question: Do the muscles of animals work the same as the muscles of humans in regards to growth?
comment: Their muscles are like ours, responsive to conditioning but limited by genetics. Sporting animals will have a different body composition compared to their couch potato counterparts. Their muscles also atrophy like ours, for example if casted after a break or retired from athletics. Source: none.
passages: The muscle characteristics of animals are similar in a wide range of animal sizes, though muscle sizes and shapes can and often do vary depending on environmental constraints placed on them. The muscle tissue itself maintains its contractile characteristics and does not vary depending on the size of the animal. Physiological scaling in muscles affects the number of muscle fibers and their intrinsic speed to determine the maximum power and efficiency of movement in a given animal. The speed of muscle recruitment varies roughly in inverse proportion to the cube root of the animal’s weight (compare the intrinsic frequency of the sparrow’s flight muscle to that of a stork).
   The linear bone resorption rate (M) cannot be measured directly, but it approximates a third of σ.
  
  Section::::Interspecies differences.
  
  Each vertebrate species exhibits a distinct duration of bone regeneration and remodeling, and it appears as though there is an inversely proportional relationship between the rate of bone regeneration and the phylogenetic evolution of the animal. Each remodeling period lasts 3–6 months in humans, 3 months in dogs, and 6 weeks in rabbits.
   Section::::Anatomy.
  
  Source:
  
  Section::::Anatomy.:Muscles.
  
  The following is a list of the muscles in the dog along with their origin, insertion, action and innervation.
  
  "Extrinsic muscles of the thoracic limb and related structures:"
  
  Descending superficial pectoral: originates on the first sternebrae and inserts on the greater tubercle of the humerus. It both adducts the limb and also prevents the limb from being abducted during weight bearing. It is innervated by the cranial pectoral nerves.
   Deep research into the anatomy of large mammals such as, kangaroos and other large ungulates such as deer and gazelle, suggests strongly that some sort of elastic mechanism is important for this energetic savings. Previous combination of careful experiments, with anatomical (e.g. tendon dimensions), mechanical (e.g. force plate recordings) and mathematical calculations revealed that a significant fraction of the work done with each step could be provided by the spring-like action of tendons, rather than by muscle work.
   Section::::Strength changes.
   Sauropodomorphs reached the age of sexual maturity well before they were fully-grown adults. A study by Griebeler "et al." (2013) concluded that the maximum growth rates of sauropodomorphs were comparable to those of precocial birds and the black rhinoceros but lower than the growth rates of average mammals.
   While the research on muscle fiber remodeling is on-going, there are generally accepted facts about the myofilament from the American College of Sports Medicine. It is thought that an increase in muscle strength is due to an increase in muscle fiber size, not an increase in number of muscle fibers and myofilaments. However, there is some evidence of animal satellite cells differentiating into new muscle fibers and not merely providing a support function to muscle cells.
   Naturally occurring deficiencies of myostatin of various sorts have been identified in some breeds of cattle, sheep, whippets, and humans. In each case the result is a dramatic increase in muscle mass.
  
  Section::::Structure and mechanism of action.
   Some writers suggest "M. ferox" could grow to the size of a black bear, whilst others suggest a less exceptional mass of , compared to the wolverine of . "Ekorus ekakeran", a comparable mustelid of the same period found in Africa, is estimated to have been around . Matthew described it as having short stout legs, with short feet and long non-retractible claws, similar to a modern wolverine but about twice the size, and noted that "the teeth indicate an animal fully as predaceous as the wolverine, but the skeleton points to more fossorial habits". Research comparing the joints of the forelegs to modern mammalian carnivores suggests that it waited in ambush and grappled with its prey, rather than hunting it down by pursuit like a modern cheetah.
   Thus, it is apparent that skeletal muscle fibers of humans, monkeys, and rodents share similar patterns of myofiber alterations that, in the case of monkeys and humans, are also linked to altered motor performance in response to different states of unloading, reduced usage, and return to an Earth gravitational environment.
  
