ISSN:1422-6405    

DOI:10.1159/000147967

出版商:S. Karger AG    

年代:1997

数据来源: Karger

ISSN:1422-6405    

DOI:10.1159/000147968

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The length and angles of fascicles were determined for the vastus lateralis muscle (VL) using ultrasonography in 6 subjects performing ramp isometric knee extension. The subject increased torque from zero (relax) to maximum (MVC) with the knee positioned every 15°, from 10° to 100° flexion (0° = full extension). As the knee was positioned closer to extension, fascicle length was shorter [116+4.7 (mean ± SEM) mm at 100° vs. 88+4.1 mm at 10° (relax)]. The fascicle length of the VL decreased with increasing torque at each knee position [116+4.7 (relax) to 92 ± 4.3 mm (MVC) at 100°]. On the other hand, fascicle angles increased with an increase in torque. These changes reflected the compliance of the muscle-tendon complex which increased as the knee reached a straight position. The estimated muscle force of the VL was maximal (2,052 ± 125 N) for a fascicle length of 78 ± 2.7 mm (i.e. optimum length) with the knee positioned at 70° of flexion. The relationship between muscle force and fascicle length indicated that the VL uses the ascending (knee 70°) of the forc

ISSN:1422-6405    

DOI:10.1159/000147969

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The purpose of this study was to test the hypothesis that muscle fiber length and joint moment arm are combined in such a way that maximum muscle force is produced during locomotion. Plantarflexor (soleus, SOL and medial gastrocnemius, MG) and dorsiflexor (extensor digitorum longus, EDL and tibialis anterior, TA) muscle architecture in the mouse was measured along with their associated moment arms. Fiber length varied significantly between muscles ranging from 5.7 ± 0.2 mm (MG) to 7.6 ± 0.2 mm (TA). Plantarflexor moment arms were over twice as large as dorsiflexor moment arms (1.88 ± 0.06 mm vs. 0.84 ± 0.03 mm) suggesting a greater muscle length change with joint angle for plantarflexors compared to dorsiflexors. Using a simple muscle-joint model, the active sarcomere length range in these muscle groups was calculated and proved to be quite similar between functional groups. The active range for dorsiflexors was 2.2-2.4 µm, while the active range for plantarflexors was 2.2-2.5 µm, indicating that both muscle groups operate primarily near the plateau of their length tension-relation. Finally, when calculating force produced by muscles during locomotion, the combination of moment arm and fiber length measured in all muscle groups yielded muscle-joint systems that produced near maximal forces at the velocities modeled. These data indicate that fiber length and moment arm appear to be coordinated to yield the greatest possible force production during locom

ISSN:1422-6405    

DOI:10.1159/000147970

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

Muscle mass, distribution of fiber types, fiber cross-sectional area (CSA) and selected enzyme activities were determined in rats hindlimb-suspended free of immobilization (Susp-Free), suspended with the ankle dorsiflexed (Susp-DF, soleus stretched) or plantarflexed (Susp-PF, soleus shortened) for 10 days and compared to cage-control (Con) rats. Reduction of muscle weight associated with suspension was prevented in Susp-DF rats. The mean CSAs of slow fibers were Con=Susp-DF > Susp-PF > Susp-Free and of fast and intermediate fibers tended to be Susp-DF > Con > Susp-PF=Susp-Free. Mean activities of succinate dehydrogenase (SDH), α-glycerophosphate dehydrogenase (GPD) and myofibrillar adenosine triphosphatase (mATPase) in slow and fast fibers were similar in Con and Susp-Free rats. Mean SDH activity in slow fibers was higher in Susp-DF and Susp-PF than in Con and Susp-Free. No significant differences in SDH activities of fast fibers were observed among groups. GPD activity was higher in slow fibers of Susp-DF and Susp-PF compared to Con. The mATPase activity was higher in slow fibers of Susp-DF compared to Con and Susp-Free rats and lower in fast fibers of Susp-DF compared to Con rats. Thus, when compared to control, the patterns of adaptation were more similar in the Susp-DF and Susp-PF than in the Susp-Free. Although these results are consistent with previous studies demonstrating that the load placed on a muscle can affect protein metabolism, the direction and magnitude of the adaptive responses observed in the present study were closely associated with the chronically imposed changes in muscle length, i.e. fixed at either a shortened or a lengthened position

