Endocrine System Depletion

As published in the October 1999 issue of UltraRunning Magazine. 

When ultrarunners think of running-related injuries, they usually think of conditions affecting the musculoskeletal system: the bones, the muscles, and the joints. Ultrarunning however, is strenuous on other parts of the body as well, and can lead to deficiencies in immune function ( increasing the risk of infection, flu, or colds ), disturbances in the basic senses ( temporary loss of normal vision ), or problems in responding to everyday stress. The body’s response to stress; from everyday, on-the-job stress to stress that results from running excessive mileage in training or racing; occurs primarily in the endocrine system. This month, Karl King and I examine the normal function of the endocrine system, its role in the body’s response to extreme endurance activity, and the way in which the system gets injured as a result of extreme mileage. In addition, we present suggestions to treat an overtaxed endocrine system and offer tips on preventing endocrine system depletion.


Let’s look at the case of a hypothetical runner named John. He is new to Ultrarunning and is extremely enthusiastic about training and racing. He has set lofty goals, attempting to run at least 10 miles per day during the year. His weekly long run is 40 miles on Saturday, followed by 30 on Sunday, except for the one weekend a month when he races either a 50 or 100 mile. John is pleased that he has been able to recover from his racing quickly. He is able to run 100 miles on the weekend and return to his daily 10 mile run on Monday without even missing a day. Just last month, he was very pleased to finish the Kettle Moraine 100 in just over 18 hours and return to conquer the Mohican 100 two weeks later in 19 hours. After Mohican, his recovery seemed a bit sluggish, but he was able to gut out his 70 mile weekend training ritual without problems. Things were going great, so he decided to enter the Finger Lakes 50 ( two weeks after Mohican ) in New York to celebrate the July 4 weekend. Ten miles into Finger Lakes, John felt sluggish, his muscles hurt, and his legs were not able to respond to the hills. By 18 miles, John was reduced to a walk, and felt as if he wanted to sleep, even though he had carbo-loaded for the run the night before. Dejected and saddened by his failure on the course, John DNFd for the first time in his short Ultrarunning career. Looking back at his training logs, John couldn’t figure out what went wrong. He’d been training hard for months and was in the best shape of his life. Maybe I need to train harder, John was overheard saying the next day. The truth is, maybe he needed to train less; or at least alter his training program; to allow his endocrine system ample time to recover from the stress of the high mileage and the hard racing.


The endocrine system is a collection of glands that produces a wide variety of chemical messengers called hormones, necessary for normal bodily functions. Hormones regulate processes as diverse as metabolism, growth, digestion, sexual development, and response to stress. The glands release the hormones directly into the bloodstream where they are transported to organs and to tissues. At these target organs and tissues, the secreted hormone evokes a specific, pre-programmed response from the targeted cells. The specific functions of the endocrine system include:

  1. regulating the chemical composition and volume of the body
  2. regulating metabolism and energy balance, including digestion
  3. regulating contraction of smooth and cardiac muscle
  4. maintaining homeostasis even during crisis events
  5. regulating components of the immune system, and
  6. regulating the integration of growth and development.

Thus, appealing to the endocrine system is one way in which the body coordinates its actions with information collected from the environment. Most runners think that long training runs are only needed to build muscle for the hours of work they will do in an ultra. Actually, long runs are just as important for training other systems to respond to stress: the heart, lungs, liver, kidneys, digestive system and the endocrine system. We often think of the momentary surge of adrenaline we get when frightened, but to run an ultra, adrenaline is needed all day. The endocrine system is responsible for teaching the body to react to the physical, emotional and mental stress of running an ultra. Most of that training is accomplished during very long runs.


While the endocrine system consists of several different glands that secrete over 50 different hormones, the hypothalamus and the pituitary gland control such a broad range of bodily functions ( and other endocrine glands ) that they are often referred to as the master control center of the endocrine system. For ultrarunners, the adrenal gland is just as important. The following is a brief description of the components of the endocrine system:

Hypothalamus: The hypothalamus is located in the brain. It regulates many aspects of the body, such as heart rate, body temperature, water balance, and the amount of glandular secretions from the pituitary. It secretes hormones that help regulate the pituitary gland and also responds to their presence in a feedback mechanism.

Pituitary Gland: This small gland is tightly connected with the hypothalamus and secretes two hormones of particular interest to runners. Anti-diuretic hormone( ADH ) promotes water re-absorption in the kidneys and is released from the pituitary when sensors in the hypothalamus determine that the blood is too concentrated, i.e., when dehydration occurs. Adrenocorticotropic hormone ( ACTH ) stimulates the adrenal gland to produce cortisol. While the pituitary secretes numerous other hormones necessary for growth and survival, a full review of these substances is beyond the scope of this article.

