Fast twitch muscle fiber development,fitness drink powder mix,best whey supplement for bodybuilding,african mango natural weight loss supplement uk - You Shoud Know

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Kevin--can you post a link to the muscle fiber characteristics chart at the top of your post? Having major every day and international sporting events nowadays and climbing popularity on the internet, an increasing number of sporting things enterprises are noticed that you consider internet promotion as a vital means intended for corporate advertising and marketing optimization, current market expansion in addition to brand developing. Knowing your personal muscle fiber make-up can be an invaluable aid when it comes to properly targeting your training program. By looking at elite athletes in different sports, you can see extreme examples of each make-up of muscle fiber.
To find the predominant fiber type in a particular muscle in your body, we need to test the repetition limits of a muscle compared to its maximum strength.
Once you've figured out your one-rep max, take a weight that is 80% of it (multiply your max weight by 0.8 to get this) and do as many reps as possible with it. If you can do only four to seven reps with 80% of your 1 RM, you have mostly fast-twitch fibers in that muscle. The reason you will only be able to do four to seven reps with 80% of your 1 RM is that fast-twitch muscle fibers are strong but don't have great endurance. The ability to get approximately ten reps with 80% of your 1 RM is the typical fiber-type mix for a muscle.
If you can do 12 to 15 or more reps with 80% of your 1 RM, your fiber make-up is probably mostly slow-twitch fibers. Though there are always differences in individuals, there are some general similarities in fiber types in muscle groups from person to person. For example, in most people, the outer, visible muscle of the calf (the gastrocnemius) is usually an even mix of slow-twitch and fast-twitch fibers, while the soleus (which lies underneath the gastrocnemius) has a higher percentage of slow-twitch fibers. Two more examples of this similarity between people include the abdominals and the hamstrings. If your fibers in a particular muscle consist primarily of slow-twitch fibers, in order to affect the greatest number of those muscle fibers, you'll need to train that muscle with higher reps, shorter rest periods, and higher volume.
Unfortunately, slow-twitch muscle fibers are limited in their potential for growth, so even if a muscle group is primarily slow twitch, you should definitely include some lower rep training to maximize the fast-twitch fibers you've got in that muscle. If you find you have a hard time gaining size in a particular muscle, it could be because it has a predominance of slow-twitch muscle fibers. If you aren't one of the lucky ones who has a predominant number of fast-twitch fibers for muscle growth, new science has shown carnosine synthesis may just change your luck. If your fibers in a particular muscle group consist primarily of fast-twitch muscle fibers, you're one of the lucky ones. If your muscles have a fairly even mix of fibers, you can evenly divide your training between focusing on the lower rep, fast-twitch fiber training and the higher rep, slow-twitch fiber training. For most of us, perhaps a mix of both types of training makes the most sense, long term, to develop each fiber equally.
Metabolic Surge—Rapid Fat Loss, The Best Exercises You've Never Heard Of, Gluteus to the Maximus—Build a Bigger Butt NOW! MicroRNA-23a has minimal effect on endurance exercise-induced adaptation of mouse skeletal muscle.
Skeletal muscles contain several subtypes of myofibers that differ in contractile and metabolic properties. Differentiation of the intracellular structure of slow- versus fast-twitch muscle fibers through evaluation of the dielectric properties of tissue.
Slow-twitch (type 1) skeletal muscle fibers have markedly greater mitochondrial content than fast-twitch (type 2) fibers.
Of Mice, Monkeys, And Men: Physiological And Morphological Evidence For Evolutionary Divergence Of Function In Mimetic Musculature. Facial expression is a universal means of visual communication in humans and many other primates. Fast-twitch muscle fibers aren't just important for sprinters and competitive weightlifters. The balance of fast-twitch and slow-twitch fibers in your body is determined by genetics, but there's still plenty you can do in your training to maximize growth and strength in the muscles you have.
In 2004, researchers found that powerlifters and Olympic weightlifters had much greater fast-twitch muscle-fiber development than bodybuilders.1 It's at least partially a question of programming. But it's also true that in the original study, bodybuilders still had larger overall muscle size.
