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Sickle Cell Trait: A Review and Recommendations for Training

Fidler, Erin MEd, ATC, CSCS

Strength and Conditioning Journal: June 2012 - Volume 34 - Issue 3 - p 28–32
doi: 10.1519/SSC.0b013e3182453c41


Chestnut Hill College, Philadelphia, Pennsylvania



Erin Fidler is the head athletic trainer and strength and conditioning specialist at Chestnut Hill College.

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Because of recent lawsuits against specific universities and the National Collegiate Athletic Association (NCAA), sickle cell trait (SCT) has become a major concern in collegiate athletics. As a result of one settlement, in August 2010, it became mandatory for all Division 1 schools to test or confirm the SCT status of new and incoming student-athletes (NCAA Division I Proposal No. 2009-75-B-1). Although mandatory screening is a relatively new approach, the NCAA has published and distributed information on SCT since the first reported death of a college football player in 1974 due to exertional sickling. Since then, there have been more than 15 reported deaths of college football players (the most recent occurring in February 2010), several college and high-school basketball players, cross-country runners, and a Golden Gloves boxer (2,8). In May of 2009, reported that “exertional sickling has become the leading cause of death of NCAA football players this decade.” Along with screening, the NCAA has been urging all collegiate institutions to educate student-athletes and staff about the complications of SCT. Becoming familiar with this condition is essential for athletes, coaches, athletic trainers, and strength and conditioning staff because of the rapid and lethal nature of a sickling collapse. Sickling injuries can easily be prevented, and with appropriate conditioning, these athletes are able to compete and excel in their sport (6,16).

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Sickle cell trait is a condition acquired through inheritance not ethnicity. It is the inheritance of one gene for normal hemoglobin (A) and one gene for sickle hemoglobin (S), giving the genotype AS. Sickle cell trait is not sickle cell anemia. Sickle cell anemia is a disease formed by 2 abnormal sickle genes (SS), causing regular health problems (1). Sickle cell trait will not turn into the disease. The sickle cell gene originated as a natural way for the body to fight malaria, eventually resulting in approximately 8% of African Americans becoming carriers. However, it can also be present in Caucasian Americans (1 in 2,000–10,000) and at a higher risk in those with Mediterranean, Middle Eastern, Indian, Caribbean, and South and Central American ancestry (8). The U.S. Armed Forces were the first to link SCT to sudden unexplained death during basic training exercises. They found that recruits with SCT were 30 times more likely to die than other recruits. Most of the sickling deaths occurred during basic training or fitness testing, which lead researchers to speculate that exercise-related death with SCT is caused by intense conditioning at a level to which the individual is not accustomed (10,12,13).

During intense maximum exercise, a decrease in oxygen levels can cause some of the red blood cells to change from their normal disc shape to a sickle or quarter moon shape. These sickled cells will adhere and block blood vessels in the muscles, kidneys, and other organs, leading to tissue death and failure. The harder and faster the athlete works, the earlier and greater the chance sickling will occur. Most sickling injuries or deaths have occurred while sprinting only 800–1200 m or between 2 and 3 minutes of intense activity. Sickling can be catastrophic if the athlete tries to exceed their limits or is pushed too far by a coach. Heat, dehydration, asthma, and high altitude are factors that can increase sickling because of the increase in physical difficulty and decrease in blood oxygen levels (8).

An athlete with SCT who is exposed to extreme physical activity at a level which he/she is not accustomed to can lead to acute exertional rhabdomyolysis. Although SCT is usually benign, exertional rhabdomyolysis can become a life-threatening concern. Military studies found that those who have SCT are 200 times more likely to experience exertional rhabdomyolysis (10,12). This condition can present when extreme physical exertion causes muscle cells to break down and release myoglobin and other cellular enzymes into the bloodstream. Myoglobin will eventually spill into the urine, making it appear dark, and possibly cause renal failure. If it progresses, electrolyte and enzyme imbalances can lead to muscle weakness and potential cardiac arrest (5,19).

Some researchers believed that red cells never sickled in living people because sickling does not occur until blood oxygen falls below 40% and that sickled cells would revert back to normal after taking up oxygen in the lungs (7). This theory, however, does not take into consideration the metabolic changes that take place with intense exercise. In a study involving SCT men cycling forcefully with the legs, sickled cells were found in venous blood from the arm (17). Therefore, as exercise increases hypoxemia, sickled cells can accumulate in the arterial circulation and not only block vessels in the muscles causing acute explosive rhabdomyolysis but can also block circulation, initiating tissue death to vital organs, such as the heart and brain (8). Blockage of blood flow to the spleen can cause splenic infarction, producing warning signs such as pain in the upper left quadrant or lower chest area, nausea, and vomiting. Symptoms of splenic infarction appear similar to pleurisy, pneumothorax, “side stitch,” and renal colic (9).

Although individuals with SCT are at a higher risk for experiencing exertional rhabdomyolysis, a recent study comparing soccer athletes versus untrained individuals shows that chronic physical activity can provide advantageous effects on endothelial activation and possibly reduce the likelihood of vascular occlusion. Plasma levels of soluble adhesion molecules and cytokines were compared between 4 groups (trained SCT carriers, trained controls, untrained SCT carriers, and untrained controls) during different stages. Blood was collected from a vein in the nondominant arm at rest, immediately after exhaustion from cycling, and after 1 hour, 2 hours, and 24 hours postexercise. A significantly higher amount of vascular adhesion molecules were detected in the untrained sickle cell group than the trained sickle cell group. Results concluded that this is the first study to find an effect of habitual physical activity on vascular adhesion molecules (3). Other researchers examined blood samples from football and basketball players and found that many of the subjects had been competing for years at high levels without knowing they were carriers or experiencing complications. In 1973, 579 black National Football League players were tested for SCT and 39 (6.7%) were positive for the trait (16). Subsequently, in 1974–75, researchers in Tennessee examined the blood samples of 142 high-school basketball and football athletes. Results revealed that 15 of these subjects (10.5%) had SCT. Some of these athletes went on to win championships and receive college scholarships with no complications from SCT (6). These studies show that athletes with SCT are not only able to compete successfully in sports but should be encouraged to be physically active.

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The 4 most common causes of nontraumatic exertional collapse in athletes include asthma, cardiac emergencies, heat illnesses, and sickling (8). All of these conditions can become fatal if not treated properly. As shown in the Table provided, when dealing with an otherwise healthy individual who suddenly collapses, one must take note of some key differences in the signs and symptoms of these conditions. Asthma is an obstruction of the airways due to inflammation and bronchospasm, making it difficult to breathe and therefore properly circulate oxygen to the body. Signs and symptoms include tightness in the chest, feeling that they are unable to “catch their breath,” coughing, and a distinct wheezing sound (14). Athletes with a history of asthma should carry a rescue inhaler prescribed by their physician at all times. Cardiac emergencies can often occur suddenly and without warning; however, sometimes they will have a history of chest pain, fainting, or dizziness with activity. If this person goes into ventricular fibrillation, they may lose consciousness, stop breathing, and possibly experience seizures (18). Sickling collapses are most commonly mistaken for heat illnesses. However, because sickling typically occurs within the first few minutes, the athlete has not been exposed to the heat long enough to significantly raise core temperature. Heat cramps will cause the muscles to lock up and tighten, producing a palpable contraction. These cramps can be extremely painful. Although sickling pain will sometimes be described as cramps, it is really more of a dull ischemic pain due to lack of blood to the muscles making them feel weak. This dull pain and weakness in the lower extremities is usually the most obvious and reliable symptom of sickling (8). Anytime an athlete with SCT complains of cramping, it should always be treated as sickling to be safe. When dealing with heat stroke, the individual may have more significant central nervous system impairment, such as confusion, seizures, or even coma (4). Signs and symptoms of sickling can appear similar to each of the conditions listed above and may not always present the same in everyone. Some individuals experiencing sickling may have pain in the upper left quadrant of the abdomen or the chest area, chest tightness, difficulty breathing, and/or not feeling like themselves. Someone suffering a sickling collapse will not lose consciousness immediately and will be able to communicate their symptoms.

Table C

Table C

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Sickling injuries and sudden death from exertional rhabdomyolysis can easily be prevented by enacting the following recommendations. These recommendations have been supported and distributed by the NCAA and the National Athletic Trainer's Association.

  1. Screening athletes and active individuals before participation will help those involved in training and conditioning to recognize at-risk athletes (11). Most people do not know their status, even if they were tested at birth, and therefore will not accurately complete a health history questionnaire. Although including SCT status on a preparticipation questionnaire is a step in the right direction, a simple blood test will confirm the trait and can be done through a family physician. Even though all colleges and universities are not yet required to have results of sickle cell status on file, it would be in the best interest of the institution to begin requiring this for the safety of the athletes and liability of the school.
  2. Proper acclimation to activity is another way to prevent sickling. Many coaches try to push athletes to their limit in the first couple of weeks to get them back in shape after a break. Coaches should be properly educated about the negative effects, such as rhabdomyolysis, overtraining, and overuse injuries, this can cause their athletes. Athletes with SCT should especially be conditioned slowly and progressively so as to not cause complications. Year-round periodized strength and conditioning programs should be encouraged for all athletes to help them properly prepare for the stresses of practice and games. Training should be sports specific, season specific, and tailored to individual goals, needs, and abilities.
  3. Conditioning coaches should modify drills for those with SCT. They should not participate in timed sprints or miles. No repeat sprints or maximal exertion around 2–3 minutes without proper recovery time. If repeated sprints are performed, the rest time in between should be doubled or tripled. If allowed to set their own pace, these athletes will be alright. Recovery time is essential to safe participation because sickled cells will eventually go back to their normal shape when they pass through the lungs and take up oxygen.
  4. Sickle trait individuals must also stay hydrated. Dehydration is a major risk factor for sickle cell athletes. Water should never be restricted during activity, especially in a hot and humid environment. Proper hydration serves to enhance the performance level of all athletes.
  5. Sickle cell athletes should never feel singled out or uncomfortable reporting their symptoms to coaches and medical staff. Coaches should consider any symptoms of cramping, distress, or collapse a medical emergency in SCT athletes and call for help immediately.
  6. Other factors such as altitude changes, asthma, being ill, and lack of sleep should be controlled and monitored because they can contribute to complications as well.
  7. Education of athletes, coaches, team physicians, athletic trainers, and administration is extremely important in the recognition and prevention of sickling injuries. All institutions should have a policy and emergency action plan regarding SCT athletes and the management of a collapse (11).

A sickling collapse should be treated as a life-threatening emergency, and the following guidelines will need to be taken:

  • Check and monitor vital signs such as temperature, respiratory rate, blood pressure, and heart rate. Re-evaluate regularly for any changes.
  • Administer high-flow oxygen, 151 pm (if available), with a nonrebreather face mask. Oxygen should always be readily available to sickle cell athletes.
  • Cool the athlete down if necessary. Remove the athlete from the heat and sun. