By Nenad Rodic,
posted 04/05

Hormones are substances produced in the endocrine glands. They are secreted directly into the blood. Blood delivers hormones to all tissues where they are received by the specific receptors. Hormones perform various functions. Of particular interest to us are those hormones that can increase energy supply during exercise and help replace energy during recovery. Following table explains what specific hormones do.

Insulin Stimulates glucose and FFA uptake by cells
Glucagon Stimulates release of glucose from the liver and helps glycogen production out of protein
Somatostatin Decreases the secretion of insulin and glucagon
Testosterone Stimulates tissue building and
Growth hormone Stimulates tissue building and fat metabolism
Epinephrine (adrenalin) Stimulates heart rate, nerve impulse conduction, muscle contraction and breakdown of muscle glycogen and triglycerides.
Norepinephrine Stimulates heart rate and release of FFA from adipose tissue
Cortisol Stimulates release of FFAs and amino acids
Aldosterone Regulates sodium retention, water and electrolyte balance
ADH Stimulates water retention and reduces urine output
Thyroxin Increases oxygen consumption within a cell, fat and glycogen breakdown and tissue repair.
Calcitonin Calcium concentration in blood.

There are many more hormones that are important but these seem to be of most interest to us. Endurance work increases the use of glucose by muscles. This glucose needs to be replaced and that calls for an engagement of a variety of hormones. Glucagon is secreted in higher amounts to help the movement of glucose from the liver to the blood. Epinephrine and norepinephrine aid the movement of glucose and cortisol facilitates conversion of glycogen to glucose.
Cortisol, epinephrine, norepinephrine and growth hormone additionally facilitate conversion of triglycerides in the liver to FFAs that can be carried by blood to muscles.
Growth hormone is also important for muscle growth and tissue repair. How this works is not quite clear but many athletes choose synthetic HGH for faster and better recovery. This is not legal or smart.
Exercise affects secretion of hormones by making it lesser but longer lasting. This effect makes longer exercise possible without the interference from hormones causing energy imbalance. For example, exercise will cause a lesser secretion of insulin, which will help maintain a high glucose levels over a longer period and reduce the use of muscle glycogen. Additionally sudden spikes of insulin do not happen during exercise and consequently the sudden drops of blood glucose do not happen either. That’s one of the reasons why race food has a lot of glucose, fructose and quick acting sugars that would normally cause drop in blood glucose levels, but during exercise they are quite acceptable.
Basically, in our sport, with training, hormones that facilitate glycogen metabolism will secrete less actively and lower the rate of glycogen use while at the same time they will increase the metabolism of fat.
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By Nenad Rodic, founder of TriathlonPlace.com