Metabolic profile of the perivertebral muscles in small therian mammals: implications for the evolution of the mammalian trunk musculature

In order to gain a better understanding of the ancestral properties of the perivertebral muscles of mammals, this study investigated the fiber type composition of these muscles in six small, extant therians (two metatherians and four eutherians) similar in body shape to early mammals. Despite a few species-specific differences, the investigated species were very similar in their overall distribution of fiber types indicating similar functional demands on the back muscles in mammals of this body size and shape. Deep and short, mono- or multisegmental muscles (i.e., mm. interspinales, intermammillares, rotatores et intertransversarii) consistently showed the highest percentage of slow, oxidative fibers implying a function as local stabilizers of the vertebral column. Superficial and large, polysegmental muscles (i.e., mm. multifidus, sacrospinalis, iliopsoas et psoas minor) were predominantly composed of fast, glycolytic fibers suggesting they function to both globally stabilize and mobilize the spine during rapid non-locomotor and locomotor activities. Some muscles contained striking accumulations of oxidative fibers in specific regions (mm. longissimus et quadratus lumborum). These regions are hypothesized to function independently from the rest of the muscle belly and may be comparable in their functionality to regionalized limb muscles. The deep, central oxidative region in the m. longissimus lumborum appears to be a general feature of mammals and likely serves a proprioceptive function to control the postural equilibrium of the pelvic girdle and lumbar spine. The potential functions of the m. quadratus lumborum during ventilation and ventral stabilization of the vertebral column are discussed. Because representatives of the stem lineage of mammals were comparable in their body proportions and probably also locomotor parameters to the species investigated here, I suggest that the described fiber type distribution is representative of the ancestral condition in mammals. The origin of mammals was associated with a substantial enlargement of the epaxial muscles and the addition of subvertebral muscle mass. Because this novel muscle mass is mainly composed of fast, glycolytic fibers in extant species, it is plausible that these changes were associated with the evolution of increased sagittal mobility in the posterior trunk region in the therapsid ancestors of mammals. The caudally increasing role of sagittal bending in body propulsion is consistent with the overall increase in the percentage of glycolytic fibers in the cranio-caudal direction. The evolution of mammals was also associated with a loss of ribs in the posterior region of the trunk. This loss of ribs is thought to have decreased the stability of the posterior trunk, which may explain the observed greater oxidative capacity of the caudal local stabilizers. The increased need for postural feedback in the more mobile lumbar region may also explain the evolution of the proprioceptive system in the m. longissimus lumborum. Furthermore, the anatomical subdivision of the transversospinal muscle into several smaller muscle entities is suggested to facilitate their functional specialization.     

Characteristics of paravertebral muscles – fibre type distribution pattern in the pika, Ochotona rufescens (Mammalia: Lagomorpha)

The evolution of the locomotor apparatus in vertebrates is marked by major reorganizations in trunk's musculature. The hypothesized functions of mammalian back muscles in the literature are discussed under consideration of the distribution and proportion of oxidative, type‐I‐fibres, oxidative‐glycolytic, type‐IIa‐fibres and glycolytic, type‐IIb‐fibres in paravertebral muscles of a small mammal. The fibre type distribution was examined from a complete series of histological sections maintaining topographical relationships between the muscles as well as within the muscle, in order to establish the overall distribution pattern. The deep and short muscles showed the highest percentage of oxidative fibres. The larger, superficial paravertebral muscles contained the highest percentage of glycolytic fibres. Two muscles were intermediate in their proportion of fibre types. All epaxial muscles together can be interpreted as an antigravity muscle–complex counteracting enduringly against the rebound tendency caused by gravitation, comparable with antigravity muscles in limbs. A gradient from deep to superficial, or a clear regionalization of oxidative muscle fibres in central deep regions around a large intramuscular tendon was found in the m. spinalis and the m. quadratus lumborum, respectively. Concepts of the function of human back muscles as those of A. Bergmark (1989: Acta Orthop. Scand. 230 , 1) or S.G.T. Gibbons & M.J. Comerford (2001: Orthop. Division Rev. March/April, 21) were exposed to be more general within mammals. Functional specializations of different muscles and muscle parts are discussed under the consideration of evolutionary reorganization of the paravertebral musculature in tetrapods. Along the cranio‐caudal axis, the percentage of oxidative fibres was decreased in caudal direction within the same muscles, whereas the proportion of glycolytic fibres was increased. Therefore, classifications of muscles as ‘glycolytic’ or ‘oxidative’ based on biopsies or analyses of single cross‐sections may result in wrong interpretations. Changes in the proportions of the fibre type distribution pattern were mostly due to oxidative and glycolytic fibre types, whereas the percentage of oxidative‐glycolytic fibres had only minor influence. A significant positive correlation between the cross‐sectional area of the single fibre and its percentage in the area investigated were observed for oxidative fibres, whereby the size was positive correlated to the proportion of the oxidative fibres.     

