Study – Fighters Who Regain More Weight Post Weigh in Enjoy More Success

Extreme dehydration followed by rapid weight gain are common in combat sports. Many well documented injuries and even deaths are linked to these practices. But they persist because athletes believe they have a competitive advantage if they outweigh their opponents by the time of competition. A recent study revealed that these beliefs are supported.

In the study, published in International Journal of Sports Physiology and Performance and titled Rapid Weight Gain and Weight Differential Predict Competitive Success in 2100 Professional Combat-Sport Athletes, the authors reviewed both MMA and boxing athletes. They looked how much weight gain each athlete had post weigh ins and the weight differential in the bouts. They then analyzed the bout results.

708 MMA athletes were included and 1,392 boxers. In short the data revealed that “each percentage body mass increase resulted in a 7% increased likelihood of victory in MMA and a 13% increase in boxing.“. The boxers and MMA athletes that outweighed their opponents won at a higher rate with weight differential being a useful predictor of victory.

The full abstract reads as follows:

Purpose: Combat-sport athletes commonly undergo rapid weight loss prior to prebout weigh-in and subsequently rapid weight gain (RWG) prior to competition. This investigation aimed to evaluate the effect of RWG and weight differential (WD) between opponents on competitive success. 

Methods: A retrospective cohort study was performed using data from professional mixed martial arts (MMA) and boxing events held between 2015 and 2019. The primary outcome was RWG (relative and absolute) between weigh-in and competition stratified by bout winners and losers. Binary logistic regression was used to explore the relationships among bout outcome, RWG, and WD between competitors on the day of their bout. 

Results: Among 708 MMA athletes included, winners regained more relative body mass (8.7% [3.7%] vs 7.9% [3.8%], P < .01) than losers. In 1392 included male boxers, winners regained significantly more relative body mass (8.0% [3.0%] vs 6.9% [3.2%], P < .01) than losers. Each percentage body mass increase resulted in a 7% increased likelihood of victory in MMA and a 13% increase in boxing. The relationship between RWG and competitive success remained significant in regional and male international MMA athletes, as well as boxers. WD predicted victory in international mixed martial artists and boxers. WD predicted victory by knockout or technical knockout in international MMA athletes and regional boxers. 

Conclusion: This analysis of combat-sport athletes indicates that RWG and WD influence competitive success. These findings raise fair-play and safety concerns in these popular sports and may help guide risk-mitigating regulation strategies.


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