Along with intensity, fatigue is the second surefire way to increase fast-twitch muscle fiber recruitment. Making the most of this phenomenon is more a matter of how you train rather than what your program looks like.
After seeing it countless times, my colleagues Jordan Joy, Ryan Lowery, and I decided to study what happens on squats when you mimic this natural intra-set rest technique.3 We had athletes perform 4 sets of 8 maximal repetitions either with or without brief rests in the middle of the set. Make this principle work for you throughout a workout by keeping your workout density high.
The existing evidence strongly supports the conclusion that heavy lifting and muscle fatigue largely dictate the recruitment of fast-twitch muscle fibers. On heavy days, prioritize movements that recruit the most muscle, such as squats, deadlifts, bench presses, shoulder presses, dips, and pull-ups.
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As described in Chapter 4, the extraocular muscles perform two functions: optostatic and optokinetic. In principle the type of response by extraocular muscles would be controlled either by the central nervous system or by peripheral mechanisms residing in the extraocular muscles or by both.
In general, two types of striated muscles are distinguished in the skeletal muscle system: (1) "red" or dark muscles composed of fibers of small diameter and rich in sarcoplasm and (2) pale or "white" muscles with fibers of greater diameter and scanty sarcoplasm. The histologic structure of eye muscles, which perform the functions of both red and white muscles, differs in many respects from that of other striated muscles. Elastic tissue is unusually abundant in extraocular muscles of adults, so much so that it has been described as elastic bands.66 The elastic fibers are thick and are arranged parallel with the muscle fibers. In Chapter 4, it was mentioned that the nerve supply to extraocular muscles is extraordinarily rich. The abundance of nerve fibers has led to the conclusion that the all-or-nothing law, or law of isobolia, applies to eye muscles.45 According to this general principle of neuromuscular physiology, individual muscle fibers always respond with a maximum contraction to every supraliminal stimulus. The physiologic and pharmacologic properties of extraocular muscles correspond to the many unusual histologic features of these muscles. Duke-Elder and Duke-Elder30 demonstrated that the extrinsic muscles of eyes of cats contract under the influence of acetylcholine. The more quickly a muscle acts, the less it is apt to respond to acetylcholine; the more its action is one of postural tonicity, the more strongly it will respond to acetylcholine. Since the discovery that a dual motor system of slow and fast fibers exists in extraocular muscles, experiments have shown that acetylcholine, choline, and nicotine cause slow and tonic contraction of slow fibers, whereas fast fibers respond with a fast twitch. Customarily, one thinks of voluntary striated muscles as being characterized by fibers that respond to a single stimulus applied to their nerve with an ungraded fast twitch, followed by speedy relaxation, and accompanied by propagated electrical activity. Anatomical studies by Kruger43 and his school uncovered the structural basis for fast and slow fiber systems in striated muscles. The Fibrillenstruktur type of the fast fiber system is characterized anatomically by small, welldefined myofibrils, each surrounded by abundant sarcoplasm and having an even, punctate appearance as seen with the light microscope (Fig. In contrast, slow fibrils of the Felderstruktur type are clumped together in a more or less afibrillar- appearing mass of myofilaments with large, partially fused fibrils in scant sarcoplasm (Fig.
Fibrillenstruktur fibers are innervated by thick, heavily myelinated nerves joining the muscle fiber with single, typical motor and so-called en plaque end plates (Fig. With the exception of extraocular muscles, single fibers are innervated by multiple endplates in only two other muscles, the tensor tympani and the stapedius.34 The presence of multiple endplates indicates that the fiber is innervated by either multiple branches from the same nerve or by input from more than one nerve fiber. The percentage of multiple innervated muscle fibers is higher in the orbital region than in the central zone of extraocular muscles and varies with the species.53 However, the fact that both types of fibers are present in the two zones is of considerable importance when attempting to correlate the structure of the extraocular muscles with their function.