Somatic and intramuscular distribution of muscle spindles and their relation to muscular angiotypes

The distribution pattern of muscle spindles in the skeletal musculature has been reviewed in a large number of muscles (using the literature data especially from cat and man), and the relation of spindle content to muscle mass was quantitatively examined in 36 cat and 140 human muscles. In both species, the number of spindles increases with increasing muscle mass in a power law fashion of the form y=bx+a, whereby y denotes the logarithm of spindle content within a muscle, and x is the logarithm of muscle mass. For the cat, slope b and intercept a were estimated as 0.39 and 1.53, and for man as 0.48 and 1.33, respectively. The results show that the spindle content of a muscle may be related to its mass, confirming a similar analysis made previously by Banks and Stacey (Mechano receptors, Plenum Press, New York, 1988, pp. 263-269) in a different data set. With regard to the histological profile of muscle fibers, (as it is already well documented by many groups) muscle spindles tend to be located in deeper muscle regions where oxidative fibers predominate, and are far scarcer in superficial and flat muscle regions where glycolytic fibers predominate. These discrete muscle regions differ also in the properties of the vessel tree supplying them, for which the term oxidative and glycolytic "angiotype" has been used. The results from these three aspects of analysis (relation to muscle mass, relation to muscle regions with high oxidative index and relation to muscle regions with dense vascular supply) were combined with histological findings showing that spindles may be in systematic anatomical contact to intramuscular vessels. Based on these data a hypothesis is proposed according to which, both the number and intramuscular placement of muscle spindles are related to the oxidative angiotype supplying the muscle territories rich in oxidative fibers. The hypothesis is discussed.     

Interindividual variation of isolated muscle performance and fibre-type composition in the toad<Emphasis Type="Italic"> Bufo viridus</Emphasis>

Interindividual analyses of physiological performance represent one of the most powerful tools for identifying functional positive and negative linkages between various performance traits. In this study we investigated functional linkages in the whole-gastrocnemius performance of juvenile Bufo viridis by examining interindividual variation in in vitro muscle performance and muscle fibre-type composition. We used the work-loop technique to investigate the maximum in vitro power output and fatigue resistance of the gastrocnemius muscle during repeated sets of three cycles at the cycle frequency of 5 Hz, simulating an intermittent style of locomotion. We found several significant correlations between different measures of in vitro muscle performance, including a negative correlation between maximum net power output and fatigue resistance of power, indicating functional trade-offs between these performance traits. We also investigated the extent of individual variation in the proportions of different fibre types, and tested for correlations between individual variation in muscle fibre-type composition and the previously measured isolated muscle performance. Fast glycolytic fibres represented 84.0±3.4% of the muscle, while the combined slow oxidative and fast oxidative-glycolytic fibres represented 16±3.4%. We found no significant correlations between measures of in vitro muscle performance and the proportion of different fibre types in the gastrocnemius muscle. However, despite this lack of correlation between whole-muscle performance and muscle fibre-type composition data, we suggest the functional linkages detected between different measures of in vitro muscular performance have important ecological and evolutionary consequences.Communicated by I.D. Hume     

