Sex Does Not Affect Changes in Body Composition and Insulin-Like Growth Factor-I During US Army Basic Combat Training

Area of Science:

• Exercise Physiology
• Endocrinology
• Human Performance

Background:

• Insulin-like growth factor 1 (IGF-I) is recognized as a biomarker for health and body composition.
• The association between body composition changes and IGF-I levels during intense training is not well understood.

Purpose of the Study:

• To investigate the relationship between changes in body composition (lean mass and fat mass) and total serum IGF-I levels.
• To examine these relationships in a large cohort of male and female US Army basic combat training (BCT) recruits.

Main Methods:

• Dual energy x-ray absorptiometry (DXA) was used to measure body composition.
• Total serum IGF-I levels were measured at the beginning (week 1) and end (week 9) of BCT.
• Partial correlations were analyzed to assess associations while controlling for other variables.

Main Results:

• Body mass, body mass index, body fat percentage, and fat mass decreased, while lean mass increased during BCT (all p < 0.001).
• Mean IGF-I levels significantly increased from pre-BCT (176 ± 50 ng·ml⁻¹) to post-BCT (200 ± 50 ng·ml⁻¹, p < 0.001).
• Increases in IGF-I during BCT were weakly associated with increases in both lean mass (r = 0.0769, p = 0.023) and fat mass (r = 0.1055, p < 0.001), with no sex differences.

Conclusions:

• While changes in IGF-I showed a weak correlation with body composition shifts during BCT, IGF-I alone is insufficient as a biomarker for predicting these changes.
• The findings suggest that sex does not influence the changes in body composition or IGF-I levels observed during BCT.