147-506: Electrical muscle stimulation ( EMS ), also known as neuromuscular electrical stimulation ( NMES ) or electromyostimulation , is the elicitation of muscle contraction using electric impulses. EMS has received an increasing amount of attention in the last few years for many reasons: it can be utilized as a strength training tool for healthy subjects and athletes; it could be used as a rehabilitation and preventive tool for people who are partially or totally immobilized; it could be utilized as
294-474: A skeleton . The skeletal muscle cells are much longer than in the other types of muscle tissue, and are also known as muscle fibers . The tissue of a skeletal muscle is striated – having a striped appearance due to the arrangement of the sarcomeres . A skeletal muscle contains multiple fascicles – bundles of muscle fibers. Each individual fiber, and each muscle is surrounded by a type of connective tissue layer of fascia . Muscle fibers are formed from
441-417: A complex interface region known as the musculotendinous junction also known as the myotendinous junction , an area specialised for the primary transmission of force. At the muscle-tendon interface, force is transmitted from the sarcomeres in the muscle cells to the tendon. Muscles and tendons develop in close association, and after their joining at the myotendinous junction they constitute a dynamic unit for
588-764: A concentric contraction, contractile muscle myofilaments of myosin and actin slide past each other, pulling the Z-lines together. During an eccentric contraction, the myofilaments slide past each other the opposite way, though the actual movement of the myosin heads during an eccentric contraction is not known. Exercise featuring a heavy eccentric load can actually support a greater weight (muscles are approximately 40% stronger during eccentric contractions than during concentric contractions) and also results in greater muscular damage and delayed onset muscle soreness one to two days after training. Exercise that incorporates both eccentric and concentric muscular contractions (i.e., involving
735-443: A contraction, some fraction of the fibers in the muscle will be firing at any given time. In a typical circumstance, when humans are exerting their muscles as hard as they are consciously able, roughly one-third of the fibers in each of those muscles will fire at once , though this ratio can be affected by various physiological and psychological factors (including Golgi tendon organs and Renshaw cells ). This 'low' level of contraction
882-465: A feedback loop with the grey matter. Other actions such as locomotion, breathing, and chewing have a reflex aspect to them: the contractions can be initiated either consciously or unconsciously. A neuromuscular junction is a chemical synapse formed by the contact between a motor neuron and a muscle fiber . It is the site in which a motor neuron transmits a signal to a muscle fiber to initiate muscle contraction. The sequence of events that results in
1029-558: A higher capability for electrochemical transmission of action potentials and a rapid level of calcium release and uptake by the sarcoplasmic reticulum. The fast twitch fibers rely on a well-developed, anaerobic , short term, glycolytic system for energy transfer and can contract and develop tension at 2–3 times the rate of slow twitch fibers. Fast twitch muscles are much better at generating short bursts of strength or speed than slow muscles, and so fatigue more quickly. The slow twitch fibers generate energy for ATP re-synthesis by means of
1176-757: A higher density of capillaries . However, muscle cells cannot divide to produce new cells, and as a result there are fewer muscle cells in an adult than in a newborn. There are a number of terms used in the naming of muscles including those relating to size, shape, action, location, their orientation, and their number of heads. Broadly there are two types of muscle fiber: Type I , which is slow, and Type II which are fast. Type II has two divisions of type IIA (oxidative), and type IIX (glycolytic), giving three main fiber types. These fibers have relatively distinct metabolic, contractile, and motor unit properties. The table below differentiates these types of properties. These types of properties—while they are partly dependent on
1323-399: A joint in the direction of the muscle contraction, the muscle acts to decelerate the joint at the end of a movement or otherwise control the repositioning of a load. This can occur involuntarily (e.g., when attempting to move a weight too heavy for the muscle to lift) or voluntarily (e.g., when the muscle is 'smoothing out' a movement or resisting gravity such as during downhill walking). Over
1470-442: A large proportion of intracellular calcium. As a result, a large increase in total calcium leads to a relatively small rise in free Ca . The cytoplasmic calcium binds to Troponin C, moving the tropomyosin complex off the actin binding site allowing the myosin head to bind to the actin filament. From this point on, the contractile mechanism is essentially the same as for skeletal muscle (above). Briefly, using ATP hydrolysis,
1617-458: A long term system of aerobic energy transfer. These mainly include the ATPase type I and MHC type I fibers. They tend to have a low activity level of ATPase, a slower speed of contraction with a less well developed glycolytic capacity. Fibers that become slow-twitch develop greater numbers of mitochondria and capillaries making them better for prolonged work. Individual muscles tend to be
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#17328757375981764-409: A medical prescription for therapy. Prescription devices should be used under the supervision of an authorized practitioner, for the following uses: The FDA mandates that manuals prominently display contraindication, warnings, precautions and adverse reactions, including: no use for wearer of pacemaker; no use on vital parts, such as carotid sinus nerves, across the chest, or across the brain; caution in
1911-417: A mixture of various fiber types, but their proportions vary depending on the actions of that muscle. For instance, in humans, the quadriceps muscles contain ~52% type I fibers, while the soleus is ~80% type I. The orbicularis oculi muscle of the eye is only ~15% type I. Motor units within the muscle, however, have minimal variation between the fibers of that unit. It is this fact that makes
2058-537: A muscle action potential. This action potential spreads across the muscle's surface and into the muscle fiber's network of T-tubules , depolarizing the inner portion of the muscle fiber. This activates dihydropyridine receptors in the terminal cisternae , which are in close proximity to ryanodine receptors in the adjacent sarcoplasmic reticulum . The activated dihydropyridine receptors physically interact with ryanodine receptors to activate them via foot processes (involving conformational changes that allosterically activates
2205-468: A muscle, and are often termed as muscle fibers . A single muscle such as the biceps in a young adult male contains around 253,000 muscle fibers. Skeletal muscle fibers are multinucleated with the nuclei often referred to as myonuclei . This occurs during myogenesis with the fusion of myoblasts each contributing a nucleus. Fusion depends on muscle-specific proteins known as fusogens called myomaker and myomerger . Many nuclei are needed by
2352-542: A myosin head detaches myosin from actin , thereby allowing myosin to bind to another actin molecule. Once attached, the ATP is hydrolyzed by myosin, which uses the released energy to move into the "cocked position" whereby it binds weakly to a part of the actin binding site. The remainder of the actin binding site is blocked by tropomyosin . With the ATP hydrolyzed, the cocked myosin head now contains adenosine diphosphate (ADP) + P i . Two Ca ions bind to troponin C on
2499-456: A number of different environmental factors. This plasticity can, arguably, be the strongest evolutionary advantage among organisms with muscle. In fish, different fiber types are expressed at different water temperatures. Cold temperatures require more efficient metabolism within muscle and fatigue resistance is important. While in more tropical environments, fast powerful movements (from higher fast-twitch proportions) may prove more beneficial in
