Seasonal Changes in Performance Metrics, Hormonal, Hematological, and Biochemical Markers Among Semi-Professional Soccer Players: Implications for Training and Recovery.

Objectives: This study examined physiological, biochemical, and performance adaptations in 18 semi-professional male soccer players across three seasonal phases: pre-season initiation (PS), pre-competition (PC), and mid-season (MS). Methods: Assessments included physical/performance/hormonal/biochemical markers. Results: From PS to PC, body fat (Cohen's d = -0.88; p ≤ 0.01) and speed drop rate (Cohen's d = -1.52; p ≤ 0.01) significantly decreased, while V̇O(2)max (Cohen's d = 0.80; p ≤ 0.01), velocity at V̇O(2)max (Cohen's d = 1.86; p ≤ 0.01), and velocity at the second ventilatory threshold (Cohen's d = 1.54; p ≤ 0.01) significantly increased. Significant fluctuations were observed in creatine kinase (Cohen's d = 4.34; p ≤ 0.01), myoglobin (Cohen's d = 0.66; p ≤ 0.01), and cortisol (Cohen's d = -1.14; p ≤ 0.01) levels. From PS to MS, further reductions in body fat (Cohen's d = -0.81; p ≤ 0.01) and speed drop rate (Cohen's d = -1.12; p ≤ 0.01) were observed, along with significant improvements in countermovement jump performance (Cohen's d = 1.08; p ≤ 0.01) and cardiorespiratory fitness (Cohen's d ≥ 0.83; p ≤ 0.01). Creatine kinase (Cohen's d = 3.82; p ≤ 0.01), myoglobin (Cohen's d = 1.50; p ≤ 0.01), interleukin-6 (Cohen's d = 1.24; p ≤ 0.01), and testosterone (Cohen's d = 0.92; p ≤ 0.01) significantly increased. Stability in lower limb strength, flexibility, triglycerides, C-reactive protein, ferritin, liver enzymes, and most hematological parameters suggest resilience to seasonal demands. Conclusions: Seasonal training enhanced fitness and hormonal balance while maintaining physiological stability. These findings underscore the importance of periodized training to manage muscle damage and sustain an anabolic hormonal profile for peak performance. Consistent diet and training support metabolic health, while tailored recovery strategies and season-specific interventions are essential for optimizing performance and minimizing injury risk.