ENDOCRINE PHYSIOLOGY AND

STRENGTH TRAINING

How the Endocrine System Works Endocrine glands are stimulated to

release hormones (neural stimulation or chemical stimulation).

Hormones are released into blood and act upon target tissues or directly on the DNA in the nucleus of the cell.

What Do Hormones Do?

Alter the rate of intracellular protein synthesis

Change the rate of enzyme activity Modify the plasma membrane transport Induce secretory activity

Hormones and Enzymes

Hormones increase enzyme activity in one of several ways:Stimulate increased production of the

enzymeCombine with the enzyme to alter its shape

and ability to act (can increase or decrease the enzyme’s effectiveness)

Activate inactive forms of an enzyme, increasing the total quantity of active enzyme

Receptors and Hormonal Changes Every cell has a receptor to mediate the

signal or message from a hormone. These are found:Outside the cell (binding proteins)In the cell membraneOn the regulatory elements of DNA

Lock-and-Key Theory

From Essentials 2nd Edition Lock-and-Key Theory: Each receptor is highly

specific for a single hormone Cross-Reactivity

CLASSES OF HORMONES

Steroid vs. Polypeptide Hormones Steroid hormones are fat soluble and

passively diffuse across the sarcolemma.Steroid crosses sarcolemma, binds with

hormone-receptor complex (H-RC).H-RC arrives at genetic material of cell,

“opens” it, then transcriptional units are exposed to code for specific proteins.

More on Hormone-Receptor Binding The extent of a target cell’s activation

depends upon:Blood hormone levelsRelative number of target cell receptors for

that hormoneSensitivity or strength of the union between

the hormone and the receptor

Hormone-Receptor Binding Upregulation: target cells form more

receptors in response to increasing hormonal levels

Downregulation: caused by prolonged exposure to high hormone concentrations, causes a desensitizing of target cells so that they respond less vigorously to hormonal stimulation

Steroid vs. Polypeptide Hormones Polypeptide hormones are made up of

amino acids. Are not fat soluble and cannot pass the

sarcolemma, thus requiring a secondary messenger to get their message to the cell nucleus.

Examples include growth hormone, leptin, lutenizing hormone, and insulin.

Secondary Messengers and Non-steroidal Hormones Non-steroidal hormone binds with a

receptor imbedded in the plasma membrane.

This reacts with the enzyme adenylate cyclase.

Adenylate cyclase interacts with ATP and forms cyclic AMP.

cAMP activates a protein kinase which then activates a target enzyme to produce changes in cellular function.

CONTROLLING HORMONE LEVELS

Factors That Determine Hormone Levels Hormonal Stimulation: many hormones

influence the secretion of other hormones Humoral Stimulation: changing levels of

ions and nutrients in blood, bile, and other fluids can influence hormone release (increase in blood sugar leads to an increase in insulin)

Neural Stimulation: hormone release is also affected by neural activity

Feedback Control of Hormone Levels Negative feedback Positive feedback Cyclical variations

Feedback Control of Hormone Secretion Negative Feedback:

Release of the hormone has a negative effect on its own release, this prevents oversecretion of the hormone.

The controlled variable is often the activity of the target tissue. As a result, negative feedback kicks in only when the target tissue displays an appropriate level of activity.

Feedback Control, cont.

Positive feedback:Rare, but in some instances the biological

action of a hormone causes additional secretion of the hormone.

This occurs until an appropriate concentration is reached, at which point negative feedback is initiated.

Estrogen stimulates secretion of luteinizing hormone (LH), which acts on the ovaries to stimulate more estrogen, etc.

Feedback Control, cont.

Cyclical variations:Some hormones are influenced by seasonal

changes, stages of development and aging, daily cycle, or sleep.

For example, growth hormone secretion is increased during sleep.

