Victor Forge
The endocrine system uses hormones to control and coordinate the body's internal metabolism, energy levels, reproduction, growth, development, and response to injury, stress, and environmental factors. Hormones are released by most tissues and glands in the body. When muscles are exercised, they release hormones called myokines, which help fight inflammation, cancer, diabetes, and osteoporosis. The amount of anabolic hormones in the blood increases when a large amount of muscle is exercised. These hormones include testosterone, which is produced primarily in the testes in men, and growth hormone (GH), which is produced by the pituitary gland.
| Characteristics | Values |
|---|---|
| Do muscles release hormones? | Yes, muscles release hormones called myokines during strength training |
| What are myokines? | Myokines are hormones that help fight inflammation, cancer, diabetes, and osteoporosis |
| What type of hormones are released by muscles? | Anabolic hormones, including testosterone, GH, and IGF-1 |
| How does testosterone affect muscle growth? | Testosterone binds to androgen receptors inside muscle cells, signaling an increase in protein synthesis and muscle fiber size |
| How does GH affect muscle growth? | GH binds to receptors on target cell membranes, stimulating genetic machinery and acting directly on skeletal muscle |
| How does IGF-1 affect muscle growth? | IGF-1 is triggered by growth hormone and increases in the blood immediately after exercise, contributing to muscle protein synthesis |
| How does resistance exercise impact anabolic hormone release? | Resistance exercise with large muscle groups and moderate-to-high intensity increases GH, IGF-1, and testosterone levels, enhancing muscle hypertrophy and strength gains |
| What is sarcopenia? | Sarcopenia is an age-related decline in skeletal muscle mass and quality, leading to physical impairment and an increased risk of injuries |
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What You'll Learn
Resistance exercise increases growth hormone
Resistance exercise has been shown to cause a significant acute hormonal response, which is more critical to tissue growth and remodelling than chronic changes in resting hormonal concentrations. This is because resistance exercise stimulates growth hormone (GH) secretion in a load-dependent manner, with heavier loads producing larger GH responses.
Research has shown that low-load resistance exercise (RE) performed with blood flow restriction (BFR) produces potent GH responses that are similar to or exceed those produced following high-load RE. This is hypothesized to be due to the decreased venous outflow during BFR reducing the clearance of metabolic acidosis, resulting in the activation of proton-activated nociceptors and pain receptors, which are known to regulate GH secretion through stimulation of opioid receptors.
The GH response to RE is also dependent on age, with older individuals exhibiting a 4-7 fold reduction in GH secretion compared to younger individuals. Additionally, the magnitude of GH release is greater in young women than in young men. However, it is important to note that exercise interventions may not restore GH secretion to levels observed in young, healthy individuals.
The increase in GH secretion following RE is part of a group of hormones known as anabolic (building-up) hormones, which also includes insulin-like growth factor-1 (IGF-1) and testosterone. These hormones work together to increase muscle growth and strength. IGF-1, in particular, triggers a chain of events that leads to increased protein synthesis in the muscle.
In summary, resistance exercise increases growth hormone secretion, which is important for muscle growth and strength gains, especially when combined with other anabolic hormones such as IGF-1 and testosterone.
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Testosterone and muscle growth
Testosterone is a hormone that plays a critical role in muscle growth and development. It is a male sex hormone, produced primarily in the testes of men and the adrenal glands of women, although men tend to produce more of it. Testosterone levels are positively correlated with muscle protein synthesis, meaning that higher testosterone levels lead to increased muscle growth. This occurs through the stimulation of muscle cells to produce more protein, which promotes muscle growth and repair. Testosterone 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.
The role of testosterone in muscle growth is particularly significant during adolescence and early adulthood when testosterone production is at its peak. After the age of 30, testosterone levels naturally begin to decline, leading to a decrease in muscle mass. This decline in testosterone levels and muscle mass can be counteracted to some extent through proper nutrition and exercise. Strength training and multi-joint exercises, such as squats, deadlifts, and chest and shoulder presses, are particularly effective in building muscle mass. These types of exercises activate large muscle groups, releasing growth hormones and stimulating protein production, similar to the effects of testosterone.
The relationship between testosterone and muscle growth is further evidenced by studies showing that higher testosterone levels are associated with increased energy and endurance during workouts. This enables individuals with higher testosterone levels to train harder and longer, resulting in greater gains in muscle mass and strength. Additionally, testosterone plays a vital role in muscle recovery by reducing muscle damage and inflammation following intense exercise, which promotes faster recovery and prevents muscle breakdown.
While testosterone is a key factor in muscle growth, it is not the sole determinant. Other factors, such as proper nutrition, adequate rest, and a well-designed training program, are also essential for achieving optimal muscle growth and development. Furthermore, the dynamic balance between anabolic and catabolic factors in skeletal muscle influences muscle vitality and trophism. This balance is affected by various factors, including mechanical and nervous stimuli, age, hormonal changes, and nutrient intake.
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Myokines and their health benefits
Myokines are small proteins or peptides produced and released by skeletal muscle cells in response to muscular contractions. They have endocrine, autocrine, and paracrine effects, and their receptors are found in various organs and tissues, including the brain, liver, heart, and bones. The discovery of myokines has provided a biological explanation for the health benefits of exercise, particularly in reducing inflammation and the risk of chronic diseases.
Health Benefits of Myokines:
Exercise-Associated Metabolic Changes:
Myokines play a crucial role in exercise-induced metabolic changes. For example, interleukin-6 (IL-6) is a myokine that increases up to 100 times during exercise. IL-6 has an anti-inflammatory effect when released by muscles, reducing the production of pro-inflammatory compounds. This anti-inflammatory action may contribute to the beneficial effects of exercise in reducing the risk of chronic diseases such as cardiovascular disease, type 2 diabetes, cancer, and dementia.
