16 May 2014

Exercise-associated collapse in ultramarathon runners

When starting to write this post, on Friday May 16, it is the warmest day of the year in the UK, where I am currently traveling. I hear that the summer temperatures have finally arrived back home in Sweden as well today and I certainly look forward to not having to run with gloves and a winter hat any longer. I am usually not bothered by warm and hot conditions when running, on the contrary I recorded for instance my personal best half-marathon time on an exceptionally hot day. One common misunderstanding is that heat and dehydration is what causes athletes to collapse at the finish line. I recently read some articles on this subject and was surprised this collapse often is a benign condition named exercise-associated collapse (EAC) that actually has been shown to not be caused in most cases by either heat or dehydration.  In this post I will discuss what is really causing this, often quite scary, “downed runner” phenomenon and how common it is in ultramarathon running. I am also asking the question how to distinguish between non-serious benign causes of collapse and life-threatening sinister conditions requiring immediate medical treatment?

The broad definition of exercise associated collapse is often described as any athlete who is unable to stand or walk unaided during or at the completion of an athletic event. This broad condition should be distinguished from the more narrow definition of benign EAC that is “Collapse in conscious athletes who are unable to stand or walk unaided as a result of light headedness, faintness and dizziness or syncope causing a collapse that occurs after completion of an exertional
event or stopping exercise” (Roberts  “Exercise-associated collapse care matrix in the marathon” Sports Med 2007; 37: 431–3). This distinction is quite interesting as it appears that more sinister and severe cases of EAC often occur during a race, but benign EAC tend to happen in close association with the finish line (St Clair Gibson et al “Crawling to the finish line: Why do endurance runners collapse” Sports Med 2013; 43: 413-424). The reason for this is unclear, but it has been postulated by St Clair Gibson and colleagues that benign EAC might be associated with the pacing strategy and psychological and mental factors, see also for instance my previous blog post about pacing in MUT running. This type of benign EAC quite often follow a dramatic movement pattern in what St Clair Gibson and colleagues name The Foster dynamic collapse positions, see figure below, when the runner is struggling to reach the finish line in what looks almost like a primordial automated survival mode.

The Foster Dynamic Collapse Positions associated with EAC. From St Claire Gibson et al 2013

There are no good studies of how frequent both benign and severe EAC is in endurance events in general, but some estimate is from between 1/5000 to 1/20,000 in persons participating in athletic events so it is not that uncommon. There are even figures claiming EAC affects so many as 1-4% of ultramarathon runners (Hoffman et al “Medical services at ultra-endurance foot races in remote environments: Medical issues and consensus guidelines” Sports Med 2014; Epub ahead of print). The incidence of the most serious cause of EAC, sudden- death is less well known in ultramarathons, but appear to be around 1/50,000-1/259,000 in marathons (Maron et al “Risk for sudden cardiac death associated with marathon running” J Am Coll Cardiol 1996; 28: 428-431 59; Kim et al. “Cardiac arrest during long-distance running races” New Engl J Med. 2012; 366: 130–40; Webner et al. Sudden cardiac arrest and death in United States marathons. Med Sci Sports Exerc 2012; 44: 1843–5). I would think the risk for sudden cardiac death to be lower in ultramarathon runners who often are better trained and prepared than many novice marathon runners, but good studies are still lacking here.

Besides sudden death, most often due to cardiac arrest or arrhythmia, other serious causes of EAC include exercise-associated anaphylaxis [EAA] (Povesi Dascola & Caffarelli “Exercise-induced anaphylaxis: A clinical view” Ital J Pediatr. 2012; 38: 43),  exercise-associated hyponatremia [EAH] (Rogers & Hew-Butler “Exercise-associated hyponatremia: overzealous fluid consumption” Wilderness Environ Med 2009; 20: 139-43), hypoglycemia (Holtzhausen &  Noakes “Collapsed ultraendurance athlete: proposed mechanisms and an approach to management” Clin J Sport Med 1997; 7: 292-301), dehydration (Kenefick &  Sawka ” Heat exhaustion and dehydration as causes of marathon collapse” Sports Med. 2007; 37: 378-81), exertional heat stroke (Noakes “A modern classification of the exercise-related heat illnesses” J Sci Med Sport. 2008; 11: 33-9; Casa et al “Exertional heat stroke: new concepts regarding cause and care” Curr Sports Med Rep. 2012; 11: 115-23), hypothermia (Roberts “Heat and cold: what does the environment do to marathon injury?” Sports Med. 2007; 37: 400-3), sickle-cell haemoglobinopathy (Loosemore et al “Sudden exertional death in sickle cell trait” Br J Sports Med 2012; 46: 312-4), rhabdomyolysis (Szczepanik et al “Exertional rhabdomyolysis: identification and evaluation of the athlete at risk for recurrence” Curr Sports Med Rep 2014; 13: 113-9), exercise-induced bronchospasm (Bussotti et al “Respiratory disorders in endurance athletes - how much do they really have to endure?” Open Access J Sports Med. 2014; 5: 47-63) and a number of other rare disorders. Trauma in mountain ultrarunning is also rather common and should definitively be ruled out; see my previous post about this.