The electron microscopic differences between the fibrillar and field type of fibers emphasize the differences in their functions: the fibrillar type is fast fibers and the field type is slow fibers. The presence of two different fiber systems, a slow and a fast system, was confirmed by Katz and Eakins40 in experiments with succinylcholine and other depolarizing agents. Although there is abundant ultrastructural and pharmacologic evidence to support the notion of two principal fiber types (slow and fast twitch) in the human extraocular muscle, several authors have proposed classifications that are based on as many as five to six fiber types.2, 3, 53 These classifications take into account a much wider range of structural and contractile features for each fiber type than the older studies cited above. The main features distinguishing skeletal from extraocular muscle are summarized in Table 6–1 and the various characteristics of slow and fast fiber types are shown in Table 6–2.
Miller56 found the outer part of extraocular muscles of rhesus monkeys to consist of fibers with small cells having the histochemical and electromyographic characteristics of red muscles. However, these notions were dispelled by the findings of Keller and Robinson,41 which are incompatible with the existence of two muscular systems, one for saccadic and one for tonic function. Scott and Collins67 and Collins21 recorded from slow and fast fibers in the orbital and central layers of human extraocular muscles to analyze their contribution to various types of eye movements. One may hope that future work will permit application of laboratory findings in extraocular muscles to the clinical study of strabismus. There is justification in comparing the action of extraocular muscles with the action of flexor muscles of amphibians.
Regardless of what future studies may uncover, the uniqueness of the structure and function of extraocular muscles remains unquestionable.28 These muscles have many structural and therefore functional features that are present in some skeletal muscle systems and absent in others which enable them to carry out their complex and highly specialized tasks.
The effect of the autonomous nervous system on extraocular muscles is uncertain because morphologic, pharmacologic, and electrophysiologic studies have produced contradictory results.1, 11, 12, 28, 30, 31, 44, 62, 75, 76 There is no convincing evidence for sympathetic innervation of extraocular muscles. Groups of fine cross-striated fibers with centrally located nuclei surrounded by a thin, torpedoshaped capsule are found in all skeletal muscles. The peripheral and central pathways of extraocular muscle proprioception have been defined by Manni and Bortolami,52 who showed, on the basis of histologic and electrophysiologic studies, that the perikarya of first-order neurons are located in the semilunar ganglion. The functional significance of the muscle spindles, palisade endings, and other proprioceptive sensors is discussed in Chapter 2. Electrical responses have been recorded from extraocular muscles of animal eyes for many years.
Extraocular muscles are especially interesting to those engaged in electromyographic studies because of their low nerve fiber-to-muscle fiber ratio. Electromyography has proved to be of value in assessing paretic and pseudoparetic conditions of extraocular muscles, in myopathies, and in elucidating the pathophysiology of the retraction syndrome (see Chapter 21). Despite these limitations electromyography has resulted in important contributions to the kinesiology of extraocular muscles.
Electromyographically, there is no "rest" of the extraocular muscles (and no "position of rest" of the eyes). When a muscle rotates an eye into its field of action, there is an increment of electrical activity accompanied by graded inhibition of the activity of the direct antagonist (Sherrington’s law of reciprocal innervation). This initial burst is followed immediately by an orderly series of uniformly firing motor units. The presence of fast and slow fibers in extraocular muscles and their electrophysiologic characteristics and pharmacologic properties provide evidence for some of the peripheral mechanisms that contribute to the tonus of these muscles. Neurophysiologists have established that there are differences in the frequency of firing of motor neurons innervating slow and fast muscles in the hind limbs of cats and other experimental animals. Irrespective of peripheral mechanisms, the most important source of tonus of extraocular muscles is reflex in origin.
In humans, with their highly developed binocular vision, however, the most powerful tonic impulses flow from the process of vision. The wonderful valley possesses much to present for all style of adventure activities like traipsing, skiing, backpacking and mineral water rafting. Find out what they are, what your personal fiber make-up is, and how to train for maximum results. If you're working your muscles in the wrong way, you'll be cheating yourself out of hard-earned results. They are responsible for long-duration, low-intensity activity such as walking or any other aerobic activity. Keep in mind, these limits can be altered by your training and are, therefore, just rough estimates. This means you won't be able to lift quite as much, but you'll be able to do a lot more reps with it. This is because they take longer to fatigue, they recover quickly, and they require more work to maximize growth. You'll have a much easier time building mass in that muscle—fast twitch-muscle fibers have greater potential for size than slow twitch.