2646-608: A punch or throw. Part of training for rapid movements such as pitching during baseball involves reducing eccentric braking allowing a greater power to be developed throughout the movement. Eccentric contractions are being researched for their ability to speed rehabilitation of weak or injured tendons. Achilles tendinitis and patellar tendonitis (also known as jumper's knee or patellar tendonosis) have been shown to benefit from high-load eccentric contractions. In vertebrate animals , there are three types of muscle tissues : skeletal, smooth, and cardiac. Skeletal muscle constitutes
2793-436: A relatively small decrease in free Ca concentration in response to a large change in total calcium. The falling Ca concentration allows the troponin complex to dissociate from the actin filament thereby ending contraction. The heart relaxes, allowing the ventricles to fill with blood and begin the cardiac cycle again. In annelids such as earthworms and leeches , circular and longitudinal muscles cells form
2940-463: A reliance on glycolytic enzymes. Fibers can also be classified on their twitch capabilities, into fast and slow twitch. These traits largely, but not completely, overlap the classifications based on color, ATPase, or MHC ( myosin heavy chain ). Some authors define a fast twitch fiber as one in which the myosin can split ATP very quickly. These mainly include the ATPase type II and MHC type II fibers. However, fast twitch fibers also demonstrate
3087-406: A result, the sarcolemma reverses polarity and its voltage quickly jumps from the resting membrane potential of -90mV to as high as +75mV as sodium enters. The membrane potential then becomes hyperpolarized when potassium exits and is then adjusted back to the resting membrane potential. This rapid fluctuation is called the end-plate potential. The voltage-gated ion channels of the sarcolemma next to
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#17328757375983234-547: A strong contraction and a controlled lowering of the weight) can produce greater gains in strength than concentric contractions alone. While unaccustomed heavy eccentric contractions can easily lead to overtraining , moderate training may confer protection against injury. Eccentric contractions normally occur as a braking force in opposition to a concentric contraction to protect joints from damage. During virtually any routine movement, eccentric contractions assist in keeping motions smooth, but can also slow rapid movements such as
3381-483: A tendon. Multipennate muscles have fibers that are oriented at multiple angles along the force-generating axis, and this is the most general and most common architecture. Muscle fibers grow when exercised and shrink when not in use. This is due to the fact that exercise stimulates the increase in myofibrils which increase the overall size of muscle cells. Well exercised muscles can not only add more size but can also develop more mitochondria , myoglobin , glycogen and
3528-450: A testing tool for evaluating the neural and/or muscular function in vivo. EMS has been proven to be more beneficial before exercise and activity due to early muscle activation. Recent studies have found that electrostimulation has been proven to be ineffective during post exercise recovery and can even lead to an increase in Delayed onset muscle soreness (DOMS). The impulses are generated by
3675-411: A thin filament to slide over a thick filament and generate tension in the muscle. It was independently developed by Andrew Huxley and Rolf Niedergerke and by Hugh Huxley and Jean Hanson in 1954. Physiologically, this contraction is not uniform across the sarcomere; the central position of the thick filaments becomes unstable and can shift during contraction but this is countered by the actions of
3822-399: A time-varying manner. Therefore, neither length nor tension is likely to remain constant when the muscle is active during locomotor activity. An isometric contraction of a muscle generates tension without changing length. An example can be found when the muscles of the hand and forearm grip an object; the joints of the hand do not move, but muscles generate sufficient force to prevent
3969-423: A time-varying manner. Therefore, neither length nor tension is likely to remain the same in skeletal muscles that contract during locomotion. Contractions can be described as isometric if the muscle tension changes but the muscle length remains the same. In contrast, a muscle contraction is described as isotonic if muscle tension remains the same throughout the contraction. If the muscle length shortens,
4116-400: Is a predominance of type II fibers utilizing glycolytic metabolism. Because of the discrepancy in fast twitch fibers compared to humans, chimpanzees outperform humans in power related tests. Humans, however, will do better at exercise in aerobic range requiring large metabolic costs such as walking (bipedalism). Across species, certain gene sequences have been preserved, but do not always have
4263-450: Is a protective mechanism to prevent avulsion of the tendon—the force generated by a 95% contraction of all fibers is sufficient to damage the body. In multiple fiber summation , if the central nervous system sends a weak signal to contract a muscle, the smaller motor units , being more excitable than the larger ones, are stimulated first. As the strength of the signal increases, more motor units are excited in addition to larger ones, with
4410-413: Is a rapid burst of energy use as measured by oxygen consumption. Within a few minutes of initiation, the calcium level markedly decreases, the 20 kDa myosin light chains' phosphorylation decreases, and energy use decreases; however, force in tonic smooth muscle is maintained. During contraction of muscle, rapidly cycling crossbridges form between activated actin and phosphorylated myosin, generating force. It
4557-405: Is a slow twitch-fiber that can sustain longer contractions ( tonic ). In lobsters, muscles in different body parts vary in the muscle fiber type proportions based on the purpose of the muscle group. In the early development of vertebrate embryos, growth and formation of muscle happens in successive waves or phases of myogenesis . The myosin heavy chain isotype is a major determinant of
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4704-482: Is a strong resistance to lengthening an active muscle far beyond the peak of active tension. Force–velocity relationship relates the speed at which a muscle changes its length (usually regulated by external forces, such as load or other muscles) to the amount of force that it generates. Force declines in a hyperbolic fashion relative to the isometric force as the shortening velocity increases, eventually reaching zero at some maximum velocity. The reverse holds true for when
4851-535: Is also taken up by the mitochondria. An enzyme, phospholamban , serves as a brake for SERCA. At low heart rates, phospholamban is active and slows down the activity of the ATPase so that Ca does not have to leave the cell entirely. At high heart rates, phospholamban is phosphorylated and deactivated thus taking most Ca from the cytoplasm back into the sarcoplasmic reticulum. Once again, calcium buffers moderate this fall in Ca concentration, permitting
4998-499: Is attached to other organelles such as the mitochondria by intermediate filaments in the cytoskeleton. The costamere attaches the sarcomere to the sarcolemma. Every single organelle and macromolecule of a muscle fiber is arranged to ensure that it meets desired functions. The cell membrane is called the sarcolemma with the cytoplasm known as the sarcoplasm . In the sarcoplasm are the myofibrils. The myofibrils are long protein bundles about one micrometer in diameter. Pressed against
5145-642: Is available on the results obtained. In the United States, EMS devices are regulated by the U.S. Food and Drug Administration (FDA). A number of reviews have looked at the devices. Electrical muscle stimulation can be used as a training, therapeutic , or cosmetic tool. In medicine, EMS is used for rehabilitation purposes, for instance in physical therapy in the prevention muscle atrophy due to inactivity or neuromuscular imbalance, which can occur for example after musculoskeletal injuries (damage to bones , joints , muscles , ligaments and tendons ). This
