Hormones

Overview of Hormones

• Definition: Hormones are chemical messengers that regulate physiological processes in the body, influencing growth, metabolism, and the body's response to stress.

Types of Hormones

• Anabolic Hormones: Includes IGF-1, testosterone, and growth hormone, which promote muscle growth and protein synthesis.

• Catabolic Hormones: Includes cortisol, which is associated with stress response and can lead to protein breakdown.

• Minor Anabolic Effects: Insulin has some anabolic properties, mainly aiding in glucose and amino acid uptake.

Mechanisms of Action

• Hormones act through specific receptors on cells that guide physiological responses.

  • Protein Hormones: Bind to surface receptors on cells because they cannot pass through the lipid bilayer.

    • Example: Insulin stimulates glucose uptake and quick physiological changes like phosphorylation.

  • Steroid Hormones: Lipid-soluble, can pass through cell membranes, often bind to receptors in the cytoplasm or on DNA to directly influence gene expression.

    • Example: Testosterone promotes protein synthesis by activating gene transcription.

Hormone Availability and Regulation

• Receptors: Hormone receptor sensitivity can be altered.

  • Receptor downregulation can occur from chronic high levels of hormones, reducing effectiveness (common in drug use).

• Hormone Secretion and Degradation: Hormonal levels fluctuate based on timing, body fat, nutrition, and can be quickly degraded, affecting their physiological impact.

• Free vs. Bound Hormones: Only free hormones can exert physiological effects. Carrier proteins regulate the availability of steroid hormones in the blood.

Acute Exercise and Hormonal Response

• Resistance training causes acute increases in various hormones, though correlation with muscle strength and hypertrophy is complex.

  • No clear evidence shows a direct relationship between acute hormonal changes and strength or hypertrophy improvements.

  • Certain levels of hormones, such as testosterone, are necessary for hypertrophy, but acute responses alone do not predict outcomes.

The Role of Specific Hormones

• Growth Hormone: Stimulates growth across multiple body tissues; low exercise intensity does not significantly increase growth hormone levels. In older populations, growth hormone may lead to less muscle mass gain. Acromegaly presents side effects from excessive growth hormone.

• Insulin-Like Growth Factors (IGFs): Released from the liver in response to growth hormone, IGFs promote muscle growth; studies have shown complicated relationships with strength and size increases.

• Testosterone: Highest levels in the morning; has anabolic and androgenic effects, influencing muscle mass and strength. Gender differences exist in baseline levels and variations throughout the day.

• Cortisol: Peaks during stress and influences metabolism but can be harmful when chronically elevated. Exercise increases cortisol levels, particularly in high-intensity workouts.

Research Challenges

• Variability: Numerous factors—including body fat, nutrition, stress, and hormonal cycles—impact hormone levels, complicating human research studies.

• Study Design: Most studies are limited in controlling all present variables, making it challenging to draw clear conclusions regarding hormonal influence on hypertrophy and strength.

Summary of Hormonal Influence

• Anabolic hormones contribute significantly to muscle hypertrophy, yet evidence suggests complex interactions rather than straightforward correlations. Understanding and measuring these effects require careful consideration of timing, overall body condition, and hormonal context in research studies.