UFC Performance Institute – Fighters Can “Safely” Lose 10% Body Mass During Fight Week

Rapid Extreme Weight Cutting has become a norm in mixed martial arts with athletes often shedding significant pounds in the days before their official weigh ins through methods of dehydration and other extreme steps.

Many have done so without consequence while others have done so to the peril of their health with numerous well documented injuries from the practices including deaths.

The UFC’s Performance Institute recently published Volume 2 of their “Cross Sectional Performance Analysis and Projection of the UFC Athlete”. A nearly 500 page document containing dozens of articles covering a broad range of topics such as sparring, skin infections, recovery protocols and concussion protocols. Included in the document is an article addressing weight cut practices during fight week titled “Weight Cutting and Fight-Week Fueling“.

In the article the authors suggest that during fight week a “fighter can effectively and safely lose 10 percent of his or her body mass without putting health at risk“. In fairness the authors do not suggest that all of this weight be lost via dehydration noting “cutting weight is more than just sitting in a sauna until you have made weight or passed out” but rather a three pronged approach addressing “gut content, stored glycogen and body water“. The latter of course means dehydrating and the document goes on to note “The World Health Organization details 10 percent dehydration to be “life threatening.

Addressing fight week dehydration specifically the authors note as follows

“In the general population, water makes up approximately 60 percent of the human body by weight. This can be much more in fighters because of greater amounts of fat-free (or lean) mass. It is no surprise that many fighters use dehydration as a main method of cutting weight. However, not all dehydration is equal, and the risk to performance and health increases with larger amounts of dehydration. In a single training session, a fighter may lose two to three percent of body weight in sweat, so this amount is clearly not dangerous to health. Pushing this amount to four to five percent is a reasonable amount in a weight cut, but beyond this, dehydration becomes difficult and dangerous. The World Health Organization details 10 percent dehydration to be “life threatening.” Cutting weight using dehydration can be achieved by either manipulating fluid intake (e.g., drinking less fluid) and/or expelling more fluid.

A 24-hour fluid intake restriction (< 300 ml or 10 oz) normally produces one to two percent body weight loss. Urine will continue to be produced for some time, and some water will be lost in sweat and other evaporation. However, once fluid intake is reduced, urine and sweat losses become more difficult. Therefore, it makes sense not to restrict fluid too early before weigh-in, and 24 hours (or slightly less) appears optimal. There are also other ways to increase urine and sweat production, namely through water loading. Water loading (i.e., drinking large volumes of fluid for several days prior to restriction) is widespread in MMA and other weight-category sports and has been scientifically proven to work—at least for some athletes. Risks with water loading and excessive water consumption while sweating during training can lead to a clinical condition known as hyponatremia. Hyponatremia is a condition in which blood sodium drops to dangerous levels. Hospitalization, and even death, can occur. Due to these risks, the UFC PI recommends the following research-backed, water-loading protocol (see Table 74.2).

When it comes to expelling more fluid from the body, there are two different ways to do it: i) active sweating and ii) passive sweating. These methods can be combined. Active sweating is accomplished by raising the fighter’s body temperature through exercise and forcing the body to sweat in order to cool body temperature down— sometimes known as “working it off.” The benefit to this method is that many fighters have planned training sessions in the 24 hours before weigh-in, so by engaging in this planned training and not replacing any sweat losses with fluid, it causes a minimal disturbance to a fighter’s routine. The disadvantages to this method are: i) while weight loss through sweating is easy when hydrated, if a fighter is already moderately to severely dehydrated, getting further weight loss by “working it off” becomes increasingly harder and requires a lot more work than it would have initially, and ii) while some training is often planned to take place the day before weigh-in regardless of making weight, extra training to sweat the weight off can result in muscle damage, soreness, fatigue and muscle tightness.


Passive sweating is a non-exercise based method used to increase body temperature and force sweating to occur. Examples include saunas, hot baths, heated rooms, extra layers of clothing and sweat suits—among others. The benefits to these methods include less muscle soreness, less fatigue and tightness and it may be less time consuming than active sweating. The disadvantages include discomfort to the athlete (especially compared to active sweating in the early stages of a planned weight cut) and some other unfavorable physiological responses (e.g., greater disturbances in electrolyte homeostasis and fluid losses from plasma, which in turn decreases cardiovascular fitness). Despite this, these unfavorable physiological responses can be recovered from with a strategic plan given the large window between the weigh-in and fight in professional MMA. As training sessions are likely planned to occur the day before weigh-in, and sweat losses occur relatively easily in the beginning of a weight cut when one is well hydrated (and especially when water loading), a combination of active and passive sweating, alongside a fluid restriction in the last 24 hours, seems ideal.

Given the well documented injuries and even deaths from rapid extreme weight cut practices I would welcome the views of medical doctors, particularly those well versed in ringside medicine, to share their comments regarding the UFC PI’s direction for fighters. I would be happy to update this article with feedback from any physicians willing to publicly comment.


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