5292-645: Is being done on the muscle), chemical energy (of fat or glucose , or temporarily stored in ATP ) is nevertheless consumed, although less than would be consumed during a concentric contraction of the same force. For example, one expends more energy going up a flight of stairs than going down the same flight. Muscles undergoing heavy eccentric loading suffer greater damage when overloaded (such as during muscle building or strength training exercise) as compared to concentric loading. When eccentric contractions are used in weight training, they are normally called negatives . During
5439-613: Is called peristalsis , which underlies the creeping movement of earthworms. Invertebrates such as annelids, mollusks , and nematodes , possess obliquely striated muscles, which contain bands of thick and thin filaments that are arranged helically rather than transversely, like in vertebrate skeletal or cardiac muscles. In bivalves , the obliquely striated muscles can maintain tension over long periods without using too much energy. Bivalves use these muscles to keep their shells closed. Advanced insects such as wasps , flies , bees , and beetles possess asynchronous muscles that constitute
5586-447: Is called a calcium transient. This increase in calcium activates calcium-sensitive contractile proteins that then use ATP to cause cell shortening. Skeletal muscle Skeletal muscle (commonly referred to as muscle ) is one of the three types of vertebrate muscle tissue , the other being cardiac muscle and smooth muscle . They are part of the voluntary muscular system and typically are attached by tendons to bones of
5733-420: Is distinct from transcutaneous electrical nerve stimulation (TENS), in which an electric current is used for pain therapy. "The main difference is the desired outcome. TENS unit is a medical device for pain relief. The desired outcome is to reduce pain by stimulating different nerve signals. EMS fitness is also an FDA-cleared medical device but meant for muscle development. EMS fitness is designed to stimulate all
5880-505: Is expressed in other mammals, so is still accurately seen (along with IIB) in the literature. Non human fiber types include true IIb fibers, IIc, IId, etc. Further fiber typing methods are less formally delineated, and exist on more of a spectrum. They tend to be focused more on metabolic and functional capacities (i.e., oxidative vs. glycolytic , fast vs. slow contraction time). As noted above, fiber typing by ATPase or MHC does not directly measure or dictate these parameters. However, many of
6027-412: Is followed by muscle relaxation , which is a return of the muscle fibers to their low tension-generating state. For the contractions to happen, the muscle cells must rely on the change in action of two types of filaments : thin and thick filaments. The major constituent of thin filaments is a chain formed by helical coiling of two strands of actin , and thick filaments dominantly consist of chains of
Electrical muscle stimulation - Misplaced Pages Continue
6174-428: Is hypothesized that the maintenance of force results from dephosphorylated "latch-bridges" that slowly cycle and maintain force. A number of kinases such as rho kinase , DAPK3 , and protein kinase C are believed to participate in the sustained phase of contraction, and Ca flux may be significant. Although smooth muscle contractions are myogenic, the rate and strength of their contractions can be modulated by
6321-581: Is in contrast to the contractile activity of skeletal muscle cells, which relies on a single neural input. Some types of smooth muscle cells are able to generate their own action potentials spontaneously, which usually occur following a pacemaker potential or a slow wave potential . These action potentials are generated by the influx of extracellular Ca , and not Na . Like skeletal muscles, cytosolic Ca ions are also required for crossbridge cycling in smooth muscle cells. The two sources for cytosolic Ca in smooth muscle cells are
6468-400: Is known as calcium-induced calcium release and gives rise to calcium sparks ( Ca sparks ). The spatial and temporal summation of ~30,000 Ca sparks gives a cell-wide increase in cytoplasmic calcium concentration. The increase in cytosolic calcium following the flow of calcium through the cell membrane and sarcoplasmic reticulum is moderated by calcium buffers , which bind
6615-463: Is needed as this evidence is graded as low certainty. The same study also indicates that EMS may lead to increased muscle mass . Low certainty evidence indicates that adding EMS to an existing exercise programme may help people who are unwell spend fewer days confined to their beds. During EMS training, a set of complementary muscle groups (e.g., biceps and triceps) are often targeted in alternating fashion, for specific training goals, such as improving
6762-399: Is not the same as ATPase fiber typing. Almost all multicellular animals depend on muscles to move. Generally, muscular systems of most multicellular animals comprise both slow-twitch and fast-twitch muscle fibers, though the proportions of each fiber type can vary across organisms and environments. The ability to shift their phenotypic fiber type proportions through training and responding to
6909-404: Is preceded by the formation of connective tissue frameworks, usually formed from the somatic lateral plate mesoderm . Myoblasts follow chemical signals to the appropriate locations, where they fuse into elongated multinucleated skeletal muscle cells. Between the tenth and the eighteenth weeks of gestation, all muscle cells have fast myosin heavy chains; two myotube types become distinguished in
7056-473: Is thought to depend primarily on a mechanism called calcium-induced calcium release , which is based on the junctional structure between T-tubule and sarcoplasmic reticulum. Junctophilin-2 (JPH2) is essential to maintain this structure, as well as the integrity of T-tubule . Another protein, receptor accessory protein 5 (REEP5), functions to keep the normal morphology of junctional SR. Defects of junctional coupling can result from deficiencies of either of
7203-454: Is used in fiber typing vs. MHC typing, and some ATPase types actually contain multiple MHC types. Also, a subtype B or b is not expressed in humans by either method . Early researchers believed humans to express a MHC IIb, which led to the ATPase classification of IIB. However, later research showed that the human MHC IIb was in fact IIx, indicating that the IIB is better named IIX. IIb
7350-476: Is usually an action potential and the mechanical response is contraction. Excitation–contraction coupling can be dysregulated in many diseases. Though excitation–contraction coupling has been known for over half a century, it is still an active area of biomedical research. The general scheme is that an action potential arrives to depolarize the cell membrane. By mechanisms specific to the muscle type, this depolarization results in an increase in cytosolic calcium that
7497-419: The autonomic nervous system . Postganglionic nerve fibers of parasympathetic nervous system release the neurotransmitter acetylcholine, which binds to muscarinic acetylcholine receptors (mAChRs) on smooth muscle cells. These receptors are metabotropic , or G-protein coupled receptors that initiate a second messenger cascade. Conversely, postganglionic nerve fibers of the sympathetic nervous system release
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#17328757375987644-449: The erector spinae and small vertebral muscles, and are innervated by the dorsal rami of the spinal nerves . All other muscles, including those of the limbs are hypaxial, and innervated by the ventral rami of the spinal nerves. During development, myoblasts (muscle progenitor cells) either remain in the somite to form muscles associated with the vertebral column or migrate out into the body to form all other muscles. Myoblast migration
7791-476: The fusion of developmental myoblasts in a process known as myogenesis resulting in long multinucleated cells. In these cells the nuclei , termed myonuclei , are located along the inside of the cell membrane . Muscle fibers also have multiple mitochondria to meet energy needs. Muscle fibers are in turn composed of myofibrils . The myofibrils are composed of actin and myosin filaments called myofilaments , repeated in units called sarcomeres, which are
7938-404: The motor-protein myosin . Together, these two filaments form myofibrils - the basic functional organelles in the skeletal muscle system. In vertebrates , skeletal muscle contractions are neurogenic as they require synaptic input from motor neurons . A single motor neuron is able to innervate multiple muscle fibers, thereby causing the fibers to contract at the same time. Once innervated,
