Comparative study of the gastrocnemius and soleus muscles of the Egyptian desert rodent Gerbillus pyramidum and the albino rat.

The hind limb muscles of the Egyptian desert rodent Gerbillus pyramidum and the albino rat were studied macroscopically and microscopically, using ordinary and histochemical techniques. The results revealed a relatively long hind limb and a relatively long tendon of the gastrocnemius group in G. pyramidum as compared with the albino rat. The dark fibres (red) were dominant in the muscles of the former animal and its spindles similarly contained more dense intrafusal fibres than the spindles of the albino rat. The correlation between these findings and the frequency and power of movement of the hind limbs in G. pyramidum was discussed.     

The role of skin afferent in regulation of locomotion evoked by electrical epidural stimulation of spinal cord in decerebrated cats

The role of hindpaw skin afferent input in the locomotor pattern formation induced by epidural spinal cord stimulation was investigated in decerebrated cats. Locomotor activity was evoked by continuous 3-5Hz stimulation of dorsal surface of L4-L5 spinal segments. Kinematic and electromyographic activity (EMG) of m. Quadriceps, m. Semitendinosus, m. Tibialis anterior an m. Gastrocnemius lateralis before and after blocking of skin receptors in one hind limb were recorded. In addition, reflex responses in the hind limb muscles to epidural stimulation with frequency 0.5 Hz were analysed. Blocking of skin receptors of the foot with chlorothane paw irrigation or 2 % lidocaine administrated into the hind paw was performed. After blocking of skin receptors of the foot the stepping pattern changed. Stepping with dorsal foot placement and dragging during swing phase was observed. Duration of stance phase significantly decreased. Inhibition of polysynaptic activity of proximal and distal extensor muscles and distal flexor muscles of hind paw during locomotion was found. Monosynaptic responses after blocking of skin receptors of the foot changed insignificantly.     

Effect of surgery to implant motion and force sensors on vertical ground reaction forces in the ovine model

Activities of daily living (ADLs) generate complex, multidirectional forces in the anterior cruciate ligament (ACL). While calibration problems preclude direct measurement in patients, ACL forces can conceivably be measured in animals after technical challenges are overcome. For example, motion and force sensors can be implanted in the animal but investigators must determine the extent to which these sensors and surgery affect normal gait. Our objectives in this study were to determine (1) if surgically implanting knee motion sensors and an ACL force sensor significantly alter normal ovine gait and (2) how increasing gait speed and grade on a treadmill affect ovine gait before and after surgery. Ten skeletally mature, female sheep were used to test four hypotheses: (1) surgical implantation of sensors would significantly decrease average and peak vertical ground reaction forces (VGRFs) in the operated limb, (2) surgical implantation would significantly decrease single limb stance duration for the operated limb, (3) increasing treadmill speed would increase VGRFs pre- and post operatively, and (4) increasing treadmill grade would increase the hind limb VGRFs pre- and post operatively. An instrumented treadmill with two force plates was used to record fore and hind limb VGRFs during four combinations of two speeds (1.0 m/s and 1.3 m/s) and two grades (0 deg and 6 deg). Sensor implantation decreased average and peak VGRFs less than 10% and 20%, respectively, across all combinations of speed and grade. Sensor implantation significantly decreased the single limb stance duration in the operated hind limb during inclined walking at 1.3 m/s but had no effect on single limb stance duration in the operated limb during other activities. Increasing treadmill speed increased hind limb peak (but not average) VGRFs before surgery and peak VGRF only in the unoperated hind limb during level walking after surgery. Increasing treadmill grade (at 1 m/s) significantly increased hind limb average and peak VGRFs before surgery but increasing treadmill grade post op did not significantly affect any response measure. Since VGRF values exceeded 80% of presurgery levels, we conclude that animal gait post op is near normal. Thus, we can assume normal gait when conducting experiments following sensor implantation. Ultimately, we seek to measure ACL forces for ADLs to provide design criteria and evaluation benchmarks for traditional and tissue engineered ACL repairs and reconstructions.     

Muscle mass in musculoskeletal models

Most current models of musculoskeletal dynamics lump a muscle's mass with its body segment, and then simulate the dynamics of these body segments connected by joints. As shown here, this popular approach leads to errors in the system's inertia matrix and hence in all aspects of the dynamics. Two simplified mathematical models were created to capture the relevant features of monoarticular and biarticular muscles, and the errors were analyzed. The models were also applied to two physiological examples: the triceps surae muscles that plantar flex the human ankle and the biceps femoris posterior muscle of the rat hind limb. The analysis of errors due to lumping showed that these errors can be large. Although the errors can be reduced in some postures, they cannot be easily eliminated in models that use segment lumping. Some options for addressing these errors are discussed.     