SPECIFIC HORMONES

Hormone Types

Anabolic Adrenal

Primary Anabolic Hormones Testosterone Growth Hormone Insulin-Like Growth Factors

Testosterone

Primary hormone that interacts with skeletal muscle tissue. Number of effects:Promotes growth hormone response in

pituitary which influences protein synthesisCan effect nervous system (interact with

receptors on neurons and increase neurotransmitters)

Can bind to skeletal muscle fiber nuclei to result in protein synthesis

Control of Testosterone

Hypothalamus releases gonadotropin-releasing hormone (GnRH)

GnRH stimulates the anterior pituitary gland to release lutenizing hormone (LH)

LH stimulates the testes to produce testosterone

Negative feedback (too much testosterone negatively effects LH secretion)

Increasing Testosterone Through Training Large-muscle group exercises Heavy resistance (85-95% 1-RM) Moderate to high volume (multiple sets) Short rest intervals (30-90 seconds)

Growth Hormone

Secreted by anterior pituitary, effects many tissues in the body.

Works off negative feedback.

Effects of Growth Hormone Increased amino acid

transport across cell membranes

Increased protein synthesis Increased utilization of fatty

acids Increased fat breakdown Increased availability of

glucose and amino acids Decreased glucose utilization Decreased glycogen

synthesis

Increased collagen synthesis

Stimulate cartilage growth Increased retention of

Nitrogen, Sodium, Potassium, and Phosphorus

Enhanced immune function

Increases renal plasma flow, filtration, and hypertrophy

What Stimulates Growth Hormone Secretion? Decreased blood glucose Decreased blood free fatty acids Starvation, protein deficiency (very

potent) Trauma, stress, excitement Exercise Testosterone, estrogen Deep sleep

What Inhibits Growth Hormone Secretion? Increased blood glucose Increased blood free fatty acids Aging Obesity Growth hormone

Training and Growth Hormone Growth hormone seems to respond best

to moderate repetitions (10-RM) and moderate rest (60 seconds) (for males and females).

In fact, total amount of work done seems to be more important than intensity when it comes to growth hormone release.

Craig and Kang (1994)

Looked at hGH release after :75% 1-RM (15 second

set) 90% 1-RM (15 second

set) 75% & 90% sets (reps

to failure at 75%, rest 3 minutes, reps to failure at 90%)

Insulin-Like Growth Factors Mediate some of the effects of Growth

Hormone. Are secreted by the liver after the liver is

stimulated by Growth Hormone, they may be released or found in other types of cells.

May help to promote tissue repair and recovery.

Thought to stimulate satellite cell proliferation during hypertrophy.

Role in hypertrophy is controversial.

IGFs and the Skeleton

Help to regulate functions of bone cells. In genetically altered mice,

overexpressing IGFs leads to increased growth and longer tails (Yakar and Rosen, 2003)

In genetically altered mice, knocking out IGFs leads to short bones, low BMD (Yakar and Rosen, 2003)

Adrenal Hormones

Cortisol Catecholamines

Cortisol

Catabolic hormone, related to glycogen stores (when they are low, cortisol is increased to gain energy from protein).

Major effects:Converts amino acids to carbohydratesIncreases enzymes that break down proteinInhibits protein synthesisAnti-inflammatory

Role in training not clearly understood yet

Cortisol Thought to be an indication of overtraining,

but this may be exaggerated… Crewther et al (2011):

9 nationally ranked Olympic liftersFive week study; high volume weeks vs. low

volume weeksReal competitions on weeks 2 and 5Simulated competitions on weeks 1 and 4

Crewther et al (2011)

No relation between training volume and cortisol

Cortisol higher during real competitions than simulated ones

Relationship between cortisol level and performance on simulated competitions

Cortisol may be really important for performance…

Cortisol Control

Physical or mental stress stimulates the anterior pituitary to release ACTH (adreno-corticotropic hormone).

ACTH tells the adrenal glands to produce cortisol.

Works off negative feedback, I.e. when cortisol levels too high then ACTH production is reduced.

TRAINING AND THE ENDOCRINE

SYSTEM

Training’s Effects

Acute: Post-exercise Chronic: Long-term adaptations

How Exercise Effects Hormones... During and after an exercise session After a month of intense training (and

how training level influences hormonal results)

After 12 weeks of training As a result of different exercise

protocols

McCall, et al. (1999).

Effects of exercise on hormonal concentrations.

Values taken before, 1/2 way through, and 10 minutes post a strength training workout.