8085-458: The pectoral , and abdominal muscles ; intrinsic and extrinsic muscles are subdivisions of muscle groups in the hand , foot , tongue , and extraocular muscles of the eye . Muscles are also grouped into compartments including four groups in the arm , and the four groups in the leg . Apart from the contractile part of a muscle consisting of its fibers, a muscle contains a non-contractile part of dense fibrous connective tissue that makes up
8232-499: The plateau phase . Although this Ca influx only count for about 10% of the Ca needed for activation, it is relatively larger than that of skeletal muscle. This Ca influx causes a small local increase in intracellular Ca . The increase of intracellular Ca is detected by RyR2 in the membrane of the sarcoplasmic reticulum, which releases Ca in a positive feedback physiological response. This positive feedback
8379-686: The ryanodine receptor 1 (RYR1) and the voltage-gated L-type calcium channel identified as dihydropyridine receptors , (DHPRs). DHPRs are located on the sarcolemma (which includes the surface sarcolemma and the transverse tubules ), while the RyRs reside across the SR membrane. The close apposition of a transverse tubule and two SR regions containing RyRs is described as a triad and is predominantly where excitation–contraction coupling takes place. Excitation–contraction coupling (ECC) occurs when depolarization of skeletal muscles (usually through neural innervation) results in
8526-531: The ryanodine receptors (RyRs) are distinct isoforms. Besides, DHPR contacts with RyR1 (main RyR isoform in skeletal muscle) to regulate Ca release in skeletal muscle, while the L-type calcium channel (DHPR on cardiac myocytes) and RyR2 (main RyR isoform in cardiac muscle) are not physically coupled in cardiac muscle, but face with each other by a junctional coupling. Unlike skeletal muscle, E-C coupling in cardiac muscle
8673-437: The sarco/endoplasmic reticulum calcium-ATPase (SERCA) actively pumps Ca back into the sarcoplasmic reticulum, resulting in a permanent relaxation until the next action potential arrives. Mitochondria also participate in Ca reuptake, ultimately delivering their gathered Ca to SERCA for storage in the sarcoplasmic reticulum. A few of the relaxation mechanisms (NCX, Ca2+ pumps and Ca2+ leak channels) move Ca2+ completely out of
8820-580: The sarcolemma . The myonuclei are quite uniformly arranged along the fiber with each nucleus having its own myonuclear domain where it is responsible for supporting the volume of cytoplasm in that particular section of the myofiber. A group of muscle stem cells known as myosatellite cells , also satellite cells are found between the basement membrane and the sarcolemma of muscle fibers. These cells are normally quiescent but can be activated by exercise or pathology to provide additional myonuclei for muscle growth or repair. Muscles attach to tendons in
8967-438: The shoulder . During an eccentric contraction of the triceps muscle , the elbow starts the movement straight and then bends as the hand moves towards the shoulder. Desmin , titin , and other z-line proteins are involved in eccentric contractions, but their mechanism is poorly understood in comparison to cross-bridge cycling in concentric contractions. Though the muscle is doing a negative amount of mechanical work , (work
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#17328757375989114-408: The sinoatrial node or atrioventricular node and conducted to all cells in the heart via gap junctions . The action potential travels along the surface membrane into T-tubules (the latter are not seen in all cardiac cell types) and the depolarisation causes extracellular Ca to enter the cell via L-type calcium channels and possibly sodium-calcium exchanger (NCX) during the early part of
9261-436: The tendon at each end. The tendons attach the muscles to bones to give skeletal movement. The length of a muscle includes the tendons. Connective tissue is present in all muscles as deep fascia . Deep fascia specialises within muscles to enclose each muscle fiber as endomysium ; each muscle fascicle as perimysium , and each individual muscle as epimysium . Together these layers are called mysia . Deep fascia also separates
9408-418: The 19th and 20th centuries, researchers studied and documented the exact electrical properties that generate muscle movement. It was discovered that the body functions induced by electrical stimulation caused long-term changes in the muscles. In the 1960s, Soviet sport scientists applied EMS in the training of elite athletes, claiming 40% force gains. In the 1970s, these studies were shared during conferences with
9555-610: The Western sport establishments. However, results were conflicting, perhaps because the mechanisms in which EMS acted were poorly understood. Medical physiology research pinpointed the mechanisms by which electrical stimulation causes adaptation of cells of muscles, blood vessels and nerves. The U.S. Food and Drug Administration (FDA) certifies and releases EMS devices into two broad categories: over-the counter devices (OTC), and prescription devices. OTC devices are marketable only for muscle toning; prescription devices can be purchased only with
9702-536: The ability to reach for an item. The FDA rejects certification of devices that claim weight reduction. EMS devices cause a calorie burning that is marginal at best: calories are burnt in significant amount only when most of the body is involved in physical exercise: several muscles, the heart and the respiratory system are all engaged at once. However, some authors imply that EMS can lead to exercise since people toning their muscles with electrical stimulation are more likely afterwards to participate in sporting activities as
9849-399: The actin filament inwards, thereby shortening the sarcomere . Myosin then releases ADP but still remains tightly bound to actin. At the end of the power stroke, ADP is released from the myosin head, leaving myosin attached to actin in a rigor state until another ATP binds to myosin. A lack of ATP would result in the rigor state characteristic of rigor mortis . Once another ATP binds to myosin,
9996-405: The actin filaments. The troponin- Ca complex causes tropomyosin to slide over and unblock the remainder of the actin binding site. Unblocking the rest of the actin binding sites allows the two myosin heads to close and myosin to bind strongly to actin. The myosin head then releases the inorganic phosphate and initiates a power stroke, which generates a force of 2 pN. The power stroke moves
10143-469: The action of the muscle itself or by an outside force), the maximum active tension generated decreases. This decrease is minimal for small deviations, but the tension drops off rapidly as the length deviates further from the ideal. Due to the presence of elastic proteins within a muscle cell (such as titin ) and extracellular matrix, as the muscle is stretched beyond a given length, there is an entirely passive tension, which opposes lengthening. Combined, there
10290-438: The associated related changes, not a change in fiber type. There are numerous methods employed for fiber-typing, and confusion between the methods is common among non-experts. Two commonly confused methods are histochemical staining for myosin ATPase activity and immunohistochemical staining for myosin heavy chain (MHC) type. Myosin ATPase activity is commonly—and correctly—referred to as simply "fiber type", and results from
10437-406: The autonomic nervous system. As such, they allow for fine control and gradual responses, much like motor unit recruitment in skeletal muscle. The contractile activity of smooth muscle cells can be tonic (sustained) or phasic (transient) and is influenced by multiple inputs such as spontaneous electrical activity, neural and hormonal inputs, local changes in chemical composition, and stretch. This
10584-443: The basic functional, contractile units of the muscle fiber necessary for muscle contraction . Muscles are predominantly powered by the oxidation of fats and carbohydrates , but anaerobic chemical reactions are also used, particularly by fast twitch fibers . These chemical reactions produce adenosine triphosphate (ATP) molecules that are used to power the movement of the myosin heads . Skeletal muscle comprises about 35% of
10731-411: The binding sites again. The myosin ceases binding to the thin filament, and the muscle relaxes. The Ca ions leave the troponin molecule to maintain the Ca ion concentration in the sarcoplasm. The active pumping of Ca ions into the sarcoplasmic reticulum creates a deficiency in the fluid around the myofibrils. This causes the removal of Ca ions from the troponin. Thus,
