The human endocrine system regulates the production of hormones, chemicals that control cellular functions. Hormones can affect several different cells, but they only affect those with specific receptor sites.
Hormones control several physiological reactions in the body, including energy metabolism, reproductive processes, tissue growth, hydration levels, protein synthesis and breakdown in muscles, and mood. In addition, hormones are responsible for building new muscle and helping burn fat, so it is important to understand which hormones are released during training and which physiological functions they affect.
There are three main classifications of hormones: steroids, peptides, and amines (modified amino acid hormones). Each class of hormones has a unique chemical structure that determines how they act on certain receptors. Steroid hormones interact with receptors in the cell nucleus, peptide hormones are composed of amino acids and act with specific receptors on the cell membrane, and amines contain nitrogen and affect the sympathetic nervous system.
Hormones can be anabolic, meaning they help build new tissue, or catabolic, which play a role in breaking down tissue. Anabolic steroids are often referred to as a cheating method used by athletes who want to improve performance and results, however, anabolic steroids are natural chemicals produced by the body, responsible for promoting tissue growth.
Insulin is a peptide hormone produced by the pancreas. It regulates the metabolism of carbohydrates and fats. When blood sugar is elevated, insulin is released to enhance the storage and absorption of glycogen and glucose. Insulin helps lower blood glucose levels by promoting its absorption from the bloodstream into skeletal muscle or adipose tissue.
It is important to know that insulin can cause fat to be stored in adipose tissue instead of being used to stimulate muscle activity. When training begins, the sympathetic nervous system prevents the release of insulin. Therefore, it is important to avoid foods high in sugar (including sports drinks) before exercise, as they can raise insulin levels and enhance glycogen storage, rather than allowing it to be used to stimulate physical activity.
Released in response to low blood sugar, glucagon is produced by the pancreas to stimulate the release of free fatty acids from adipose tissue and increase blood glucose levels, both of which are important for stimulating exercise. As glycogen levels decrease during exercise, glucagon releases and consume the extra glycogen stored in the liver.
Cortisol is a catabolic steroid hormone produced by the adrenal glands in response to stress, low blood sugar, and exercise. This hormone supports energy metabolism during long periods of exercise by facilitating the breakdown of triglycerides and proteins to create the glucose needed as a training fuel.
Cortisol is released when the body experiences too much physical stress or does not recover enough from previous training. Although cortisol helps promote fat metabolism, too long a workout can raise cortisol levels to catabolize muscle protein for fuel, rather than conserving it to repair damaged tissues.
Epinephrine and norepinephrine
These amine hormones play an important role in aiding the sympathetic nervous system in energy production and in regulating bodily functions during cardiorespiratory activities. Classified as catecholamines, epinephrine and norepinephrine are separate but related hormones.
Epinephrine, often called adrenaline because it is produced by the adrenal glands, affects heart function, raises blood sugar (to help as a training fuel), promotes the breakdown of glycogen for energy, and supports fat metabolism. Norepinephrine performs many of the same functions as epinephrine but also narrows blood vessels in parts of the body that are not involved in training.
Testosterone is a steroid hormone produced by Leydig testicular cells in men and ovaries in women, with small amounts produced by the adrenal glands of both sexes.
Testosterone is responsible for the resynthesis of proteins in muscles and the recovery of muscle proteins damaged by training, and it plays a significant role as an aid in the growth of skeletal muscles. Testosterone acts on specific receptors and is produced in response to training that damages muscle proteins.
Growth hormone (HGH) is an anabolic peptide hormone secreted by the anterior pituitary gland that stimulates cell growth. Like all hormones, HGH acts at specific receptor sites and can produce several reactions, including increasing the synthesis of muscle protein responsible for muscle growth, increasing bone mineralization, supporting immune function, and promoting lipolysis or fat metabolism.
The body produces HGH during the REM sleep cycle, and production is stimulated by high-intensity training such as strength training, explosive power training, or cardiorespiratory exercises.
Insulin-like growth factor
Insulin-like growth factor (IGF) has a molecular structure similar to insulin and its production is stimulated by the same mechanisms that produce HGH. IGF is a peptide hormone that is produced in the liver and supports the function of HGH to repair proteins damaged during training, making it an important hormone to promote muscle growth.
Neurotropic Brain Factor
Brain-derived neurotrophic factor (BDNF) is a neurotransmitter that helps produce new cells in the brain.
BDNF production is closely linked to HGH and IGF production – the same workouts that raise levels of these hormones increase BDNF levels.
High-intensity training can stimulate anabolic hormones for muscle growth while increasing BDNF levels, which can help improve cognitive function.
Understanding how training affects hormones that affect physiological functions can help plan training, to achieve your goals. Hormones have both short-term and long-term reactions to exercise.
In the acute phase, immediately after the training unit itself, testosterone, HGH, and IGF are produced to repair tissue damage caused by training. In the long run, there is an increase in receptor sites and binding proteins that allow testosterone, HGH, and IGF to be used more efficiently in tissue recovery and muscle growth.
If the goal is to increase muscle mass: testosterone, HGH, and IGF levels depend on the response to mechanical stress created during strength training. Moderate to heavy loads applied to failure generate high levels of mechanical force, resulting in greater damage to muscle proteins, which signals the production of testosterone, HGH, and IGF for protein recovery, which in turn results in muscle growth.
Although there are countless hormones responsible for the almost infinite range of physiological functions that constantly occur in the human body, the above hormones are directly affected by physical activity, and they play an important role in helping the body adapt to imposed physical training requirements.
It is clear that the nervous and muscular systems play an important role in determining the results of a training program, but the reality is that hormones affect many physiological adjustments to physical activity and this should not be forgotten.