There’s a strong belief amongst combat sport athletes that having a higher body mass than their opponent provides a competitive advantage, and therefore increases their likeliness to win.
There’s emerging evidence that this theory may hold true in non-striking, grappling based sports such as judo when done safely (Reale et al, 2016), but is less apparent in striking based sports such as boxing.
Many combat sport athletes use rapid weight loss (RWL) strategies to ‘make weight’, then adopt rapid weight gain (RWG) strategies to replenish and rehydrate over the course of 24 hours.
Of which, MMA athletes appear to follow this RWL-RWG strategy to a greater extent than boxers, wrestlers and BJJ athletes.
When RWL is taken to greater magnitudes via dehydration, the likeliness of brain trauma, kidney injury and in some cases death can result.
To combat extreme RWL-RWG cycles, the California State Athletic Commission (CSAC) have introduced two weigh-ins for MMA athletes: 24 hours prior and on the day of competition to determine whether the athletes have regained more than 10% of their body mass.
Kirk et al (2020) assessed the data from 5 professional MMA events held in California (4 x UFC and 1 x Bellator MMA) to determine the effect of rapid weight gain on winning and losing.
Of the 62 fights being assessed (no heavyweights), there was no statistical difference in an athlete winning or losing based on how much weight was regained post ‘weighing in’…and therefore provides no competitive advantage regardless of how the bout ended: strikes, submission or decisions.
To further this point, analysis by Daniele et al (2016) found no effect of RWG and success in 71 boxing championship bouts.
Interestingly, the increase in body mass via RWG placed the athletes in 1-2 weight categorises higher than their actual weight division.
Considering the notion that RWL-RWG cycles do not determine success in MMA, it should hopefully discourage extreme weight making practices and spark conversations between governing bodies, the athlete and coach on what weight division is best to compete in.
Understandably, it isn’t an easy decision for an athlete to change weight categories due to scheduled fights, sponsors, politics etc. But ultimately, more sensible weight loss and weight regain strategies are needed, and this data provides a novel insight and stepping stone in making this change.

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