10878-455: The body becomes ready, fit, willing and able to take on physical activity. "Strength training by NMES does promote neural and muscular adaptations that are complementary to the well-known effects of voluntary resistance training". This statement is part of the editorial summary of a 2010 world congress of researchers on the subject. Additional studies on practical applications, which came after that congress, pointed out important factors that make
11025-668: The body of humans by weight. The functions of skeletal muscle include producing movement, maintaining body posture, controlling body temperature, and stabilizing joints. Skeletal muscle is also an endocrine organ . Under different physiological conditions, subsets of 654 different proteins as well as lipids, amino acids, metabolites and small RNAs are found in the secretome of skeletal muscles. Skeletal muscles are substantially composed of multinucleated contractile muscle fibers (myocytes). However, considerable numbers of resident and infiltrating mononuclear cells are also present in skeletal muscles. In terms of volume, myocytes make up
11172-441: The body wall of these animals and are responsible for their movement. In an earthworm that is moving through a soil, for example, contractions of circular and longitudinal muscles occur reciprocally while the coelomic fluid serves as a hydroskeleton by maintaining turgidity of the earthworm. When the circular muscles in the anterior segments contract, the anterior portion of animal's body begins to constrict radially, which pushes
11319-422: The cells as well. As Ca concentration declines to resting levels, Ca2+ releases from Troponin C, disallowing cross bridge-cycling, causing the force to decline and relaxation to occur. Once relaxation has fully occurred, the muscle is able to contract again, thus fully resetting the cycle. The sliding filament theory describes a process used by muscles to contract. It is a cycle of repetitive events that cause
11466-445: The contraction is concentric; if the muscle length lengthens, the contraction is eccentric. Muscle contractions can be described based on two variables: force and length. Force itself can be differentiated as either tension or load. Muscle tension is the force exerted by the muscle on an object whereas a load is the force exerted by an object on the muscle. When muscle tension changes without any corresponding changes in muscle length,
11613-507: The cytosol binds to Troponin C by the actin filaments . This bond allows the actin filaments to perform cross-bridge cycling , producing force and, in some situations, motion. When the desired motion is accomplished, relaxation can be achieved quickly through numerous pathways. Relaxation is quickly achieved through a Ca buffer with various cytoplasmic proteins binding to Ca with very high affinity. These cytoplasmic proteins allow for quick relaxation in fast twitch muscles. Although slower,
11760-475: The depolarization of the muscle fiber at the neuromuscular junction begins when an action potential is initiated in the cell body of a motor neuron, which is then propagated by saltatory conduction along its axon toward the neuromuscular junction. Once it reaches the terminal bouton , the action potential causes a Ca ion influx into the terminal by way of the voltage-gated calcium channels . The Ca influx causes synaptic vesicles containing
11907-401: The device and are delivered through electrodes on the skin near to the muscles being stimulated. The electrodes are generally pads that adhere to the skin. The impulses mimic the action potential that comes from the central nervous system , causing the muscles to contract. The use of EMS has been cited by sports scientists as a complementary technique for sports training, and published research
12054-439: The difference between effective and ineffective EMS. This in retrospect explains why in the past some researchers and practitioners obtained results that others could not reproduce. Also, as published by reputable universities, EMS causes adaptation, i.e. training, of muscle fibers. Because of the characteristics of skeletal muscle fibers, different types of fibers can be activated to differing degrees by different types of EMS, and
12201-542: The direct assaying of ATPase activity under various conditions (e.g. pH ). Myosin heavy chain staining is most accurately referred to as "MHC fiber type", e.g. "MHC IIa fibers", and results from determination of different MHC isoforms . These methods are closely related physiologically, as the MHC type is the primary determinant of ATPase activity. However, neither of these typing methods is directly metabolic in nature; they do not directly address oxidative or glycolytic capacity of
12348-498: The elastic myofilament of titin . This fine myofilament maintains uniform tension across the sarcomere by pulling the thick filament into a central position. Cross-bridge cycling is a sequence of molecular events that underlies the sliding filament theory. A cross-bridge is a myosin projection, consisting of two myosin heads, that extends from the thick filaments. Each myosin head has two binding sites: one for adenosine triphosphate (ATP) and another for actin. The binding of ATP to
12495-443: The elbow as the hand moved from the leg to the shoulder (a biceps curl ). A concentric contraction of the triceps would change the angle of the joint in the opposite direction, straightening the arm and moving the hand towards the leg. In eccentric contraction, the tension generated while isometric is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract. Rather than working to pull
12642-463: The end plate open in response to the end plate potential. They are sodium and potassium specific and only allow one through. This wave of ion movements creates the action potential that spreads from the motor end plate in all directions. If action potentials stop arriving, then acetylcholine ceases to be released from the terminal bouton. The remaining acetylcholine in the synaptic cleft is either degraded by active acetylcholine esterase or reabsorbed by
12789-531: The environment has served organisms well when placed in changing environments either requiring short explosive movements (higher fast twitch proportion) or long duration of movement (higher slow twitch proportion) to survive. Bodybuilding has shown that changes in muscle mass and force production can change in a matter of months. Some examples of this variation are described below. American lobster , Homarus americanus , has three fiber types including fast twitch fibers, slow-twitch and slow-tonic fibers. Slow-tonic
12936-465: The extracellular Ca entering through calcium channels and the Ca ions that are released from the sarcoplasmic reticulum. The elevation of cytosolic Ca results in more Ca binding to calmodulin , which then binds and activates myosin light-chain kinase . The calcium-calmodulin-myosin light-chain kinase complex phosphorylates myosin on the 20 kilodalton (kDa) myosin light chains on amino acid residue-serine 19, enabling
13083-399: The fascicles can vary in their relationship to one another, and to their tendons. These variations are seen in fusiform , strap , and convergent muscles . A convergent muscle has a triangular or fan-shape as the fibers converge at its insertion and are fanned out broadly at the origin. A less common example of a parallel muscle is a circular muscle such as the orbicularis oculi , in which
13230-438: The fiber. When "type I" or "type II" fibers are referred to generically, this most accurately refers to the sum of numerical fiber types (I vs. II) as assessed by myosin ATPase activity staining (e.g. "type II" fibers refers to type IIA + type IIAX + type IIXA ... etc.). Below is a table showing the relationship between these two methods, limited to fiber types found in humans. Subtype capitalization
13377-461: The fibers are longitudinally arranged, but create a circle from origin to insertion. These different architectures, can cause variations in the tension that a muscle can create between its tendons. The fibers in pennate muscles run at an angle to the axis of force generation. This pennation angle reduces the effective force of any individual fiber, as it is effectively pulling off-axis. However, because of this angle, more fibers can be packed into
