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PubMed1997

Effect of hypoenergetic feeding and high-carbohydrate refeeding on muscle tetanic tension, relaxation rate, and fatigue in slow- and fast-twitch muscles in rats.

Studies using nuclear magnetic resonance have shown that undernutrition affects muscle performance and energetics. It is unclear to what extent underfeeding and refeeding influence the availability of muscle glycogen, net glycogenolysis, skeletal muscle wasting, and recovery. We hypothesized that muscle performance is independent of muscle size and weight, is specific to muscle type, and is unrelated to muscle glycogen concentrations. Slow- and fast-twitch muscles were studied in three groups of adult male Wistar rats: well-fed controls, hypoenergetically fed (Hypo) rats, and rats refed for 4 d after the hypoenergetic diet. Glycogen concentrations and net glycogenolysis; serum glucose, insulin, and protein concentrations; and muscle weight, protein, and cross-sectional area were studied relative to the performance of both types of muscles. Our study controlled for muscle size, weight, and type and electrolyte-micronutrient deficiency. Undernutrition affected muscle performance in five ways. First, compared with controls, fatigue increased only in the soleus muscles of Hypo rats yet the maximal relaxation rate (MRR) decreased in both the soleus and extensor digitorum longus (EDL) muscles. Second, muscle glycogen concentrations did not significantly correlate with fatigue in either the soleus or the EDL although net glycogenolysis was significantly correlated with fatigue in the soleus (r = -0.64; P > 0.01 < 0.05). Third, lower glycogen concentrations did not hinder net glycogenolysis in the EDL of Hypo rats or the soleus of refed rats. Fourth, muscle weight, size, and protein were dissociated from function. Fifth, refeeding did not restore muscle endurance; however, the MRR of the soleus normalized. In conclusion, glycogen values and muscle performance did not correlate but net glycogenolysis correlated with fatigue in the soleus. Also, there was a dissociation between muscle weight, size, and protein and muscle function during hypoenergetic feeding and refeeding.

Animals↗
PubMedDate not supplied

Projections of sympathetic non-noradrenergic neurons to skeletal muscle arteries in guinea-pig limbs vary with the metabolic character of muscles.

This study set out to examine in detail the distribution of axons of sympathetic non-noradrenergic neurons innervating the arterial bed in skeletal muscles of the forelimb and hindlimb of guinea-pigs. The distribution of non-noradrenergic axons with immunoreactivity to vasoactive intestinal peptide (VIP) was examined in limb muscles of different histochemical character. The immunohistochemical demonstration of myosin heavy chain from fast-twitch muscle, and the histochemical demonstration of adenosine triphosphatase and succinic dehydrogenase, were used to determine the muscle fibre profile of 6 different limb muscles. Muscles included the oxidative type I muscle fibre-rich accessory semimembranosus muscle, the predominantly glycolytic type II muscle fibre-rich cranial gracilis and biceps brachii muscles and the plantaris, gastrocnemius medial head and triceps brachii long head of mixed muscle fibre composition. The frequency with which the VIP-immunoreactive (VIP-IR) axons innervated intramuscular arterial vessels was compared between categories of muscles defined by their muscle fibre profile. This study demonstrated that the projection of non-noradrenergic sympathetic neurons to skeletal muscle vasculature was widespread in guinea-pig limb muscles, but that it was not uniform. VIP-IR axons were more likely to innervate the arterial vasculature of muscles with a high proportion of type I and/or oxidative muscle fibres than of muscles with a large proportion of type IIb muscle fibres. This relationship between the distribution of sympathetic non-noradrenergic axons and the metabolic characteristics of muscle suggests that these presumed vasodilator neurons have an important role in matching blood flow to the particular metabolic demands of different limb muscles.

Animals↗
PubMed1997

Reciprocal signaling between Drosophila epidermal muscle attachment cells and their corresponding muscles.