This will help you to develop all the fibers in your muscles, maximizing your ultimate development. It will help you to get better results from your training by allowing you to more specifically target your training according to the exact specifications of your muscles.


He has a degree in Physical Education and Psychology and has been inventing new training techniques for more than 16 years. The products on this site are not intended to diagnose, treat, cure, or prevent any disease.
Transcriptional control of fiber-type specification and adaptation has been intensively investigated over the past several decades.
Accordingly, we sought to determine whether the dielectric properties of these two fiber types differed, consistent with their distinct intracellular morphologies.
Humans have the most complex facial display repertoire among primates; however, gross morphological studies have not found greater complexity in human mimetic musculature. Fast-twitch muscle fibers are indeed the largest and most powerful muscular movers in your body.
These range on a spectrum from the smaller, endurance-based, slow-twitch fibers to the larger fast-twitch fibers designed for strength and power activities. Specifically, consider two variables when trying to activate fast-twitch muscle fibers: the amount of weight you lift and how you manage fatigue during sets.
The traditional bodybuilding program focuses on the 8-12 repetition range with moderately heavy loads and 60-90 seconds of rest between sets. This is because, unlike powerlifters, they had also drastically increased the size of their slow-twitch muscle fibers. For example, most lifters take brief rest periods between repetitions when a set becomes painful.
We found that intra-set rest decreased fatigue, but it also prevented the body from recruiting the fast-twitch muscle fibers.
If you find yourself pausing when a movement gets difficult, you may be short-changing your gains! Here's what I mean: An athlete who takes 2 hours to perform 15 sets has low density, while an athlete who performs 15 sets in 30 minutes has extremely high density.
On your 8-12 repetition days, keep workout density high and hammer out repetitions one after the other. It may last a minute, or an hour, or a day, or a year, but eventually it will subside and something else will take its place.
Neural adaptations to resistive exercise: mechanisms and recommendations for training practices. We are your personal trainer, your nutritionist, your supplement expert, your lifting partner, your support group. The optostatic function requires that the muscles maintain a state of postural tonicity; the optokinetic function requires that quick, tetanic contractions be performed. We have only sketchy information of the finer details of the central nervous system control of tonic and saccadic extraocular movements, but we have gained a little more insight into the structural differentiation and physiologic and pharmacologic responses of the extraocular muscles. Red muscles relax more slowly than white muscles, and their metabolism increases much less during contraction than that of white muscles.
One portion is a peripheral orbital layer along the muscle surface and faces the orbit, which contains thin fibers with many mitochondria. These longitudinal fibers are interconnected by transverse elastic fibers that form a rather dense network around the muscle fibers.
The amount of total contraction of a muscle depends on the number of fibers taking part in a contraction.
Rehms60 stated that eye muscles require and receive more oxygen than other skeletal muscles. Acetylcholine produces a strong contraction of smooth muscles in invertebrates and of some skeletal muscles in lower vertebrates, but has slight, if any, effect on skeletal muscles of mammals.
The response of extraocular muscles to neuromuscular blocking agents is of clinical interest, since these drugs are often used during general anesthesia. Repetitive stimuli of relatively high frequency are required to maintain a tetanic contraction of these fibers. Within iliofibularis muscle of the frog, Sommerkamp was able to separate a group of fibers that responded to acetylcholine by a twitch and a second group of fibers (the "tonus bundle") in which acetylcholine produced a slow, tonic contraction. He stated that the system giving twitch responses had a Fibrillenstruktur, and the system responsible for the slow contractions had a Felderstruktur. Although polyneuronal innervation occurs in several types of vertebrate muscles, Bach-y-Rita and Lennerstrand7 were not able to demonstrate this function in the extraocular muscles of cats. Transverse section of human inferior oblique muscle showing Fibrillenstruktur (arrows) and Felderstruktur fibers.