Tissue Regeneration and Repair:
Myokines are involved in tissue regeneration and repair. For instance, IL-6 has a positive impact on muscle stem cell proliferation, aiding in muscle regeneration and hypertrophic growth. This mechanism ensures the availability of sufficient muscle progenitors during muscle regeneration and growth.
Brain Health:
Myokines also influence brain health. Animal studies suggest that cathepsin B, a myokine released during running, enters the bloodstream and stimulates the release of brain-derived neurotrophic factor (BDNF). BDNF helps brain cells grow and survive, enhancing learning and memory. Another myokine, irisin, may also increase BDNF levels in the brain.
Bone Health:
Myokines are believed to play a role in bone health, although much of the research in this area is still in its early stages. A novel myokine called osteonectin or SPARC (secreted protein acidic and rich in cysteine) is known to be vital for bone mineralization and cell-matrix interactions.
Immunomodulation:
Myokines participate in immunomodulation, influencing the immune system's function. The release of IL-6 by muscles, for example, can help regulate energy metabolism and control metabolic functions, including glucose production.
While the specific mechanisms are still being investigated, myokines provide a compelling explanation for the health benefits of physical activity. Understanding the role of these muscle-derived compounds may lead to further insights into disease prevention and treatment.
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IGF-1 and protein synthesis
Skeletal muscles do produce and release myokines, which work in a hormone-like fashion and exert specific endocrine effects on visceral fat. These myokines are released when the skeletal muscles contract.
Insulin-like growth factor 1 (IGF-1) is a small peptide structurally bound by 70 amino acids. It is a part of the superfamily of polypeptides that has evolved as a group of hormones and binding proteins with potent anabolic functions related to growth and health. IGF-1 stimulates protein synthesis and inhibits protein breakdown in skeletal muscle. The anabolic effects of IGF-1 are seen in muscles from burned and unburned rats, where IGF-1 stimulated protein synthesis and inhibited protein breakdown in a dose-dependent fashion. The maximal effect of IGF-1 on protein synthesis was observed at a hormone concentration of 100 ng/mL.
The liver is the organ chiefly responsible for the production of serum IGF-1. However, IGF-1 is also produced in the muscles. The mechanisms that underpin anabolic resistance to anabolic stimuli (protein and resistance exercise) are multifactorial and may be driven by poor lifestyle choices (increased sedentary time and reduced dietary protein intake) as well as an inherent dysregulated mechanism in old muscles. The IGF-1, Akt/Protein Kinase B, and mechanistic target of rapamycin (mTOR) pathway is the primary driver between mechanical contraction and protein synthesis and may be a site of dysregulation between old and younger people.
Exercise has been shown to activate several different pathways in muscle, including AKT, MAPK (ERK1, ERK2), and calcineurin. Exercise also induces the synthesis of IGF-1 in muscle. The effects of IGF-1 are mediated mainly by the type 1 IGF receptor (IGFR1), which signals through the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. This pathway is of particular importance as it increases protein synthesis and inhibits protein degradation.
Administration of IGF-1 acutely activates muscle protein synthesis, but a 1-year administration did not result in increased lean body mass. Increased muscle protein synthesis has been reported in elderly subjects with low serum GH following 1 month of GH or IGF-1 treatment. Similarly, increased muscle protein synthesis was also observed in young, healthy men following GH administration at rest and after an overnight fast.
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GH and testosterone for strength training
Skeletal muscle is an endocrine organ that produces and releases myokines, which exert specific endocrine effects on visceral fat. The dynamic balance between anabolic and catabolic status in human skeletal muscle is related to factors such as mechanical and nervous stimuli, age, hormonal changes, and nutrient intake. Anabolic hormones, including testosterone and growth hormone (GH), play a crucial role in muscle growth and strength training.
Testosterone, produced primarily in the testes in men and the adrenal glands in women, has a significant impact on human physiology, including tissue growth. During strength training, testosterone binds to androgen receptors inside muscle cells, signalling an increase in protein synthesis and muscle fibre size. Testosterone also stimulates growth hormone secretion and enhances the presence of neurotransmitters, contributing to tissue growth and increased muscle strength.
GH, secreted by the pituitary gland, binds to receptors on target cells, activating intracellular signalling processes that stimulate genetic machinery in the cell nuclei. It can act directly on skeletal muscle and stimulate the production of IGF-1 in the liver and muscles. IGF-1, or insulin-like growth factor-1, is part of the same hormone group as GH and testosterone. It triggers a chain of events that promotes protein synthesis in muscles.
Research has shown that resistance exercises that engage large muscle groups and moderate-high intensity weights lead to significant increases in GH, IGF-1, and testosterone levels. These hormonal elevations result in superior strength training gains, with notable increases in muscle strength and size. For example, a study comparing two training groups revealed that the group performing additional leg exercises to increase anabolic hormone concentration achieved a 37% increase in arm strength, while the other group only achieved a 9% increase.
Furthermore, the combination of testosterone and GH supplementation in older men has been shown to improve body composition and muscle performance. Testosterone supplementation resulted in gains in lean mass, muscle strength, and endurance, with reductions in fat mass. The addition of GH supplementation further enhanced these outcomes.
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Frequently asked questions
Yes, muscles release hormones. When muscles are worked, they release hormones called myokines, which help to fight inflammation, cancer, diabetes, and osteoporosis.
Myokines are hormones that are released by skeletal muscles. They work in a hormone-like fashion, exerting specific endocrine effects on visceral fat.
During exercise, the body releases anabolic hormones, including growth hormone (GH), insulin-like growth factor-1 (IGF-1), and testosterone. These hormones are important for muscle growth and strength gains.
