Physiological Biomarkers of Overtraining Syndrome in Competitive Long-Distance Runners Affiliated with Athletics Federations in Oyo State, South West Nigeria

Background: Overtraining syndrome results from an imbalance between training load and recovery, producing persistent performance decrements, hormonal dysregulation, and autonomic nervous system alterations. Nigerian competitive athletics lacks standardised physiological monitoring protocols for detecting early overtraining, exposing athletes to risk of injury and prolonged performance decline. Objectives: This study aims to identify physiological biomarkers of overtraining syndrome, including resting heart rate, heart rate variability, morning cortisol, testosterone-to-cortisol ratio, and mood state, in competitive long-distance runners affiliated with Oyo State athletics associations and to correlate biomarker profiles with training load and performance metrics. Methods: Fifty runners will be assessed during high-intensity training blocks and compared with low-intensity recovery periods using a repeated measures crossover design. Morning heart rate and heart rate variability will be recorded daily by wearable monitors. Saliva will be collected on assessment days for cortisol and testosterone quantification. The Profile of Mood States questionnaire will assess psychological wellbeing. Wilcoxon signed-rank tests and mixed-effects regression will be applied. Expected Outcomes: Runners during high training load phases are anticipated to show elevated cortisol, reduced testosterone-to-cortisol ratios, suppressed heart rate variability, and worse mood state scores consistent with early overtraining syndrome. Conclusion: Findings will support the adoption of evidence-based physiological monitoring within Nigerian competitive athletics coaching. Keywords: overtraining syndrome, cortisol, heart rate variability, long-distance runners, Oyo State.