Chris Eubank Jr. missed weight by just 0.05lbs (23 grams) ahead of his highly anticipated clash with Conor Benn last weekend - a tiny margin that cost him a massive £375,000. But why does such a minuscule weight difference (roughly the weight of four sheets of A4 paper) matter so much in combat sports?
Author
- Adam Taylor
Professor of Anatomy, Lancaster University
Boxing, like most combat sports, uses weight classes to keep competition fair, strategic and safe . These classes exist to ensure that skill, not brute size, determines the outcome of a fight.
By grouping fighters based on weight, the sport encourages more balanced match-ups that test a combination of power, speed, reach, endurance and skill.
Where does weight come from?
The body has two main "compartments" where weight can be lost from: fat mass and lean body (or fat-free) mass.
Fat mass is self-explanatory and is influenced by sex, age, activity and other factors. A healthy percentage of body fat is about 25% for men and 30% for women .
Lean mass includes just about everything else. About 50% is skeletal muscle, with organs, bones and water being the other 50%.
Naturally, athletes try to lose fat while preserving lean mass - especially muscle, which plays a critical role in performance.
How weight loss begins
Preparing for a fight usually starts eight to 12 weeks before the bout, depending on the opponent, previous fights and training history.
While there's no universal rule for how much weight a fighter should drop, many aim to lose around 10% of their body weight.
The primary goal? Cut fat without losing strength - a delicate process that combines nutrition, exercise and timing.
How is weight lost?
There are three major routes: reducing energy intake through fasting and dieting while increasing exercise . This is typically undertaken gradually with a long-term plan and a balanced diet that is focused on reducing fat mass and fuelling muscles.
Within a few days of the weigh-in, more extreme measures are used, aimed at removing excess fluid from the body. These measures include heated activities, such as running or wrestling while wearing specialised suits or extra-layers to increase sweating when exercising.
Stopping or limiting fluid intake can even go as far as spitting out saliva.
Finally, in the most brutal category are the things that are advised against because they can cause harm, such as taking laxatives , diuretics or enemas .
Normal defecation is likely to reduce the body weight by about 100-130g . However, depending on diet, it can be as much as 470g .
Using laxatives or enemas can clear out the digestive tract , sometimes shedding about a kilogram of weight. Although this is risky and discouraged by health experts.
By the time the weigh-in comes, everything that can be shed is pretty much gone and the athletes are in a dangerous physiological state.
Reducing water intake while increasing water loss leads to reductions in body water content which directly reduces blood and plasma volume , extracellular water and haemoglobin mass - all things that are key for health and transporting energy, ions and minerals around the body.
This fine physiological balancing act can result in a boxer collapsing before or at the weigh-in.
Low blood sugar levels, dehydration and reduced oxygen delivery put a serious strain on the body. If this progresses too far, the blood can become too thick - increasing the risk of clotting - while the kidneys may begin to fail and the nervous system can start to malfunction.
After weigh-ins
Clearly, boxers and other combat athletes cannot fight in this depleted state, so weigh-ins typically happen the day before the fight. In Britain, the British Board of Boxing Control stipulates a weigh-in must happen 24 to 36 hours before a fight .
Once the weigh-in is done, efforts to replenish those depleted resources are undertaken with fluids and electrolytes, combined with easily digestible carbohydrates to replenish glycogen stores in the body.
The fluids are an important part of many body systems including muscle. Skeletal muscle is 76% water and dehydration has been shown to reduce muscle strength by 2% and muscle power by 3% .
Similarly, glycogen stores need to be replenished and this can take up to 24 hours . Glycogen accounts for 1-2% of skeletal muscle volume and is the main energy source for muscle contraction - a key requirement in boxing. Any deficiency is likely to result in poorer performance.
After the weigh-in, studies show that victorious boxers regain more weight (8%) than losers (6.9%). And for each per cent more weight gained between weigh-in and bout, there was a 13% increase in the likelihood of victory in the fight.
And after months of sacrifice, relentless training and physical strain, it must feel terrific to regain a bit of weight.
Adam Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