Fry, et al. (2000). Studied 22 participants in a

national junior-level Olympic-style weightlifting camp, 4 weeks in duration

Each participant had placed in the top three in their weight class in national competition

Fry, et al, cont.

Training involved two phases:First week involved 3-4 sessions/dayWeeks two through four involved 1-2

sessions/dayOlympic-style lifting workouts, 70-100% of 1-

RM, sets of 1-5 reps Testing before and after week one, after

week four

Fry, et al, cont.

Testing conducted around the following session: 15 vertical jumps (1/3 seconds)Snatch (1/15 seconds), add 5 kg each lift

until failureSnatch pulls, 3x10x65% 1-RMBlood drawn pre-exercise, 5 minutes post-

exercise, and 15 minutes post-exercise

Fry, et al, cont.

Results: elite and non-elite

improved their total (average of 1.6% for elite, 1% for non-elite)

elite responded differently hormonally to the high-volume training than the non-elite

Fry, et al, cont.

Applications?Keep the limitations of this study in mind;

very small select sample size under very specific conditions

Indicates that the elite group tolerated the high volume training better (smaller hormonal response)

Genetic, results of training, little bit of both?

McCall, et al. (1999).

Studied 11 college-aged men. 12 week strength training study,

3x/week, 8 exercises (4 for biceps brachii) 3x10-RM, 1 minute rest.

Took resting hormone measurements before and after the 12 week study.

McCall, et al. (1999). Resting hormone concentrations don’t change

much after 12 weeks of strength training in this study.

Cortisol decreases, but little change on everything else.

Smilios, I., et al. (2003). Studied 11 men with 2-8 years resistance training

experience Looked into:

How # of sets (2, 4, or 6) effects hormonal values after a maximum strength, muscular hypertrophy, and strength endurance protocol; and

The hormonal response among the three protocols when intensity, reps, and rest were kept constant

Smilios, et al. (2003)

All 3 protocols used the following exercises: bench press, lat pulldown, squat, overhead press

Maximum Strength (MS) sets of 5 with 3’ rest; intensity reduced on each set to allow 5 reps to be completed (from 88% to 79.51% on 6th set)

Muscular Hypertrophy (MH) sets of 10 repetitions, 2’ rest; intensity reduced from 75% to 58.94%

Strength Endurance (SE) sets of 15 repetitions, 1’ rest; intensity reduced from 60% to 45.3%

Smilios, et al. (2003).

Blood samples were drawn before, after, after+15 minutes, and after+30 minutes

Experimenters looked at lactate, testosterone, growth hormone, and cortisol

Lactate and Training

Strength endurance produced the highest lactate levels, followed by MH, followed by MS.

No real differences between 2, 4, or 6 sets on lactate production.

Lactate and Training, 4 sets

0

2

4

6

8

10

12

Lactate

SEMHMS

Testosterone and Training MS, MH, and SE did not differ on

testosterone concentrations. Concentrations were statistically no

different from control for MS, MH, SE for 2, 4, or 6 sets.

Growth Hormone and Training Type of protocol effects growth

hormone:Higher for SE, followed by MH, followed by

MS4 sets seemed to yield the greatest release

of growth hormone

Type of Training and Growth Hormone, 4 sets

02468

101214161820

hGH

SEMHMS

# of Sets and Growth Hormone, MH Protocol

0

2

4

6

8

10

12

hGH

2 sets4 sets6 sets

Cortisol and Training

Cortisol levels were highest for MH, followed by SE, followed by MS for all conditions except 2 sets (there SE>MH>MS).

Number of sets did not effect cortisol levels

Applications?

Reps/set and # of sets influences hormonal response

Training for MS will not have the same type of hypertrophic response as training with greater volume.

Acute vs. Chronic Adaptations The body responds acutely. However:

In as little as five weeks exercise stops having an acute response.

Suggests there is a need for variation.

Acute vs. Chronic Adaptations There are no chronic changes in hormones in the

literature with the exception of a decrease in resting cortisol levels.

Reasons for this:Training may not be challenging enough.

Unlikely since subjects make gains.Training may not last long enough.There may not be changes to resting hormonal

levels from training. Suggest that acute training drive’s the muscle’s response.