Thyroid hormones, performance, and psychological changes on overtraining in female distance runners

Statement of the Problem: Overtraining (OT) is common in endurance sports. Perturbations in the hormonal milieu are common throughout OT literature. Thyroid hormones (TH) are altered by energy imbalances, and these imbalances are often present in female endurance athletes. Thyroid hormones also regulate metabolism, energy production, and therefore they may play a role in commonly cited symptoms of OT in these athletes. Alterations in TH status often occur slowly, and research investigating TH and their relationship in overtrained athletes is sparse. PURPOSE: The purpose of this study was to investigate relationships in TH and commonly cited symptoms of OT in collegiate track and field (T&F) endurance runners. METHODS: Sixteen female track and field middle (MD; n=9; age: 20.21 +/- 1.49 yrs; height: 167.86 +/- 5.04 cm; body mass: 57.97 +/- 5.05 kg; VO2MAX: 53.62 +/- 6.04 ml/kg/min) and long (LD; n=7; age: 20.47 +/- 1.53 yrs; height: 162.48 +/- 6.11 cm; body mass: 56.15 +/- 5.99 kg; VO2MAX: 61.94 +/- 3.29 ml/kg/min) distance runners participated in a 14 week descriptive study. Thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4), were collected at the beginning of the indoor T&F (PRE) and end of the outdoor T&F season (POST). Dietary intake and vertical jump power (VJP) were tested at PRE, MID, and POST season. A fatigue scale was administered weekly, and percent change (DeltaRT) in race time (season best v.s. championship performance) was calculated. Wilcoxon-sign ranked tests were used to determine changes in hormonal, dietary, and performance measures over time. Spearman's rho correlation coefficient was used to determine relationships between thyroid hormones, dietary intake, performance variables, and commonly cited symptoms of overtraining. Statistical significance was set at an alpha level of p ≤ 0.05. RESULTS: Fatigue was significantly lower at week 2 compared to MID season (p=0.016), week 12 (p=0.018) and POST (p=0.007). There was a significant correlation between fatigue at week 12 and running performance at the end of the season (rho= -0.741, p= 0.004). Vertical jump power significantly increased PRE to MID season in MD and LD. Power significantly deceased MID to POST in MD. There were no significant changes in TSH, T3 and T4 from PRE to POST. There were significant correlations between total caloric intake at POST and peripheral hormones (T3 POST; rho = 0.900, p= 0.037. T4 POST; rho= 0.667, p=0.050). The percent change (PDelta) in T3 from PRE to POST was significantly correlated with running performance at the end of the season (rho=-0.700, p=0.036). Most of the subjects fell below current the RDA for carbohydrates and protein at PRE and POST. There was a significant relationship between caloric intake relative to lean body mass (kcal•kgLBM-1) at PRE and fatigue at week 1 (PRE) (rho= -0.521, p=0.046). CONCLUSION: There were no significant differences between PRE and POST thyroid hormone concentration. Thyroid hormones are related to other variables of important in assessing the overall training state of the endurance athlete. Resting thyroid hormone concentrations may change too slowly to be a frequently used marker of monitoring overtraining status. Using weekly fatigue scales, monitoring dietary intake, and the utilization of VJP may be more readily available markers to assess overtraining and overall training status of collegiate female endurance runners.