This case report describes 3-year longitudinal changes in body composition and water turnover in a world-class male judo athlete, providing proof of concept for high-precision monitoring that offers insights into body water dynamics and seasonal physiological variations for developing safer weight-management strategies in combat sports.
Key Findings
Results
The world-class male judo athlete's body mass increased by 2.7 kg between his second and third collegiate years, with fat-free mass accounting for approximately three-quarters of this gain.
Fat-free mass (FFM) increased by 1.9 kg between the second and third years
Similar increases in body mass and FFM were observed between the second and fourth years
Measurements were conducted annually over 3 years (second to fourth collegiate years)
Body composition was assessed using the deuterium dilution method
Results
The athlete maintained a rigorous training load of 11 sessions per week throughout the study period, including during recovery from injury.
During injury recovery periods, the athlete substituted intensive resistance training for judo to maintain training load
The training load of 11 sessions/week was maintained across all measurement periods
This consistent training load occurred across the 3-year study spanning second to fourth collegiate years
Results
Seasonal fluctuations in water turnover (WT) were observed throughout the study period, reflecting varying training loads and competition schedules.
Water turnover and total body water were both assessed using the deuterium dilution method
Fluctuations in WT accompanied changes in body composition
The seasonal variations in WT corresponded to changes in training demands and competitive calendar
Measurements were conducted annually during the three collegiate years
Conclusions
This case report provides a proof of concept for high-precision longitudinal monitoring of body water dynamics and physiological variations in a world-class athlete.
The deuterium dilution method was used to assess both water turnover and total body water
The study represents one of the limited longitudinal datasets on the physiology of world-class athletes in weight-category sports
The authors describe the findings as offering 'valuable insights into body water dynamics and seasonal physiological variations'
The authors propose this monitoring approach could inform 'safer weight-management strategies in judo and other combat sports'
What This Means
This research followed a world-class male college judo competitor over three years, tracking changes in his body composition and how much water his body cycled through (called water turnover). Using a precise scientific technique involving a safe form of hydrogen called deuterium, researchers measured his total body water and water turnover annually. Over the study period, the athlete gained about 2.7 kg of body mass, and roughly three-quarters of that gain was lean muscle mass rather than fat — a sign of productive athletic development. Even when injured, he kept up an intense schedule of 11 training sessions per week by switching to heavy resistance training instead of judo practice.
The researchers also found that the athlete's water turnover fluctuated with the seasons, rising and falling in sync with heavier training periods and competition schedules. This suggests that tracking water turnover could be a useful tool for understanding how an athlete's body is responding to training demands over time. Because combat sports like judo involve weight-class competition, athletes often engage in rapid and sometimes dangerous weight-cutting practices before events, and understanding normal water dynamics could help design safer approaches.
This research suggests that detailed, long-term physiological monitoring of elite athletes — even in a single-person case study format — can reveal meaningful patterns in how the body changes in response to training and competition cycles. The findings highlight the potential value of the deuterium dilution method as a high-precision tool for tracking athletes in weight-category sports, which could eventually contribute to evidence-based guidelines for safer weight management in judo and similar combat sports.
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Takubo N, Kondo E, Uchizawa A, Hiraoka H, Masuchi K, Okada H, et al.. (2026). Longitudinal changes in body composition and water turnover in a world-class male judo athlete: A case report.. Physiological reports. https://doi.org/10.14814/phy2.70965