  Section::::Computer-based simulation information.
   While microbats only have claws on the thumbs of their forelimbs, most megabats have a clawed second digit as well; only "Eonycteris", "Dobsonia", "Notopteris", and "Neopteryx" lack the second claw. The first digit is the shortest, while the third digit is the longest. The second digit is incapable of flexion. Megabats' thumbs are longer relative to their forelimbs than those of microbats.
   Neoteny is not a ubiquitous trait of the human phenotype. Human expression timing, compared to chimpanzee, has a completely different trajectory uncovering that there is no uniform shift in developmental timing. Humans undergo this neotenous shift once sexual maturity is reached. A question prompted by the Mehmet Somel et al. study, is whether or not human-specific neotonic changes are indicative of human- specific cognitive traits. The tracking of where developmental landmarks occur in humans and other primates is a step towards a better understanding of how neoteny manifests specifically in our species and how it may contribute to our specialized features, such as smaller jaws. In humans, the neotonic shift is concentrated around a group of gray matter genes. This shift in neotonic genes also coincides with cortical reorganization that is related to synaptic elimination and is at a much more rapid pace over others during adolescence. It is also linked to the development of linguistic skills and the development of certain neurological disorders like ADHD.
   Section::::Animal models.:Muscle Development and Other Regulation.
   A male standing erect can be up to tall and weigh up to . Males have an average weight of , females of . Males in captivity, however, are noted to be capable of reaching weights up to . Males stand upright at , females at . According to the late John Aspinall a silverback gorilla in his prime has the physical strength of seven or eight Olympic weightlifters, but this claim is unverified. Western gorillas frequently stand upright, but walk in a hunched, quadrupedal fashion, with hands curled and knuckles touching the ground. This style of movement requires long arms, which works for western gorillas because the arm span of gorillas is larger than their standing height.
   It is important to take under consideration that metabolic benefits of elastic structures are probably most apparent for larger animals, rather than small organisms such as insects. This results from a simple fact, that larger animals can exert much higher forces on their tendons and ligaments during movement, compared to small animals.
  
  Section::::Elastic mechanisms for power attenuation.
   A 2017 study indicates that juveniles were born with a robust build similar to the adults. Comparison of the bones of juvenile "S. fatalis" specimens from La Brea with those of the contemporaneous American lion revealed that the two cats shared a similar growth curve. Felid forelimb development during ontogeny (changes during growth) has remained tightly constrained. The curve is similar to that for modern cats such as tigers and cougars, but shifts more towards the robust direction of the axes than is seen in modern felids.
  
  Section::::Paleobiology.:Paleopathology.
   Uncommon in human anatomy, the levator claviculae is nearly always present in most other mammals — including gibbons, orangutans, and chimpanzees. There are yet no phylogenetic explanations for its absence in humans.
  
  Section::::History.
   The MYF6 gene is physically linked to the MYF5 gene on chromosome 12, and similar linkage is observed in all vertebrates. Mutations in the mouse Myf6 gene typically exhibit reduced levels of Myf5. Despite reductions in muscle mass of the back and defective rib formation, Myf6 mutants still exhibit fairly normal skeletal muscle. This demonstrates that Myf6 is not essential for the formation of most myofibers, at least in the strains of mice tested.
  
  In zebrafish, Myf6/Mrf4 is expressed in all terminally differentiated muscle examined, but expression has not been reported in muscle precursor cells.
  
  Section::::Clinical significance.
   While the exact mechanism of myofilament alteration in response to exercise is still being studied in mammals, some interesting clues have been revealed in Thoroughbred race horses. Researchers studied the presence of mRNA in skeletal muscle of horses at three distinct times; immediately before training, immediately after training, and four hours after training. They reported statistically significant differences in mRNA for genes specific to production of actin. This study provides evidence of the mechanisms for both immediate and delayed myofilament response to exercise at the molecular level.
   Section::::Form.:Insertion and origin.:Insertion.
  