ISSN:1422-6405    

DOI:10.1159/000147971

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

In the skeletal muscle fiber organization of many vertebrate muscles, serial arrangements or linkages of muscle fibers along the muscle or fascicle are commonly found. These serially linked muscle fibers employ distinct junctional morphologies from muscle to muscle. Notable are the end-to-end linkages of muscle fibers through tendinous intersections (TIs), where many fibers end onto a continuous connective tissue plate with folded terminations similar to myotendinous junctions. Besides this end-to-end linkage, overlapping linkages or arrangements occur among nonspanning fibers terminating intrafascicularly. These nonspanning fibers bear tapering terminations with direct cell-cell (myomuscular) junctions or without any specialized junctions. Despite their overlapping linkages or tapering profiles, nonspanning fibers maintain a uniform sarcomere length along the linked fibers, suggesting that the overlapping-linked nonspanning fibers are equivalent to the end-to-end linked fibers in their mechanical capacity. However, the junctional compliance could differ in their extracellular elastic components and their organization at junctional sites, e.g., direct mechanical (myomuscular) junctions vs. indirect linkages through connective tissue. Increasing evidence suggests that the elastic components, including muscle fibers as well as connective tissues, are more critical than previously thought for the mode and/or the efficiency of tension transmission among serially arranged fibers and thus for the mechanical properties of the muscle.

ISSN:1422-6405    

DOI:10.1159/000147972

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

To examine the effects of numerous complex branched fibers (CBF) on whole muscle contractile properties, we established a model of myopathic muscles containing a large number of CBF by repeated local injection of bupivacaine hydrochloride (Marcaine) into the plantaris (PLA) muscle. Marcaine injections were administered once weekly for 10 weeks into the right PLA muscles of Wistar male rats. The in situ contractile properties of Marcaine-injected PLA muscles (I-PLA) were examined under urethane anesthesia, and compared with the contralateral (control) PLA muscle (C-PLA). Numerical and morphological examination using the modified nitric acid fiber digestion method and scanning electron microscopy showed that Marcaine resulted in an 8-fold increase in the number of branched fibers in the I-PLA muscles and about 70% of these fibers were CBF. The latter were composed of ten or more muscle fibers fused together along with many thin and thick, long and short daughter branches. The time to peak tension of twitch and tetanus, and 1/2 relaxation time were significantly longer in I-PLA muscles, representing a shift to slow muscle characteristics. However, the total area of slow fibers/muscle cross-sectional area was similar in I-PLA and C-PLA muscles. Aggregates of same-type fibers (slow fibers) with small and large diameters were observed, reflecting an expected cross-sectional property of CBF. Our results suggest that the appearance of several CBF in a muscle is associated with a shift towards slower contractile properties in the affected muscle.

ISSN:1422-6405    

DOI:10.1159/000147973

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The spatial representation of muscle spindles (Sps) in the small (-0.2 g), simply structured capsularis muscle that crosses anterior to the cat’s hip joint was compared with the distribution of the slow oxidative (SO) and few ( < 10%) fast oxidative-glycolytic (FOG) fibers of which it is composed to see if their distributions were consistent with a hypothesis that sensory input from Sps influences the incidence of extrafusal fiber types. In frozen sections from 4 muscles, FOG fibers were enumerated along 1-mm strips across the muscle’s maximum width, and between the ‘superficial’ surface and the ‘deep’ one that contacts the joint. The locations of Sps in complete serial sections of 2 paraffin-embedded muscles, one perfused with the hip joint flexed and the other with it extended, were plotted on an outline of each muscle at its midlength, and their numbers and density in horizonal and sagittal ‘strata’ determined. In general, the incidence of Sps increased down the superficial-to-deep axis, while FOG fibers became fewer, as is consistent with support of SO status by Sp input. Along the craniocaudal axis, i.e. width, the numbers of FOG fibers rose toward the hip joint, but this was not associated with a monomodal gradient of Sps. In the extended muscle, however, the lengths of the axial bundle and capsular space of Sps in the half of the muscle next to the joint exceeded those in the longer, cranial half, implying that under stretch the input from Sps became higher toward the joint. In the non-extended muscle these lengths did not differ, although the lengths of extrafusal fibers isolated from 2 macerated muscles and normalized according to sarcomere length decreased linearily by -50% along the craniocaudal axis. It is explained that if elastic resistance of a Sp’s sensory region exceeded that of an equivalent length of septal tissue in-series, the progressive shift in the ratio of compliances across this trapezoidally-shaped muscle should result in relatively greater lengthening of Sps at the shorter border as the muscle was extended. Levels of discharge conducive to transition of some motor units to the FOG type might be attained. Thus, gradients in the discharge of Sps (but not necessarily incidence) along both transverse and superficial-to-deep axes may be consistent with Sp sensory input influencing the distribution of at least these typ

