(41) MATURITY-ASSOCIATED LONGITUDINAL VARIATIONS IN RESISTANCE EXERCISE-INDUCED ACUTE HORMONAL RESPONSES IN YOUNG MALE ATHLETES

Resistance training is recognized as an effective method for improving performance variables (e.g., muscle strength and motor skills) in young athletes. However, the implications of maturity-associated changes in hormonal responses for the training of young athletes are unclear.

Purpose: This study aimed to examine the maturity-associated longitudinal changes in exercise-induced hormonal responses in male adolescent athletes.

Methods: Fifteen junior high school male athletes volunteered to participate in this study. On the basis of the difference between the predicted age at peak height velocity (APHV) and the chronological age (CA) at baseline, the participants were assigned to either the pre-PHV group (CA< APHV, n=7, CA: 12.9±0.6 years, APHV: 13.4±0.6 years) or the post-PHV group (CA >APHV, n=8, CA: 13.0±0.5 years, APHV: 12.2±0.6 years). Salivary testosterone (T) and cortisol (C) levels were evaluated before (PRE), immediately after (POST), and 15 min after basic resistance exercise using body weight. The T-to-C ratio (T:C ratio) was calculated and used as an indicator of a positive anabolic state. Measurements were performed in May 2018 (baseline) and May 2019, and the participants’ consecutive 1-year data were analyzed. Separate 2 (groups)×2 (years)×3 (measurement times) repeated-measures analyses of variance were performed for the 1-year biological maturity-associated changes in exercise-induced hormonal responses.

Results: For the T levels, significant main effects of year (p< 0.001, η²_p=0.42) and group (p=0.025, η²_p=0.18) were found, with a significant three-way interaction (p=0.035, η²_p=0.12). The main effects of measurement time were not significant. At one year from baseline, the T levels were significantly higher in the post-PHV group than in the pre-PHV group at PRE (p=0.007, d=1.13) and 15 min after exercise (p=0.024, d=1.00). Significant main effects of measurement time were observed for the C levels (p< 0.001, η²_p=0.35). Significant decreases from POST to 15 min after exercise were identified within the pre-PHV group at baseline (p=0.007, d=0.72). In the post-PHV group, significant decreases were observed at 15 min after exercise in the baseline evaluation (15 min after exercise vs. PRE: p=0.02, d=0.84 15 min after exercise vs. POST: p=0.02, d=0.57) and at both measurement times after exercise in the 1-year evaluation (POST vs. PRE: p=0.02, d=0.40 15 min after exercise vs. PRE: p=0.004, d=0.56). Significant main effects of year (p=0.049, η²_p=0.14) and measurement time (p< 0.001, η²_p=0.30) were observed for the T:C ratio. In the post-PHV group, the T:C ratio at all measurement times was significantly higher at 1 year than at baseline (p=0.026-0.05, d=0.81-0.97). In the 1-year evaluation, the T:C ratio was significantly higher at 15 min after exercise than at PRE (p=0.011, d=0.54) and POST (p=0.023, d=0.45) in the post-PHV group and significantly higher at 15 min after exercise than at POST (p=0.034, d=0.53) in the pre-PHV group.

Conclusions: The maturity level of junior high school male athletes is not sufficient for exercise-induced T secretion responses to occur, although the T levels naturally increase with age. PRACTICAL APPLICATION: When setting training goals for adolescent athletes, coaches and trainers should place a lower priority on muscle synthesis or hypertrophy than on any other performance improvement variable.


Acknowledgements:

This study was supported by a grant from JSPS KAKENHI (JP20K19514), the National Strength and Conditioning Association Japan (NSCA JAPAN), and Foundation for Growth Science. The authors thank all of the athletes who participated in this study. No potential conflicts of interest were reported by the authors.