  The "insertion" of a muscle is the structure that it attaches to and tends to be moved by the contraction of the muscle. This may be a bone, a tendon or the subcutaneous dermal connective tissue. Insertions are usually connections of muscle via tendon to bone. The insertion is a bone that tends to be distal, have less mass, and greater motion than the origin during a contraction.
  
  Section::::Form.:Muscle fibres.
  
  Muscles may also be described by the direction that the muscle fibres run in.
   More recently, myofilament protein changes have been studied in humans in response to resistance training. Again, researchers are not completely clear about the molecular mechanisms of change, and an alteration of fiber-type composition in the myofilament may not be the answer many athletes have long assumed. This study looked at the muscle specific tension in the quadriceps femoris and vastus lateralis of forty-two young men. Researchers report a 17% increase in specific muscle tension after a period of resistance training, despite a decrease in the presence of MyHC, myosin heavy-chain. This study concludes that there is no clear relationship between fiber-type composition and in vivo muscle tension, nor was there evidence of myofilament packing in the trained muscles.
   Both the architecture and type of muscle play a crucial role in determining foot contact time and production of GRF. In humans, it has been shown that sprinters have longer muscle fascicle lengths and smaller pennation angles than non-sprinters. This contributes by increasing the muscle's shortening velocity. Other studies have shown that particular muscle fiber types are favored in sprinters versus non-sprinters, as well as within different levels of sprinters. Faster individuals tend to have a greater percentage of Type II (fast-twitch) muscle fibers. Higher percentage of fast-twitch muscle fibers lead to increased force production capability, as well as increased speed of contractions leading to shorter contact times.
   The muscles used in elongation and shortening maintain support through the constant volume principle and their antagonistic relationships with each other. These mechanisms are seen often in prey capture of shovelnose frogs and chameleons, as well as in the human tongue and many other examples. In some frogs, the tongue elongates up to 180% of its resting length. Extra-oral tongues show higher length/width ratios than intra-oral tongues, allowing for a greater increase in length (more than 100% of resting length, as compared to intra-oral tongues at only about 50% of resting length increase). Greater elongation lengths trade off with the force produced by the organ; as the length/width ratio is increased elongation increases while force is decreased. Squids have been shown to use muscular hydrostat elongation in prey capture and feeding as well.
   Section::::Mode of action.:Feed enzymes.
  
  Animal feeds contain varying levels of indigestible nutrients and undesired components such as fiber, phytate or proteins with antigenic effects. Different feed enzymes such as, carbohydrases, phytases or proteases, can be included in feeds to improve the utilization of energy and nutrients or to degrade several undesired components. Moreover, some enzymes (e.g. amylases, lipases) can be added to the feed of young animals in order to support the endogenous enzyme secretions.
  
  Section::::Mode of action.:Immune stimulants.
   Compared to our closest living relatives, chimpanzees and bonobos, Homo sapiens' skeletal muscle is on average about 1.35 to 1.5 times weaker when normalized for size. As little biomechanical difference was found between individual muscle fibers from the different species, this strength difference is likely the result of different muscle fiber type composition. Humans' limb muscles tend to be more biased toward fatigue-resistant, slow twitch Type I muscle fibers. While there is no proof that modern humans have become physically weaker than past generations of humans, inferences from such things as bone robusticity and long bone cortical thickness can be made as a representation of physical strength. Taking such factors into account, there has been a rapid decrease in overall robusticity in those populations that take to sedentism. For instance, bone shaft thickness since the 17th and 18th centuries have decreased in the United States, indicating a less physically stressful life. This is not, however, the case for current hunter gatherer and foraging populations, such as the Andaman Islanders, who retain overall robusticity. In general, though, hunter gatherers tend to be robust in the legs and farmers tend to be robust in the arms, representing different physical load (i.e., walking many miles a day versus grinding wheat).
  