The presence of the T system and the abundance of sarcoplasmic reticulum may serve to transmit excitatory impulses with greater rapidity; the large concentration of mitochondria between the fibrils may be related to the considerable oxidative requirements associated with twitch contractions. Kern42 showed that the superior rectus muscle of the rabbit consists of two layers, an upper thin layer made up of Felderstruktur fibers, and a lower layer, the bulk of the muscle, composed of Fibrillenstruktur fibers. The responses of the Fibrillenstruktur strips were proportionately lower than those of the Felderstruktur strips and returned rapidly to the baseline level, whereas tensions of the latter strips remained elevated for longer than 10 minutes and returned to the baseline level after the drug was washed out. These authors found that the initial effect of succinylcholine on the superior rectus muscle of cats was to increase the baseline tension without an effect on the twitch response.
Response of the superior rectus muscle (SR) and the anterior tibial muscle (TA) of the cat to succinylcholine. If this were so, then two separate neural pathways would exist, one for the saccadic and the other for the tonic function, each with its own separate supranuclear component and subnuclei in the oculomotor complex. The central part of these muscles consisted of fibers with large cells having the characteristics of white muscles.
These authors induced saccadic, pursuit, and vergence movements in alert, unanesthetized monkeys while simultaneously recording the electric responses from cells of the abducens nucleus by means of microelectrodes. During fixation in different eye positions, the fast fibers are inactive outside the field of action of the muscle. Extraocular muscles contain different types of muscle fibrils with intricate ultramicroscopic structures and fibers with highly differentiated nerve endings.
Whereas the peripheral nerve process innervates the muscle spindle, the central nerve processes terminate in the ipsilateral portion of the spinal trigeminal nucleus and in the main sensory trigeminal nucleus. Following Bjork’s study8 of electromyography of human eyes in 1952 and subsequent elaboration by a number of researchers, important contributions have been made toward understanding of the function of extraocular muscles in normal and pathologic states. The anatomical motor unit consists of the neuron cell body, its axon, and the muscle fibers innervated by that axon. In essence, electromyographic studies have given incontrovertible proof for certain basic facts that were known, or assumed to be known, from physiologic or clinical experience. In primary position and with the eyes grossly fixed, extraocular muscles are never electrically silent but manifest a tonic activity.
Similarly, in extreme gaze to the right, the left medial rectus fires maximally while the left lateral rectus is electrically silent.
Electromyogram of saccadic movement showing saccadic burst in the agonistic medial rectus muscle. Miller55 found that they are initiated by a sudden burst of motor unit activity of the agonist with corresponding inhibition in the antagonist (Fig.
The firing rate of the motor unit depends on the angular displacement from primary position. This exciting new knowledge must not obscure the fact that the tonus of extraocular muscles is basically regulated by neural influences. As a consequence, motor neurons with larger afterhyperpolarization have frequencies of discharge appropriate to the slow muscles they innervate. A certain tonus within the central nervous system is kept up by stimuli from sensory sources. Psychooptical reflexes have superseded in importance such unconditioned reflexes as those that arise from proprioception and the vestibular system. Type 2B fibers are built for explosive, very short-duration activity such as Olympic lifts.
These athletes can have up to 80% or more of slow-twitch muscle fibers in their bodies, making them extremely efficient over long distances. Recently, microRNA (miRNA)-mediated posttranscriptional gene regulation has attracted increasing attention. The longitudinal and transverse dielectric spectrum of the ex vivo rat soleus (a predominantly type 1 muscle) and the superficial layers of rat gastrocnemius (predominantly type 2) (n = 15) were measured in the 1 kHz-10 MHz frequency range and modeled to a resistivity Cole-Cole function.