Fiber‐type composition in the perivertebral musculature of lizards: Implications for the evolution of the diapsid trunk muscles

The perivertebral musculature of lizards is critical for the stabilization and the mobilization of the trunk during locomotion. Some trunk muscles are also involved in ventilation. This dual function of trunk muscles in locomotion and ventilation leads to a biomechanical conflict in many lizards and constrains their ability to breathe while running (“axial constraint”) which likely is reflected by their high anaerobic scope. Furthermore, different foraging and predator‐escape strategies were shown to correlate with the metabolic profile of locomotor muscles in lizards. Because knowledge of muscle's fiber‐type composition may help to reveal a muscle's functional properties, we investigated the distribution pattern of muscle fiber types in the perivertebral musculature in two small lizard species with a generalized body shape and subjected to the axial constraint (Dipsosaurus dorsalis, Acanthodactylus maculatus) and one species that circumvents the axial constraint by means of gular pumping (Varanus exanthematicus). Additionally, these species differ in their predator‐escape and foraging behaviors. Using refined enzyme‐histochemical protocols, muscle fiber types were differentiated in serial cross‐sections through the trunk, maintaining the anatomical relationships between the skeleton and the musculature. The fiber composition in Dipsosaurus and Acanthodactylus showed a highly glycolytic profile, consistent with their intermittent locomotor style and reliance on anaerobic metabolism during activity. Because early representatives of diapsids resemble these two species in several postcranial characters, we suggest that this glycolytic profile represents the plesiomorphic condition for diapsids. In Varanus, we found a high proportion of oxidative fibers in all muscles, which is in accordance with its high aerobic scope and capability of sustained locomotion. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Histochemical and biochemical plasticity of muscle fibers in the little brown bat (Myotis lucifugus)

Summary Fiber composition, and glycolytic and oxidative capacities of the pectoralis, gastrocnemius, and cardiac muscles from active and hibernating little brown bats (Myotis lucifugus) was studied. The data were used to test two hypotheses: First, since hibernating bats maintain the capability of flight and make use of leg muscles to maintain a roosting position all winter, the fiber composition of the pectoralis and gastrocnemius muscles should not change with season. Second, we tested the hypothesis of Ianuzzo et al. (in press), who propose that the oxidative potential of mammalian cardiac muscle should increase with increasing heart rate while glycolytic potential should not. Our results indicate that the fiber composition of the pectoralis muscle was uniformly fast-twitch oxidative (FO)_ regardless of the time of year, as predicted. However, the gastrocnemius muscle exhibited a change in FO composition from 83% in active to 61% in hibernating animals. Contrary to the variable change in histochemical properties with metabolic state, a trend of reduced maximal oxidative (CS) and glycolytic (PFK) potential during hibernation in both flight and leg muscles was apparent. The oxidative potential of flight and leg muscles decreased by 15.2% and 56.5%, respectively, while the glycolytic potential of the same muscles decreased by 23.5% and 60.5%, respectively. As predicted, the glycolytic potential of cardiac muscle remained constant between active and hibernating bats, although there was a significant decrease (22.0%) in oxidative potential during hibernation.Abbreviations FO fast-twitch oxidative - FG fast-twitch glycolytic - SO slow-twitch oxidative - Vmax maximal enzyme activity - PFK phosphofructokinase - CS citrate synthase     

Capillarity and fibre types in locomotory muscles of wild mallard ducks (Anas platyrhynchos)

