Testosterone and Training Adaptations

Testosterone: Synthesis and Effects

Testosterone Synthesis and Cholesterol

  • Testosterone is synthesized from cholesterol.
  • Cholesterol, despite its negative reputation, plays an important role in the body.
  • There's ongoing debate regarding the impact of dietary cholesterol intake on health, with some concerns about its link to heart disease being questioned.

Effects and Characteristics of Testosterone

  • Testosterone is crucial for differentiating between male and female sexual characteristics.
  • It exhibits a diurnal effect, with concentrations being highest in the morning.
  • The molecular structure of testosterone is derived from cholesterol.

Steroid Hormone Biosynthesis

  • Cholesterol is the precursor for several hormones, including:
    • Pregnenolone
    • Progesterone
    • DHEA
    • Testosterone
    • Oestradiol (via aromatization of testosterone)
    • DHT (via 5α-reductase conversion of testosterone)
    • Cortisol (a glucocorticoid)
    • Aldosterone (a mineralocorticoid)

Sex Differences in Testosterone Secretion

  • Males:
    • The hypothalamus releases gonadotropin-releasing hormone (GnRH).
    • GnRH stimulates the anterior pituitary gland to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
    • LH stimulates Leydig cells in the testes to produce testosterone.
    • FSH stimulates Sertoli cells to induce spermatogenesis.
  • Females:
    • Testosterone is secreted from the ovaries and adrenal gland.

Training and Testosterone

  • Training induces hormonal responses, including anabolic effects from insulin-like growth factor, growth hormone, and testosterone.
  • Testosterone, being a steroid hormone, can cross the cell phospholipid bilayer and interact with androgen receptors (AR).
  • This interaction can directly impact the cell's nucleus, promoting muscle hypertrophy.

Detailed Interactions of Testosterone

  • DHEA, a precursor to testosterone, is converted by enzymes such as 17β-hydroxysteroid dehydrogenase and 3β-hydroxysteroid dehydrogenase.
  • Testosterone can be converted to dihydrotestosterone (DHT) by 5α-reductase enzymes to exert its physiological actions and bind to androgen receptors.
  • Estrogens can be synthesized from androgens.
  • Exercise can influence testosterone and DHT levels.
  • These hormones impact cell signaling pathways (AKT, P70S6K1, mTOR) to increase muscle protein synthesis and muscle mass.
  • Testosterone affects glucose metabolism through the AKT pathway, influencing GLUT4 transporters and increasing insulin sensitivity.

Testosterone Production and Sex Differences

  • Adult males produce about 7mg of testosterone per day.
  • Females produce approximately 10% of this amount.
  • Historically, this difference was thought to explain variations in hypertrophic responses and muscle mass between sexes, as well as strength differences.

Testosterone Responses to Exercise

  • Study by Sartu in 2015 examined testosterone responses in lean, obese individuals, and those supplemented with DHEA and exercise training.
  • Obese individuals generally have low muscle DHT concentrations without intervention.
  • Exercise can significantly boost DHT concentrations.
  • 5α-reductase activity follows a similar pattern.

Testosterone and Performance

  • Basal testosterone levels are related to explosiveness.
  • Countermovement jump performance is positively correlated with basal testosterone levels (r ≈ 0.62 for men, r ≈ 0.48 for women).
  • Sports with a greater anaerobic component tend to have athletes with higher basal testosterone levels.
  • The relationship between anaerobic activity, genetics, and trainability affects basal testosterone levels.

Testosterone and Muscle Fiber Types

  • A causal relationship may exist between basal testosterone levels and the development of type II muscle fibers.
  • Type II fiber hypertrophy is related to the concentration of circulating basal testosterone.
  • Cross-sectional area of type II fibers is significantly correlated with changes in free testosterone.