13524-593: The fibers of a skeletal muscle. It is thought that by performing endurance type events for a sustained period of time, some of the type IIX fibers transform into type IIA fibers. However, there is no consensus on the subject. It may well be that the type IIX fibers show enhancements of the oxidative capacity after high intensity endurance training which brings them to a level at which they are able to perform oxidative metabolism as effectively as slow twitch fibers of untrained subjects. This would be brought about by an increase in mitochondrial size and number and
13671-405: The flight muscles in these animals. These flight muscles are often called fibrillar muscles because they contain myofibrils that are thick and conspicuous. A remarkable feature of these muscles is that they do not require stimulation for each muscle contraction. Hence, they are called asynchronous muscles because the number of contractions in these muscles do not correspond (or synchronize) with
13818-473: The frequency of muscle action potentials increases such that the muscle contraction reaches its peak force and plateaus at this level, then the contraction is a tetanus . Length-tension relationship relates the strength of an isometric contraction to the length of the muscle at which the contraction occurs. Muscles operate with greatest active tension when close to an ideal length (often their resting length). When stretched or shortened beyond this (whether due to
13965-510: The great majority of skeletal muscle. Skeletal muscle myocytes are usually very large, being about 2–3 cm long and 100 μm in diameter. By comparison, the mononuclear cells in muscles are much smaller. Some of the mononuclear cells in muscles are endothelial cells (which are about 50–70 μm long, 10–30 μm wide and 0.1–10 μm thick), macrophages (21 μm in diameter) and neutrophils (12-15 μm in diameter). However, in terms of nuclei present in skeletal muscle, myocyte nuclei may be only half of
14112-403: The groups of muscles into muscle compartments. Two types of sensory receptors found in muscles are muscle spindles , and Golgi tendon organs . Muscle spindles are stretch receptors located in the muscle belly. Golgi tendon organs are proprioceptors located at the myotendinous junction that inform of a muscle's tension . Skeletal muscle cells are the individual contractile cells within
14259-475: The gut and blood vessels. Because these cells are linked together by gap junctions, they are able to contract as a functional syncytium . Single-unit smooth muscle cells contract myogenically, which can be modulated by the autonomic nervous system. Unlike single-unit smooth muscle cells, multiunit smooth muscle cells are found in the muscle of the eye and in the base of hair follicles. Multiunit smooth muscle cells contract by being separately stimulated by nerves of
14406-467: The higher end of any sport tend to demonstrate patterns of fiber distribution e.g. endurance athletes show a higher level of type I fibers. Sprint athletes, on the other hand, require large numbers of type IIX fibers. Middle-distance event athletes show approximately equal distribution of the two types. This is also often the case for power athletes such as throwers and jumpers. It has been suggested that various types of exercise can induce changes in
14553-407: The highly organized alternating pattern of A bands and I bands. Excluding reflexes, all skeletal muscle contractions occur as a result of signals originating in the brain. The brain sends electrochemical signals through the nervous system to the motor neuron that innervates several muscle fibers. In the case of some reflexes , the signal to contract can originate in the spinal cord through
14700-405: The human body, making up around 40% of body weight in healthy young adults. In Western populations, men have on average around 61% more skeletal muscle than women. Most muscles occur in bilaterally-placed pairs to serve both sides of the body. Muscles are often classed as groups of muscles that work together to carry out an action. In the torso there are several major muscle groups including
14847-440: The incompressible coelomic fluid forward and increasing the length of the animal. As a result, the front end of the animal moves forward. As the front end of the earthworm becomes anchored and the circular muscles in the anterior segments become relaxed, a wave of longitudinal muscle contractions passes backwards, which pulls the rest of animal's trailing body forward. These alternating waves of circular and longitudinal contractions
14994-399: The innervated muscle is called the latent period , which usually takes about 10 ms and is caused by the time taken for nerve action potential to propagate, the time for chemical transmission at the neuromuscular junction, then the subsequent steps in excitation-contraction coupling. If another muscle action potential were to be produced before the complete relaxation of a muscle twitch, then
15141-432: The inside of the sarcolemma are the unusual flattened myonuclei. Between the myofibrils are the mitochondria . While the muscle fiber does not have smooth endoplasmic cisternae, it contains sarcoplasmic reticulum . The sarcoplasmic reticulum surrounds the myofibrils and holds a reserve of the calcium ions needed to cause a muscle contraction. Periodically, it has dilated end sacs known as terminal cisternae . These cross
15288-407: The joint to equilibrium effectively increases the damping of the joint. Moreover, the strength of the damping increases with muscle force. The motor system can thus actively control joint damping via the simultaneous contraction (co-contraction) of opposing muscle groups. Smooth muscles can be divided into two subgroups: single-unit and multiunit . Single-unit smooth muscle cells can be found in
15435-430: The largest motor units having as much as 50 times the contractile strength as the smaller ones. As more and larger motor units are activated, the force of muscle contraction becomes progressively stronger. A concept known as the size principle, allows for a gradation of muscle force during weak contraction to occur in small steps, which then become progressively larger when greater amounts of force are required. Finally, if
15582-710: The length-tension relationship. Unlike skeletal muscle, the contractions of smooth and cardiac muscles are myogenic (meaning that they are initiated by the smooth or heart muscle cells themselves instead of being stimulated by an outside event such as nerve stimulation), although they can be modulated by stimuli from the autonomic nervous system . The mechanisms of contraction in these muscle tissues are similar to those in skeletal muscle tissues. Muscle contraction can also be described in terms of two variables: length and tension. In natural movements that underlie locomotor activity , muscle contractions are multifaceted as they are able to produce changes in length and tension in
15729-412: The load opposing its contraction. During a concentric contraction, a muscle is stimulated to contract according to the sliding filament theory . This occurs throughout the length of the muscle, generating a force at the origin and insertion, causing the muscle to shorten and changing the angle of the joint. In relation to the elbow , a concentric contraction of the biceps would cause the arm to bend at
15876-549: The long run. In rodents such as rats, the transitory nature of their muscle is highly prevalent. They have high percentage of hybrid muscle fibers and have up to 60% in fast-to-slow transforming muscle. Environmental influences such as diet, exercise and lifestyle types have a pivotal role in proportions of fiber type in humans. Aerobic exercise will shift the proportions towards slow twitch fibers, while explosive powerlifting and sprinting will transition fibers towards fast twitch. In animals, "exercise training" will look more like
16023-497: The major muscle groups to elicit strength and endurance adaptations." In the case of TENS, the current is usually sub-threshold, meaning that a muscle contraction is not observed. For people who have progressive diseases such as cancer or chronic obstructive pulmonary disease, EMS is used to improve muscle weakness for those unable or unwilling to undertake whole-body exercise. EMS may lead to statistically significant improvement in quadriceps muscle strength, however, further research