Six locomotory muscles from wild mallard ducks (Anas platyrhynchos) were analysed by histochemical methods. Special care was taken in sample procedure in order to describe the heterogeneity found throughout each muscle. Capillarity and fibre-type distributions were correlated to the functional implications and physiological needs of each muscle. Comparisons between our results and similar previous reports on dabbling and diving ducks are also discussed. Muscles from the leg presented the most heterogeneous fibre-type distributions, which are correlated to the wide range of terrestrial and aquatic locomotory performances shown by these animals. More specialized muscles such as pectoralis, used almost exclusively for flapping flight, had more homogeneous fibretype distributions, whereas muscles from the wing presented a high proportion of glycolytic fibres probably recruited during non-steady flapping flight. Deep muscle pectoralis zones and parts of the gastrocnemius which are closer to the bone are remarkable for their high capillarity indices and oxidative capacities, which suggests that these parts are recruited during sustained flapping flight and swimming. However, two different strategies for achieving these high oxygen needs are evident, indicating that the fibre cross-sectional area plays an important role in the modulation of the oxygen supply to the muscle cells.Abbreviations AChE acetylcholinesterase - cap mm^-2 number of capillaries per square millimeter - CD capillary density - C/F capillary-to-fibre ratio - EMR muscle extensor metacarpialis radialis - FCSA fibre cross-sectional area - FD fibre density - FG fast glycolytic - FOG fast oxidative glycolytic - GLE muscle gastrocnemius lateralis (pars externa) - GPDH -glycerophosphate dehydrogenase - ITC muscle iliotibialis cranialis - m-ATPase myofibrillar adenosine triphosphatase - OFA oxidative fibre area - OFN oxidative fibre number - PEC muscle pectoralis - SCH muscle scapulohumeralis caudalis - SDH succinate dehydrogenase - SO slow oxidative - TSC muscle scapulotriceps or triceps scapularis     

Functional differentiation of fore- and hindlimb muscles inMacaca fuscata determined on the basis of enzymatic activities

When the functional differentiation of 83 kinds of limb and trunk muscles ofMacaca fuscata was investigated on the basis of the activities of two glycolytic enzymes [lactate dehydrogenase (LDH) and aldolase] and one oxidative enzyme [succinate dehydrogenase (SDH)], the forelimb rather than the hindlimb muscles proved have higher oxidative activities. These results indicated that, inMacaca fuscata, the forelimb muscles have a higher resistance to fatigue, and that the hindlimb muscles have a higher tetanic tension on the basis of the relationships between enzymatic activities and functional properties of the muscle fiber types. These findings were interpreted in relation to the fact thatMacaca fuscata is a quadrupedal primate with arboreal habits, as compared with nonprimate terrestrial quadrupeds. The two-joint muscles and the superficial muscles contract more rapidly than do the other muscles in the hindlimb, thereby suggesting that both types of muscles readily adapt to quick movement.     

大鼠和家兔生后发育各阶段比目鱼肌纤维的比较

为研究大鼠与家兔骨骼肌各类型肌纤维的数量和二维分布以及生后发育对其影响,取生后2d和2、4、6、8、10周龄(体重10g和32、95、190、280、320g)大鼠及生后2d和2、4、8、12、16、20、24周龄(体重100g和220、400、750、1200、1600、2100、2500g)家兔的比目鱼肌做琥珀酸脱氢酶染色。实验结果表明,大鼠和家兔比目鱼肌纤维被分成Ⅰ型(SO),ⅡX型(FO)和ⅡA型(FOG)3型。使用图像分析系统分析每型肌纤维在生后发育各阶段的相关变化,大鼠和家兔比目鱼肌中：Ⅰ型纤维分布于整块肌肉,其数量随着生后发育而增加。幼体ⅡX型纤维分布在整块肌肉中,其数量随生后发育而减少;ⅡA型分布在肌肉中深层,数量几乎无变化;至成体时只有少量的ⅡX和ⅡA分布在肌表层。整个发育期间未见ⅡB型纤维。ⅡA型纤维直径最大,Ⅰ型中等,而ⅡX型最小。家兔3型肌纤维的平均横切面积比大鼠的大。这些结果表明大鼠和家兔后肢肌各种类型肌纤维的数量比例和分布随生长过程发生改变。     

