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These can be categorised into “Catabolic” and “Anabolic”. Anabolic hormones are responsible for muscle growth and repair. Catabolic hormones are responsible for protein breakdown.
Catabolic Hormones
Glucagon
Stimulates fat and liver breakdown and gluconeogenesis
Glucagon gets released from the pancreas. Its primary function is to increase blood glucose levels by increasing the release of glucose from the liver and activating gluconeogenesis, the conversion of amino acids and other small compounds such as lactic acid into glucose
Epinephrine
Stimulates fat, liver and muscle breakdown
Epinephrine (aka Adrenaline) is released from the adrenal glands in response to low blood glucose levels and stimulation of resistance exercise
Adrenaline promotes the breakdown of liver glycogen to glucose and its release into the blood. It is also responsible for an increase in breakdown of fat and increased blood flow to the muscle
Norepinephrine
Stimulates fat and liver glycogen breakdown
Norepinephrine (aka Noradrenaline) is primarily released from nerve endings in blood vessels in response to exercise. The higher the intensity the greater the increase
Cortisol
Stimulates fat, liver glycogen and muscle protein breakdown
Cortisol is probably the most well known catabolic hormone by strength training athletes. It is released by the adrenal gland when blood glucose levels are low and during intense exercise.
Cortisol generates fuel for working muscles. During exercise your muscles use metabolic priority system for generation of energy. First carbohydrate is used, then fat and last of all protein. Because of the tremendous stress that resistance training puts on muscles, the metabolic priority system is ignored.
When cortisol is released it causes breakdown of protein, carbohydrate, then fat, an increase in plasma amino acids specifically glutamine and BCAA’s
Elevated cortisol levels have enormous implications for strength training athletes. The greater the cortisol release the more protein degradation. Therefore it’s easy to see why cortisol is the main reason for strength training plateaus
Anabolic Hormones
Testosterone
Blocks cortisol and stimulates protein synthesis
Testosterone has androgenic effects and anabolic effects. Androgenic effects include changes in sex organs, voice pitch, hair growth, aggressiveness. Anabolic effects include accelerated growth of muscle, bone and red blood cells
Testosterone has a cortisol blocking effect and is for this reason somewhat anti-catabolic. The only down side is that when cortisol is blocked, after time higher levels of cortisol get released. This is why a bodybuilder usually loses a lot of weight when he comes off steroids
Testosterone also has a positive effect on protein synthesis, increasing it. Testosterone may speed muscle recovery
Growth Hormone
Stimulates bone and cartilage growth and protein synthesis
Growth hormone stimulates muscle growth, increases breakdown of fat and inhibits carbohydrate metabolism
IGF-I
Stimulates growth of bone, cartilage and muscle
IGF-1 stands for insulin like growth factor. The primary effect of IGF-1 is stimulation of protein synthesis in bone, cartilage and muscle. Its release is controlled by the intensity of muscle contractions
Insulin
Multiple effects on muscle protein synthesis, protein degradation and glycogen replenishment
Insulin is responsible for transportation of glucose into cells. High levels of insulin combined with carbohydrate has been shown to increase fat synthesis and decrease fat breakdown. However while its true high levels of insulin promote fat synthesis, they do not necessarily do the same in all circumstances. The degree to whichinsulin promotes fat storage, carbohydrate storage or protein synthesis at any given times depends on the state of the persons body. Muscle cells are more insulin sensitive after exercise. If glucose and amino acids are available at this time, insulin will help synthesis muscle proteins and muscle glycogen at a very rapid rate and very little fat will be synthesised and stored in adipose
References
[Lukaszewska, J. Biczowa, B., Bobilewicz, D. “Effect of physical exercise on plasma cortisol and growth hormone levels in young weightlifters” Polska,2:149-158, 1976]
[Mcmurray, R.G. Eubank, T.K. and Hackney A.C. “Nocturnal hormonal responses to resistance exercise”, European journal of applied Physiology, 72:121-126, 1995]
[Van Loon L.J., Kruijshoop, M. verhagen, H. “Ingestion of protein hydrolysate and amino acid-carbohydrate mixtures increases post exercise plasma insulin responses in men” journal of nutrition, 120: 2508-2513, 2000]
[Kraemer, W.J, Hakkinen, S.V., Newton, R.U. “Hormonal and growth factor responses to heavy exercise training protocols” journal of applied Physiology, 69:1442-50,1990]