Directed intercellular interactions between distinct cell types underlie the basis for organogenesis during embryonic development. This paper focuses on the establishment of the final somatic muscle pattern in Drosophila, and on the possible cross-talk between the myotubes and the epidermal muscle attachment cells, occurring while both cell types undergo distinct developmental programs. Our findings suggest that the stripe gene is necessary and sufficient to initiate the developmental program of epidermal muscle attachment cells. In stripe mutant embryos, these cells do not differentiate correctly. Ectopic expression of Stripe in various epidermal cells transforms these cells into muscle-attachment cells expressing an array of epidermal muscle attachment cell-specific markers. Moreover, these ectopic epidermal muscle attachment cells are capable of attracting somatic myotubes from a limited distance, providing that the myotube has not yet been attached to or been influenced by a closer wild-type attachment cell. Analysis of the relationships between muscle binding and differentiation of the epidermal muscle attachment cell was performed in mutant embryos in which loss of muscles, or ectopic muscles were induced. This analysis indicated that, although the initial expression of epidermal muscle-attachment cell-specific genes including stripe and groovin is muscle independent, their continuous expression is maintained only in epidermal muscle attachment cells that are connected to muscles. These results suggest that the binding of a somatic muscle to an epidermal muscle attachment cell triggers a signal affecting gene expression in the attachment cell. Taken together, our results suggest the presence of a reciprocal signaling mechanism between the approaching muscles and the epidermal muscle attachment cells. First the epidermal muscle attachment cells signal the myotubes and induce myotube attraction and adhesion to their target cells. Following this binding, the muscle cells send a reciprocal signal to the epidermal muscle attachment cells inducing their terminal differentiation into tendon-like cells.

Animals↗
PubMed1997

Human facial muscles: dimensions, motor endplate distribution, and presence of muscle fibers with multiple motor endplates.

BACKGROUND: Extrafusal muscle fibers of human striated skeletal muscles are known to have a uniform innervation pattern. Motor endplates (MEP) of the "en plaque" type are located near the center of muscle fibers and distributed within the muscles in a narrow band. The aim of this study was to evaluate the innervation pattern of human facial muscles and compare it with that of skeletal muscles. METHODS: Ten facial muscles from 11 human cadavers were dissected, the nerve entrance points located, and the dimensions measured. All muscles were stained in toto for MEPs using Acetylcholinesterase (AChE) and examined under the microscope to determine their location. Single muscle fibers were teased to evaluate the stained MEPs. RESULTS: The length of the different facial muscles varied from 29 to 65 mm, which correlated to the length of the corresponding muscle fibers. MEP zones were found on the muscles in the immediate vicinity of the nerves' entrance points and located eccentrically. Numbers and locations varied from muscle to muscle. Three MEP zone distribution patterns were differentiated: numerous small MEP zones were evenly spread over the muscle, a predominant MEP zone and two to three small zones were spread at random, and two to four MEP zones of equal size were randomly scattered. One MEP of the "en plaque" type was found in 73.8% of the muscle fibers and two to five MEPs were found in 26.2%. The distances between the multiple MEPs on one muscle fiber varied from 10 to 500 microm. CONCLUSIONS: This study suggests that facial muscles differ from skeletal muscles regarding distribution and number of MEPs. The eccentric location of MEP zones and multiple MEPs suggests there is an independent mechanism of neural regulation in the facial muscle system.

Acetylcholinesterase↗
PubMed1996

Activation of type-identified motor units during centrally evoked contractions in the cat medial gastrocnemius muscle. III. Muscle-unit force modulation.

