Skeletal 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 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.
Muscle memory is a form of procedural memory that involves consolidating a specific motor task into memory through repetition, which has been used synonymously with motor learning. When a movement is repeated over time, the brain creates a long-term muscle memory for that task, eventually allowing it to be performed with little to no conscious effort. This process decreases the need for attention and creates maximum efficiency within the motor and memory systems. Muscle memory is found in many everyday activities that become automatic and improve with practice, such as riding bikes, driving motor vehicles, playing ball sports, typing on keyboards, entering PINs, playing musical instruments, poker, martial arts, swimming, dancing, and drawing.
A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). A skeletal muscle cell is long and threadlike with many nuclei and is called a muscle fiber. Muscle cells develop from embryonic precursor cells called myoblasts.
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations, poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, excessive amount of apoptosis of cells, and disuse or lack of exercise or disease intrinsic to the tissue itself. In medical practice, hormonal and nerve inputs that maintain an organ or body part are said to have trophic effects. A diminished muscular trophic condition is designated as atrophy. Atrophy is reduction in size of cell, organ or tissue, after attaining its normal mature growth. In contrast, hypoplasia is the reduction in the cellular numbers of an organ, or tissue that has not attained normal maturity.
Muscle fatigue is when muscles that were initially generating a normal amount of force, then experience a declining ability to generate force. It can be a result of vigorous exercise, but abnormal fatigue may be caused by barriers to or interference with the different stages of muscle contraction. There are two main causes of muscle fatigue: the limitations of a nerve’s ability to generate a sustained signal ; and the reduced ability of the muscle fiber to contract.
20-Hydroxyecdysone is a naturally occurring ecdysteroid hormone which controls the ecdysis (moulting) and metamorphosis of arthropods. It is therefore one of the most common moulting hormones in insects, crabs, etc. A phytoecdysteroid produced by various plants, including Cyanotis vaga, Ajuga turkestanica and Rhaponticum carthamoides, its purpose is presumably to disrupt the development and reproduction of insect pests. In arthropods, 20-hydroxyecdysone acts through the ecdysone receptor. Although mammals lack this receptor, 20-hydroxyecdysone affects mammalian biological systems. 20-Hydroxyecdysone is an ingredient of some supplements that aim to enhance physical performance. In humans, it is hypothesized to bind to the estrogen receptor beta (ERβ) protein-coding gene.
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 is followed by muscle relaxation, which is a return of the muscle fibers to their low tension-generating state.
Strength training, also known as weight training or resistance training, involves the performance of physical exercises that are designed to improve physical strength. It is often associated with the lifting of weights. It can also incorporate a variety of training techniques such as bodyweight exercises, isometrics, and plyometrics.
Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,400 metres (8,000 ft) above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations. At intermediate altitudes, the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced.
Myosatellite cells, also known as satellite cells, muscle stem cells or MuSCs, are small multipotent cells with very little cytoplasm found in mature muscle. Satellite cells are precursors to skeletal muscle cells, able to give rise to satellite cells or differentiated skeletal muscle cells. They have the potential to provide additional myonuclei to their parent muscle fiber, or return to a quiescent state. More specifically, upon activation, satellite cells can re-enter the cell cycle to proliferate and differentiate into myoblasts.
Sarcopenia is a type of muscle loss that occurs with aging and/or immobility. It is characterized by the degenerative loss of skeletal muscle mass, quality, and strength. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. The muscle loss is related to changes in muscle synthesis signalling pathways. It is distinct from cachexia, in which muscle is degraded through cytokine-mediated degradation, although the two conditions may co-exist. Sarcopenia is considered a component of frailty syndrome. Sarcopenia can lead to reduced quality of life, falls, fracture, and disability.
Myofilaments are the three protein filaments of myofibrils in muscle cells. The main proteins involved are myosin, actin, and titin. Myosin and actin are the contractile proteins and titin is an elastic protein. The myofilaments act together in muscle contraction, and in order of size are a thick one of mostly myosin, a thin one of mostly actin, and a very thin one of mostly titin.
Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness and causes disability.
Performance-enhancing substances (PESs), also known as performance-enhancing drugs (PEDs), are substances that are used to improve any form of activity performance in humans.
Muscle hypertrophy or muscle building involves a hypertrophy or increase in size of skeletal muscle through a growth in size of its component cells. Two factors contribute to hypertrophy: sarcoplasmic hypertrophy, which focuses more on increased muscle glycogen storage; and myofibrillar hypertrophy, which focuses more on increased myofibril size. It is the primary focus of bodybuilding-related activities.
Anabolic steroids, also known as anabolic-androgenic steroids (AAS), are a class of drugs that are structurally related to testosterone, the main male sex hormone, and produce effects by binding to the androgen receptor (AR). Anabolic steroids have a number of medical uses, but are also used by athletes to increase muscle size, strength, and performance.
The metabolic window is a term used in strength training to describe the 2 hour period after exercise during which nutrition can shift the body from a catabolic state to an anabolic one. Specifically, it is during this period that the intake of protein and carbohydrates can aid in the increase of muscle mass.
A myokine is one of several hundred cytokines or other small proteins and proteoglycan peptides that are produced and released by skeletal muscle cells in response to muscular contractions. They have autocrine, paracrine and/or endocrine effects; their systemic effects occur at picomolar concentrations.
Trenbolone enanthate, known by the nickname Trenabol, is a synthetic and injected anabolic–androgenic steroid (AAS) and a derivative of nandrolone which was never marketed. It is the C17β enanthate ester and a long-acting prodrug of trenbolone. Trenbolone enanthate was never approved for medical or veterinary use but is used in scientific research and has been sold on the internet black market as a designer steroid for bodybuilders and athletes.
Epigenetics of physical exercise is the study of epigenetic modifications to the cell genome resulting from physical exercise. Environmental factors, including physical exercise, have been shown to have a beneficial influence on epigenetic modifications. Generally, it has been shown that acute and long-term exercise has a significant effect on DNA methylation, an important aspect of epigenetic modifications.