The distribution of motoneurons supplying hind limb muscles in the clawed toad, Xenopus laevis

The distribution of motoneurons in the lumbar spinal cord (spinal segments 8-10) of the clawed toad, Xenopus laevis, was studied with the horseradish peroxidase technique. In a total of 13 different hind limb muscles this tracer was applied in a slow-release gel. Motoneurons innervating a particular hind limb muscle were clustered in longitudinally arranged motor pools. Motor pools of different muscles did show considerable overlap both in the rostrocaudal and transverse plane. But, the various motor pools clearly show a somatotopic organization of motoneurons even in such a condensed lumbar spinal cord as in Xenopus laevis. Motoneurons innervating more distally positioned muscles are generally found in more caudal segments, while proximal muscles (with the exception of the m. adductor magnus) are supplied by motoneurons more or less throughout the lumbar enlargement. Flexor muscles usually are innervated by motoneurons situated ventrolaterally in the ventral horn, extensor muscles by dorsomedially found motoneurons. This pattern is particularly apparent for proximal (thigh) muscles, less so for more distal (shank and foot) muscles. The present data are in keeping with those obtained with the retrograde cell degeneration technique in ranid frogs and are consistent with observations in other tetrapods, although a more clear separation of motor pools is evident in "higher" vertebrates such as birds and mammals.     

Effects of aging and life-long physical training on collagen in slow and fast skeletal muscle in rats

Summary Intramuscular collagen in a slow (m. soleus) and a fast (m. rectus femoris) skeletal muscle was studied by biochemical, morphometric, and immunohistochemical methods. Wistar white rats of 1, 4, 10, and 24 months were used as experimental animals. Our aim was to evaluate the effects of life-long physical training (treadmill running, 5 days a week for 1, 3, 9, and 23 months depending on the age attained). The biochemical concentration of collagen was higher in m. soleus than in m. rectus femoris and it increased in youth and in old age in m. soleus. The trained rats had higher concentrations of collagen than the untrained rats at 10 and 24 months. The morphometrically measured area-fractions of both the endomysium and perimysium were higher in m. soleus than in m. rectus femoris. The age-related increase in intramuscular connective tissue was of endomysial origin. The immunohistochemical staining of type-I, -III, and -IV collagens indicated the more collagenous nature of m. soleus as compared with m. rectus femoris for all major collagen types; this was most marked for type-IV collagen of basement membrane. The results indicate that both age and endurance-type physical training further distinguish the slow and fast muscles with respect to their connective tissue.     

Muscle capillary supply in hind limb and diaphragm of the common shrew (Sorex araneus)

Shrew species of the subfamily Soricinae have unusually high metabolic rates when compared to Crocidurinae shrews and other similar-sized mammals. The aim of this study was to clarify whether the high basal metabolic rate of Soricinae shrews is reflected in a high capillary density in their muscles. To this end, the capillary supply of four limb muscles and diaphragm of the common shrew (Sorex araneus) was quantified from cross-sectioned muscles. The capillary densities of the limb muscles were 2575 ± 329, 3111 ± 299, 2812 ± 197 and 2752 ± 173 capillaries mm⁻² fibre area in gastrocnemius lateralis, g. medialis, plantaris and soleus, respectively. Capillary density of the shrew diaphragm (6691 ± 1057) was double that of the limb muscles. This value is among the highest ever measured in mammals. In general, the capillary supply in the hind limb of the common shrew is about 3–4 times higher than commonly found in the leg muscles of the laboratory rat or other bigger mammals, but similar to those in Crocidurinae shrews and some small rodents. Thus the high resting metabolism of the common shrew is not associated with an extraordinarily high capillary density. The apparent disparity between basal metabolic rate and muscle capillary supply in S. araneus is probably due to the small aerobic scope of shrews in the subfamily Soricinae. Accepted: 22 January 1998     

Energy metabolism in relation to oxygen supply in contracting rat skeletal muscle

The regulation of the energy metabolism in contracting skeletal muscle is under close control, and several regulating factors have been reported. The aim of this study was to investigate the importance of the oxygen supply as a limiting factor for muscle performance during contractions and recovery from contractions. To perform well-controlled standardized experiments on contracting skeletal muscle, the perfused rat hind limb model was developed. The 31P NMR technique was adapted to the rat hind limb model. This enabled continuous nondestructive monitoring of the energy state at various levels of muscular activity. Significant correlations were found between oxygen delivery and oxygen consumption, lactate release, and glucose uptake, respectively. An increased degree of fatigue was observed at lower oxygen deliveries. In both soleus and gastrocnemius muscles, oxygen delivery correlated with the intramuscular concentrations of phosphocreatine (PCr), lactate, and glycogen. The 31P NMR experiments showed a correlation between oxygen delivery and the steady-state level of PCr/inorganic phosphate (Pi) during the contraction period. The rate of recovery in PCr/Pi after the contraction was also dependent on oxygen delivery. The results demonstrate a causal relationship between oxygen supply and energy state in contracting as well as recovering skeletal muscles.     

