondriopathy, including mildly increased glycogen, lipid, and/or succinate dehydrogenase staining, and one case had more prominent evidence of underlying mitochondrial disease with marked subsarcolemmal staining. Most cases (nine of 10) had abnormal mitochondrial morphology on electron microscopy. All were found to have mitochondrial electron transport chain (ETC) abnormalities and met diagnostic criteria for mitochondrial disease. We did not ascertain any patients who had isolated fiber type abnormalities and normal respiratory chain analysis during the period of study. We conclude that mitochondrial ETC disorders may represent an etiology of at least a subset of muscle fiber type abnormalities. To establish an etiologic diagnosis and to determine the frequency of such changes in mitochondrial disease, we suggest analysis of ETC function in individuals with fiber type changes in skeletal muscle, even in the absence of light histological features suggestive of mitochondrial disorders.     

The role of FFM accumulation and skeletal muscle architecture in powerlifting performance

The purpose of this study was to determine the distribution and architectural characteristics of skeletal muscle in elite powerlifters, and to investigate their relationship to fat-free mat (FFM) accumulation and powerlifting performance. Twenty elite male powerlifters (including four world and three US national champions) volunteered for this study. FFM, skeletal muscle distribution (muscle thickness at 13 anatomical sites), and isolated muscle thickness and fascicle pennation angle (PAN) of the triceps long-head (TL), vastus lateralis, and gastrocnemius medialis (MG) muscles were measured with B-mode ultrasound. Fascicle length (FAL) was calculated. Best lifting performance in the bench press (BP), squat lift (SQT), and dead lift (DL) was recorded from competition performance. Significant correlations (P≤0.01) were observed between muscle distribution (individual muscle thickness from 13 sites) and performance of the SQT (r=0.79 to r=0.91), BP (r=0.63 to r=0.85) and DL (r=0.70 to r=0.90). Subscapular muscle thickness was the single best predictor of powerlifting performance in each lift. Performance of the SQT, BP, and DL was strongly correlated with FFM and FFM relative to standing height (r=0.86 to 0.95, P≤0.001). FAL of the triceps long head and vastus lateralis were significantly correlated with FFM (r=0.59, P≤0.01; 0.63, P≤0.01, respectively) and performance of the SQT (r=0.45; r=0.50, respectively; P≤0.05), BP (r=0.52; r=0.56, respectively; P≤0.05), and DL (r=0.56; r=0.54, respectively; P≤0.01). A significant positive correlation was observed between isolated muscle thickness and PAN for triceps long-head (r=0.64, P≤0.01) and gastrocnemius medialis (r=0.48, P≤0.05) muscles, but not for vastus lateralis (r=0.35). PAN was negatively correlated with powerlifting performance. Our results indicate that powerlifting performance is a function of FFM and, therefore, may be limited by the ability to accumulate FFM. Additionally, muscle architecture appears to play an important role in powerlifting performance in that greater fascicle lengths are associated with greater FFM accumulation and powerlifting performance. Electronic Publication     

Determination of three-dimensional muscle architectures: validation of the DTI-based fiber tractography method by manual digitization

In the last decade, diffusion tensor imaging (DTI) has been used increasingly to investigate three-dimensional (3D) muscle architectures. So far there is no study that has proved the validity of this method to determine fascicle lengths and pennation angles within a whole muscle. To verify the DTI method, fascicle lengths of m. soleus as well as their pennation angles have been measured using two different methods. First, the 3D muscle architecture was analyzed in vivo applying the DTI method with subsequent deterministic fiber tractography. In a second step, the muscle architecture of the same muscle was analyzed using a standard manual digitization system (MicroScribe MLX). Comparing both methods, we found differences for the median pennation angles (P < 0.001) but not for the median fascicle lengths (P = 0.216). Despite the statistical results, we conclude that the DTI method is appropriate to determine the global fiber orientation. The difference in median pennation angles determined with both methods is only about 1.2° (median pennation angle of MicroScribe: 9.7°; DTI: 8.5°) and probably has no practical relevance for muscle simulation studies. Determining fascicle lengths requires additional restriction and further development of the DTI method.     