Benign EAC is an exclusionary diagnosis when the more serious causes of collapse have been ruled out (Roberts “Exercise associated collapse in endurance events: a classification system” Phys Sportsmed 1989; 17: 49-59; Holtzhausen et al “Clinical and biochemical characteristics of collapsed ultra-marathon runners” Med Sci Sports Exerc 1994; 26: 1095–101; Speedy et al “Exercise-associated collapse: postural hypotension, or something deadlier?” Phys Sportsmed. 2003; 31: 23–9). There are a number of good recent reviews about benign EAC and the treatment for this (Asplund et al “Exercise-associated collapse: an evidence-based review and primer for clinicians” Br J Sports Med. 2011; 45: 1157-62; Anley et al “A comparison of two treatment protocols in the management of exercise-associated postural hypotension: a randomized clinical trial” Br J Sports Med 2011; 45: 1113–8”; Childress et al “Exertional collapse in the runner: evaluation and management in fieldside and office-based settings” Clin Sports Med. 2010 Jul;29(3):459-76; Brennan & O'Connor ”Emergency triage of collapsed endurance athletes: a stepwise approach to on-site treatment” Phys Sportsmed 2005; 33: 28-35; Holtzhausen & Noakes. “Collapsed ultraendurance athlete: proposed mechanisms and an approach to management” Clin J Sport Med  1997; 7: 292–301). As mentioned, benign EAC is often occurring in close proximity to the finish line and is one of the more common reasons for being admitted to the medical tent after a marathon. It can also occur in association with the finish line and there are several Youtube videos available of quite scary episodes of EAC where the runner assume the Foster positions mentioned above.

The causes (etiology) of benign EAC is believed to be postural hypotension with reduced blood flow to the brain due to inadequate venous return necessary to maintain adequate blood pressure associated with a low heart rate and highly a activated symphatic and parasymphatic nervous system. The treatment is cessation of the exercise, when watching the videos below I am always surprised why the runner is not being taken out from the race immediately and helped, and lying the runner down in the supine position on his/her back and raising the legs/pelvis to facilitate blood flow to the brain (the so called Trendelenburg position), skin cooling and offering of moderate oral hydration. If the consciousness is not improved immediately, further evaluation with measurement of vital signs (pulse rate/ blood pressure/ temperature [rectal]/ saturation), heart auscultation, ECG if possible, and laboratory analysis (glucose, sodium, CPK, creatinine in particular). A possible diagnostic and treatment algorithm proposed by Asplund and colleagues is shown below, however, I think any standard emergency protocol that the medical service team at the race is comfortable with can be followed. In the case of benign EAC most runners can be released from the medical tent at the finish line within one hour. There are no good studies of the risk of a repeated benign EAC when having experienced it once, but the risk appears to be low and I am aware of a large number of both elite and amateur runners like myself who have had a scary example of an EAC only once in a long running career. There are speculations that lower-body compression garments might prevent against EAC, but there are no good studies of this.

Treatment algorithm of EAC. From Asplund et al 2011.

I have myself experienced an EAC a couple of years ago, not when I was running but after a tough indoor spinning cycle exercise. It was a real case of syncope as everything suddenly went black and I fell of the bike, luckily after I had clipped out my cycling shoes as it otherwise might have been quite painful (even though it hurt quite much anyway when I regained my conscience lying on the floor). I thought it was due to the heat in the room, but know now that it most likely was caused by postural hypotension when I stopped exercising too abruptly. So, in closing, do not stop immediately at the finish but continue to jog and walk for a while. And pace yourself reasonable.

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