Jump to:



The downed runner/collapsed athlete involves anyone who cannot stand or walk unaided, either during or at the completion of an endurance athletic event.


Exercise-associated collapse may be secondary to a variety of causes, including cardiovascular compromise (e.g. postural hypotension, cardiac arrhythmia), heat-related illness (e.g. hyperthermia, hypothermia), electrolyte abnormalities (e.g. hyponatremia, hypoglycemia, rhabdomyolysis, drug toxicity), respiratory compromise (e.g. asthma, exercise associated anaphylaxis), musculoskeletal injury (e.g. cramps, fracture, tendon tear), and other medical  conditions (e.g. sickle cell trait, seizures).

Epidemiology including risk factors and primary prevention

Running in the United States continues to remain popular as over 49 million went running at least once in 2021. Though most will never experience a significant illness or injury, some runners may be at risk resulting in a medical encounter. Exercise-associated collapse is the most common reason for a medical encounter, often occurring during marathons (85-89%).2,3 Fortunately, cardiac fatalities are rare, with the incidence higher in marathons (1.01-2.33 per 100,000) than half-marathons (0.27 per 100,000).4-6 Risk factors for exercise-associated collapse include medical illnesses (e.g., coronary disease, sickle cell trait), medications (including supplements), inappropriate training, warmer temperature, increased humidity, increased consumption of water (hyponatremia), weight gain, race time > 4 hours, low body mass index (BMI). Male runners are at greater risk of cardiovascular and heat-related collapse.5


The pathophysiology of exercise-associated collapse in the runner will depend upon the exact cause. The three most common areas are:

  • Cardiovascular: Exercise-associated postural hypotension is due to the abrupt cessation of lower extremity muscle pumping actions, cutaneous vasodilatation with venous pooling of blood in the lower extremities and reduced baroreflex control, resulting in orthostatic intolerance. An acute coronary event will occur from excessive stress/fatigue in the setting of preexisting or acute coronary/cardiac abnormalities (atherosclerosis, hypertrophic cardiomyopathy, myocarditis, arrhythmia, etc.).4-8
  • Heat-related illness: Thermoregulatory compromise resulting in excessive heat gain (hyperthermia) or heat loss (hypothermia) due to hypothalamic dysregulation. Hyperthermia is secondary to excessive exercise, increased ambient temperature/humidity, inability to sweat, compromised cardiovascular reserves and/or medications. Hypothermia is secondary to cold ambient temperature in the setting of fatigue or glycogen depletion.8-10
  • Electrolyte abnormalities: Hyponatremia is multifactorial in nature and is related to increased water ingestion, rhabdomyolysis and/or defects in the hormonal/renal control mechanism.7-9 Studies suggest a linear relationship between water consumption, weight gain and hyponatremia.12-15 Inappropriate stimulation of vasopressin due to excessive exercise, fatigue and emotional stress may cause increased excretion of sodium or decreased excretion of water leading to fluid retention and serum sodium dilution.12-14 Hypoglycemia is due to depletion of glycogen stores with inadequate intake of nutrition.
  • Sickle Cell Trait: Though the mechanism is not clear, it has been postulated that individuals with sickle cell trait may experience exercise associated collapse due to a combination of factors including dehydration of red cells making them “sticky”, profound lactic acidosis and extreme hypoxemia as well as hyperthermia in working muscles.16

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Cardiovascular illness: Postural hypotension is the most common etiology for collapse, typically occurring after crossing the finish line. The athlete cannot stand and may briefly lose consciousness. Most athletes recover with minimal treatment. Sudden loss of consciousness before the end of the race suggests a more serious cardiac event (coronary event, arrhythmia).