In vivo visualization of the levator ani muscle subdivisions using MR fiber tractography with diffusion tensor imaging

Understanding the levator ani complex architecture is of major clinical relevance. The aim of this study was to determine the feasibility of magnetic resonance (MR) fiber tractography with diffusion tensor imaging (DTI) as a tool for the three-dimensional (3D) representation of normal subdivisions of the levator ani. Ten young nulliparous female volunteers underwent DTI at 1.5 T MR imaging. Diffusion-weighted axial sequence of the pelvic floor was performed with additional T2-weighted multiplanar sequences for anatomical reference. Fiber tractography for visualization of each Terminologia Anatomica-listed major levator ani subdivision was performed. Numeric muscular fibers extracted after tractography were judged as accurate when localized within the boundaries of the muscle, and inaccurate when projecting out of the boundaries of the muscle. From the fiber tracking of each subdivision the number of numeric fibers (inaccurate and accurate) and a score (from 3 to 0) of the adequacy of the 3D representation were calculated. All but two volunteers completed the protocol. The mean number of accurate fibers was 17 ± 2 for the pubovisceralis, 14 ± 6 for the puborectalis and 1 ± 1 for the iliococcygeus. The quality of the 3D representation was judged as good (score = 2) for the pubovisceralis and puborectalis, and inaccurate (score = 0) for the iliococcygeus. Our study is the first step to a 3D visualization of the three major levator ani subdivisions, which could help to better understand their in vivo functional anatomy.     

Fast low‐angle shot diffusion tensor imaging with stimulated echo encoding in the muscle of rabbit shank

In the past, spin‐echo (SE) echo planar imaging(EPI)‐based diffusion tensor imaging (DTI) has been widely used to study the fiber structure of skeletal muscles in vivo. However, this sequence has several shortcomings when measuring restricted diffusion in small animals, such as its sensitivity to susceptibility‐related distortions and a relatively short applicable diffusion time. To address these limitations, in the current work, a stimulated echo acquisition mode (STEAM) MRI technique, in combination with fast low‐angle shot (FLASH) readout (turbo‐STEAM MRI), was implemented and adjusted for DTI in skeletal muscles. Signal preparation using stimulated echoes enables longer effective diffusion times, and thus the detection of restricted diffusion within muscular tissue with intracellular distances up to 100 µm. Furthermore, it has a reduced penalty for fast T₂ muscle signal decay, but at the expense of 50% signal loss compared with a SE preparation. Turbo‐STEAM MRI facilitates high‐resolution DTI of skeletal muscle without introducing susceptibility‐related distortions. To demonstrate its applicability, we carried out rabbit in vivo measurements on a human whole‐body 3 T scanner. DTI parameters of the shank muscles were extracted, including the apparent diffusion coefficient, fractional anisotropy, eigenvalues and eigenvectors. Eigenvectors were used to calculate maps of structural parameters, such as the planar index and the polar coordinates θ and ? of the largest eigenvector. These parameters were compared between three muscles. θ and ? showed clear differences between the three muscles, reflecting different pennation angles of the underlying fiber structures. Fiber tractography was performed to visualize and analyze the architecture of skeletal pennate muscles. Optimization of tracking parameters and utilization of T₂‐weighted images for improved muscle boundary detection enabled the determination of additional parameters, such as the mean fiber length. The presented results support the applicability of turbo‐STEAM MRI as a promising method for quantitative DTI analysis and fiber tractography in skeletal muscles. Copyright © 2013 John Wiley & Sons, Ltd.     

Anaerobic threshold,skeletal muscle enzymes and fiber composition in young female cross-country skiers

Anaerobic threshold (AT) and maximum oxygen uptake (max V?_o2) were determined in 15 young female cross-country skiers, aged 15–20 years, during incremental bicycle ergo-meter exercise. Succinate dehydrogenase (SDH), malate dehydrogenase (MDH), citrate synthase (CS) and lactate dehydrogenase (LDH) were analyzed biochemically and percentage of slow twitch fibres (%ST fibres, myosin adenosine triphosphatase staining) histochemically in muscle samples obtained from m. vastus lateralis. Max V?_o2 correlated significantly with anaerobic threshold in ml×kg^-1×min^-1 (mlAT) but when AT was expressed in percent of max V?o2 (%AT) the correlation was insignificant. Significant correlations were found between %AT and SDH (r=0.63) and between mlAT and CS (r=0.58). Max V?_o2 showed no significant correlations with the enzymes studied or %ST fibres. The results of the study seem to support the hypothesis that anaerobic threshold is related to oxidative capacity of muscle.     

