Endocrine System Depletion
By Jay Hodde and Karl King
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
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.
The Depleted Runner
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.
Endocrine System Fatigue and Recovery
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, keep 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
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 Adrenaline
Urination shortly after the run begins Adrenaline
Increasing heart and respiration rate as the run goes on Adrenaline
Hands and feet swell late in the run Vasopressin, Aldosterone
Nausea when running only on carbohydrate Gastrin, CCK
Elation after hours of running Endorphins
Appetite suppression Endorphins
Improved memory ACTH
Inhibition of inflammatory response Cortisol
Ability to run on low calorie input Cortisol, Adrendaline,
Growth hormone, Glucagon
Slow healing after the run Cortisol
Healing during sleep Growth hormone
Weak immune system response Cortisol
Copyright 1999 Karl King, all rights reserved.