Heat-related illness: Hyperthermia varies from heat exhaustion (headache, dizziness, weakness, euthermic or mild hyperthermia, moist skin, tachycardia, +/- altered mental status) to more severe heat stroke (weakness, temp > 40oC/104oF, dry skin, tachycardia, seizures, severely altered mental status or coma). Hypothermia may be mild (shivering, tachycardia, tachypnea, temp 32-35oC), moderate (loss of shivering, bradypnea, bradycardia, arrhythmia, CNS depression, temp 28-32oC) or severe (pulmonary edema, bradycardia, coma temp < 28o C).

Electrolyte abnormalities: Hyponatremia (Na < 135 mmol/L) may be mild (dizziness, nausea, muscle cramping, no significant confusion), moderate (headache, vomiting, lethargy, agitation, confusion), or severe (seizure, loss of consciousness). Hypoglycemia may be mild (weakness, tremor, lightheadedness, diaphoresis, tachycardia, no significant mental status change), or severe (significant change in mental status including coma).

Respiratory: Respiratory compromise may occur in asthma (dyspnea, tachycardia, altered mental status) or exercise-associated anaphylaxis (pruritus, urticaria, flushing, dyspnea, chest tightness, headache).

Acute musculoskeletal injury: Often mild in nature (muscle strain, tendonitis), typically involving the lower extremities. More severe injuries may represent a fracture or tendon tear.

Neurocognitive: Seizures will present with loss of consciousness and collapse with muscle twitching.

Sickle Cell Trait: Most runners with sickle cell trait will not experience complications from exercise. Runners who experience complications will report the acute onset of severe leg pain and difficulty ambulating that does not improve with rest. If not treated appropriately, symptoms can progress and lead to multi-organ failure.

Specific secondary or associated conditions and complications

Prompt recognition and treatment of all conditions is essential to avoid significant morbidity or mortality, depending upon the cause of collapse as outlined above.

Essentials of Assessment


On-scene providers often must triage, assess, and take initial measures without knowing much if any of the patient’s history.8-10,16,17 Pertinent history should include:

  • Location of collapse: Collapse in the middle of a race is more likely to represent a serious condition (e.g., myocardial infarction), versus collapse at the finish.
  • Current symptoms
  • Past medical history: Cardiac disease, diabetes, history of exercise-associated collapse, sickle cell trait
  • Current medications, supplements and drug use
  • Nutritional intake: Type and amount of fluid / food ingested before and during the race
  • Pre- and post-race weight (if known)

Physical examination

While on the course, address life-threatening issues focusing on level of responsiveness, airway patency, breathing, circulation and any obvious bleeds and other exposures (e.g., open fractures). Once stabilized, a secondary assessment should occur in the medical tent or hospital. Focus on vital signs: temperature (rectal is most accurate to detect hyperthermia), blood pressure (including orthostatics), heart rate, respiratory rate, O2 level; cardiopulmonary system: heart rate, rhythm, murmurs, respirations, wheezing, rales, rhonchi; neurocognition: alertness, orientation, immediate/delayed recall, concentration, balance, cranial nerves, speech. Finally assess musculoskeletal system: strength, sensation, reflexes, limb alignment, spine/limb stability.

Functional assessment

The emotional state of the endurance athlete could entail depression, anxiety or other psychological reason for mood impairment. An assessment should include understanding the athlete’s purpose for running (e.g., milestone, charity, qualification for future race).

Laboratory studies

Potential onsite tests include

  • Blood sodium – evaluate for hyponatremia (Na < 135 mmol/L)
  • Blood glucose – evaluate for hypoglycemia (Glu < 65-70 mg/dL)
  • Blood BUN/creatinine – assess renal function, hydration status
  • Blood CPK – assess for rhabdomyolysis
  • Urine sodium, osmolality, myoglobin – assess renal function, hydration status, rhabdomyolysis.


Imaging modalities (e.g., x-rays, magnetic resonance imaging [MRIs]) are not typically available on-site. Ultrasound may be used to assess for specific types of injuries (e.g., musculoskeletal injuries, cardiac).