1. The aim of this study was to examine the extent of muscle-unit force modulation due to motoneuron firing-rate variation in type-identified motor units of the cat medial gastrocnemius (MG) muscle, and to investigate the contribution of muscle-unit force modulation to whole-muscle force regulation. The motoneuron discharge patterns recorded from 8 pairs of motor units during 12 smoothly graded muscle contractions evoked by stimulation of the mesencephalic locomotor region (MLR) were used to reactivate those units in isolation to estimate what their force profiles would have been like during the evoked whole-muscle contractions. 2. For most motor units, muscle-unit force modulation was similar to motoneuron firing-rate modulation, in that muscle-unit force increased over a limited range (120-600 g) of increasing whole-muscle tension and was then maintained at a near maximal (> 70%) output level as muscle force continued to rise. Most muscle units also decreased their force outputs over a slightly larger range of declining whole-muscle force before relaxing. This second finding was best explained by the counterclockwise hysteresis recorded in the motor units' frequency-tension (f-t) relationships. 3. In those instances when whole-muscle force fluctuated just above the recruitment threshold of a motor unit, a substantial percentage (10-25%) of the change in whole-muscle force could be accounted for by force modulation in that motor unit alone. This finding suggested that few motor units in the pool were simultaneously simultaneously undergoing force modulation. To evaluate this possibility, the extent of parallel muscle-unit force modulation within the 8 pairs of simultaneously active motor units was evaluated. As with parallel motoneuron firing-rate modulation, the extent of parallel muscle-unit force modulation was limited to unit pairs of the same physiological type and recruitment threshold. In several instances, pairs of motor units displayed parallel motoneuron firing-rate modulation but did not show parallel muscle-unit force modulation because of the nature of the motor units' f-t relationships. 4. The limited extent of parallel muscle-unit force modulation seen in these experiments implies that the major strategy for force modulation in the cat MG muscle, involving contractions estimated to reach 30-40% of maximum, may be motor-unit recruitment rather than motor-unit firing-rate variation with resulting force modulation. Given, however, that the majority of motor units are already recruited at these output levels (< 40%), it is proposed that motor-unit firing-rate variation with resulting force modulation may take over as the major muscle force modulating strategy at higher output levels.

Animals↗
PubMed1992

Influence of muscle geometry on shortening speed of fibre, aponeurosis and muscle.

The influence of muscle geometry on muscle shortening of the gastrocnemius medialis muscle (GM) of the rat was studied. Using cinematography, GM geometry was studied during isokinetic concentric activity at muscle lengths ranging from 85 to 105% of the optimum muscle length. The shortening speed of the distal fibre, the proximal aponeurosis and the muscle were determined, as well as the effect of rotation of the distal fibre and the proximal aponeurosis on the muscle speed of shortening. The results show that, due to the geometrical configuration, muscle shortening speed is not only determined by the speed of the fibre, but also to a large extent by the aponeurosis shortening speed. At optimum muscle length, the fibre and aponeurosis shortening speeds expressed relative to the muscle shortening speed amounted to 84% and 6%, respectively. At shorter muscle length, fibre speed relative to muscle speed decreased to values as low as 35%, whereas that of aponeurosis increased to values as high as 31%. Angular effects on the muscle speed of shortening can explain 10% of the muscle shortening speed at optimum muscle length and up to 34% of the muscle speed at shorter muscle length. In addition, a model was formulated to simulate the geometrical effects on muscle speed. This model, incorporating both fibre and aponeurosis length changes, contains a transfer function relating the shortening speeds of fibre and aponeurosis to muscle speed. The muscle shortening speed calculated using this transfer function demonstrated no significant differences with the speed measured experimentally.

Analysis of Variance↗
PubMed1979

Neural control of skeletal muscle cholinesterase: a study using organ-cultured rat muscle.