Quantitative study of the microvascular pattern in tourniquet-induced muscle ischemia

Experiments were carried out on 40 adult Wistar rats to determine the effect of the application of a pneumatic tourniquet on the capillary network of the tibialis anterior muscles. The tourniquet was applied for four hours to the right hind limb above the knee. During the degeneration processes (6 to 24 hours postischemia), the capillary density and capillary-to-fiber ratio decreased significantly with respect to a control group of untreated animals. In the subsequent regenerative processes, there was a greater increase of fiber density than of capillary density, resulting in a capillary-to-fiber ratio lower than that of the control group. In the last period (30 to 90 days postischemia), both capillary density and fiber density returned to normal values.     

Hip extensor EMG and forelimb/hind limb weight support asymmetry in primate quadrupeds

Higher weight support on the hind limb than forelimb is among the distinctive characteristics of primate quadrupeds. Although often assumed to be due to a more posteriorly positioned whole body center of mass, there are little data to support such a difference. Reynolds (1985. Am J Phys Anthropol 67:335-349) notes that the distribution of forces on the limbs can also be influenced by average limb posture, but suggests that this effect is too small to account for the asymmetry in weight support observed in primates. Instead, he proposes that high hind limb forces are brought about by an active process of shifting weight off the forelimbs and onto the hind limbs through use of hind limb retractors. In this study, we use video records of walking animals to explore the degree to which average limb posture in primates and other quadrupedal mammals deviates from vertical, and use electromyography to test Reynolds' model of hind limb retractor activity and posterior weight shift. The limb posture results indicate that primate forelimbs oscillate about a vertical or slightly retracted axis, and though the hind limbs are slightly protracted, the magnitude of deviation from vertical is too small to have a major effect on weight support distribution. The electromyographic results reveal higher levels of hip extensor activity in antipronograde primates that bear a higher proportion of weight on their hind limbs. This lends support to Reynolds' suggestion that some primates use muscles to actively shift weight onto hind limbs to relieve stresses on forelimbs less well structured for weight support.     

Maintenance of skeletal muscle energy homeostasis during prolonged wintertime fasting in the raccoon dog (<Emphasis Type="Italic">Nyctereutes procyonoides</Emphasis>)

The raccoon dog (Nyctereutes procyonoides) is a canid species with autumnal fattening and prolonged wintertime fasting. Nonpathological body weight cycling and the ability to tolerate food deficiency make this species a unique subject for studying physiological mechanisms in energy metabolism. AMP-activated protein kinase (AMPK) is a cellular energy sensor regulating energy homeostasis. During acute fasting, AMPK promotes fatty acid oxidation and enhances glucose uptake. We evaluated the effects of prolonged fasting on muscle energy metabolism in farm-bred raccoon dogs. Total and phosphorylated AMPK and acetyl-CoA carboxylase (ACC), glucose transporter 4 (GLUT 4), insulin receptor and protein kinase B (Akt) protein expressions of hind limb muscles were determined by Western blot after 10 weeks of fasting. Plasma insulin, leptin, ghrelin, glucose and free fatty acid levels were measured, and muscle myosin heavy chain (MHC) isoform composition analyzed. Fasting had no effects on AMPK phosphorylation, but total AMPK expression decreased in m. rectus femoris, m. tibialis anterior and m. extensor digitorum longus resulting in a higher phosphorylation ratio. Decreased total expression was also observed for ACC. Fasting did not influence GLUT 4, insulin receptor or Akt expression, but Akt phosphorylation was lower in m. flexor digitorum superficialis and m. extensor digitorum longus. Three MHC isoforms (I, IIa and IIx) were detected without differences in composition between the fasted and control animals. The studied muscles were resistant to prolonged fasting indicating that raccoon dogs have an effective molecular regulatory system for preserving skeletal muscle function during wintertime immobility and fasting.     

