8 Hormones Involved
in Exercise
Provided by American Council on Exercise
In
the movie Fletch, released the
same year that ACE was founded (1985), comedian Chevy Chase plays the role of
Irwin “Fletch” Fletcher, a reporter working undercover to expose drug dealing
on the beaches of Los Angeles. Over the course of his investigation, Fletch
assumes a variety of creative characters as he identifies the corrupt
businessmen and cops involved in the drug-dealing ring. In one scene, Fletch
pretends to be an airplane mechanic and tries to fib his way into a hangar by
saying he was there to check the ball bearings. “It’s all ball bearings
nowadays,” is one of the most memorable quotes of this iconic
‘80s movie.
If you work as a personal trainer or group
fitness instructor you have no doubt been asked how exercise can help someone
achieve a specific goal. If you want a fun, but honest way to answer these
questions, you can channel your inner Fletch by replying, “It’s all hormones
nowadays.”
The endocrine system regulates the production
of hormones, which are chemicals that control cellular functions. Hormones can
affect a number of different cells; however, they only influence the ones with
specific receptor sites. Hormones control a number of physiological reactions
in the body including energy metabolism, reproductive processes, tissue growth,
hydration levels, synthesis and degradation of muscle protein, and mood.
Hormones are responsible for both building new muscle and helping to burn fat,
so it is important to have an understanding of which ones are released in
relation to exercise as well as understanding the physiological functions they
influence.
There are three major classifications of
hormones: steroid, peptide and amines (modified amino acid hormones). Each
class of hormones has a unique chemical structure that determines how it
interacts with specific receptors. Steroid hormones interact with receptors in
the nucleus of a cell, peptide hormones are comprised of amino acids and work
with specific receptors sites on the cell membrane, and amines contain nitrogen
and influence the sympathetic nervous system.
Hormones can either be anabolic, which means
they help build new tissue, or catabolic because they play a role in breaking
tissue down. The term “anabolic steroids” is often mentioned as a method of
cheating used by athletes who want to improve performance; however, anabolic
steroids are actually natural chemicals produced by the body that are
responsible for promoting tissue growth.
Listed below are some important exercise and
hormones along with the physiological functions they control.
Insulin
A peptide hormone produced by the pancreas,
insulin regulates carbohydrate and fat metabolism. When blood sugar is
elevated, insulin is released to promote the storage and absorption of glycogen
and glucose. Insulin helps reduce levels of glucose in the blood by promoting
its absorption from the bloodstream to skeletal muscles or fat tissues. It is
important to know that insulin can cause fat to be stored in adipose tissue
instead of being used to fuel muscle activity. When exercise starts, the
sympathetic nervous system suppresses the release of insulin; consequently, it
is important to avoid foods with high levels of sugar (including sports drinks)
before exercise because it can elevate insulin levels and promote glycogen
storage instead of allowing it to be used to fuel physical activity. Wait until
the body has started sweating before using any sports drinks or energy
gels.
Glucagon
Released in response to low levels of blood
sugar, glucagon is produced by the pancreas to stimulate the release of free
fatty acids (FFAs) from adipose tissue and increase blood glucose levels, both
of which are important for fueling exercise activity. As glycogen levels are
depleted during exercise, glucagon releases additional glycogen stored in the
liver.
Cortisol
Cortisol is a catabolic steroid hormone
produced by the adrenal gland in response to stress, low blood sugar and
exercise. It supports energy metabolism during long periods of exercise by
facilitating the breakdown of triglyceride and protein to create the glucose
necessary to help fuel exercise. Cortisol is released when the body experiences
too much physical stress or is not sufficiently recovered from a previous
workout. While cortisol helps promote fat metabolism, exercising for too long
can elevate levels of cortisol to catabolize muscle protein for fuel instead of
conserving it to be used to repair damaged tissues.
