Rhabdomyolysis is the process which, due to extreme impact on the body or for example extensive endurance sports the muscle breakdown releases an excessive amount of enzymes, electrolytes, myoglobin, muscle fibres and more waste substances into the blood circulation. Myoglobin is the substance that for instance produces the darker color urine and can get very dark when you’re getting to much dehydrated. A substantial amount of this waste can and will be filtered out of the blood by the kidneys, liver or sweating but in certain cases the kidneys can get clogged and will stop functioning resulting in (permanent) kidney failure.
‘Non steroidal anti inflammatory drug’ also called NSAIDs are painkillers that have as it says an inflammatory effect and reduces body temperature. These types of painkillers also have an unwanted effect on the kidneys which is slowing down the function of filtering the blood and speed up the process of this kidney failure.
Ultrarunning is managing pain
Pain is a signal from the body that something is wrong and that you should slow down or stop doing what you’re doing. Ultrarunners tend to constantly push their pain threshold and continue where others will stop. Ultrarunners usually have the experience to understand the different types of pain and exhaustion and know which can be ignored and which ones cannot and will result in long-term or permanent damage. So, it is just a matter of considering how much it is worth to continue or finish a race.
Always remember when it gets though that you signed up for it and that you just have to deal with it. Sometimes it is said that ultrarunning is a sport where the ones who can handle pain best will get farthest and using painkillers is seen as a form of cheating.
If you really have to take any painkillers than take Paracetamol and don’t use any NSAIDs. Examples of NSAIDs are Ibuprofen, Diclofenac, Naproxen, Asperine and more. Paracetamol is not an NSAID and takes the edge of the pain as well. The head of the medical team during the Belgium Legends Trail once told me that you should not use more than 4.000 mg per 24 hours. Keep in mind that there is also a positive gain in pain and that is that it will keep you awake during your nights in multiday races. Your second, third even the fourth night is a hell when it comes to lack of sleep. Pain wil keep you awake and when taking Paracetamol you will find yourself more falling asleep during your runs and hallucinations will even get worse. Best thing to delay this falling asleep and hallucinations thing is to sleep for just 1 or 2 hours every night in order to respect your biological clock. It will even make you move faster during the day and you will make up the time lost easily and will enjoy your race more.
I occasionally use paracetamol during a race but if I do this is in the last quarter of the race to just enjoy the last part a bit more. What I sometimes do after a multiday ultrarun is taking 1.000 mg Paracetamol (and a few beers) before I go to bed. It will help against restless leggs and just makes you sleep a bit better because the pains are less.
I am just an ultrarunner for many years and not a doctor and have just read on this topic a lot and talked to medics about it. The above is just a summary of my knowledge on this topic. If you want to read more on this topic I have collected a few articles and studies which mention their sources. If you have kidney problems talk to a doctor.
Rhabdomyolysis: Pathogenesis, Diagnosis, and Treatment
Acute kidney injury due to rhabdomyolysis and renal replacement therapy: a critical review
Let’s Break It Down: Rhabdomyolysis In Ultramarathons
Ibuprofen and Its Effects During Ultramarathons
NSAIDs (Ibuprofen, Naproxen, Aspirin) and Acetaminophen/Paracetamol for runners, impairs healing and interferes with hydration
Rhabdomyolysis: Prolonged and high-intensity exercises, impact on renal function
Oral non-steroidal anti-inflammatory drug use in recreational runners participating in Parkrun UK: Prevalence of use and awareness of risk
Pain reliever linked to kidney injury in endurance runners
A Runner’s Guide to Over-the-Counter Pain Medicine