1. It has been proposed that the influence of innervation on the cholinesterase activity (ChE) of skeletal muscle and on end-plate ChE in particular is mediated by trophic substance(s) moved by axonal transport and released from nerve. We have tested this hypothesis using rat extensor digitorum longus (e.d.l.) and diaphragm muscles denervated in vitro for several days and then maintained in organ culture to assay putative trophic substance(s). 2. The cholinesterase activity (ChE) of rat extensor digitorum longus (e.d.l.) muscles decreased dramatically after 5 days of denervation in vivo as previously reported. The ChE of rat e.d.l. muscles denervated in vivo for 3 days and then maintained in organ culture for 2 days was essentially identical to that of muscles denervated 5 days in vivo. 3. The ChE OF E.D.L. MUSCLES DENERVATED IN VIVO FOR 3 DAYS AND THEN MAINTAINED FOR 2 DAYS IN CULTURE MEDIUM SUPPLEMENTED WITH SCIATIC NERVE OR INNERVATED MUSCLE EXTRACT WAS SIGNIFICANTLY HIGHER THAN THAT OF MUSCLES DENERVATED IN VIVO FOR 5 DAYS OR DENERVATED IN VIVO FOR 3 DAYS AND THEN CULTURED FOR 2 DAYS IN CULTURE MEDIUM ALONE. Supplementing the culture medium with brain or spinal cord extract also significantly increased the ChE of organ-cultured e.d.l. muscles. 4. Supplementing the culture medium with liver or spleen extract or with the extract of muscle denervated for 3--7 days in vivo before extraction did not increase the ChE or organ-cultured e.d.l. muscles. 5. The effect of muscle extract on the ChE of organ-cultured e.d.l. muscles was dose dependent and occurred gradually reaching a maximum after approximately 24 h of culture. 6. Substance(s) which increased the ChE of organ-cultured e.d.l. muscles were found to accumulate in transected sciatic nerve in the region just proximal to the site of transection where substances moved by axonal transport are known to accumulate. 7. Media conditioned with neurally stimulated e.d.l. or diaphragm muscles caused a substantial and highly significant increase in the ChE of e.d.l. or diaphragm muscles denervated in vivo and then maintained in organ culture. Media conditioned in the same way with unstimulated muscles did not increase the ChE OF ORGAN-CULTURED MUSCLES. 8. The active substance(s) released by neural stimulation continued to be released when muscle contraction was blocked by adding D-tubocurarine to the medium during conditioning but the release of these substance(s) was significantly reduced when magnesium (10mM) was added to the medium during conditioning. 9 The substance(s) released by neural stimulation selectively increased ChE in the end-plate region. In diaphragm segments denervated in vivo and then maintained in medium conditioned with neurally stimulated muscle, there was a 102% increase in end-plate ChE but no detectable increase in background ChE. 10...

Animals↗
PubMed1989

Effect of sepsis on calcium uptake and content in skeletal muscle and regulation in vitro by calcium of total and myofibrillar protein breakdown in control and septic muscle: results from a preliminary study.

Because high calcium concentration in vitro stimulates muscle proteolysis, calcium has been implicated in the pathogenesis of increased muscle breakdown in different catabolic conditions. Protein breakdown in skeletal muscle is increased during sepsis, but the effect of sepsis on muscle calcium uptake and content is not known. In this study the influence of sepsis, induced in rats by cecal ligation and puncture, on muscle calcium uptake and content was studied. Sixteen hours after cecal ligation and puncture or sham operation, calcium content of the extensor digitorum longus (EDL) and soleus (SOL) muscles was determined with an atomic absorption spectrometer. Calcium uptake was measured in intact SOL muscles incubated in the presence of calcium 45 (45Ca) for between 1 and 120 minutes. Total and myofibrillar protein breakdown was determined in SOL muscles, incubated in the presence of different calcium concentrations (0; 2.5; 5.0 mmol/L), and measured as release into the incubation medium of tyrosine and 3-methylhistidine (3-MH), respectively. Calcium content was increased by 51% (p less than 0.001) during sepsis in SOL and by 10% (p less than 0.05) in EDL muscle. There was no difference in 45Ca uptake between control and septic muscles during the early phase (1 to 5 minutes) of incubation. During more extended incubation (30 to 120 minutes), muscles from septic rats took up significantly more 45Ca than control muscles (p less than 0.05). Tyrosine release by incubated SOL muscles from control and septic rats was increased when calcium was added to the incubation medium, and at a calcium concentration of 2.5 mmol/L, the increase in tyrosine release was greater in septic than in control muscle. Addition of calcium to the incubation medium did not affect 3-MH release in control or septic muscle. The results suggest that calcium uptake and content in skeletal muscle are increased during sepsis and that high calcium concentrations in vitro stimulate nonmyofibrillar protein breakdown. Muscles from septic animals may be more sensitive to the effect of calcium in vitro than muscles from nonseptic rats. Whether increased calcium uptake and content in skeletal muscle is partly responsible for accelerated muscle proteolysis during sepsis remains to be determined.

