Dominic Stone
The endocrine system releases hormones during and after the production of muscular force. These hormones, such as epinephrine, help muscles produce force. Skeletal muscle is an endocrine organ that releases molecules called myokines, which act in a hormone-like fashion. Myokines are released during strength training and help fight inflammation, cancer, diabetes, and osteoporosis. They also play a role in muscle crosstalk with other tissues and controlling whole-body homeostasis. Additionally, skeletal muscle produces Brain-Derived Neurotrophic Factor (BDNF), which is involved in promoting muscle fiber fat oxidation and muscle development. Furthermore, resistance exercise increases the concentration of anabolic hormones in the blood, such as testosterone and growth hormones, leading to greater increases in strength and muscle size.
| Characteristics | Values |
|---|---|
| Do muscles produce hormones? | Skeletal muscle produces and releases molecules called myokines that act in a hormone-like fashion. |
| What are myokines? | Myokines are muscle-derived factors that have beneficial effects on peripheral and remote organs. |
| What are the important types of myokines? | Interleukin (IL)-6, IL-8, IL-15, Brain-Derived Neurotrophic Factor (BDNF), and Leukemia Inhibitory Factor (LIF). |
| How do myokines help? | Myokines help to fight inflammation, cancer, diabetes, osteoporosis, and cardiovascular disease. |
| How does exercise influence myokine production? | Physical activity and exercise influence the production and balance of myokines, reducing the risk of chronic diseases. |
| How do hormones influence muscle contraction? | Hormones like epinephrine help muscles produce force, while testosterone and growth hormones stimulate muscle protein synthesis and growth. |
| How does resistance exercise impact hormone levels? | Resistance exercise increases the concentration of anabolic hormones in the blood during and after exercise, leading to greater muscle strength and size gains. |
| What is the role of skeletal muscle? | Skeletal muscle plays a role in posture, locomotion, and energy production and consumption, influencing whole-body energy metabolism. |
| How does aging affect muscle hormone production? | Aging leads to a decline in muscle quantity and quality (sarcopenia), impacting the balance between anabolic and catabolic factors. |
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What You'll Learn
Skeletal muscle is an endocrine organ
The endocrine system releases hormones during and after the production of muscular force. For example, the hormone epinephrine helps muscles produce force, while hormones like testosterone stimulate muscle protein synthesis and growth. Resistance exercise increases the concentration of anabolic hormones in the blood during and after exercise.
Skeletal muscle has been identified as a secretory organ that releases myokines, which are proteins released by muscle cells in response to contractions. Myokines act in an autocrine, paracrine, or endocrine hormone-like fashion. They have been shown to exert beneficial effects on peripheral and remote organs, including the liver, pancreas, and adipose tissue. The secretion of myokines may also lead to a new pharmacological approach for the treatment of clinical disorders.
The dynamic balance between anabolic and catabolic status in human skeletal muscle is related to various factors, such as mechanical and nervous stimuli, age, hormonal changes, and nutrient intake. This balance deteriorates with aging, leading to sarcopenia, an age-related decline in muscle quantity and quality. Physical activity and exercise play a crucial role in maintaining muscle health and preventing sarcopenia.
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Myokines are released during strength training
Skeletal muscle is an endocrine organ that releases myokines, which are cytokines and other peptides produced, expressed, and released by muscle fibres. Myokines are released during strength training and mediate communication between muscle and other organs, including the brain, adipose tissue, bone, liver, gut, pancreas, vascular bed, and skin, as well as within the muscle itself. They exert their effects on, for example, cognition, lipid and glucose metabolism, browning of white fat, bone formation, endothelial cell function, hypertrophy, skin structure, and tumour growth.
Different muscle fibre types, including slow-twitch, oxidative, intermediate twitch, and fast-twitch muscle fibres, release different clusters of myokines during contraction. This implies that varying the types of exercise, particularly aerobic training, endurance training, and muscle contraction against resistance (strength training), may offer differing myokine-induced benefits. For example, endurance training has been shown to increase circulating FGF-21 levels, which has anti-diabetic effects by stimulating glucose transport in adipose tissue and increasing energy expenditure and insulin sensitivity.
Myostatin, LIF, IL-6, and IL-7 are involved in muscle hypertrophy and myogenesis, while BDNF and IL-6 are involved in AMPK-mediated fat oxidation. BDNF, in particular, has been shown to regulate neuronal development and modulate synaptic plasticity, with studies demonstrating improved memory and learning in response to exercise. Decorin is another myokine secreted during muscular contraction against resistance, which plays a role in muscle growth.
In summary, myokines released during strength training have a broad range of effects on the body, including improving metabolic health, enhancing cognitive function, and promoting muscle growth. Further research into the specific roles of myokines may lead to the development of new therapeutic targets and pharmacological approaches for treating clinical disorders.
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Testosterone and muscle growth
Testosterone is a hormone that is vital for building and maintaining muscle mass. It is produced primarily in the testicles of men and the ovaries and adrenal glands of women, although men tend to produce more of it. Testosterone levels are positively correlated with muscle protein synthesis, which means that higher testosterone levels lead to increased muscle growth and development.
Testosterone plays a crucial role in muscle recovery by reducing muscle damage and inflammation following intense exercise, which promotes faster recovery and prevents muscle breakdown. It also increases the number of receptors on muscle cells that bind to other anabolic hormones, such as insulin-like growth factor 1 (IGF-1), further enhancing its muscle-building effects. Testosterone affects the type of muscle fibres in the body, with fast-twitch fibres being better for explosive movements and weightlifting as they generate more force. Higher testosterone levels are associated with an increased number of fast-twitch muscle fibres.