Relationships between range of motion,Lo, and passive force in five strap-like muscles of the feline hind limb

The relationships between range of motion, optimal length for force production (l_o), and passive force provide useful insights into the structure and function of muscles but are unknown for most individual muscles. We measured these values and examined their relationships in five strap-like muscles of the cat hind limb: caudofemoralis, semitendinosus, sartorius anterior, tenuissimus, and biceps femoris anterior. The range of motion relative to l_o was found to vary significantly between different muscles and even between different specimens of the same muscle. The passive force-length (FL) curve was found to be correlated with both l_o and l_max (maximal in situ muscle length) but was correlated more strongly with l_max. The mean passive force produced by these muscles at l_max was less than 7% of estimated maximal isometric force, suggesting that passive force may not be important in these muscles during normal activation patterns. The variance in passive FL curves between specimens of the same muscle was found to be significantly lower when length was scaled by l_max as opposed to l_o. These results suggest that l_max may provide a more useful scaling factor for generic models of muscle. However, the passive length-tension properties of mammalian muscle appear to reflect a complex mix of structures at both the myofilament and connective tissue levels that may differ depending on muscle-fiber architecture and perhaps on the history of trophic influences on a particular specimen. © 1996 Wiley-Liss, Inc.     

Force, work and power output of lower limb muscles during human maximal-effort countermovement jumping.

The purpose of this study was to simulate human maximal-effort countermovement jumping with a three-dimensional neuromusculoskeletal model. The specific aim was to investigate muscle force, work and power output of major lower limb muscles during the motion. A neuromusculoskeletal model that has nine rigid body segments, 20 degrees of freedom, 32 Hill-type lower limb muscles was developed. The neural activation input signal was represented by a series of step functions with step duration of 0.05 s. The excitation-contraction dynamics of the contractile element, the tissues around the joints to limit the joint range of motion, as well as the foot-ground interaction were implemented. A simulation was started from a standing posture. Optimal pattern of the activation input signal was searched through numerical optimization with a goal of maximizing the height reached by the mass center of body after jumping up. As a result, feasible kinematics, ground reaction force profile and muscle excitation profile were generated. It was found that monoarticular muscles had major contributions of mechanical work and power output, whereas biarticular muscles had minor contributions. Hip adductors, abductors and external rotator muscles were vigorously activated, although their mechanical work and power output was minor because of their limited length change during the motion. Joint flexor muscles such as m. iliopsoas, m. biceps femoris short head and m. tibialis anterior were activated in the beginning of the motion with an effect of facilitating the generation of a countermovement.     

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。     

Chronic polyelectromyography in awake, unrestrained animals.

A procedure is described for making an implantable electrode array for recording EMG activity in muscles of awake, unrestrained animals (rats and cats) at rest, during rhythmic activity and in response to various reflexogenic stimuli. The electrode array consists of a percutaneous connector (covered with Dow-Corning Silastic Medical Adhesive), steel wire spiral leads contained in silicone tubing and silicone plate probes with platinum electrodes. These plate probes can be fixed either to the bone underneath the muscle, slipped under the fascia, or fixed between muscles. EMG records are presented of postural activity and ambulation in rats, mastication in cats and unilateral and bilateral spinal and supraspinal reflex responses in rat hind limb muscles up to 6 months after implantation. The advantages (and drawbacks) of this technique and its possible uses in neurophysiology are enumerated in the discussion.     

Myofilament lengths of cat skeletal muscle: theoretical considerations and functional implications.

The cat is the primary model for neuromuscular research. However, sarcomere geometry, in particular thin-myofilament lengths of cat skeletal muscles, is not known, thus preventing adequate muscle modeling on the sarcomere level. The purpose of this study was to determine thin-myofilament lengths in cat skeletal muscle. It was found that average thin-myofilament lengths of cat tibialis anterior muscles (1.12 microns) were larger than the average values reported for frog (approximately 0.95 microns), rat (1.09 microns), and rabbit muscles (1.09 microns) and were smaller than the values reported for monkey (1.16 microns) and human skeletal muscles (1.27 microns). According to the cross-bridge theory of muscular contraction, this result implies that the range of sarcomere length on the ascending limb of the force-length relation for cat muscle is between those of frog, rat, and rabbit on the one side and monkey and human on the other side. It is speculated that the differences in thin-myofilament lengths of different animals are related to the functional demands of these muscles in everyday movement tasks. Isolated experimental observations appear to support this speculation.     