This study examines the microanatomical aspects of mimetic musculature to test the hypotheses related to human mimetic musculature physiology, function, and evolutionary morphology. Compare this with powerlifters, who train largely in a 1-5 repetition range with very heavy weights and 3-5 minutes of rest. Based on this research, it is clear that bodybuilders looking to maximize gains should incorporate heavy low-rep training sessions in addition to the traditional 8-12 repetition range for improved fast-twitch muscle fiber development, and thus greater growth. When you do this intentionally, it is known as cluster set training, but what I'm talking about is largely subconscious, such as when a subject in my lab pauses between reps during a difficult set of squats. By shortening your rest periods on traditional bodybuilding days, your slow-twitch muscle fibers will fatigue much sooner and fast-twitch muscle fiber recruitment will skyrocket. If I quit, however, it lasts forever." Keep fighting and pushing, and your body will adapt accordingly. We provide the technology, tools, and products you need to burn fat, build muscle, and become your best self. These two contradictory functions are served by two different sets of muscles in the skeletal muscle system. The structure of the extraocular muscles and its possible relation to their function will be discussed first. This layer encloses a second portion, the central or bulbar layer, close to the globe, which consists of thicker muscle fibers with variable mitochondrial content. Only denervated muscles of mammals or embryonic mammalian muscles react strongly to acetylcholine. In contrast, smooth and other slowly contractile muscle systems do not react to a single stimulus applied to their nerve, but they do respond with a slow, maintained graded contraction to a few repetitive stimuli, unaccompanied by electrical activity. In the course of time, the two systems have been demonstrated in skeletal muscles of amphibians, reptiles, and birds, but not of mammals. Light microscopic and electron microscopic examinations show a well-developed sarcoplasmic reticulum, a regular tubular (T) system in each sarcomere, a straight Z line, and a well-marked M line or thickening of the filaments in the middle of the A band.
Unlike typical skeletal muscle, Felderstruktur fibers are innervated by multiple grapelike nerve terminals, so-called en grappe endings, derived from efferent nerves of small diameter arranged linearly or in loose collections and scattered throughout the muscle from origin to insertion (see Fig. The virtual absence of the T system and the sparse sarcoplasmic reticulum and mitochondrial concentration may be evidence for the slow, tonic contraction of the field type of fiber structures and their lesser demand for oxidative metabolism. An intermediate area between the outer and central zones was made up of a mixture of large and small cells. Since publication of the studies by Daniel,24 Cooper and Daniel,22 and others, there is no doubt that human extraocular muscles also contain muscle spindles.
Second-order neurons have been identified in these nuclei and project on the cerebellum and the mesodiencephalic areas.
Basically, electromyography consists of oscilloscopic recording of suitably amplified electrical activities of a muscle.
All this puts limitations on the use of electromyography in studying the physiology of the motor functions of the eyes. The contributions of electromyography to the anomalies of ocular movements are discussed in the appropriate place in various chapters dealing with these anomalies. Complete inactivity of electrical discharge in extraocular muscles is encountered only in deep sleep or deep anesthesia. Note the graded increase in electrical activity in the right medial (RMR) and left lacteral rectus (LLR) muscles with corresponding decrease in activity all the way to zero in the right lateral (RLR) and left medial rectus (LMR) muscles as the eyes perform a levoversion movement. Large movements (15° to 20°) cause a second or third saccadic burst representing efforts to overcome a lag in fixation. The percentages of these different fiber types that your muscles are made of can help you determine exactly how you should train each particular muscle group in your body. Type 2A fibers are designed for short-to-moderate duration, moderate-to-high intensity work, as is seen in most weight-training activities. You want to use an isolation exercise because any exercise that uses any other muscle groups will skew the results. You should still strive to use weights that are as heavy as possible that will cause you to reach failure in those higher rep ranges.
MiR-23a targets key molecules regulating contractile and metabolic properties of skeletal muscle, such as myosin heavy-chains and peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1?).
Major differences were especially apparent in the dielectric spectrum in the 1 to 10 MHz range. Samples from the orbicularis oris muscle (OOM) and the zygomaticus major (ZM) muscle in laboratory mice (N?=?3), rhesus macaques (N?=?3), and humans (N?=?3) were collected.


Red muscles are more continuously active and serve the function of postural activity; white muscles are muscles of locomotion and quick activity. They vary in diameter from 9 µm to 17 µm, with fibers as fine as 3 µm having been seen,72 but these muscles also contain coarse fibers up to 50 µm in width.
