What are the primary energy sources the body uses during a marathon?

The body primarily uses glucose and glycogen (from muscles and liver) for immediate energy, shifting to fatty acids from fat stores as glycogen depletes.

What hormones are released during a marathon and what do they do?

Hormones like adrenaline, noradrenaline, cortisol, growth hormone, glucagon, ADH, and aldosterone are released to regulate metabolism, mobilize fuel, manage stress, and maintain fluid and electrolyte balance.

Do marathon runners experience a "runner's high," and what causes it?

Yes, runners often experience a "runner's high" due to the release of neurotransmitters like endorphins and endocannabinoids, which provide pain relief and feelings of euphoria or calm.

What are some metabolic byproducts produced during a marathon?

Metabolic byproducts include lactate (which can also be used as fuel), carbon dioxide, heat, and reactive oxygen species (free radicals).

Why is hydration and electrolyte balance important for marathon runners?

Sweating during a marathon leads to significant losses of water and crucial electrolytes (sodium, potassium, chloride, magnesium), which are vital for nerve, muscle, and fluid balance, and must be replenished to prevent dehydration and imbalances.

What Does Your Body Release During a Marathon?

When you run a marathon your body will release?

During a marathon, your body orchestrates a complex symphony of physiological responses, releasing a cascade of hormones, neurotransmitters, metabolic byproducts, and essential energy substrates to sustain prolonged effort, regulate vital functions, and manage the immense physical and mental stress.

Energy Substrates and Fuel Utilization

To power over 26 miles of continuous running, your body strategically mobilizes various energy sources:

Glucose: The immediate and preferred fuel for high-intensity exercise. Your body maintains blood glucose levels through several mechanisms.
Glycogen: Stored forms of glucose found in your liver and muscles.
- Muscle Glycogen: Primarily fuels the working muscles directly.
- Liver Glycogen: Released into the bloodstream as glucose to maintain blood sugar levels, crucial for brain function and to supply other muscles.
Fatty Acids: As glycogen stores deplete (often hitting the "wall" around miles 18-20), your body increasingly relies on fat oxidation. Fatty acids are mobilized from adipose tissue (body fat stores) and converted into energy. This process is more efficient for long-duration, lower-intensity efforts but requires more oxygen per unit of ATP.

Hormonal Responses

A marathon triggers significant changes in your endocrine system, releasing hormones that regulate metabolism, fluid balance, and stress:

Catecholamines (Adrenaline/Epinephrine & Noradrenaline/Norepinephrine): These "fight or flight" hormones surge, increasing heart rate, blood pressure, and respiratory rate. They also stimulate glycogenolysis (breakdown of glycogen) and lipolysis (breakdown of fats) to make more fuel available.
Cortisol: A primary stress hormone, cortisol increases during prolonged exercise. It plays a role in glucose metabolism, mobilizing glucose from non-carbohydrate sources (gluconeogenesis) and facilitating fat utilization. While beneficial acutely, chronically elevated cortisol can have negative effects.
Growth Hormone: Released to promote fat breakdown and spare glucose, further contributing to the shift towards fat oxidation as a fuel source.
Glucagon: This hormone increases to counteract the drop in blood glucose, primarily by stimulating the liver to release glucose from its glycogen stores and to produce new glucose.
Antidiuretic Hormone (ADH) / Vasopressin: Released in response to increased plasma osmolality (due to fluid loss) and decreased blood volume. ADH acts on the kidneys to reabsorb water, helping to conserve body fluid and prevent dehydration.
Aldosterone: Released from the adrenal glands, aldosterone promotes sodium retention in the kidneys, which in turn helps to retain water and maintain blood volume and electrolyte balance.