The amount of anabolic hormones in the blood, such as testosterone and growth hormone (GH), increases when a large amount of muscle is exercised. This leads to greater strength training gains and increased muscle size. Resistance exercise naturally increases the concentration of anabolic hormones in the blood during exercise and for approximately one hour afterward. Testosterone stimulates muscle cells to produce more protein, which promotes muscle growth and repair.
While testosterone is an important factor in muscle growth and development, it is not the only factor. Proper nutrition, adequate rest, and a well-designed training programme are also essential for achieving optimal results. Testosterone levels in men naturally start to decline after the age of 30, and this can lead to decreased muscle mass and increased body fat. However, the rate of decline varies from person to person, and some men experience a more significant decrease in testosterone levels than others.
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Muscle-controlled synthesis and degradation of metabolites
Skeletal muscle is an endocrine organ that plays a key role in the human body's physical activities, such as locomotion and postural retention. It also acts as an energy production and consumption system, influencing the body's overall energy metabolism. The growth or loss of skeletal muscle mass can impact metabolism, locomotion, eating habits, and respiration. Therefore, excessive muscle loss can be a negative prognostic indicator for various diseases, including cancer, organ failure, infections, and unhealthy ageing.
Muscle protein synthesis (MPS) is a metabolic process that involves incorporating amino acids into skeletal muscle proteins. The synthesis of myofibrillar proteins, such as myosin, actin, tropomyosin, and troponin, is primarily responsible for changes in skeletal muscle mass following resistance training. On the other hand, mitochondrial proteins are synthesized in response to endurance-type training. MPS can be measured through various methods, including the precursor-product method, which determines the muscle protein fractional synthesis rate (FSR).
The balance between anabolic and catabolic factors is crucial for skeletal muscle health. This balance is influenced by factors such as mechanical and nervous stimuli, age, hormonal changes, and nutrient intake. Age-related muscle loss, known as sarcopenia, is characterized by a decline in muscle quantity and quality, leading to a gradual slowing of movement and increased risk of injuries. However, exercise and nutrition can help combat muscle loss and improve muscle function.
Testosterone, produced primarily in the testes in men and the adrenal glands in women, significantly impacts human physiology and tissue growth. During resistance exercise, testosterone binds to receptors inside muscle cells, signaling increased protein synthesis and muscle fiber growth. Additionally, muscle contractions stimulate the release of growth hormones (GH) from the pituitary gland, which can act directly on skeletal muscle and stimulate the production of insulin-like growth factors (IGF) in the liver and muscles.
The gut microbiota also plays a role in muscle metabolism by generating metabolites like amino acids (glycine and alanine) and the neurotransmitter precursor choline, which positively regulate muscle mass. Urolithin A, a metabolite found in pomegranates, nuts, and berries, has been shown to improve muscle function in ageing by activating mitophagy and exhibiting anti-inflammatory properties.
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The anti-inflammatory effects of exercise
Physical inactivity leads to the accumulation of visceral fat, which activates inflammatory pathways in the body. This chronic inflammation is associated with the development of insulin resistance, atherosclerosis, neurodegeneration, and tumour growth, and subsequently, a range of diseases.
The anti-inflammatory effect of regular exercise may be twofold: it can reduce visceral fat mass, thereby decreasing the release of adipokines, and it can induce an anti-inflammatory environment with each session of exercise. This anti-inflammatory environment includes the release of interleukin-6 (IL-6) from contracting muscle fibres, which stimulates the appearance of other anti-inflammatory cytokines such as IL-1ra and IL-10, and inhibits the production of pro-inflammatory cytokines like TNF-alpha. IL-6 also enhances lipid turnover, stimulating lipolysis and fat oxidation.
Other mechanisms by which exercise exerts its anti-inflammatory effects include increased circulating numbers of IL-10-secreting regulatory T cells, downregulation of Toll-like receptor expression on monocytes, reduction in circulating numbers of pro-inflammatory monocytes, and inhibition of monocyte and/or macrophage infiltration into adipose tissue.
In summary, the anti-inflammatory effects of exercise are multifaceted and have been shown to have a positive impact on health, providing protection against a range of diseases associated with physical inactivity and chronic inflammation.
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Frequently asked questions
Yes, muscles produce hormones. When muscles are worked, they release hormones called myokines, which have anti-inflammatory effects and help fight cancer, diabetes, and osteoporosis.
Myokines are molecules produced by skeletal muscles that act in an autocrine, paracrine, or endocrine hormone-like fashion. The most important of these substances are interleukin (IL)-6, IL-8, IL-15, Brain-Derived Neurotrophic Factor (BDNF), and Leukemia Inhibitory Factor (LIF).
Myokines have been shown to have multiple health benefits, including reducing the risk of cardiovascular disease, type 2 diabetes, cancer, dementia, and depression. They also play a role in regulating whole-body homeostasis and metabolism.
Physical activity and exercise training have been shown to increase myokine production and improve human health. Resistance exercise, in particular, increases the concentration of anabolic hormones in the blood during and after exercise, leading to greater increases in strength and muscle size.
Other hormones involved in muscle contraction include testosterone, growth hormone (GH), and insulin-like growth factor (IGF). These hormones stimulate muscle protein synthesis, regeneration, and growth.
