Hormonal Control and Energy Expenditure During Exercise

Endocrine System

All tissues or glands that secrete hormones

Hormone

A chemical substance produced or released by an endocrine gland and transported by the blood to a specific target tissue

Target Cells

Cells that possess specific hormone receptors

Roles of the Endocrine System

1. 1. Monitors internal environment (temp.)

2. 2. Coordinates integration of physiological systems during rest and exercise

3. 3. Maintains homeostasis during exercise: substrate metabolism, fluid balance

Anabolic vs. Catabolic Hormones

Anabolic: Promote building of tissue (insulin, IGF, testosterone, GH)

Catabolic: Degrade cell proteins (cortisol and progesterone)

Steroid vs. Nonsteroid hormones

Steroid: Chemical structure similar to cholesterol

-Lipid soluble (diffuse through membranes)

-Reproductive hormones, cortisol, aldosterone

Nonsteroid: derived from protein, peptides

-Cannot easily cross cell membranes

Two types of nonsteroid hormones

1. 1. Peptide hormones: produced by thyroid and adrenal medulla (oxytocin)

2. 2. Amino-Acid derived - water soluble (epi)

What is the primary mechanism that the endocrine systems maintains homeostasis?

Negative Feedback

Downregulation and example

Decreased cellular sensitivity to a hormone from a decreased # of cell receptors

(Insulin resistance - cell fails to respond to insulin)

What is the mechanism for a steroid hormone crossing a membrane?

Direct gene activation - steroid hormone directly enters cell and activates receptor complex in the cytoplasm, the complex enters the nucleus and activates certain genes resulting in mRNA directing protein synthesis

What is the mechanism for a nonsteroid hormone crossing the cell membrane?

The hormone binds to a receptor in the membrane triggering a series of reactions that lead to the formation of a second messenger (cAMP →PKA) cellular changes

What hormone is released from the pituitary gland? What does it do?

Growth Hormone (GH)

Promotes muscle hypertrophy and fat metabolism

Released in proportion to exercise intensity

What hormone(s) are released from the Thyroid gland and what do they do?

T3 and T4 - increased with exercise

Increase in basal metabolic rate (BMR), protein synthesis, #/size of mitochondria, glucose uptake, glycolysis and gluconeogenesis

What hormones are released by the Adrenal Medulla and what do they do?

Catecholamines (fight or flight)

Epi (80%) and Norepi (20%)

Increase HR, metabolic rate, glycogenolysis,

What hormone(s) are released by the Adrenal Cortex and what do they do?

Cortisol

Stimulates gluconeogenesis

Increased mobilization of FFAs

Depressed immune reactions

Anti-inflammatory

What hormones are released by the pancreas and what do they do?

Insulin: lowers BG - inhibits gluconeogenesis

Glucagon: Raises BG - promotes glycogenesis and gluconeogenesis

Adequate glucose during exercise requires?

1. Glucose release by the liver

2. Glucose uptake by muscles

Which hormones increase curculation of glucose?

Glucagon, epi, norepi, cortisol

What is the amount of glucose released dependant on during exercise?

Exercise intensity (adreniline + muscle glycogen usage) and duration (liver glycogen use)

Describe the relationship between glucose and insulin during exercise

Insulin enables glucose uptake in muscle.

-Insulin concentrations decrease as more glucose is used instead.

(KNOW) How can athletes manipulate the endocrine system with resistance training?

1. 1. Recruit more muscle fibers

2. 2. Use heavy loads and large muscle groups

3. 3. Moderate to high volume (reps*weight)

4. 4. Short rest intervals (30-60s)

5. 5. Use workouts with higher lactate concentrations

What hormones stimulate Lipolysis?

Decreased insulin, epi, norepi, cortisol, GH

When is lipolysis accelerated?

Endurance exercises when glycogen stores are depleted

What happens to plasma volume during exercise?

Decreases from increased BP and sweating

What hormone(s) are released for fluid and electrolyte regulation, what do they do?

Antidiuretic hormone (ADH): minimizes water loss

Aldosterone: Na+ retention in the kidneys

What hormone is secreted by the kidneys? what does it do?

EPO - stimulates RBC production

(manipulated by athletes training at high altitudes or more oxygen being carried to muscles)

Where is the brain’s appetite control center?

hypothalamus

What hormone is secreted by the stomach and pancreas?