Comparison of the Molecular Forms of the Cholinesterases in Tissues of Normal and Dystrophic Chickens

Abstract: The levels and molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and pseudocholinesterase (ΦChE, EC 3.1.1.8) were examined in various skeletal muscles, cardiac muscles, and neural tissues from normal and dystrophic chickens. The relative amount of the heavy (H_c) form of AChE in mixed-fibre-type twitch muscles varies in proportion to the percentage of glycolytic fast-twitch fibres. Conversely, muscles with higher levels of oxidative fibres (i.e., slow-tonic, oxidative-glycolytic fast-twitch, or oxidative slow-twitch) have higher proportions of the light (L) form of AChE. The effects of dystrophy on AChE and ΦChE are more severe in muscles richer in glycolytic fast-twitch fibres (e.g., pectoral or posterior latissimus dorsi, PLD); there is no alteration of AChE or ΦChE in a slow-tonic muscle. In the pectoral or PLD muscles from older dystrophic chickens, however, the AChE forms revert to a normal distribution while the ΦChE pattern remains abnormal. Muscle ΦChE is sensitive to collagenase in a similar way as is AChE, thus apparently having a similar tailed structure. Unlike skeletal muscle, cardiac muscle has very high levels of ΦChE, present mainly as the L form; AChE is present mainly as the medium (M) form, with smaller amounts of L and H_c. The latter pattern of AChE forms resembles that seen in several neural tissues examined. No alterations in AChE or ΦChE were found in cardiac or neural tissues from dystrophic chickens.     

Morphology, histochemistry, and function of epaxial cervical musculature in the horse (Equus caballus).

The semispinalis capitis and splenius muscles of the horse were analyzed for gross morphology, microarchitecture, fiber length, and fiber type. Although these two muscles are similar in size and anatomical position, they are very different from one another in structural design and histochemistry, implying diverse functional roles in the animal's behavior. The histochemical staining profile was limited to two fiber types: slow oxidative and fast glycolytic. The splenius muscle has simple architecture, long fibers, and a 60/40 ratio of SO to FG cross-sectional area. The semispinalis capitis has complex architecture with short-fibered, concentric compartments dorsal to its central tendon and longer-fibered compartments ventrally. The entire dorsal region has an increasing gradient of slow oxidative fiber percentage from caudal to cranial (58-71% SO). In contrast, the ventral region has a decreasing gradient of slow oxidative fibers from caudal to cranial (48-67% FG). These patterns can be interpreted within the context of the cervical musculature during locomotion and posture to indicate the functional advantages of this organization.     

Lumbar and abdominal muscle activity during walking in subjects with chronic low back pain: Support of the “guarding” hypothesis?

It has been hypothesized that changes in trunk muscle activity in chronic low back pain (CLBP) reflect an underlying “guarding” mechanism, which will manifest itself as increased superficial abdominal – and lumbar muscle activity. During a functional task like walking, it may be further provoked at higher walking velocities. The purpose of this cross sectional study was to investigate whether subjects with CLBP show increased co-activation of superficial abdominal – and lumbar muscles during walking on a treadmill, when compared to asymptomatic controls. Sixty-three subjects with CLBP and 33 asymptomatic controls walked on a treadmill at different velocities. Surface electromyography data of the erector spinae, rectus abdominis and obliquus abdominis externus muscles were obtained and averaged per stride. Results show that, compared to asymptomatic controls, subjects with CLBP have increased muscle activity of the erector spinae and rectus abdominis, but not of the obliquus abdominis externus. These differences in trunk muscle activity between groups do not increase with higher walking velocities. In conclusion, the observed increased trunk muscle activity in subjects with CLBP during walking supports the guarding hypothesis.     

