Exercise-Induced Hormone Elevations Are Related to Muscle Growth

Area of Science:

• Exercise Physiology
• Endocrinology
• Sports Science

Background:

• Muscle hypertrophy is influenced by various physiological factors.
• The endocrine response to resistance exercise is a key area of investigation for understanding muscle growth.
• Previous research suggests a link between hormones and muscle adaptation, but specific relationships require further elucidation.

Purpose of the Study:

• To examine the relationship between the endocrine response to resistance exercise and muscle hypertrophy in resistance-trained men.
• To determine if different resistance training protocols (high-volume vs. high-intensity) differentially affect hormonal responses and muscle growth.
• To utilize Partial Least Squares Structural Equation Modeling (PLS-SEM) to analyze these complex relationships.

Main Methods:

• 26 resistance-trained men participated, with muscle size (vastus lateralis, rectus femoris) measured pre- and post-training.
• Participants were randomized to either a high-volume (VOL) or high-intensity (INT) resistance training program.
• Hormonal responses (testosterone, growth hormone, IGF-1, cortisol, insulin) were assessed via area-under-the-curve (AUC) analysis across multiple time points during weeks 1 and 8.
• PLS-SEM was employed to model the relationships between baseline muscle size, hormonal AUCs, and post-training muscle size.

Main Results:

• The PLS-SEM model explained 73.4% of the variance in post-training muscle size.
• Significant positive pathways were observed between testosterone levels and both pre-existing and post-training muscle size.
• The model's predictive ability for post-training muscle size was notably high when analyzed separately for the INT (R=0.882) and VOL (R=0.987) groups.

Conclusions:

• Exercise-induced elevations in testosterone appear to be independently related to muscle growth in resistance-trained men.
• The findings suggest that testosterone plays a significant role in mediating muscle hypertrophy, irrespective of the specific resistance training protocol employed.
• This study provides valuable insights into the hormonal mechanisms underpinning muscle adaptation to resistance exercise.