Biochemical Assessment of Hydration Status in Long-Distance Runners During a Road Race in Lagos

Adequate hydration is essential for optimal athletic performance and prevention of exercise-induced metabolic disturbances, and the biochemical characterization of hydration status changes during road racing events in a tropical Nigerian climate is valuable for sports medicine and athlete safety. This study assesses hydration status and associated biochemical changes in long-distance runners participating in a 21-kilometre road race in Lagos. Forty-two registered race participants were recruited. Venous blood samples and urine specimens were collected one hour before the race, immediately post-race, and two hours post-race. Serum osmolality was determined by freezing point depression. Plasma sodium, potassium, creatinine, urea, haematocrit, and haemoglobin were measured by standard methods. Urine specific gravity, osmolality, and colour were assessed as hydration indicators. Sweat rate was estimated from pre- and post-race body weight measurements adjusted for fluid intake. Results show a statistically significant increase in serum osmolality, serum sodium, haematocrit, urea, and creatinine immediately post-race compared to baseline, indicating significant dehydration-induced haemoconcentration. Mean body weight loss was 2.1 percent, exceeding the 2 percent threshold associated with performance impairment. Urine specific gravity exceeded 1.020 in 67 percent of runners immediately post-race. Two runners showed serum sodium above 145 millimoles per litre, consistent with hypernatraemia. Biochemical values largely normalized two hours post-race in adequately rehydrating athletes. The study recommends structured fluid supplementation protocols for road race events in Lagos and similar tropical settings. Keywords: hydration status, long-distance runners, serum osmolality, exercise biochemistry, Lagos.