Epinephrine and
Norepinephrine
These amine hormones play an important role
in helping the sympathetic nervous system (SNS) produce energy and in
regulating the body’s function during cardiorespiratory exercise. Classified as
catecholamines, epinephrine and norepinephrine are
separate but related hormones. Epinephrine, often referred to as adrenaline
because it is produced by the adrenal gland, elevates cardiac output, increases
blood sugar (to help fuel exercise), promotes the breakdown of glycogen for
energy and supports fat metabolism. Norepinephrine performs a number of the
same functions as epinephrine, while also constricting blood vessels in parts
of the body not involved in exercise.
Testosterone
Testosterone is a steroid hormone produced by
the Leydig cells of the testes in males and the
ovaries of females, with small amounts produced by the adrenal glands of both
genders. Testosterone is responsible for muscle protein resynthesis
and the repair of muscle proteins damaged by exercise, and plays a significant
role in helping grow skeletal muscle. Testosterone works with specific receptor
sights and is produced in response to exercise that damages muscle
proteins.
Human Growth Hormone
Human growth hormone (HGH) is an anabolic
peptide hormone secreted by the anterior pituitary gland that stimulates
cellular growth. Like all hormones, HGH works with specific receptor sites and
can produce a number of responses, including increasing muscle protein
synthesis responsible for muscle growth, increasing bone mineralization,
supporting immune system function and promoting lipolysis, or fat metabolism.
The body produces HGH during the REM cycles of sleep and is stimulated by
high-intensity exercise such as heavy strength training, explosive power
training or cardiorespiratory exercise at or above the onset of blood lactate
(OBLA, the second ventilatory threshold).
Insulin-like Growth
Factor
Insulin-like growth factor (IGF) has a
similar molecular structure to insulin and is stimulated by the same mechanisms
that produce HGH. IGF is a peptide hormone produced in the liver and supports
the function of HGH to repair protein damaged during exercise, which makes it
an important hormone for promoting muscle growth.
Brain-derived
Neurotrophic Factor
Brain-derived neurotrophic factor (BDNF) is a
neurotransmitter that helps stimulate the production of new cells in the brain.
The production of BDNF is closely related to the production of HGH and IGF—the
same exercises that elevate levels of those hormones also increase amounts of
BDNF. High-intensity exercise can stimulate anabolic hormones for muscle growth
while elevating levels of BDNF, which can help improve cognitive
function.
Understanding how exercise influences the
hormones that control physiological functions can assist you in developing effective
exercise programs for your clients. Hormones have both short- and long-term
responses to exercise. In the acute phase immediately post-exercise,
testosterone (T), HGH and IGF are produced to repair damaged tissue. Over the
long-term, there is an increase in the receptor sites and binding proteins,
which allow T, HGH and IGF to be used more effectively for tissue repair and
muscle growth. For clients who want muscle growth, the levels of T, HGH and IGF
are produced in response to the amount of mechanical stress created during
resistance-training exercises. Moderate to heavy loads performed until
momentary fatigue generate high levels of mechanical force, which creates more
damage to muscle protein, which signals the production of T, HGH and IGF to repair
protein, which results in muscle growth.
While there are a myriad of hormones
responsible for an almost infinite number of physiological functions, the
hormones listed above are directly influenced by physical activity and play
important roles in helping the body adapt to the imposed physical demands of
exercise. Many fitness professionals understand that the nervous and muscular
systems play important roles in determining the outcomes of an exercise
program. However, the reality is that hormones influence many of the
physiological adaptations to physical activity. That means that, “It’s all hormones nowadays,” is the appropriate response to
many questions about how the human body
responds to exercise.
AUTHOR
Pete McCall
Pete McCall, MS, CSCS, is an ACE Certified
Personal Trainer and long-time player in the fitness industry. He has been
featured as an expert in the Washington Post, The
New York Times, Los
Angeles Times, Runner's
World and Self. He holds a master's
degree in exercise science and health promotion, and several advanced
certifications and specializations with NSCA and NASM.