Ghrelin - increased hunger

What hormone is secreted from adipose tissue?

Leptin - decreases hunger

How does Ghrelin change with lose of weight and training in people?

Ghrelin does not change in people who do not lose wight from exercise, but it increases significantly in those who do lose weight.

-Acute bouts of mod-vig. intensity exercise can temportarily supporess appetite (decreased ghrelin)

What does a Direct Calorimetry measure?

Measures heat production to determine how much energy was expended. (60% is converted to heat)

What does indirect calorimetry measure?

Respiratory gases from oxidative metabolism

What is VO2 (with dot about the V)

The volume of O2 consumed per minute

What is Respiratory Exchange Ratio?

Ratio of COs expired to O2 used - tells us the substrate use

1.0 = 100% glucose

.71 or below = 100% fat

0.85 = Crossover Point

Rest = 0.80

How to calculate kcal/day

= liters of O2 consumed/day x kcal used per liter of O2(comes from RER)

ex. 2L of O2 with RER = 0.85 → 4.86 × 2 = 9.72 kcal/min x 30min = 292 kcal

Explain the difference bwtn BMR and RMR

BMR: rate of energy expenditure at rest after 8 hrs of sleep and 12 hrs of fasting (minimum amount of energy required by the body to sustain cellular functions , related to FF body mass and surface area)

RMR: expediture at rest (less struct than BMR)

What factors influence metabolic rates?

Age (decreases with age), Body temp. (increases with higher temp.), stress, hormones, body surface area exercise intensity

Why is VO2max so helpful?

Point when O2 consumption doesn’t increase (Best single measurement of aerobic fitness)

non-weight nearing activites = L/min

Body weight normalized = ml O₂ * kg⁻¹ * min⁻¹

What are the biological differences in VO2max

women have lower FFM and low hemoglobin

What is oxygen deficit in Anaerobic energy

The difference between the oxygen required for a given exercise intensity (steady state) and the actual consumption

What is EPOC

Excess postexercise oxygen consumption - elevated O2 consumption above resting levels after exercise (72h) - replenishing ATP-PCr stores

What is the best indicator of endurance performance?

Lactate Threshold - higher=better endurance - point when they can no longer only use aerobic pathway)

What is Economy of Effort?

Spending less energy with good form - increases with distance of race

Multifactorial Phenomenon

-Economy increases with distance of race

-Practice leads better economy of movement (form)

-Varies with type of exercise

Successful Endurance Athletes have these:

1. High VO2max

2. Higher lactate threshold

3. High economy of effort

4. High percentage of type 1 muscle fibers

What is the largest influence for daily energy expenditure?

Activity level and body factors: age, sex, size, weight, FFM

What is fatigue caused from

-Decreased rate of energy delivery

-Accumulation of by-products

-Failure of the muscle contractile mechanism

-Alterations in neural control of muscle contraction

What mechanisms do fatigue depend on:

-Fiber type

-training status and diet

-type and intensity of exercise

What are the byproducts of fatigue?

1. Inorganic P

2. Heat

3. Lactic Acid

4. Hydrogen Ions

What are the different types of neuromuscular fatigue?

1. Neural Transmission: at neuromuscular junction

2. Central Nervous System

Critical Power

Highest metabolic rate that is maintained entirely by oxidative metabolism (highest exercise intensity without exhaustion)

Types of Muscle soreness and how long they last?

1. Acute Muscle Soreness: minutes to hours

2. DOMS: appears one to two das after exercise (from eccentric) - Structural Damage - creatine kinase

What is Rhabdomyolysis

death of muscle fibers released into the bloodstream

What causes soreness?

Immune System Function: Neutrophils and macrophages

How does DOMS affect performance?

Reduced muscle force generation

-muscle damage

-failure in excitation-contraction coupling

-Loss of contractile protein

What is the neuromuscular response for muscle cramps

Excitation of muscle spindle and inhibition of Golgi tendon organs occur resulting in abnormal a-motor neuron activity and reduced inhibitory feedback.

How does heat cramps happen?

Electrolyte depletion primarily sodium and chloride

Why is DOMS important?

Stimulating muscle hypertrophy to maximiz training response