Distribution patterns of the glucose transporters GLUT4 and GLUT1 in skeletal muscles of rats (Rattus norvegicus), pigs (Sus scrofa), cows (Bos taurus), adult goats, goat kids (Capra hircus), and camels (Camelus dromedarius)

Earlier studies demonstrated that forestomach herbivores are less insulin sensitive than monogastric omnivores. The present study was carried out to determine if different distribution patterns of the glucose transporters GLUT1 and GLUT4 may contribute to these different insulin sensitivities. Western blotting was used to measure GLUT1 and GLUT4 protein contents in oxidative (masseter, diaphragm) and glycolytic (longissimus lumborum, semitendinosus) skeletal muscle membranes of monogastric omnivores (rats and pigs), and of forestomach herbivores (cows, adult goats, goat kids, and camels). Muscles were characterized biochemically. Comparing red and white muscles, the isocitrate dehydrogenase (ICDH) activity was 1.5-15-times higher in oxidative muscles of all species, whereas lactate dehydrogenase (LDH) activity was 1.4-4.4-times higher in glycolytic muscles except in adult goats. GLUT4 levels were 1.5-6.3-times higher in oxidative muscles. GLUT1 levels were 2.2-8.3-times higher in glycolytic muscles in forestomach herbivores but not in monogastric animals. We conclude that GLUT1 may be the predominant glucose transporter in glycolytic muscles of ruminating animals. The GLUT1 distribution patterns were identical in adult and pre-ruminant goats, indicating that GLUT1 expression among these muscles is determined genetically. The high blood glucose levels of camels cited in literature may be due to an "NIDDM-like" impaired GLUT4 activity in skeletal muscle.     

Adaptation of muscle fibre types and capillary network to acute denervation and shortlasting reinnervation

We postulated that, in rat extensor digitorum longus muscle (EDL), the length of capillaries per fibre surface area (Lcap/Sfib) and per fibre volume (Lcap/Vfib) could reflect fibre-type transformations accompanied by changes in oxidative metabolic profile and selective fibre-type atrophy. We excised rat EDL muscle 2 weeks after the sciatic nerve was cut (acute denervation; DEDL) and 4 weeks after the nerve was crushed (early reinnervation; REDL) and characterised muscle fibre-type transformation by the expression of myosin heavy-chain isoforms and by succinate dehydrogenase (SDH) and nicotinoamide adenine dinucleotide-tetrazolium reductase (NADH-TR) reactions. The numerical percentage (N/N) and area percentage (A/A) of pure and hybrid fibres and their diameter were determined, as was the A/A of SDH- and NADH-TR-positive fibres. The length of capillaries per fibre length (Lcap/Lfib), Lcap/Sfib and Lcap/Vfib were estimated in REDL and Lcap/Vfib in DEDL. In DEDL, the type 2x and 2b fibres evidently atrophied, with the N/N of type 2x fibres being lower and that of hybrid fibres higher. In REDL, the N/N of hybrid fibres was even higher, consequent to a lower N/N of type 2b fibres; however, fibre diameters approached values of the control EDL. Compared with control EDL, denervated and reinnervated muscles exhibited a higher A/A of oxidative fibres. This is probably the result of fibre-type transformation and selective fibre atrophy. We conclude that capillary length does not change during acute denervation and early reinnervation. The obtained higher values of Lcap/Sfib and Lcap/Vfib are related to changes in muscle fibre cross-sectional area. This study was supported by the Slovenian Research Agency and the Ministry of Education, Youth and Sport of the Czech Republic (KONTAKT grant no. 9-06-6 and grant no. LC06063).     

Architectural and histochemical diversity within the quadriceps femoris of the brown lemur (Lemur fulvus)