Neurotransmitters and Mood Modulators

The brain's chemistry undergoes profound changes, influencing perception of pain, fatigue, and mood:

Endorphins: These endogenous opioid peptides are well-known for their analgesic (pain-relieving) effects and contribute to feelings of euphoria, often termed the "runner's high." They help runners push through discomfort.
Endocannabinoids: Similar to the compounds found in cannabis, these lipid-based neurotransmitters also contribute to the runner's high, promoting feelings of calm and reducing anxiety and pain.
Dopamine: Involved in reward, motivation, and motor control. Its release can contribute to feelings of pleasure and sustained effort.
Serotonin: Plays a role in mood, sleep, and appetite. During prolonged exercise, changes in serotonin levels are implicated in central fatigue.

Metabolic Byproducts and Waste

Intense and prolonged metabolic activity inevitably produces various byproducts:

Lactate (Lactic Acid): Produced during glycolysis when oxygen supply isn't sufficient for the rate of energy demand. Lactate is not merely a waste product; it's a valuable fuel source that can be converted back to glucose in the liver or used directly by other muscles and the heart for energy.
Carbon Dioxide (CO2): The primary gaseous waste product of aerobic respiration, exhaled through the lungs.
Heat: Energy conversion is not 100% efficient, and a significant amount of energy is released as heat. This necessitates robust thermoregulation mechanisms, including sweating, to prevent overheating.
Reactive Oxygen Species (ROS) / Free Radicals: Increased oxygen consumption during prolonged exercise can lead to the generation of ROS, which can cause cellular damage. The body has endogenous antioxidant defense systems to counteract this.

Electrolytes and Water

Sweating is the body's primary cooling mechanism, leading to significant losses:

Water: Lost through sweat and respiration, leading to potential dehydration if not adequately replaced.
Electrolytes: Crucial minerals lost in sweat, including sodium, potassium, chloride, and magnesium. These are vital for nerve impulse transmission, muscle contraction, fluid balance, and numerous enzymatic reactions. Imbalances can lead to muscle cramps, fatigue, and more severe conditions like hyponatremia.

Inflammatory and Stress Markers

The physical stress of a marathon triggers an inflammatory response and muscle damage:

Cytokines (e.g., Interleukin-6 - IL-6): Released by working muscles, these signaling proteins play complex roles in inflammation, immune response, and energy metabolism. While some are pro-inflammatory, IL-6 can also have anti-inflammatory effects and stimulate glucose uptake.
Creatine Kinase (CK): An enzyme released into the bloodstream when muscle cells are damaged. Elevated CK levels are a common indicator of muscle breakdown following intense exercise.
Myoglobin: An oxygen-binding protein found in muscle tissue. Its presence in the blood (myoglobinuria) indicates significant muscle damage.

Practical Implications for Marathon Runners

Understanding these physiological releases is critical for optimal performance and recovery:

Strategic Fueling: Proper carbohydrate loading before and during the race ensures adequate glycogen stores and blood glucose.
Hydration and Electrolyte Balance: Consistent fluid intake with electrolyte replenishment is paramount to prevent dehydration and hyponatremia.
Pacing: Managing intensity helps optimize fuel utilization and mitigate the accumulation of metabolic byproducts.
Recovery: Recognizing the inflammatory and muscle damage markers underscores the importance of rest, nutrition, and active recovery strategies post-race to facilitate repair and adaptation.
Mental Fortitude: Acknowledging the role of neurotransmitters like endorphins can help runners mentally prepare for and push through the inevitable discomfort.

The body mobilizes glucose, glycogen, and fatty acids for energy, shifting to fat as glycogen depletes to sustain prolonged effort.
A cascade of hormones, including catecholamines, cortisol, and glucagon, regulates metabolism, fluid balance, and stress responses during the race.
Neurotransmitters like endorphins, endocannabinoids, and dopamine influence pain perception, mood, and motivation, contributing to phenomena like the "runner's high."
Metabolic byproducts such as lactate, carbon dioxide, and heat are produced, requiring efficient removal and thermoregulation.
Significant water and electrolyte losses through sweating necessitate strategic hydration and replenishment to prevent dehydration and maintain essential bodily functions.

Marathon Running: What Your Body Releases, Energy, Hormones, and Recovery