Animals↗
PubMed1999

Observations on the number, distribution and morphological peculiarities of muscle spindles in the tensor tympani and stapedius muscle of man.

Although the middle ear muscles have been described for the first time more than four hundred years ago their role in modulation and transmission of sound is not yet fully understood. Surprisingly very little is known about proprioceptors in these muscles, especially in man, although this seems to be the key to the understanding of their various functions. Therefore, the question for proprioceptive sensory organs in these muscles is still relevant. The tensor tympani and stapedius muscles of four women who had donated their bodies to our institute were taken. Complete serial sections of these muscles were made which were either impregnated with silver, stained with ferric oxide for acidic polysaccharides or incubated with antibodies against S-100 protein. Thereby four to eight (mean five) muscle spindles distributed along the whole muscle could be detected in the tensor tympani muscles. These spindles contain one to three intrafusal muscle fibres and their length ranges from 140 to 4270 microm (mean 1492.8 microm). Furthermore, in three stapedius muscles one to two (mean 1.7) muscle spindles were found. They were from 350 to 500 microm (mean 482 microm) long and contained only one intrafusal muscle fiber. Regarding the diameter of intrafusal muscle fibers in both, the tensor tympani as well as the stapedius muscle, no difference to extrafusal muscle fibers of these muscles could be detected. The structure of these spindles differs considerably from those found in skeletal muscles. The morphological findings presented strongly suggest that muscle spindles occur regularly in both middle ear muscles. The results presented herein are consistent with clinical findings obtained from electromyographic studies and may help to elucidate all functions the middle ear muscles might serve in man.

Aged↗
PubMed2001

Biarticular and monoarticular muscle activation and injury in human quadriceps muscle.

We hypothesized that activation of the quadriceps femoris muscle group during eccentric exercise is related to the increase in magnitude of several markers of muscle injury that developed during the next week. Fourteen male subjects performed six to eight sets of five to ten repetitions of single-leg eccentric-only seated knee extension exercise. Magnetic resonance (MR) images were collected before and immediately after exercise and on days 2-4 and 6 after eccentric exercise. Changes in maximal voluntary contraction (MVC), perceived soreness, muscle volume and muscle transverse relaxation of water protons (T2) were determined for the quadriceps femoris muscle group each day. Changes in muscle volume and T2 were determined every day for each muscle [vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), rectus femoris (RF)] of the quadriceps femoris group. Post-exercise T2 was greater than pre-exercise T2 (P < 0.05) for all muscles. The acute deltaT2 (Post-Pre) was similar (P>0.05) among VL, VM, VI, and RF [5.5 (0.3) ms], suggesting that the four muscles were equally activated during eccentric exercise. In the week after eccentric exercise, subjects experienced delayed-onset muscle soreness (DOMS) and all muscles demonstrated a delayed increase in T2 above pre-exercise values (P < 0.05), suggesting that muscle injury had occurred. For the quadriceps femoris muscle group, there was no correlation between acute deltaT2 and delayed (peak T2 during days 2, 3, 4, 6 minus pre-exercise T2) deltaT2 (r=0.04, P>0.05). Similar results were obtained when VL, VM, VI and RF were examined separately. Of the four muscles in quadriceps femoris, the biarticular RF experienced greater muscle injury [delayed deltaT2= 15.2 (2.0) ms] compared to the three monoarticular vasti muscles [delayed deltaT2 = 7.7 (1.3) ms; P< 0.05]. We propose that the disproportionate muscle injury to RF resulted from an ineffective transfer of torque from the knee to hip joint during seated eccentric knee extension exercise, thus causing RF to dissipate greater energy than normal. We conclude that in humans, muscle activation is not a unique determinant of muscle injury.

