Hydration Status and Thermal Stress as Predictors of Fatigue and Performance Decline in Sub-Elite Soccer Players

Background. Soccer players competing in tropical climates experience combined dehydration, thermal strain, and metabolic stress, yet field-based evidence linking these factors to performance decline remains limited. Objectives. This study aimed to examine the predictive relationships between hydration status, thermal stress, metabolic factors, and fatigue-related performance decline in sub-elite soccer players under tropical heat conditions. Materials and Methods. Thirty male sub-elite soccer players (22.4 ± 3.1 years) participated in a simulated 90-minute match conducted in temperatures ranging from 31 to 33°C, with relative humidity levels between 65 and 75%. Hydration (bioimpedance), blood lactate, muscle temperature, heart rate, shooting accuracy, and anaerobic power (RAST) were assessed pre-, mid-, and post-match. Repeated-measures ANOVA and multiple regression were used (p < 0.05). Results. TBW decreased significantly (−4.2%), while lactate (1.3 → 10.4 mmol·L⁻¹) and muscle temperature (33.4 → 37.1°C) increased across match segments (p < 0.001). Shooting accuracy (−14%) and peak anaerobic power (−4.6%) declined post-match. Regression analysis identified ΔTBW (β = −0.41, p = 0.008) and peak lactate (β = 0.48, p = 0.003) as significant predictors of fatigue (R² = 0.61). Conclusions. The findings indicate that loss of hydration, thermal strain, and metabolic accumulation are all important signs of a subject’s deterioration in performance levels under tropical match conditions. Athletes can improve their health and performance by drinking enough fluids and keeping their body temperature under control.