Darren Till missed weight by 3.5 lbs for his headlining fight against Stephen Thompson at UFC Liverpool, but the bout is going ahead after stipulations were put in place, including a stipulation that Till weigh 188 lbs or less at 1pm local time Sunday.

Till claimed to be 200 lbs in the cage against Donald Cerrone - which isn’t a far-fetched claim, as a 30lbs weight cut isn’t unheard of in the UFC. If we assume Till was around 200 lbs fully hydrated here, 188 lbs is him still suffering over 5% dehydration. The symptoms of moderate dehydration include tiredness, muscle cramps and headaches.

Fighters will also dehydrate as they compete, and starting a bout already dehydrated means the effects of further dehydration will be exacerbated, which would not only affect performance, but could increase the chance of injury, and depending on how well the cerebral spinal fluid has been replenished, may also increase the risk of traumatic brain injury.

A complicating factor is that the body doesn’t rehydrate in a uniform way. You can’t take a specific type of water that will rehydrate your brain or your spinal fluid first. If there is uneven rehydration, Till might end up with a very limited amount of time to try to rehydrate vital muscles.

Rehydration normally stops several hours before a fight, to avoid things like bloating, or the body still utilizing energy to break food down while in the cage. In Till’s case, being at 188 lbs at 1pm will only give him around 8 hours maximum to regain another 12 lbs, or around 4-6 hours if he stops rehydrating at the normal time.

The body can only absorb so much water at a time, so chugging gallons of water at 1pm won’t be enough to rehydrate Till. In addition to this it takes time, sometimes hours, for ingested fluids to circulate to where they’re needed for hydration. The takeaway is that there’s little chance Till goes into the cage fully hydrated. It’s very likely he goes into the cage with his body still working on getting back to a normal state, never mind ready for elite athletic competition.

It can be difficult for a doctor to tell exactly how hydrated a fighter is, especially while they’re rehydrating. A specific gravity test would be thrown off by the large amounts of fluids passing through the kidneys, and there’s no good way to test how hydrated the brain or CSF is with a physical exam. Still, doctors can check for obvious physical and cognitive symptoms that would be indicative of a concerning amount of dehydration.

The California State Athletic Commission (CSAC) has been at the forefront of efforts to reform weight cutting in the USA, implementing a 10 point plan to reduce the amount of weight fighters are cutting, including making fighters who cut significantly over 10% of their body weight—something considered “severe dehydration” medically—move up a weight class.

Here’s what CSAC executive director Andy Foster had to say about how California would handle today’s situation with Till and Wonderboy:

“Safety is obviously the first and foremost thing. 188 lbs happens to be the limit of the 10 point plan [for a welterweight]. More than that would be an indication of severe dehydration. If he has cut more than that, it would indicate it’s a very large cut, and we would be looking at whether or not he should be moving up a weight class.”

“[A welterweight weighing much over 188 lbs on fight night] would absolutely raise flags for us, but unless the fighter was just grossly unhealthy I don’t see it as a situation where we would kill the fight; as long as it wasn’t a medical situation.”

“There has to be a lot of medical supervision, and after this is over there needs to be some thought put into ‘what can we do to ensure this doesn’t happen again?’ If a fighter who fights at 170 lbs is over 188 lbs the next day, we have to have a conversation about whether or not we should be sanctioning bouts for them at 170 lbs.”

“How do we best address situations like this? I don’t like it when we have to put stipulations when we have to limit the hydration of a fighter. Obviously we can check to make sure they’re hydrated, but I don’t want fighters to have to cut twice, or not get back to where they need to be.”

“The alternative is to cancel the fight, but if the fighter is medically able to do it, it would be better to move forward with the fight as long as it’s safe, and then address the issue on the regulatory side after the fight. Killing a fight is a fairly extreme option, [so] as long as it’s safe, I think the fight could proceed [if the] doctors agree. The fighters wouldn’t have to go ahead, this is on them, if they agree on the [stipulation].”

“The ideal situation is to not get to this point and stop it on the front end, and make fighters who have to cut a lot get with the right person and cut down in ways that don’t require severe dehydration.”

The UFC acting as its own regulator for this event throws up an immediate conflict of interest. Should the main event be cancelled, the UFC will lose out. There’s pressure to make sure the bout goes ahead.

Since a specific gravity test is unreliable while a person is drinking large amounts of fluids, there’s no objective measurement of whether or not a fighter is too dehydrated to safely compete. That means the call will be a subjective one, likely made by a doctor employed by the UFC. That’s not an ideal situation for anyone, but it’s the one we’re in now.