Adult↗
PubMed1992

Adaptation in synergistic muscles to soleus and plantaris muscle removal in the rat hindlimb.

Although the soleus muscle comprises only 6% of the ankle plantar flexor mass in the rat, a major role in stance and walking has been ascribed to it. The purpose of this study was to determine if removal of the soleus muscle would result in adaptations in the remaining gastrocnemius and plantaris muscles due to the new demands for force production imposed on them during stance or walking. A second purpose was to determine whether the mass or the fiber type of the muscle(s) removed was a more important determinant of compensatory adaptations. Male Sprague-Dawley rats underwent bilateral removal of soleus muscle, plantaris muscle, or both muscles. For comparison, compensatory hypertrophy was induced in soleus and plantaris muscles by gastrocnemius muscle ablation. After forty days, synergist muscles remaining intact were removed. Mass, and oxidative, glycolytic, and contractile enzyme activities were determined. Despite its role in stance and slow walking, removal of the soleus muscle did not elicit a measurable alteration in muscle mass, or in citrate synthase, lactate dehydrogenase, or myofibrillar ATPase activity in gastrocnemius or plantaris muscles. Similarly, removal of the plantaris muscle, or soleus and plantaris muscles, had no effect on the gastrocnemius muscle, suggesting that this muscle was able to easily meet the new demands placed on it. These results suggest that amount of muscle mass removed, rather than fiber type, is the most important stimulus for compensatory hypertrophy. They also suggest that slow-twitch motor units in the gastrocnemius muscle play an important role during stance and locomotion in the intact animal.

Adaptation, Physiological↗
PubMed2002

Remodelling of capillary networks around muscle fibres in the extensor digitorum longus muscle of the normal aged rat.

Structural changes of capillaries around muscle fibres following their degeneration and regeneration were further examined in the extensor digitorum longus muscle of the 24-month-old normal rat. Bundles of muscle fibres were divided into three types: muscle bundles consisting of large muscle fibres exclusively more than 35 microm in diameter (type 1), various-sized muscle fibres ranging from 10 to 60 microm in diameter (type 2) and only small muscle fibres 20-40 microm in diameter (type 3). The mean number of capillaries around a muscle fibre was extremely high in the type 3 muscle bundle (4.83) and much lower in the type 2 muscle bundle (2.72) compared with that in the type 1 muscle bundle (3.48). Capillaries in the type 1 muscle bundle were round or oval in shape and were of the continuous type. In the type 2 muscle bundle, capillaries around large degenerating muscle fibres showed an irregularly compressed shape and the scaffolds of basal laminae were often found around them, being a result of the destruction of capillaries. On the other hand, small-sized capillaries less than 5 microm in diameter, being possibly regenerating capillaries, were found around small (probably regenerating) muscle fibres and often had a small number (less than 10) of fenestrae. Capillaries in the type 3 muscle bundle, similar in shape and size to those in the type 1, frequently branched or joined, but some of them were partially destroyed. These findings suggest that capillaries degenerate and regenerate to remodel capillary networks around the muscle fibres following their degeneration and regeneration, and that to effectively supply oxygen and nutrients to regenerating muscle fibres, capillaries temporarily form fenestrae and then the capillary networks become dense by sprouts from the existing capillaries, but excess capillaries may be gradually destroyed following maturation of the muscle fibres.

Aging↗
PubMed1992

Geometry of blood-tissue exchange in bat flight muscle compared with bat hindlimb and rat soleus muscle.

