Background Judo competitions are divided into weight classes. Some athletes reduce their body weight in short time in order to obtain a competitive advantage over lighter opponents. Fast weight loss comprises dehydration strategies that could place the athletes at health risk. Since nutrition is often the missing piece in the athlete's knowledge, the judoka is not aware of the risk taken. Hypohydration leads to a diminution of function and so has many negative effects on health (musculoskeletal and neurological).

Objective To assess the feasibility of a Bioelectrical Impedance Analysis (BIA) based hydration status monitoring system before the competition and to compare it with a urine color chart scaling system.

Design Observational descriptive study with anonymous data collection after informed consent during the Team Championship finals of the Swiss Judo Federation (SJV).

Setting Field measurements on the competition day just after the official selection weight-in through BIA octopolar fluid balance electrical measurement, questionnaire data.

Participants All accepting male athletes of the elite national Swiss teams.

Risk factor assessment Body weight, hydration habitus and status.

Main outcome measurements Extracellular/Intracellular and Total body water content status before entering the fighting mat (precompetitive hydration status).

Results 35 out of 48 athletes accepted to participate. 54% were under the current accepted euhydration status, but only 14% were in the non optimal urine color group. 70% had inappropriate drinking habits.

Conclusions Bioelectrical Impedance Analysis (BIA) is a quick way to determine the total water content of competitive judokas on the field without being invasive and seems to be more precise than a color chart evaluation. Clinical application: it can help the Judo community to gather better knowledge on hydration problems. We expect this system to be part of a national and an international strategy of tracking hydration questions.