Supplemental assessment tools

An electrocardiogram (ECG) can be done to assess cardiac rhythm. This can be performed using an automated cardiac defibrillator, and even smartwatches or fitness trackers, if a full ECG is not available. Further cardiac testing (echocardiogram, stress test) will depend upon diagnosis. Screening for sickle cell hemoglobin will help identify the presence of sickle cell trait.

Early predictions of outcomes

Early defibrillation has the greatest impact on cardiac arrest survival. Survival rates decrease 7-10% per minute for every minute defibrillation is delayed.4,5,8


Environmental risk factors contributing to exercise-associated collapse include warmer temperatures, increased humidity and lack of acclimatization to altitudes.

Professional issues

Communication of an athlete’s medical status must be handled in a confidential manner. Questions from the media should be handled only by the race medical director.

Rehabilitation Management and Treatments

Available or current treatment guidelines

A variety of published papers exist that summarize the evaluation and treatment of the collapsed running athlete.8-10,12,16 Several organizations have provided position statements related to the treatment of heat-related illness10,11 exercise-associated hyponatremia13,14 and sickle cell crisis.16 All emphasize the importance of rapid evaluation and treatment to avoid significant morbidity and mortality.

At different disease stages

Cardiovascular illness: If the athlete is not hyperthermic, institute supportive care (i.e. dry off, keep warm/cool, lay flat with legs elevated, remove wet clothes). Hydrate with oral or intravenous fluids (only after measuring electrolytes), as appropriate. Most athletes can be discharged to home. If there is a concern for cardiac arrest, activate advanced cardiopulmonary life support, including establishing a patent airway, IV access and defibrillator/cardiac monitor. Once stable, transfer to a medical facility.4,8,9,18

Heat-related illness: In cases of hyperthermia, milder forms can successfully be treated with rest, hydration and active cooling (Temp > 102° F), as appropriate. Cooling methods include whole body ice immersion (rate 17° F/ hr) or rotating ice packs around neck, axilla and groin (rate 15° F/ hr). Stop active cooling at 102° F. Milder forms may be discharged, while more severe cases require transfer to a medical facility. In hypothermia, milder forms undergo passive external warming (blankets) or active external rewarming (heated blankets, forced heated air). Moderate/severe cases should undergo rewarming and transfer to a medical facility.10,11

Electrolyte abnormalities: In cases of hyponatremia, avoid isotonic and hypotonic fluids. Milder forms will respond to fluid restriction or oral hypertonic fluids, close observation, natural diuresis and discharge to home once stable. For moderate/severe cases, consider 100 ml of 3% NaCl over 10 minutes x 2, oxygen, and transfer to medical facility. In hypoglycemia, milder forms will respond to 15-20 g of fast-acting carbohydrate, rechecking glucose level until normal. Moderate/severe cases may require Glucagon injection, dextrose (50%) in water (D50W) and transfer to medical facility. In cases of rhabdomyolysis or drug toxicity, stabilize and transfer to a medical facility.9,12-15

Respiratory: Most cases of asthma may be treated with supplemental oxygen and bronchodilators (e.g., beta-2 agonists). Severe cases should be transferred to a medical facility. If there is concern for exercise-associated anaphylaxis, maintain airway patency, provide epinephrine, supplemental oxygen, and transfer to medical facility.

Acute musculoskeletal injury: Treatment should be to stabilize the injured area. Cramps may be treated with rest, massage and stretching, hydration and medication (e.g., muscle relaxants). Any concern for fracture, ligament injury or tendon tear should prompt transfer to medical facility.

Neurocognitive: Any athlete experiencing a seizure should be stabilized and transferred to a local medical facility.

Sickle Cell Trait: Athletes suspected of sickle cell crisis should be assessed for responsiveness and secondary organ failure while activating emergency medical services. Once stable, transfer to a medical facility for further work-up and treatment.16

Coordination of care

Rapid assessment and treatment of the collapsed athlete requires efficient, well-coordinated care. Team members should be instructed prior to the race regarding roles, treatment protocols, location of medical supplies, communication capabilities and medical chain of command. Athletes assessed in the field should be transferred to medical tents or medical facilities if not stable to return to the race.