Schiefferdecker66 therefore believed that the elastic fibers grow from the perimysium into the endomysium. In the lower vertebrates the differences in reaction to acetylcholine are indicative of the nature of muscles. There are also pharmacologic differences between these two systems, which, in general, are present in spatially unrelated muscle groups. The nuclei of the fibers are usually located peripherally and are only infrequently centrally located (Figs.
Mayr53 considers the presence or absence of the M band as a distinguishing sign between the two fiber types unreliable. The experimental work of Asmussen and Kiessling4 has shown that fast twitch fibers respond to denervation with atrophy and slow twitch fibers with hypertrophy.
Keller and Robinson concluded that there was a single common pathway for saccadic, pursuit, and vergence movements.41 The undeniable differences in muscle fiber types then would have to be correlated with some other functional differences in the oculomotor system. Conversely, slow fibers are active even in extreme positions of gaze outside the field of action of the muscle. This seems more probable when one considers that even such anatomically and embryologically closely related muscles as the levator of the upper lid in humans28 and the retractor bulbi in the rabbit42 do not share the peculiarities of extraocular muscles. The density of these spindles is about the same as in skeletal muscle51 and their presence is not, as had originally been assumed, age-related.9 Whether extraocular muscle spindles are capable of providing proprioceptive information is a subject of debate. These data refer to animal studies and there is no information yet on the route of centripetal information from the extraocular muscles in humans. It should be be noted that the applicability of electromyography is, for technical reasons, limited.
With return to the primary position the RLR and LMR resume their activity and increase it in the ensuing dextroversion while the activity in the RMR and LLR decreases. The duration of the initial burst is proportional to the extent of the movement (30 ms for a 2.5° movement to 150 ms for a 40° movement).
These findings are in accord with those made by optical and electro-oculographic recordings of eye movements. World-class sprinters can have up to 80% or more of fast-twitch muscle fibers in their bodies, making them extremely fast, strong, and powerful but with limited endurance. Specifically, the gastrocnemius demonstrated a well-defined, higher center frequency than the soleus muscle, whereas the soleus muscle showed a greater difference in the modeled zero and infinite resistivities than the gastrocnemius. Fiber type proportions (slow-twitch and fast-twitch), fiber cross-sectional area, diameter, and length were calculated, and means were statistically compared among groups. For every gram of carbohydrate you store, you also draw about 3 grams of water into the muscle. One can appreciate the fineness of fibers of extraocular muscles if their diameters are compared with those of fibers of the gluteus maximus (90 µm to 100 µm). He also thought that the abundance of elastic tissue was a factor in fine regulation of eye movements.
Bjork attributed these differences to the low nerve fiber-to-muscle fiber ratio of the motor units in extraocular muscles. According to Cheng and Breinin,18 the synaptic membrane of these terminals has only a few rudimentary invaginations and the terminal axon contains granular as well as agranular synaptic vesicles. For example, Keller and Robinson found fibers with a discharge frequency of 150 spikes per second with the eye in primary position, that is, during the entire time the animal was awake. Their activity increases nonlinearly as the eye begins to fixate more and more in the field of action of the muscle. The introduction of electrodes into the muscles is easy only for rectus muscles, although some discomfort is always part of this procedure. Figure 6–7 also shows that in a waking person a muscle may be electrically silent only when in extreme positions out of its field of action.
In Lennerstrand G, Bach-y-Rita P, eds: Basic Mechanisms of Ocular Motility and Their Clinical Implications. Ruskell GL: The fine structure of human extraocular muscle spindles and their potential propriocepive capacity. When compared with wild-type mice, protein markers of mitochondrial content, including PGC-1?, and cytochrome c oxidase complex IV (COX IV), were significantly decreased in the slow soleus muscle, but not the fast plantaris muscle of miR-23a Tg mice. These findings are consistent with the fact that soleus tissue has larger and more numerous mitochondria than gastrocnemius. Results showed that macaques had the greatest percentage of fast fibers in both muscles (followed by humans) and that humans had the greatest percentage of slow fibers in both muscles. Thus, bodybuilders who optimize fast-twitch fiber development will obtain a fuller and denser look onstage. The anterior tibial muscle did not respond with a rise in baseline tension, but its twitch response was abolished with much lower doses of the drug than in the superior rectus muscle. As Bjork8 had already determined from electromyographic studies, this amounts to an intensity and duration far in excess of that required from other muscle systems. This innervational pattern is similar during slow following movements; however, during fast saccades, both slow and fast fibers are activated maximally during the first phase of the saccades, then begin to decay logarithmically to their new equilibrium with a time constant of about half the duration of the saccade. Most current research seems to indicate that there may indeed be sensory feedback from muscle spindles even though the role of this inflow under casual conditions of seeing is by no means clear (see also p. This basic technique may be highly refined by use of various electronic components for integration, analysis, and storage of responses. Whenever an eye diverges, an increment in the electrical activity occurs in the lateral rectus muscle.