ISSN:1422-6405    

DOI:10.1159/000147974

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The extensor carpi radialis muscle of the horse is deceptive at first appearance. It has a fusiform shape similar to other forearm extensor muscles. The fiber arrangement also appears long and relatively parallel. However, it may contain two or more compartments that correlate with differing functional roles. Histochemical and immunocytochemical analysis of proximal and distal regions of the muscle (n = 9) demonstrate that the proximal portion of the muscle is composed of a mean of 13% type I, presumed slow twitch, and 61% type lib, presumed fast twitch fibers. In contrast, the distal compartment is composed of a mean of about 43% type I and only 22% type lib fibers. The type I and IIa fibers are all highly aerobic based on nicotinamide dinucleotide tetrazolium reductase reactions. Correlative data regarding the myosin isoforms has been obtained with 4% SDS-PAGE analysis of myosin heavy chain isoforms which demonstrate isoforms migrating at rates similar to rat type I, IIa, and IIx. The latter has been referred to as type IIB/X in a study of the horse’s gluteus medius muscle. We propose that the in-series ‘compartmentalization’ of the muscle, while not conforming strictly to the definitions of neuromuscular compartments, relates to the insertion of the lacertus fibrosus, a distal slip of the biceps brachii, upon the extensor carpi radialis. Earlier studies demonstrated a high proportion of type I fibers in the equine lateral biceps brachii which were thought to stabilize the shoulder during long periods of quiet standing. Because of action imposed on the distal compartment by the biceps brachii, slow and fatigue-resistant functions are part of the limb’s passive stay apparatus to effect long-term standing by the horse. Thus, the fatigue-resistant compartments of biceps brachii and extensor carpi radialis may constitute an in-series arrangement of the two muscles. The proximal compartment is suited to provide powerful, more fatigable contractions during locomotion and likely affects stress or strain within the distal postural comp

ISSN:1422-6405    

DOI:10.1159/000147975

出版商:S. Karger AG    

年代:1997

数据来源: Karger

摘要:

The architectural properties and fiber-type composition of the cat hip ‘cuff’ muscles, i.e. the deep layer of muscles encircling the hip joint, were determined. The muscles studied included the gluteus minimus, obturator internus and externus, gemellus superior and inferior, pyriformis, quadratus femoris and capsularis. In addition, the fiber-type composition was determined for the iliacus muscle. Compared to other lower limb muscles, the cuff muscles were small (–0.2 to 2.7 g) and short (–15 to 40 mm long) and had short mean fiber lengths (–7 to 12 mm long), small angles of fiber pinnation (< 12°), and small physiological cross-sectional areas (–0.2 to 2.8 cm2). The percentage of the cross-sectional area comprised of slow fibers ranged from 24 to 95% with this value being over 50% in 5/9 muscles studied. The small angle of pinnation and short fiber lengths optimize force production and the relatively high percentage of slow fibers suggest a high level of activation. Both of these properties are consistent with a hip stabilization role for these muscles. In addition, the high percentage of slow fibers suggests a high spindle density and a possible role of these muscles in providing proprioceptive feedback to the central nervous system for the control of posture an

ISSN:1422-6405    

DOI:10.1159/000147976

出版商:S. Karger AG    

年代:1997

数据来源: Karger