Patient & family education

Most long-distance, mass-event races have “race expos” at packet pick-up prior to the event. This is a potential time for medical staff to provide educational lectures regarding preventive strategies for avoiding serious medical illnesses. Recreational athletes may also find an array of evidence-based and professional resources on-line.

Emerging/unique interventions

The majority of athletes who experience exercise-associated collapse will be treated appropriately and discharged to home. The incidence of a fatal cardiac event in long-distance running events is low (1.01 per 100,000 marathoners; 0.27 per 100,000 half-marathoners).4

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Any physician covering a running event should be prepared to assess and treat the collapsed runner in an efficient manner, remembering: Primary assessment focuses on addressing life-threatening illnesses, Secondary assessment addresses common medical illnesses, while noting:

  • Hyperthermia requires rapid cooling ideally through whole-body ice immersion.
  • Isotonic/hypotonic fluids should be avoided in cases of hyponatremia.

Educate athletes prior to discharge about preventive strategies (e.g., training, nutrition, environment) and warning signs or red flags that may prompt them to seek urgent medical evaluation.

Cutting Edge/Emerging and Unique Concepts and Practice

There are a growing number of racers participating in longer-distance events (e.g., ultramarathons). Limited research3,8 suggests that ultramarathon runners experience different rates of injuries and hyponatremia than marathon runners. Current research is focusing on identifying risk factors for collapse and the role of aggressive use of hypertonic solutions for hyponatremia in these athletes.

Gaps in the Evidence-Based Knowledge

There is limited data on exercise-associated collapse at longer-distance, mass-event races due to a lack of uniform data collection and definition of terms.  A recent consensus statement published standardized definitions for sports events, medical encounters, severity of illness/injury, diagnostic categories, as well as standardized research methodology and data reporting.18 More data following these guidelines is needed to update the epidemiology of exercise-associated collapse, to optimize prevention strategies of race related-injuries, and to improve preparation of medical personnel at these events.