基于DTI技术的健康成人胼胝体、扣带回、中脑白质纤维束密度随年龄变化关系的研究

目的:应用磁共振弥散张量成像(diffusion tensor imaging,DTI)技术定量探讨健康成人胼胝体、扣带回、中脑纤维束密度随年龄变化的关系。方法:将125例健康志愿者按年龄分成五组(第一组16~30岁,20例;第二组31~45岁,34例;第三组46~60岁,24例;第四组61~75岁,22例;第五组76~90岁,25例),行3T磁共振(magnetic resonance imaging,MRI)扫描,获取脑T1和DTI图像。所有DTI数据经DTI Studio软件预处理并追踪得到脑白质纤维束,手工设置三个感兴趣区,即胼胝体、扣带回和中脑,统计各区的纤维束密度(fiber tract density,FD),将所有数据输入SPSS软件进行统计学分析。结果:得到了三个感兴趣区的纤维束走行,其中胼胝体区纤维束成辐射状分布,走行有向前、后、左、右方向;扣带回区纤维束走行大致为前、后方向;中脑区纤维束走行大致为上、下方向,追踪结果分别与它们各自的解剖学结构相一致。对三个区的纤维束密度的统计学分析结果为:(1)胼胝体区,各年龄组的FD均存在显著差异(P0.05),且随着年龄的增长,胼胝体区纤维束密度逐渐降低。(2)扣带回区,各年龄组的FD均存在显著差异(P0.05),第一组的左、右侧扣带回FD存在显著性差异(P0.05),在其左、右区,各年龄组的FD相互比较均具有显著性差异(P0.05);进一步分析得到,左侧扣带回区FD随年龄增长的下降趋势大于右侧。(3)中脑区,各年龄组的FD无显著性差异(P0.05),在其左、右区,各年龄组的FD无显著性差异(P0.05)。结论:随着年龄增长,胼胝体、扣带回区内FD明显降低。磁共振弥散张量成像技术的量化指标FD可以用来了解脑白质纤维束的变化。     

Musculotendinous architecture of pathological supraspinatus: A pilot in vivo ultrasonography study

Architectural changes associated with tendon tears of the supraspinatus muscle (SP) have not been thoroughly investigated in vivo with the muscle in relaxed and contracted states. The purpose of this study was to quantify the geometric properties within the distinct regions of SP in subjects with full‐thickness tendon tears using an ultrasound protocol previously developed in our laboratory, and to compare findings with age/gender matched normal controls. Twelve SP from eight participants (6 male/2 female), mean age 57 ± 6.0 years, were investigated. Muscle geometric properties of the anterior region (middle and deep parts) and posterior region (deep part) were measured using image analysis software. Along with whole muscle thickness, fiber bundle length (FBL) and pennation angle (PA) were computed for architecturally distinct regions and/or parts. Pathologic SP was categorized according to the extent of the tear in the tendon (with or without retraction). In the anterior region, mean FBL of the pathologic SP was similar with normal controls; however, mean PA was significantly smaller in pathologic SP with retraction compared with normal controls, in the contracted state (P < 0.05). Mean FBL in the posterior region in both relaxed and contracted states was significantly shorter in the pathologic SP with retraction compared with normal controls (P < 0.05). Findings suggest FBL changes associated with tendon pathology vary between the distinct regions, and PA changes are related to whether there is retraction of the tendon. The ultrasound protocol may provide important information on architectural changes that may assist in decision making and surgical planning. Clin. Anat., 2013. © 2012 Wiley Periodicals, Inc.     