Adrenal Glands: We have two adrenal glands, one on top of each kidney in the lower back. Each gland consists of an outer layer called the cortex and an inner core called the medulla. Secretion from the adrenal medulla is controlled via the nervous system, whereas ACTH controls secretion from the adrenal cortex. The major hormones produced by the adrenal medulla are adrenaline ( also called epinephrine ) and a related hormone called noradrenaline ( norepinehprine ). These hormones cause the changes that occur during an emergency situation ( the fight-or-flight response ). Such changes include: increased heart and breathing rate, increased blood flow to muscles, cessation of digestion, and increased blood glucose levels and metabolic rate. The adrenal cortex produces two main classes of hormones: glucocorticoids and mineralcorticoids. It also produces small amounts of both male and female sex hormones. The main glucocorticoid hormone, cortisol, promotes the breakdown of muscle proteins into amino acids that enter blood. The resulting increase in amino acid levels in the blood then causes higher glucose blood levels when the liver breaks down these amino acids. Cortisol also favors metabolism of fatty acids over carbohydrates. This hormone works in opposition to insulin, raising blood glucose levels. In a different mode, cortisol counteracts the inflammatory response that can lead to the pain and swelling of joints in arthritis and bursitis. The main mineral corticoid hormone is aldosterone. When blood volume or sodium levels drop, a hormone called rennin is released from the kidneys and indirectly causes the release of aldosterone. Aldosterone causes sodium re-absorption by the kidneys, resulting in increased water and blood volumes. The hormone also increases arterial constriction, which in turn increases blood pressure.


The endocrine system can become fatigued just like a muscle that is continually overworked. At some point it just can’t produce the stress hormones as it should. A tired ( but not damaged ) muscle may recover in 24 to 48 hours, but it takes an overused endocrine system weeks to recover. The stress of running an ultra requires a major response from the endocrine system, but that system requires time to recover. Hormonal levels start to normalize in the hours after the run, but it may take days before excess hormones have cleared the system. It is not unusual to feel really high from adrenaline and endorphins for 24 hours after an ultra, but then depression often sets in. During the ultra, cortisol serves the body well by mobilizing energy stores and reducing inflammation. Afterwards, it temporarily blocks the desirable effects of insulin, and repair of the body is slowed. Even when the cortisol levels fall to normal after a few days, there are lingering effects from the disturbance of the endocrine system. Symptoms may include: apathy toward work or training, inability to concentrate, changes in sleep patterns, appetite suppression, reduced libido, increased thirst, diarrhea, susceptibility to colds, and menstrual disturbances in women. If the body is called upon to respond to stress again, adequate levels of cortisol cannot be produced, resulting in a crash after too much running. The varied nature of these symptoms points to suppression at the level of the central nervous system hypothalamus/pituitary axis. That is, it isn’t just one gland that isn’t working right nor is it some simple nutrient deficiency. The driving force for the suppression is not currently known, but could be related to reduced blood flow, desensitization of the hypothalamus or pituitary caused by leg muscle breakdown byproducts, or a down-regulation of axis function brought on by prolonged, abnormally high cortisol levels. Since the mechanisms are not known, there is currently no magic-bullet that can be used to recover in a short time. With rest from stressful situations recovery times can range from three to twelve weeks. Note that this is longer than the time required for adequate muscle repair; the two may in fact be related. It makes no sense to have a strong endocrine response when damaged muscles are not prepared for an ultra effort. The best way to limit endocrine recovery time is to not stress the system too hard in the first place. That implies being fully trained and rested for the event one is about to run, then minimizing stress during the run. It is obvious that those who have properly trained with long runs, speed work, and weights are able to withstand the stress of an ultra better than those who run with minimal training. During the run, one cannot avoid the course and its challenges, but one can reduce stress by good pacing and by maintaining hydration, caloric and electrolyte status. Stress hormones are low when one is at the starting line. It’s when one runs short of water, short of blood glucose, and has electrolyte disturbances that the level of stress hormones increases dramatically. There is a mental component as well: We are less likely to be stressed if we treat our run as a joyous adventure instead of a life-and-death struggle. We will get plenty of challenge from the course; let’s not add unnecessary excess baggage.


The endocrine system needs to perform well during a run, so take good care of it. Train adequately without overtraining, run at a sensible pace, and maintain a good intake of water, food and electrolytes. Enjoy the experience as you go. Your endocrine system responds to stress from any source, so if possible, avoid stress at work and at home, as well as self-imposed stress such as performance anxiety. Expect to rest until your endocrine function is back to normal. Avoid falling into the restless schedule of our hypothetical runner John: Before you sign up for a bunch of ultras in a row, plan for adequate rest between each one. If you train heavily, plan a number of weeks to allow your system time to recover. You will know that you are well recovered when your legs feel energetic in training runs and have no hesitancy to run. Once you’ve built up a strong endurance base, you won’t lose anything from a good rest. The endocrine system is highly active during and after endurance exercise. Here are some experiences common to ultrarunners and the endocrine system hormone(s) that may play a role in each of them. Note that some of these phenomena can have multiple causes, so hormonal response may not be the sole cause of the experience.

Difficulty sleeping the night before
Urination shortly after the run begins
Increasing heart and respiration rate as the run goes on
Hands and feet swell late in the run
Vasopressin, Aldosterone
Nausea when running only on carbohydrate
Gastrin, CCK
Elation after hours of running
Appetite suppression
Improved memory
Inhibition of inflammatory response
Ability to run on low calorie input
Cortisol, Adrendaline, Growth hormone, Glucagon
Slow healing after the run
Healing during sleep
Growth hormone
Weak immune system

Copyright 1999 Karl King, all rights reserved.