Making weight is the easy part. What you do in the hours after you step off the scale decides whether you fight at your best or fight flat.
Weight loss is primarily through diet in the weeks before your fight, manipulation of gut fill and muscle glycogen stores in the 3-4 days prior to weigh in, and controlled dehydration in the 24 hours prior to weigh in.
If weighing in the same day as your fight, avoid cutting more than 2-3% of your body weight through dehydration. If weigh in is the day before, you can push it a little more as there is more time to rehydrate. Be careful though! Excessive dehydration is dangerous.
The next section explains how to turn your cut into a timed rehydration plan: how much fluid to take, how much sodium it needs to carry, and the pace to drink it at so it stays down. The calculator itself sits on its own page — the link to it is below.
How the numbers are worked out
Total fluid. You need to replace more than you lost, because not all of what you drink is retained. You will only retain about 2/3 of what you drink. The working figure is 1.5 litres for every kilogram lost.
Sodium. Water alone will not rehydrate you. Without sodium to hold it in the bloodstream, most of it is passed as urine within a couple of hours. Each litre of the plan needs roughly 1000mg of sodium behind it, which is one serving of DRVN Threshold per litre or about 1/2 a teaspoon of salt per litre.
Food. Keep meals light, low fat high glycaemic foods (white pasta, rice etc...) are great, aiming for 60 grams of carbs an hour in small meals. Don't eat a large meal within a few hours of your fight.
Pace. The first 500ml goes down fast in the first 15 minutes after weigh in because early volume matters most. After that the limit is roughly 1000 ml an hour. Drink too much in one go and you overwhelm gastric emptying, which means bloating, sloshing and, at worst, vomiting the lot back up. Aim to drink a little every 10-15 minutes. In the hour before the fight, keep to sips.
A word on the cut itself
This tool assumes the cut has already happened. It will not tell you how to lose the weight, and it is deliberately conservative about the pace of putting it back.
If the calculator tells you the fluid cannot be replaced in the time you have, that is not a problem to solve by drinking faster. It means the cut was too big for the turnaround, and the answer is a smaller cut next time or a different weight class.
Severe dehydration is genuinely dangerous, not just bad for performance. If you are cutting more than about 5% of your body weight, do it with a coach and a nutritionist who know your history. This calculator is general guidance, not medical advice, and it is no substitute for either.
Sweat Sodium content
Sweat contains high levels of sodium and potassium. Some of these are reabsorbed by your sweat glands back into your body, but the harder you sweat, the less the electrolytes are reabsorbed. Basically sodium secretion outpaces reabsorption as sweat rate rises.
Why does this matter? At higher sweat rates, your electrolyte losses will be proportionally higher. This means athletes training hard and sweating hard, or individuals with particularly high sweat rates, have a greater need for electrolyte replacement than those working at a slower pace.
Sodium content of sweat varied considerably between individuals, with a range of 200-2000 mg of sodium per litre, and an average sodium content of approximately 1000 mg sodium per litre.
To really test your sweat sodium content, lab tests can be performed to individualise your supplementation plan, using a variety of methods (localised patches, whole body washdown, pilocarpine sweat test…). These tests are unfortunately not accessible for most people, due to availability and cost and are more important for professional athletes.
For most people, 1000 mg sodium will be about right to replace losses.
Particularly salty sweater may need more than this.
Indicators of salty sweaters:
- Do you notice salt marks on kit and clothing after workouts?
- Does your sweat sting your eyes or any little cuts/grazes, or does it taste very salty?
- Do you feel faint or dizzy when you stand up quickly when exercising?
- Do you get muscle cramps towards the end of training sessions?
- Do you crave salty foods particularly after training?
- Do you find training in the heat a lot less pleasant than training partners do?
If you said yes to a lot of these questions, you may be a particularly salty sweater and may need more sodium than other people. If most answers were no's, you probably are a low salt sweater.
If you think you might be a salt sweater, try and take a slightly higher dose of DRVN (1.5 times the normal dose is a good starting point) or whatever product you use during your next session and see if your answers change.
Make sure the training session is comparable in intensity and environmental conditions to get an accurate feel.
Sweat loss calculation
Sweat rates vary considerably between individuals-we all have a friend who always seems drenched in sweat the moment the sun comes out and one who never seems to break a sweat no matter how hard they train.
Harder work, high humidity and hotter environmental temperatures will both increase sweat rate. Larger individuals and males tend to sweat more. It is really useful to have a feel for what your sweat rate is to really improve your hydration plan during workouts so you can get the most out of them
Sweat loss is quite easy to work out if you have a set of accurate scales. Weigh yourself before and after a session, track anything you drank or ate along the way, and the Sweat Rate Calculator linked below does the arithmetic.
Try not to go to the bathroom during the test, or it will throw off the result.
Sweat rates of 0.5 - 1.5 litres per hour are normal, and drinking about a litre of fluid per hour around exercise is about right.
Sweat rates of greater than 1.5 litres per hour are considered high, and a greater fluid intake is needed.
Sweat rates over 2.5 litres per hour can be hard to keep on top of during a session as drinking that much is hard, and too much stomach fill can impact exercise. Prehydration becomes more important and accepting a degree of dehydration at the end of the session can be important.
You do not need to exactly match your sweat rate, drinking a bit less or a bit more is fine. Accuracy matters more during longer endurance sessions (2 hours+) where overhydration and hyponatraemia can become more of a risk if you drink too much.