Physiologically related features of muscle morphology are considered with regard to functional adaptation for locomotor and postural behavior in the brown lemur (Lemur fulvus). Reduced physiological cross-sectional area, estimated maximum excursion of the tendon of insertion, length of tendon per muscle fasciculus, and areal fiber type composition were examined in the quadriceps femoris in order to assess the extent of a "division of labor" among four apparent synergists. Each of these four muscles in this prosimian primate displays a distinguishing constellation of morphological features that implies functional specialization during posture and normal locomotion (walk/run, galloping, leaping). Vastus medialis is best suited for rapid whole muscle recruitment and may be reserved for relatively vigorous activities such as galloping and leaping (e.g., small cross-sectional area per mass, long excursion, predominance of fast-low oxidative fibers, relatively little tendon per fasciculus). In theory, rectus femoris could be employed isometrically in order to store elastic strain energy during all phasic activities (e.g., large cross-sectional area per mass, short excursion, predominance of fast-high oxidative fibers, large amount of tendon per fasciculus). Vastus intermedius exhibits an overall morphology indicative of a typical postural muscle (e.g., substantial cross-sectional area, short excursion, predominance of slow-high oxidative fibers, large amount of tendon per fasciculus). The construction of vastus lateralis reflects an adaptation for high force, relatively high velocity, and resistance to fatigue (e.g., large cross-sectional area, long excursion, most heterogeneous distribution of fiber types, large amount of tendon per fasciculus); this muscle is probably the primary contributor to a wide range of locomotor behaviors in lemurs. Marked dramatic architectural disparity among the four bellies, coupled with relative overall fiber type heterogeneity, suggests the potential for exceptional flexibility in muscle recruitment within this mass. One interpretation of this relatively complex neuromuscular organization in the brown lemur is that it represents an adaptation for the exploitation of a three-dimensional arboreal environment by rapid quadrupedalism and leaping among irregular and spatially disordered substrates.     

Response of the trunk muscles to training assessed by magnetic resonance imaging and muscle strength.

A group of 12 sedentary medical students (1 man and 11 women aged 21-27 years) participated in a strength training programme for the trunk muscles lasting 18 weeks. The maximal isometric flexion and extension forces of the trunk muscles were measured before the training and at 18 weeks by dynamometer. The cross-sectional area of the back muscles, i.e. erector spinae, multifidus and psoas muscles, was measured from magnetic resonance images (spin echo sequence TR/TE 1500/80, slice thickness 10 mm) obtained at the L4-L5 disc level before the training, at 11 and 18 weeks. During training, no significant change in the body mass or body fat content was found. Muscle forces or muscle cross-sectional area were not related to body mass. There was a significant increase in both trunk muscle cross-sectional area (psoas muscle P < 0.001 and back muscles P < 0.01) and trunk muscle forces (flexion and extension forces P < 0.01) during the training but no direct association between the muscle cross-sectional area and strength of the flexors and extensors was detected before or after the training.     

Fiber‐type distribution of the perivertebral musculature in Ambystoma

Many salamanders locomote in aquatic and terrestrial environments. During swimming, body propulsion is solely produced by the axial musculature generating lateral undulations of the trunk and tail. During terrestrial locomotion, the trunk is oscillated laterally in a standing wave, and body propulsion is achieved by concerted trunk and limb muscle action. The goal of this study was to increase our knowledge of the functional morphology of the tetrapod trunk. We investigated the muscle‐fiber‐type distribution and the anatomical cross‐sectional area of all perivertebral muscles in Ambystoma tigrinum and A. maculatum. Muscle‐fiber‐type composition was determined in serial cross‐sections based on m‐ATPase activity. Five different body segments were investigated to test for cranio‐caudal changes along the trunk. The overall fiber‐type distribution was very similar between the species, but A. tigrinum had relatively larger muscles than A. maculatum, which may be related to its digging behavior. None of the perivertebral muscles possessed a homogeneous fiber‐type composition. The M. interspinalis showed a distinct layered organization and may function to ensure the integrity of the spine (local stabilization). The M. dorsalis trunci exhibited the plesiomorphic pattern for notochordates in having a distinct superficial layer of red and intermediate fibers, which covered the central white fibers; therefore, it is suggested to function as a mobilizer and a stabilizer of the trunk, but, may also be involved in modulating body stiffness. Similarly, the M. subvertebralis showed clear regionalizations, implying functional subunits that can stabilize and mobilize the trunk as well as modulate of body stiffness. Cranio‐caudally, neither the fiber‐type composition nor the a‐csa changed dramatically, possibly reflecting the need to perform well in both aquatic and terrestrial habitats. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Morphology and histochemistry of the ambiens muscle of the red-eared turtle (Pseudemys scripta)