16170-402: The majority of muscle mass in the body and is responsible for locomotor activity. Smooth muscle forms blood vessels , the gastrointestinal tract , and other areas in the body that produce sustained contractions. Cardiac muscle makes up the heart, which pumps blood. Skeletal and cardiac muscles are called striated muscle because of their striped appearance under a microscope, which is due to
16317-425: The market, some have obtained FDA certification. Muscle contraction Muscle contraction is the activation of tension -generating sites within muscle cells . In physiology , muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as when holding something heavy in the same position. The termination of muscle contraction
16464-400: The modifications induced depend on the pattern of EMS activity. These patterns, referred to as protocols or programs, will cause a different response from contraction of different fiber types. Some programs will improve fatigue resistance, i.e. endurance, others will increase force production. Luigi Galvani (1761) provided the first scientific evidence that current can activate muscle. During
16611-431: The molecular interaction of myosin and actin, and initiating contraction and activating the myosin ATPase . Unlike skeletal muscle cells, smooth muscle cells lack troponin, even though they contain the thin filament protein tropomyosin and other notable proteins – caldesmon and calponin. Thus, smooth muscle contractions are initiated by the Ca -activated phosphorylation of myosin rather than Ca binding to
16758-471: The muscle contraction is described as isometric. If the muscle length changes while muscle tension remains the same, then the muscle contraction is isotonic. In an isotonic contraction, the muscle length can either shorten to produce a concentric contraction or lengthen to produce an eccentric contraction. In natural movements that underlie locomotor activity, muscle contractions are multifaceted as they are able to produce changes in length and tension in
16905-438: The muscle fiber from one side to the other. In between two terminal cisternae is a tubular infolding called a transverse tubule (T tubule). T tubules are the pathways for action potentials to signal the sarcoplasmic reticulum to release calcium, causing a muscle contraction. Together, two terminal cisternae and a transverse tubule form a triad . All muscles are derived from paraxial mesoderm . During embryonic development in
17052-443: The muscle is stretched – force increases above isometric maximum, until finally reaching an absolute maximum. This intrinsic property of active muscle tissue plays a role in the active damping of joints that are actuated by simultaneously active opposing muscles. In such cases, the force-velocity profile enhances the force produced by the lengthening muscle at the expense of the shortening muscle. This favoring of whichever muscle returns
17199-420: The myosin head pulls the actin filament toward the centre of the sarcomere. Following systole, intracellular calcium is taken up by the sarco/endoplasmic reticulum ATPase (SERCA) pump back into the sarcoplasmic reticulum ready for the next cycle to begin. Calcium is also ejected from the cell mainly by the sodium-calcium exchanger (NCX) and, to a lesser extent, a plasma membrane calcium ATPase . Some calcium
17346-472: The myosin head will again detach from actin and another cross-bridge cycle occurs. Cross-bridge cycling is able to continue as long as there are sufficient amounts of ATP and Ca in the cytoplasm. Termination of cross-bridge cycling can occur when Ca is actively pumped back into the sarcoplasmic reticulum. When Ca is no longer present on the thin filament, the tropomyosin changes conformation back to its previous state so as to block
17493-468: The neck that show a potential inverse trend of fiber type percentages (one muscle has high percentage of fast twitch, while the complementary muscle will have a higher percentage of slow twitch fibers). The complementary muscles of turtles had similar percentages of fiber types. Chimpanzee muscles are composed of 67% fast-twitch fibers and have a maximum dynamic force and power output 1.35 times higher than human muscles of similar size. Among mammals, there
17640-536: The need for long durations of movement or short explosive movements to escape predators or catch prey. Skeletal muscle exhibits a distinctive banding pattern when viewed under the microscope due to the arrangement of two contractile proteins myosin , and actin – that are two of the myofilaments in the myofibrils . The myosin forms the thick filaments, and actin forms the thin filaments, and are arranged in repeating units called sarcomeres . The interaction of both proteins results in muscle contraction. The sarcomere
17787-497: The neurotransmitter acetylcholine to fuse with the plasma membrane, releasing acetylcholine into the synaptic cleft between the motor neuron terminal and the neuromuscular junction of the skeletal muscle fiber. Acetylcholine diffuses across the synapse and binds to and activates nicotinic acetylcholine receptors on the neuromuscular junction. Activation of the nicotinic receptor opens its intrinsic sodium / potassium channel, causing sodium to rush in and potassium to trickle out. As
17934-465: The neurotransmitters epinephrine and norepinephrine, which bind to adrenergic receptors that are also metabotropic. The exact effects on the smooth muscle depend on the specific characteristics of the receptor activated—both parasympathetic input and sympathetic input can be either excitatory (contractile) or inhibitory (relaxing). There are two types of cardiac muscle cells: autorhythmic and contractile. Autorhythmic cells do not contract, but instead set
18081-417: The next twitch will simply sum onto the previous twitch, thereby producing a summation . Summation can be achieved in two ways: frequency summation and multiple fiber summation . In frequency summation , the force exerted by the skeletal muscle is controlled by varying the frequency at which action potentials are sent to muscle fibers. Action potentials do not arrive at muscles synchronously, and, during
18228-491: The nuclei present, while nuclei from resident and infiltrating mononuclear cells make up the other half. Considerable research on skeletal muscle is focused on the muscle fiber cells, the myocytes, as discussed in detail in the first sections, below. However, recently, interest has also focused on the different types of mononuclear cells of skeletal muscle, as well as on the endocrine functions of muscle, described subsequently, below. There are more than 600 skeletal muscles in
18375-471: The number of action potentials. For example, a wing muscle of a tethered fly may receive action potentials at a frequency of 3 Hz but it is able to beat at a frequency of 120 Hz. The high frequency beating is made possible because the muscles are connected to a resonant system, which is driven to a natural frequency of vibration. In 1780, Luigi Galvani discovered that the muscles of dead frogs' legs twitched when struck by an electrical spark. This
18522-409: The object from being dropped. In isotonic contraction , the tension in the muscle remains constant despite a change in muscle length. This occurs when a muscle's force of contraction matches the total load on the muscle. In concentric contraction, muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. This occurs when the force generated by the muscle exceeds
18669-612: The others. Most skeletal muscles in a human contain(s) all three types, although in varying proportions. Traditionally, fibers were categorized depending on their varying color, which is a reflection of myoglobin content. Type I fibers appear red due to the high levels of myoglobin. Red muscle fibers tend to have more mitochondria and greater local capillary density. These fibers are more suited for endurance and are slow to fatigue because they use oxidative metabolism to generate ATP ( adenosine triphosphate ). Less oxidative Type II fibers are white due to relatively low myoglobin and
18816-546: The pace of contraction for other cardiac muscle cells, which can be modulated by the autonomic nervous system. In contrast, contractile muscle cells (cardiomyocytes) constitute the majority of the heart muscle and are able to contract. In both skeletal and cardiac muscle excitation-contraction (E-C) coupling, depolarization conduction and Ca release processes occur. However, though the proteins involved are similar, they are distinct in structure and regulation. The dihydropyridine receptors (DHPRs) are encoded by different genes, and
