There are several endocrine hormones and growth factors that contribute to muscular hypertrophy and fat burning. These are chemical messengers released from various endocrine glands due to stimulation from the nervous system, or other hormones. Each hormone can be classified as an anabolic (building up) or catabolic (breaking down).
Let’s start out with a look at the anabolic hormones:
Growth hormone (GH) is produced in the anterior pituitary gland of the brain. This hormone is released following resistance training. Among its many functions is stimulating insulin-like growth factor (IGF) in muscles. IGF is one of the factors responsible for the division of satellite cells during the repair process. The other contributing factors include fibroblast growth factor (FGF) and hepatocyte growth factor (HGF).
Testosterone
Another anabolic hormone of utmost importance for hypertrophy is testosterone, which is secreted in the testes. It is also known as the androgen (male) hormone. Testosterone levels are elevated during resistance exercise and the hormone acts to increase protein synthesis. This allows for optimal
repair of muscle fibers. In addition, it increases satellite cell count along with the number of androgen receptors in muscles, leading to greater hypertrophy.
Insulin
Insulin is also an anabolic hormone capable of increasing protein synthesis. It is produced in the pancreas and it mainly functions in activating glucose uptake in cells, such as muscle cells. It can also transport amino acids. During exercise, insulin sensitivity increases due to a muscle's additional need for glucose. This not only enhances glucose uptake, but also the uptake of amino acids, thus stimulating protein synthesis.
Glucagon
Unlike insulin, the catabolic hormone glucagon increases blood glucose. This hormone, also produced in the pancreas, breaks down fat to release glucose into the blood during periods when blood glucose levels are low. This can occur while performing cardio on an empty stomach and is
beneficial when trying to burn fat.
Cortisol
Cortisol is also released when blood glucose levels are low. It is a catabolic hormone secreted by the adrenal glands, and is often referred to as the stress hormone, as stress increases cortisol levels. When secreted, cortisol converts fatty acids and amino acids into glucose. This can negatively affect hypertrophy by slowing down or even preventing protein synthesis, as the amino acids needed for this process would be converted to glucose.
Epinephrine and Norepinephrine
Two catabolic hormones that help boost performance during training are epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones, produced in the adrenal glands, are released during exercise, especially high-intensity resistance exercise. The benefits of epinephrine and norepinephrine include increased strength, increased blood flow, and increased secretion of the anabolic hormone testosterone.
Irisin
Another hormone released during exercise is irisin. This hormone is secreted by muscles. Your body comprises two types of fat cells: white and brown. White adipose tissue, or white fat, is used by the body to store energy in the form of triglycerides. This kind of fat has little mitochondria, hence its white color.
The other type of fat, brown adipose tissue, or brown fat, is used to burn energy. Unlike white fat, it contains an abundance of mitochondria, which explains its brown color.
Brown fat expends energy via non-shivering thermogenesis, and it is highly activated during cold conditions. Most people only have a small amount of brown fat in their bodies. Also, as they age, the levels of brown fat decrease. There are, however, individuals with higher amounts of brown fat than the normal population, which gives them an advantage in terms of burning calories, due to the increased thermogenesis and thus increase in metabolism.
It is possible though to increase brown fat by performing intense exercise on a regular basis. This is because intense exercise causes muscles to release the hormone irisin, which converts white fat to brown fat. Irisin helps convert the energy-storing white fat cells to the energy-burning brown fat cells. By doing so, it causes an increase in metabolism, thus allowing your body to burn more calories.