Six fiber types have been described in the ambiens muscle of red-eared turtles. These include one slow oxidative type, two fast oxidative types, two fast oxidative and glycolytic types, and one fast glycolytic type. Fiber types are non-randomly distributed throughout cross sections of the muscle. There is a decreasing gradient of oxidative staining and an increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle. The slow oxidative fibers are predominantly located within one or two fascicles of the superficial surface of the muscle. The fast glycolytic fibers are predominant in deep fascicles. In contrast to previous reports of histochemically monotypic intrafusal fibers in turtle muscle, ambiens muscle spindles have been observed containing one to eleven intrafusal fibers, including two fiber types. Fiber diameter and area are consistently smaller than observed in most extrafusal fibers. Spindles are predominantly located in superficial and cranial fascicles of the ambiens muscle and are located in regions characterized by extrafusal fibers with high oxidative activity.     

Differential adaptations during growth spurt and in young adult rat muscles

During the post-weaning growth and maturation period (25/90 days after birth), rat limb muscles are submitted to specific adaptations. Our aim was to characterize the mechanical properties of two muscles that are opposite in terms of fibre-type distribution, the soleus and the extensor digitorum longus (EDL) muscles of male Wistar rats. Results showed a fast-to-slow fibre-type transition in soleus while no modification in fibre-type distribution was observed in EDL. A growth-induced increase in muscle force was observed. Soleus underwent an increase in twitch kinetics, but EDL showed no modification. Resistance to fatigue was higher in 90-day-old soleus but not modified in the EDL. Surprisingly, analysis of maximal shortening velocity showed a decrease in both soleus and EDL. Finally, tension/extension curves indicated a growth-induced increase in series elastic stiffness in the two muscles. These results suggest that during this growth period, skeletal muscles are submitted to differential adaptations. Moreover, whereas adaptation of biomechanical properties observed can be explained partly by an adaptation of fibre profile in soleus, this is not the case for EDL. It is suggested that changes in muscle architecture, which are often disregarded, could explain some variations in mechanical properties, especially when muscles undergo an increase in both mass and length.     

Histochemical and biochemical properties of flight muscle fibers in the little brown bat,Myotis lucifugus

Summary The purpose of this investigation was (1) to determine the fiber composition of pectoralis muscle of the little brown bat,Myotis lucifugus; (2) to compare the fiber composition of this muscle with two of the animal's accessory flight muscles; and (3) to study the effect of hibernation on pectoralis muscle fiber composition. Bat skeletal muscle fibers were also compared with those of white laboratory rats (Rattus norvegicus). Bat pectoralis muscles possessed exceptionally high oxidative capacities as indicated by their succinate dehydrogenase activities, but relatively low glycolytic potentials (phosphofructokinase activities). Muscle histochemistry demonstrated that fiber composition of bat pectorlis muscle was homogeneous; all fibers possessed high aerobic and low glycolytic potentials, and high myofibrillar ATPase activities indicating fast contractile properties. In contrast, accessory flight muscles possessed three distinguishable fiber types. During hibernation there was a significant decline in oxidative potential, no change in glycolytic potential, and no alteration in basic fiber composition of bat pectoralis muscle. The findings of this study suggest that pectoralis muscles ofM. lucifugus may approach the ultimate adaptation of a mammalian locomotory muscle for aerobic generation of muscular power.Abbreviations FG fast-twich glycolytic - FOG fast-twitch-oxydative-glycolytic - -GPDH -glycerophosphate dehydrogenase - LDH lactate dehydrogenase - NADH-D reduced nicotinamide adenine dinucleotide diaphorase - PFK phosphofructokinase - SDH succinate dehydrogenase - SO slowtwich-oxidative