18963-511: The process of somitogenesis the paraxial mesoderm is divided along the embryo 's length to form somites , corresponding to the segmentation of the body most obviously seen in the vertebral column . Each somite has three divisions, sclerotome (which forms vertebrae ), dermatome (which forms skin), and myotome (which forms muscle). The myotome is divided into two sections, the epimere and hypomere, which form epaxial and hypaxial muscles , respectively. The only epaxial muscles in humans are
19110-587: The properties of individual fibers—tend to be relevant and measured at the level of the motor unit, rather than individual fiber. Slow oxidative (type I) fibers contract relatively slowly and use aerobic respiration to produce ATP. Fast oxidative (type IIA) fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic respiration (glycolysis), can fatigue more quickly than slow oxidative fibers. Fast glycolytic (type IIX) fibers have fast contractions and primarily use anaerobic glycolysis. The FG fibers fatigue more quickly than
19257-413: The protein filaments within each skeletal muscle fiber slide past each other to produce a contraction, which is explained by the sliding filament theory . The contraction produced can be described as a twitch , summation, or tetanus, depending on the frequency of action potentials . In skeletal muscles, muscle tension is at its greatest when the muscle is stretched to an intermediate length as described by
19404-413: The ryanodine receptors). As ryanodine receptors open, Ca is released from the sarcoplasmic reticulum into the local junctional space and diffuses into the bulk cytoplasm to cause a calcium spark . The action potential creates a near synchronous activation of thousands of calcium sparks and causes a cell-wide increase in calcium giving rise to the upstroke of the calcium transient . The Ca released into
19551-459: The same functional purpose. Within the zebrafish embryo, the Prdm1 gene down-regulates the formation of new slow twitch fibers through direct and indirect mechanisms such as Sox6 (indirect). In mice, the Prdm1 gene is present but does not control slow muscle genes in mice through Sox6 . In addition to having a genetic basis, the composition of muscle fiber types is flexible and can vary with
19698-399: The same muscle volume, increasing the physiological cross-sectional area (PCSA). This effect is known as fiber packing, and in terms of force generation, it more than overcomes the efficiency-loss of the off-axis orientation. The trade-off comes in overall speed of muscle shortening and in the total excursion. Overall muscle shortening speed is reduced compared to fiber shortening speed, as is
19845-421: The short-term, strength training involving both eccentric and concentric contractions appear to increase muscular strength more than training with concentric contractions alone. However, exercise-induced muscle damage is also greater during lengthening contractions. During an eccentric contraction of the biceps muscle , the elbow starts the movement while bent and then straightens as the hand moves away from
19992-524: The size principal of motor unit recruitment viable. The total number of skeletal muscle fibers has traditionally been thought not to change. It is believed there are no sex or age differences in fiber distribution; however, proportions of fiber types vary considerably from muscle to muscle and person to person. Among different species there is much variation in the proportions of muscle fiber types. Sedentary men and women (as well as young children) have 45% type II and 55% type I fibers. People at
20139-432: The skeletal muscle cell for the large amounts of proteins and enzymes needed to be produced for the cell's normal functioning. A single muscle fiber can contain from hundreds to thousands of nuclei. A muscle fiber for example in the human biceps with a length of 10 cm can have as many as 3,000 nuclei. Unlike in a non-muscle cell where the nucleus is centrally positioned, the myonucleus is elongated and located close to
20286-526: The specific fiber type. In zebrafish embryos, the first muscle fibers to form are the slow twitch fibers. These cells will undergo migration from their original location to form a monolayer of slow twitch muscle fibers. These muscle fibers undergo further differentiation as the embryo matures. In larger animals, different muscle groups will increasingly require different fiber type proportions within muscle for different purposes. Turtles , such as Trachemys scripta elegans , have complementary muscles within
20433-399: The synaptic knob and none is left to replace the degraded acetylcholine. Excitation–contraction coupling (ECC) is the process by which a muscular action potential in the muscle fiber causes myofibrils to contract. In skeletal muscles, excitation–contraction coupling relies on a direct coupling between two key proteins, the sarcoplasmic reticulum (SR) calcium release channel identified as
20580-423: The total distance of shortening. All of these effects scale with pennation angle; greater angles lead to greater force due to increased fiber packing and PCSA, but with greater losses in shortening speed and excursion. Types of pennate muscle are unipennate , bipennate , and multipennate . A unipennate muscle has similarly angled fibers that are on one side of a tendon. A bipennate muscle has fibers on two sides of
20727-406: The transmission of force from muscle contraction to the skeletal system. Muscle architecture refers to the arrangement of muscle fibers relative to the axis of force generation , which runs from a muscle's origin to its insertion . The usual arrangements are types of parallel , and types of pennate muscle . In parallel muscles, the fascicles run parallel to the axis of force generation, but
20874-423: The tropomyosin-troponin complex again covers the binding sites on the actin filaments and contraction ceases. The strength of skeletal muscle contractions can be broadly separated into twitch , summation, and tetanus . A twitch is a single contraction and relaxation cycle produced by an action potential within the muscle fiber itself. The time between a stimulus to the motor nerve and the subsequent contraction of
21021-414: The troponin complex that regulates myosin binding sites on actin like in skeletal and cardiac muscles. Termination of crossbridge cycling (and leaving the muscle in latch-state) occurs when myosin light chain phosphatase removes the phosphate groups from the myosin heads. Phosphorylation of the 20 kDa myosin light chains correlates well with the shortening velocity of smooth muscle. During this period, there
21168-453: The two proteins. During the process of calcium-induced calcium release, RyR2s are activated by a calcium trigger, which is brought about by the flow of Ca through the L-type calcium channels. After this, cardiac muscle tends to exhibit diad structures, rather than triads . Excitation-contraction coupling in cardiac muscle cells occurs when an action potential is initiated by pacemaker cells in
21315-498: The use during pregnancy, menstruation, and other particular conditions that may be affected by muscle contractions; potential adverse effects include skin irritations and burns Only FDA-certified devices can be lawfully sold in the US without medical prescription. These can be found at the corresponding FDA webpage for certified devices. The FTC has cracked down on consumer EMS devices that made unsubstantiated claims; many have been removed from
21462-449: The various methods are mechanistically linked, while others are correlated in vivo . For instance, ATPase fiber type is related to contraction speed, because high ATPase activity allows faster crossbridge cycling . While ATPase activity is only one component of contraction speed, Type I fibers are "slow", in part, because they have low speeds of ATPase activity in comparison to Type II fibers. However, measuring contraction speed
21609-412: Was one of the first forays into the study of bioelectricity , a field that still studies the electrical patterns and signals in tissues such as nerves and muscles. In 1952, the term excitation–contraction coupling was coined to describe the physiological process of converting an electrical stimulus to a mechanical response. This process is fundamental to muscle physiology, whereby the electrical stimulus
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