Increased SCE levels in Mediterranean Italian buffaloes affected by limb malformation (transversal hemimelia)

In recent years some buffalo farms in Campania have reported the birth of calves with limb malformation, especially with transversal hemimelia. We investigated 20 Mediterranean Italian buffaloes (8 males and 12 females) from one day to six months of age, of which 10 were affected by transversal hemimelia (group 1) and 10 were healthy controls (group 2). The following clinical and radiological patterns were observed in the malformed animals: hind limbs amputated, the right amputated off the second tarsus bones and the left amputated off the proximal epiphysis metatarsus, and the right thoracic limb hypoplasic (1 female); left hind limb amputated off the proximal epiphysis metatarsus (2 females and 1 male); left hind limb amputated off the third tarsus bones (1 female); left hind limb amputated off the tibia (1 female and 1 male); left hind limb amputated off the distal epiphysis metatarsus (1 female); left hind limb amputated off the first phalanx (1 male); right hind limb amputated off the proximal epiphysis metatarsus (1 male). In their malformed limbs all the animals presented more or less developed outlines of claws. The mean rate of SCE/cell in animals with transversal hemimelia was 8.80 +/- 3.19, that of the controls 6.61 +/- 2.73. The difference was statistically significant (P < 0.001).     

Outbreak of hind limb paralysis in young CFW Swiss Webster mice

An outbreak of paralysis among 16- to 20-week-old CFW Swiss Webster sentinel mice developed in one of our barrier facilities. Two months after arrival and over a period of four weeks, six of 400 mice purchased from an approved vendor, developed progressive hind limb paralysis without other clinical signs of disease. On the basis of the histopathologic changes and negative serologic test results, lymphoblastic lymphoma causing compression of the spinal cord was diagnosed. There were two leading features to this outbreak: its unusual epidemiologic presentation, and the localization of the lesions principally in the lumbar muscles. A presumptive diagnosis of retroviral infection with Abelson's murine leukemia virus (A-MuLV) was established on the basis of histopathologic and immunohistochemical findings. Little is known about retroviral status in many commercial colonies, and few users report presence of spontaneous lymphomas. This report points out complications derived from commercially available animals that carry endogenous retroviruses. It also emphasizes the need of diagnosing and reporting clusters of hind limb paralysis or lymphomas in mice to assess the prevalence and relevance of retroviral infections in commercial colonies.     

Changes in muscle size and architecture following 20 days of bed rest

Five healthy men carried out a program of head-down bed rest (BR) for 20 days. Before and after BR, a series of cross-sectional scans of the thigh were performed using magnetic resonance imaging, from which volumes of the quadriceps muscles were determined and physiological cross-sectional areas (PCSA) were calculated. Muscle thickness and pennation angles of the triceps brachii, vastus lateralis, and triceps surae muscles were also determined by ultrasonography. During BR, subjects performed unilateral isokinetic knee extension exercises every day. The contralateral limb served as a control. Decrease in PCSA after BR was greater in the control (-10.2 +/- 6.3%) than in the trained limb (-5.2 +/- 4.2%). Among the quadriceps, vastus intermedius in the control limb was predominantly atrophied by BR with respect to the volume and PCSA, and the rectus femoris showed the greatest training effect and retained its size in the trained limb. Decreases in muscle thicknesses in leg muscles were not prevented by the present exercise protocol, suggesting a need for specific exercise training for these muscles. Neither trained nor control muscles showed significant changes in pennation angles in any muscles after BR, suggesting that muscle architecture does not change remarkably by muscle atrophy by up to 10%.     

Effects of high-intensity sprint training on skeletal muscle blood flow in rats.

The regional blood flow response (via radioactive microspheres) was determined for female rats after 6 wk of high-intensity sprint training (HIST) or limited cage activity as the animals exercised at work loads that would elicit maximal O2 uptake. Blood flow to the different organs of the abdominal region was greatly reduced during maximal exercise conditions, and the magnitude of the reduction appeared to be similar for both the HIST group of rats and their sedentary (SED) control counterparts. Of the 20 different hindlimb muscles examined in the present study, blood flow to the soleus, plantaris, gastrocnemius, flexor hallicus longus, vastus lateralis, rectus femoris, biceps femoris, and adductor magnus and brevis muscles was significantly greater (P less than 0.05) in the HIST rats during maximal exercise conditions than in the SED control rats. Correspondingly, blood flow to the total hindlimb during maximal exercise was also significantly greater in the HIST rats than in the SED control rats [240 +/- 18 vs. 192 +/- 15 (SE) ml.min-1.100 g-1]. These results support the contention that the increase in maximal cardiac output that is produced by HIST in the rat is primarily directed toward the working skeletal muscle and not toward the organs found in the abdominal region. We conclude from these experiments that HIST will produce significant adaptations in central cardiac function and skeletal muscle blood flow in the rat.