We investigated the relationship between capillary-to-fiber geometry and muscle aerobic capacity by comparing the bat flight muscle (pectoralis muscle), i.e., an ultimate case of extreme O2 demand in a mammalian skeletal muscle, with bat hindlimb and rat soleus muscles. At a given sarcomere length (2.1 microns), fiber cross-sectional area was considerably smaller in bat muscles (pectoralis 318 +/- 10 microns 2, hindlimb 447 +/- 35 microns 2) than in rat soleus muscle (2,027 +/- 125 microns 2). Capillary number per fiber cross-sectional area was much greater in bat pectoralis (6,394 +/- 380/mm2) than in bat hindlimb and rat soleus muscle (2,865 +/- 238 and 1,301 +/- 129/mm2, respectively; all values normalized to 2.1-microns sarcomere length). At the same sarcomere length (2.1 microns), the degree of tortuosity and branching of capillaries were significantly greater in bat pectoralis than in bat hindlimb and rat soleus muscle. In bat flight muscle, capillary length per fiber volume was very high (9,025 +/- 342/mm2). It was 2.2- and 5.4-fold larger than in bat hindlimb and rat soleus, respectively. Mitochondria occupied 35.3 +/- 1.2, 16.5 +/- 1.3, and 6.1 +/- 0.9% of the muscle fiber volume in bat pectoralis, hindlimb, and rat soleus muscles, respectively. There was a strong correlation between capillary length (as well as capillary surface) per fiber volume and mitochondrial volume density in all muscles. Considering capillary supply and mitochondrial volume on an individual fiber basis, we found that 1) the number of capillaries around a fiber was linearly related to mitochondrial volume per micron length of fiber in the muscles but that 2) capillary surface per fiber surface, at given mitochondrial volume per micron length of fiber, was about twice as large in bat pectoralis as in rat soleus muscle, whereas in bat hindlimb it was intermediate between that in bat pectoralis and that in rat soleus muscle. This was due to the differences in fiber size (rat soleus greater than bat muscles) and capillary-to-fiber ratio (bat pectoralis greater than hindlimb) between the muscles. It is notable that in the bat, the substantially greater O2 transfer capacity of the flight muscle compared with hindlimb was achieved by increasing the size of the capillary-to-fiber interface, i.e., capillary-to-fiber surface, via an increase in capillary number rather than by substantially reducing fiber size.

Animals↗
PubMed1995

[Histological changes, muscle force and fatigability after electrical stimulation to experimentally paralyzed muscles].

In order to use functional electrical stimulation effectively in paralyzed muscle treatment, changes in the maximal muscle force, muscle fatigue, and histological changes were evaluated in electrically stimulated muscles. Study 1. Tissue damage by percutaneous intramuscular electrodes implanted into the quadriceps muscle was examined in rat. Stimulation was conducted at various output voltages, and for various durations of time, in order to assess the histological changes in the muscle around the electrodes. Study 2. Electrodes were implanted into the bilateral quadriceps and gastrocnemius muscles of adult cat, and the unilateral muscles were then stimulated from 3 weeks following the transection of the spinal cord at the T9 level. Stimulus parameters were divided into two groups; as "A" stimulation: at -8V for 15min twice/week, and as "B" stimulation: at -16V for 30 min 4 times/week. The histological changes were examined using the myofibrillar ATPase method to determine the diameters and occupation ratios for each muscle fiber type. RESULTS. Study 1. Significant tissue damage began to occur when the voltage output created the maximum muscle contraction force. Until that critical voltage point was reached, tissue damage was not significant, regardless of the duration of the stimulation. Study 2. The maximum muscle force decreased until 4 weeks after the transection, then increased regardless of the presence of electrical stimulation. The muscle fatigability of the non-stimulated muscle was greater than that of the stimulated muscle. High voltage, long duration, and frequent stimulation was effective in controlling fatigue. The ratio of type I fibers was higher in the stimulated muscle. There was no evidence, however, of suppressing muscle fiber atrophy after electrical stimulation. These results suggested that electrically stimulating paralyzed muscles was effective for suppressing muscle fatigue, and for reducing the ratio of type I fibers. In clinical use, the output voltage should be kept below the voltage that induces the maximum muscle contraction to prevent tissue damage.

Animals↗
PubMed1987

Development of wing-bud-derived muscles in normal and wingless chick embryos: a computer-assisted three-dimensional reconstruction study of muscle pattern formation in the absence of skeletal elements.