Androgen Signaling and Resistance Exercise

  • Hypothalamic-pituitary-gonadal axis influences androgen concentrations.
  • Exercise may alter androgen concentrations, binding proteins, and tissue uptake.
  • Skeletal muscle steroidogenesis can occur.
  • Intramuscular signaling is affected by androgen receptors, which can be up or down-regulated with exercise.
  • AR transcriptional potency can also be altered.

Androgen Receptors and Resistance Training

  • Post-exercise, androgen receptor density increases up to 48 hours after exercise.
  • This suggests cells become more receptive to testosterone.
  • Expression of androgen receptor proteins also increases.

Age-Related Adaptations to Resistance Training

  • Serum testosterone concentrations after exercise show a similar change between young and older adults, although the elevation may last longer in younger adults.
  • After 21 weeks of chronic resistance training, older adults may experience a greater increase in testosterone concentration post-exercise.

Androgen Receptor Protein Concentration Changes

  • Androgen receptor concentrations tend to increase post-exercise.

Relationship Between Testosterone and Androgen Receptors

  • Study by Huber et al. in 2017 examined this relationship in fed and fasted states.
    • Fasted State:
      • Testosterone increases initially after exercise but returns to baseline within 10 minutes.
      • No changes in androgen receptor content 60 minutes post-exercise.
    • Fed State:
      • After the initial increase, testosterone returns to baseline and drops below it for the remainder of the 60 minutes.
      • Androgen receptor content increases, potentially indicating greater testosterone uptake into cells.
  • Adequate nutrition around training sessions is crucial.

Androgen Receptors and Hypertrophy

  • Study by Athenine in 2011 showed associations between androgen receptor protein concentration, changes in muscle cross-sectional area, and relative changes in lean body mass.

Factors Impacting Testosterone Release

  • To maximize testosterone release:
    • Focus on large muscle group exercises (compound lifts).
    • Use heavy resistances (≥ 70% of 1RM).
    • Perform a moderate to high volume of exercise (multiple sets and exercises).
    • Use short rest intervals (30 seconds to 1 minute).
  • More resistance-trained individuals typically have a more favorable testosterone response to exercise.

Intensity, Volume, and Testosterone Responses

  • Studies have examined the effects of intensity and volume on acute total testosterone responses.
    • Weiss et al. (3 sets of 4 exercises to failure with 80% of 1RM, 2-minute rest intervals) found a significant increase in testosterone.
    • Radimas et al. (compared 1 set vs. 6 sets of 10 repetitions of squats) found no change in the 1-set group but a significant increase in the 6-set group.
  • Mixed evidence exists regarding the impact of one-minute rest intervals on serum testosterone levels.

Programming Considerations

  • Training sessions designed to evoke an increase in testosterone release may not be optimal for strength and athletic performance development.
  • Prioritize performance gains over chasing hormonal responses.

West et al. Study: Hormone Response vs. Performance

  • Compared a "high hormone" protocol (designed to maximize hormonal response) with a "low hormone" protocol.
  • The high hormone group showed greater increases in lactate, growth hormone, testosterone, free testosterone, and cortisol.
  • However, there was no difference in type II muscle fiber cross-sectional area or elbow flexor cross-sectional area between the groups.
  • Acute rises in hormonal concentrations post-resistance training may have limited impact on long-term adaptive responses.
  • No relationship (r = 0.001) was found between the increase in testosterone and hypertrophic responses.

Key Takeaways

  • Training for acute hormonal fluctuations may not maximize hypertrophy or strength.
  • Exercise volume, intensity, and nutrient timing are more important for stimulating muscle protein synthesis.
  • Hierarchy of Relevance to Hypertrophy:
    1. Anabolic steroids (strongest effect, not advocated)
    2. Muscle fiber recruitment and exercise volume (mechanical strain)
    3. Dietary intake (protein source and timing)
    4. Exercise load
    5. Acute exercise-induced hormone release (smallest effect)
  • The study by Sato et al. (12 weeks of resistance training) provides valuable insights.
  • High-intensity interval training (HIIT) can potentially positively impact testosterone levels.