Rapid weight gain predicts fight success in mixed martial arts - evidence from 1,400 weigh-ins.

We aimed to analyze whether rapid weight gain (RWG) between the official weigh-in and the time of the fight was associated with fight success in MMA. A total of 700 professional MMA fights involving 1,400 weigh-ins from 21 MMA promotions regulated by the California State Athletic Commission were analyzed. Multilevel logistic regression accounting for individual (i.e. athlete) and cluster levels (i.e. fights) was used to analyze the association of all measures with a theoretical relationship with the dependent variable and without interdependency with one another (i.e. %RWG, sex, body mass division, competition level) with the fight outcome (i.e. win or loss). The odds ratios (OR) with 95% confidence intervals (95%CI) were calculated. The highest mean %RWG was found for the flyweight, bantamweight, featherweight, and lightweight divisions. The %RWG significantly predicted the fight outcome (ß = 0.044; OR = 1.045; 95%CI = 1.014-1.078;  = 0.005) so that for each 1% of additional RWG, the chance of winning increased by 4.5%. With the largest sample to date and in a "real-world" scenario, the present results suggest that the magnitude of RWG is linked to the chance of winning in MMA combats. It is suggested that regulatory commissions, confederations, and event organisers should consider regulating RWG, considering that, despite its detrimental impact on the athletes' health and performance, the potential advantage might stimulate athletes to invest in rapid weight loss, followed by gain after the official weigh-in to increase their chance of winning.