Acute weight cycling and hydration status in elite kickboxers: a repeated-measures field study

This study aimed to monitor acute changes in body weight and hydration status—measured via urine-specific gravity (USG) and urine color (UC)—in elite-level kickboxers during a real-world competitive environment. The research sought to provide critical insights into current weight-management practices and the prevalence of hypohydration during the pre-competition period. Using a cohort repeated-measures design, ten elite male kickboxers (age: 20.5 ± 2.8 years) were monitored at four distinct time points: one week before the competition (T1), one day before the official weigh-in (T2), at the official weigh-in (T3), and on the competition day (T4). Body weight was measured using a calibrated scale, and body composition was assessed via bioelectrical impedance. Hydration status was evaluated through midstream urine samples analyzed for USG and UC. Hypohydration was defined as a USG ≥ 1.020. Athletes underwent significant rapid weight loss (RWL), losing an average of 3.1 ± 1.7 kg (4.2%) in the week leading up to the weigh-in. This was followed by a rapid weight regain (RWG) of 3.3 ± 1.4 kg (4.8%) between the weigh-in and the start of the competition. Hydration markers worsened significantly as weight decreased, with USG and UC values peaking at the official weigh-in (1.030 ± 0.006 and 7.3 ± 1.3, respectively), indicating peak hypohydration. Notably, while 50% of athletes were hypohydrated at T1, all remained hypohydrated on competition day (T4) despite the substantial weight regain. The results indicate that elite kickboxers engage in significant RWL followed by RWG that returned athletes to their starting body weight. However, this weight gain does not equate to recovery of a euhydrated state, as the vast majority of athletes remain hypohydrated at the start of competition. Coaches and athletes should implement personalized, professional rehydration plans rather than relying on acute weight gain as a proxy for hydration recovery.