Assessment of passive muscle elongation using Diffusion Tensor MRI: Correlation between fiber length and diffusion coefficients

In this study we investigated the changes in fiber length and diffusion parameters as a consequence of passive lengthening and stretching of the calf muscles. We hypothesized that changes in radial diffusivity (RD) are caused by changes in the muscle fiber cross sectional area (CSA) as a consequence of lengthening and shortening of the muscle. Diffusion Tensor MRI (DT‐MRI) measurements were made twice in five healthy volunteers, with the foot in three different positions (30° plantarflexion, neutral position and 15° dorsiflexion). The muscles of the calf were manually segmented on co‐registered high resolution anatomical scans, and maps of RD and axial diffusivity (AD) were reconstructed from the DT‐MRI data. Fiber tractography was performed and mean fiber length was calculated for each muscle group. Significant negative correlations were found between the changes in RD and changes in fiber length in the dorsiflexed and plantarflexed positions, compared with the neutral foot position. Changes in AD did not correlate with changes in fiber length. Assuming a simple cylindrical model with constant volume for the muscle fiber, the changes in the muscle fiber CSA were calculated from the changes in fiber length. In line with our hypothesis, we observed a significant positive correlation of the CSA with the measured changes in RD. In conclusion, we showed that changes in diffusion coefficients induced by passive muscle stretching and lengthening can be explained by changes in muscle CSA, advancing the physiological interpretation of parameters derived from skeletal muscle DT‐MRI.     

Cortex‐sparing fiber dissection: an improved method for the study of white matter anatomy in the human brain

Classical fiber dissection of post mortem human brains enables us to isolate a fiber tract by removing the cortex and overlying white matter. In the current work, a modification of the dissection methodology is presented that preserves the cortex and the relationships within the brain during all stages of dissection, i.e. ‘cortex‐sparing fiber dissection’. Thirty post mortem human hemispheres (15 right side and 15 left side) were dissected using cortex‐sparing fiber dissection. Magnetic resonance imaging study of a healthy brain was analyzed using diffusion tensor imaging (DTI)‐based tractography software. DTI fiber tract reconstructions were compared with cortex‐sparing fiber dissection results. The fibers of the superior longitudinal fasciculus (SLF), inferior fronto‐occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF) and uncinate fasciculus (UF) were isolated so as to enable identification of their cortical terminations. Two segments of the SLF were identified: first, an indirect and superficial component composed of a horizontal and vertical segment; and second, a direct and deep component or arcuate fasciculus. The IFOF runs within the insula, temporal stem and sagittal stratum, and connects the frontal operculum with the occipital, parietal and temporo‐basal cortex. The UF crosses the limen insulae and connects the orbito‐frontal gyri with the anterior temporal lobe. Finally, a portion of the ILF was isolated connecting the fusiform gyrus with the occipital gyri. These results indicate that cortex‐sparing fiber dissection facilitates study of the 3D anatomy of human brain tracts, enabling the tracing of fibers to their terminations in the cortex. Consequently, it is an important tool for neurosurgical training and neuroanatomical research.     

Pro‐ and macroglycogenolysis in contracting rat skeletal muscle

Glycogen is present in skeletal muscle in smaller acid‐insoluble proglycogen particles and larger acid‐soluble macroglycogen particles. The present study was designed to investigate the relative contribution of pro‐ and macroglycogen to glycogenolysis during muscle contractions. Rats were subjected to a glycogen‐depleting exercise bout and refed with either a carbohydrate‐rich or fat‐rich diet, resulting in widely different muscle glycogen contents. The following day, isolated hindlimbs were perfused and electrically stimulated to contract for 10 min. Pre‐ and postcontraction muscle samples of soleus, white and red gastrocnemius were analysed for pro‐ and macroglycogen. Contractions caused significant reductions in both pro‐ and macroglycogen in all glycogen groups and muscle types. In glycogen‐supercompensated gastrocnemius muscles, the relative utilization of macroglycogen was significantly higher than the relative utilization of proglycogen. In muscles with normal to low initial glycogen contents, proglycogen was much more abundant than macroglycogen and therefore contributed more to glycogenolysis in absolute numbers. In conclusion, both proglycogen and macroglycogen are suitable substrates during skeletal muscle contractions, although macroglycogen, when amply available, seems to be more easily broken down. This may provide an explanation for the dependence of the glycogenolytic rate on the total muscle glycogen content.