EXERCISE HORMONES II

💪 How Hormones Help Maintain Glucose

Think of glucose as the fuel your body uses during exercise. Hormones help keep the right amount of this fuel available by:

Getting glucose into your muscles: Hormones help your muscles take up glucose and burn fat for energy. This is called glucose uptake and fatty acid oxidation.
Growing blood vessels: They help grow blood vessels in your muscles so they can get more fuel.
Making more glucose: Hormones tell your liver to produce more glucose and break down stored fats (triglyceride breakdown).
Reducing inflammation: Exercise helps lower chronic inflammation, which is good for reducing the risk of diseases like heart disease and diabetes.

🏋 Muscle as an Endocrine Gland

Did you know that your muscles actually produce hormones? When you exercise, your muscles release substances called myokines. These myokines help create an anti-inflammatory environment, which is one of the reasons why regular exercise is so good for you.

⚡ Control of Muscle Glycogen Utilization

During intense exercise, your body needs a lot of energy quickly. Here’s what happens:

Epinephrine increases: Your body releases a hormone called epinephrine (also known as adrenaline), which gives you an energy boost.
Glycogen is used up: Your muscles start using up their stored form of glucose, called glycogen, more rapidly.

Glycogenolysis is the process of breaking down glycogen into glucose. The more intense the exercise, the more glycogenolysis occurs. Epinephrine is a big trigger for this process.

📉 Epinephrine and Cyclic AMP

Epinephrine causes glycogen breakdown through something called the cyclic AMP pathway. Calcium ions (Ca++) also play a role.

⚙ Control of Glycogenolysis

Epinephrine binds to receptors, which starts a chain reaction involving cyclic AMP and calcium, ultimately converting glycogen to glucose.

⛽ Hormones and Substrate Utilization

The type of fuel your body uses during exercise depends on how hard and how long you exercise.

Strenuous exercise relies more on carbohydrates (CHO).
Prolonged exercise relies more on fat.

Hormones control:

How muscle glycogen is used.
How glucose is released from the liver and fatty acids from fat tissue.

🧬 Glycogen

How quickly glycogen is used depends on how intense the exercise is. Because glycogen stores are limited, your body tries to conserve glycogen through training adaptations. Many athletes use "carb loading" to maximize glycogen stores before an event.

🫀 Epinephrine and Norepinephrine

Epinephrine and norepinephrine are hormones that prepare you for "fight or flight."

During very intense exercise, these hormones increase, especially in trained individuals.
During less intense exercise, they decrease after training.
These hormones increase heart rate and blood pressure.

They use a substance called cAMP to trigger a cascade of events that:

Release glycogen from muscles
Increase glucose release from the liver
Increase fat release
Interfere with glucose uptake

These are fast-acting hormones that help maintain blood glucose during exercise.

🏃‍♀ Role of Catecholamines in Substrate Mobilization

Epinephrine binds to receptors, leading to signals that cause glycogenolysis (the breakdown of glycogen).

📈 Catecholamines and Exercise Intensity

Epinephrine and norepinephrine increase as exercise gets more intense.
Epinephrine and norepinephrine increase as exercise lasts longer.

⛽ Glycogen Depletion

Glycogen depletion increases with both time and intensity of exercise.

🔑 Redundancy

Epinephrine triggers glycogenolysis.

🧪 Propranolol Study

A study using a drug called propranolol (a beta-blocker) showed that calcium ions play a significant role in glycogenolysis.

🦴 Calcium

Muscle cells need calcium to contract.

🚴 Single Leg Cycling

In a single leg cycling study, glycogen was only depleted in the working leg, suggesting calcium and other factors are key.

💥 Maximum Glycogen Breakdown

Catecholamines control maximum glycogen breakdown. Both epinephrine/cAMP and calcium/calmodulin are involved. Trained individuals can release more epinephrine during maximal exercise, giving them greater access to energy from glycogen.

⬇ Training

Training leads to:

Less glucose released.
Stable plasma glucose levels.
Less glucose uptake in the muscle for the same workload.
Higher plasma norepinephrine during exercise.

The goal of training is to conserve muscle glycogen!

🛢 Substrate Mobilization from Fat and Liver (Glucose)

Catecholamines help release energy from fat and the liver.

🧪 Insulin and Glucagon

Insulin and glucagon are also influenced by catecholamines.

Insulin helps with the uptake and storage of glucose and fatty acids. Its levels decrease during exercise.
Glucagon has the opposite effect.

🩸 Regulation of Blood Glucose

During exercise, glucose is taken up much faster than at rest, even when insulin decreases.

🚴 Contraction-Mediated Glucose Uptake

During exercise, muscles can take up glucose independently of insulin.

🤔 Key Questions

Why does plasma insulin go down during exercise?
Why does a trained person see a smaller % change in insulin compared to an untrained person?
Why does glucagon go up in an untrained person vs. a trained person?

📉 Sympathetic Nervous System on Substrate Mobilization

The sympathetic nervous system plays a role in mobilizing substrates during exercise.

📊 Hormonal Responses to Exercise

Hormones work together to manage fuel during exercise.

↔ Hormone-Substrate Interaction

High levels of lactic acid can affect fat breakdown.

脂肪 What About on Fat?

Epinephrine, norepinephrine, and glucagon increase the breakdown of triglycerides into fatty acids, while insulin, lactate, and H+ ions decrease it. Hormone-Sensitive Lipase (HSL) is the enzyme responsible for this.

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