  1. Statista, Number of running and jogging participations in the United Sdtates from 2010 to 2021. https://www.statista.com/statistics/190303/running-participants-in-the-us-since-2006/ (accessed August 23, 2023)
  2. Roberts WO. 12-yr profile of medical injury and illness for the Twin Cities Marathon. Med Sci Sports Exerc. 2000;32(9):1549-1555.
  3. Krabak BJ, Waite B, Schiff MA. Study of injury and illness rates in multiday ultramarathon runners. Med Sci Sports Exerc. 2011;43(12):2314-2320.
  4. Kim JH, Malhotra R, Chiampas G, et al. Cardiac arrest during long-distance running races. N Engl J Med. 2012:366(2):130-140.
  5. Gerardin B, Guedeney P, Bellemain-Appaix A, Levasseur T, Mustafic H, Benamer H, Monsegu J, Lamhaut L, Montalescot G, Aubry P, Collet JP; Groupe de Réflexions sur la Cardiologie Interventionnelle. Life-threatening and major cardiac events during longdistance races: updates from the prospective RACE PARIS registry with a systematic review and meta-analysis. Eur J Prev Cardiol. 2021 May 22;28(6):679-686.
  6. Krabak BJ, Roberts WO, Tenforde AS, Ackerman KE, Adami PE, Baggish AL, Barrack M, Cianca J, Davis I, D’Hemecourt P, Fredericson M, Goldman JT, Harrast MA, Heiderscheit BC, Hollander K, Kraus E, Luke A, Miller E, Moyer M, Rauh MJ, Toresdahl BG, Wasfy MM. Youth running consensus statement: minimising risk of injury and illness in youth runners. Br J Sports Med. 2021 Mar;55(6):305-318
  7. Breslow RG, Giberson-Chen CC, Roberts WO. Burden of Injury and Illness in the Road Race Medical Tent: A Narrative Review. Clin J Sport Med. 2021 Nov 1, 31(6): e499-e505.
  8. Asplund CA, O’Connor FG, Noakes TD. Exercise-associated collapse: an evidenced-based review and primer for clinicians. Br J Sports Med. 2011;45:1157-1162.
  9. Hoffman M, Bassett P, Hill J, Khodaee, M, Krabak BJ, Lipman G, Pasternal P, Roger I, Sheer B, Townes DA. Medical services at ultra-endurance foot races in remote environments: medical issues and consensus guidelines. Sport Med. 2014 Aug:44(8): 1055-69.
  10. Roberts WO, Armstrong LE, Sawka MN, Yeargin SW, Heled Y, O’Connor FG. ACSM Expert Consensus Statement on Exertional Heat Illness: Recognition, Management, and Return to Activity. Curr Sports Med Rep. 2023 Apr 1;22(4):134-149
  11. Casa DJ, DeMartini JK, Bergeron MF, Csillan D, Eichner ER, Lopez RM, Ferrara MS, Miller KC, O’Connor F, Sawka MN, Yeargin SW. National athletic trainers’ association position statement: Exertional heat illnesses. J Athl Train. 2015Sep: 50(9): 986-1000.
  12. Knechtle B, Chlíbková D, Papadopoulou S, Mantzorou M, Rosemann T, Nikolaidis PT. ExerciseAssociated Hyponatremia in Endurance and Ultra-Endurance Performance-Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review. Medicina (Kaunas). 2019 Aug 26;55(9):537.
  13. Hew-Butler T, Loi V, Pani A, Rosner MH. Exercise-Associated Hyponatremia: 2017 Update. Front Med (Lausanne). 2017;4:21.
  14. Hew-Butler T, Rosner MH, Fowkes-Godek S, Dugas JP, Hoffman MD, Lewis DP, Maughan RJ, Miller KC, Montain SJ, Rehrer NJ, Roberts WO, Rogers IR, Siegel AJ, Stuempfle KJ, Winger JM, Verbalis JG. Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Br J Sports Med. 2015 Nov;49(22):1432-46
  15. Noakes TD, Sharwood K, Speedy D, et al. Three independent biological mechanisms cause exercise-associated hyponatremia: evidence from 2,135 weighed competitive athletic performances. Proc Natl Acad Sci USA.2005;102(51):18550-18555. Epub 2005 Dec 12.
  16. O’Connor FG, Franzos MA, Nye NS, Nelson DA, Shell D, Voss JD, Anderson SA, Coleman NJ, Thompson AA, Harmon KG, Deuster P.  Summit on Exercise Collapse Associated with Sickle Cell Trait: Finding the “Way Ahead”.Curr Sports Med Rep. 2021 Jan 1;20(1):47-56
  17. Childress MA, O’Connor FG, Levine BD. Exertional collapse in the runner: evaluation and management in fieldside and office-based settings. Clin Sports Med. 2010;29:459-476.
  18. Schwellnus M, Kipps C, Roberts WO, et al. Medical encounters (including injury and illness) at mass community-based endurance sports events: an international consensus statement on definitions and methods of data recording and reporting. Br J Sports Med. 2019;53(17):1048-1055. doi:10.1136/bjsports-2018-100092

Original Version of the Topic:

Brian J. Krabak, MD, MBA, Andrew H. Gordon, MD, PhD. Downed runner. Published 7/2/2012

Previous Version(s) of the Topic:

Brian J. Krabak, MD, MBA. Downed runner. Published 8/23/2016

Brian Krabak, MD, MBA, FACSM, Amanda T. Wise, DO. Downed runner. 12/8/2020

Author Disclosure

Brian Krabak, MD, MBA, FACSM
Nothing to Disclose