Davidowitz J, Chiarandini DJ, Philips G, et al: Morphological variation along multiply innervated fibers of rat extraocular muscles. Evaluation of tissue at high frequency could provide a novel approach for assessing intracellular structure in health and disease. Macaques and humans typically did not differ from one another in morphometrics except for fiber length where humans had longer fibers. However, Eisler33 believed it to be a secondary, mechanical phenomenon produced by frequent small pulls on the extraocular muscles. Scattered mitochondria and elements of sarcoplasmic reticulum (arrows) lie in the indistinct mass of myofilaments (X18,00). On the other hand, units in which the threshold lies lateral to the primary position are recruited into activity for only brief periods of lateral gaze or during lateral saccades. The work of these investigators leaves little doubt that both slow and fast fibers contribute to tonic and phasic activity but not necessarily simultaneously in the case of tonic activity. They are active when the head is erect, and they also regulate the position of the eyes with every movement of the head. Following 4 weeks of voluntary wheel running, there was no difference in the endurance exercise capacity as well as in several muscle adaptive responses including an increase in muscle mass, capillary density, or the protein content of myosin heavy-chain IIa, PGC-1?, COX IV, and cytochrome c. Although sample sizes are low, results from this study may indicate that the rhesus macaque OOM and ZM muscle are specialized primarily to assist with maintenance of the rigid dominance hierarchy via rapid facial displays of submission and aggression, whereas human musculature may have evolved not only under pressure to work in facial expressions but also in development of speech.
Peachey59 subdivided fiber types according to their electron microscopic characteristics into five groups, and similar classifications have been suggested by others.2, 53 Miller54 drew attention to the microstructural changes that extraocular muscles undergo with advancing age.
Multichannel recordings have recently been obtained after insertion of electrodes into the muscles during surgical procedures. These results show that miR-23a targets PGC-1? and regulates basal metabolic properties of slow but not fast twitch muscles. Keller and Robinson conclude that it would be remarkable if such large differences in synaptic transmission and muscle metabolism were not reflected in morphologic differences. The recordings were performed days after surgery and without discomfort to the patient, after which the electrodes simply pulled out of the muscle.17 This approach may hopefully provide better information on electrical activity of the extraocular muscles. Asmussen G, Kiessling A: Hypertropy and atrophy of mammalian extraocular muscle fibres following denervation. Demer JL, Oh SY, Poukens V: Evidence of active control of rectus extraocular muscle pulleys. Elevated levels of miR-23a did not impact on whole body endurance capacity or exercise-induced muscle adaptations in the fast plantaris muscle. Denny-Brown D: The histological features of striped muscle in relation to its functional activity.
Lennerstrand G, Tian S, Han Y: Effects of eye proprioceptive activation on eye position in normal and exotropic subjects. Dietert SE: The demonstration of different types of muscle fibers in human extraocular muscle by electron microscopy and cholinesterase staining. Lukas JR, Aigner M, Blumer R, et al: Number and distribution of neuromuscular spindles in human extraocular muscles. Sodi A, Corsi M, Faussone-Pellegrini MS, et al: Fine structure of the receptors of the myotendinous junction of human extraocular muscles.
Bach-y-Rita P, Lennerstrand G: Absence of polyneural innervation in cat extraocular muscles. Duke-Elder S, Duke-Elder PM: The contraction of the extrinsic muscles of the eyes by choline and nicotine.
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