The mechanisms whereby the normal pattern of muscles within the developing chick limb bud is generated are largely unexplored. It has been proposed that the muscle pattern is established independently of the pattern for the limb skeletal elements to which the muscles normally attach (Shellswell and Wolpert: "The Pattern of Muscle and Tendon Development in the Chick Wing."In: Vertebrate Limb and Somite Morphogenesis. Cambridge University Press, Cambridge, pp. 71-86, 1977). To further examine this possibility we studied the formation of the proximal wing muscles in normal and wingless chick embryos. The muscles of the shoulder region (including the pectoralis) arise as part of the dorsal and ventral premuscle masses of the developing limb bud. These secondarily migrate out of the limb to take origin from the pectoral girdle while inserting onto the humerus (Sullivan: Aust. J. Zool., 10:458-516, 1962). With rare exceptions, wingless embryos have complete absence of wing skeletal elements, but they may possess more than 40% of the normal volume of wing-bud-derived muscles. The muscles that remain in wingless embryos are primarily shoulder muscles, and to a varying extent, the pectoralis. The question we sought to answer was whether in wingless embryos the proximal wing muscles could form a normal pattern in the absence of the humerus and distal wing skeletal elements. By examining three-dimensional reconstructions of the proximal wing region in normal and wingless embryos, we found that the initial subdivision of the dorsal and ventral premuscle masses proceeded normally in the absence of the wing skeleton. This resulted in a grossly normal pattern of proximal wing muscles despite the absence of wing skeletal elements. However, some subsequent cleavages of individual muscles within premuscle mass divisions did not occur in wingless embryos. This suggests that the skeleton may be required for this step in muscle morphogenesis to occur. We also observed that the wing-bud-derived muscles in wingless embryos were nearly always anchored to the pectoral girdle at both ends. Sometimes this resulted in muscles making abnormal tendonous fusions with other muscles derived from the opposite (i.e., dorsal or ventral) premuscle mass. Therefore, attachment to the skeleton may be important for some facet of muscle development. Finally, the supracoracoideus muscle was absent in all but one wingless embryo we examined in the present study. In that one, it was substantially reduced in volume compared to normal. absence of this muscle, the space normally occupied by the supracoracoideus was maintained beneath the pectoralis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2004

Relationship between muscle length and moment arm on EMG activity of human triceps surae muscle.

PURPOSE: The purpose of this experiment was to evaluate the effects of both muscle length and moment arm (MA) on the electromyographic (EMG) and force output of the triceps surae (TS) muscle. RELEVANCE: It is well recognized that changes in muscle length affect both the muscle's force generating capacity as well as its twitch speed. This relationship is well established in animal preparations. Contrary to animal experiments where length can be directly manipulated in isolated muscles, human experiments require that all muscle length changes be secondary to changes in a joint angle. Such experimental manipulations therefore produce changes in not only muscle length, but also in the muscle's MA. The relative effect of muscle length and MA changes on muscle EMG has not been determined in previous experiments. METHODS: This study was executed in two phases. First, using fresh human cadaver lower limbs, data were gathered describing the relationship between knee and ankle angle changes for maintenance of a constant TS muscle length, while its MA at the ankle joint has been changed. In the second phase of the study, results obtained from phase one were applied to 10 healthy adult human subjects to measure the EMG (surface and fine wire) activity of TS at three different conditions: when both length and MA were shortened, when muscle length was decreased given a constant MA and when MA was shortened given a constant muscle length. RESULTS: A significant increase in muscle activity was found as both the length and MA of TS muscle were shortened. A similar pattern of increased muscle activity was observed when the MA was shortened given a constant muscle length. No significant change in TS activity was found when muscle length was shortened, given a constant MA at the ankle joint. CONCLUSIONS: The findings of this study indicate that changes in the Achilles tendon MA predominate over the muscle length variations in determining the level of TS activity when generating plantar flexion torque.

Ankle Joint↗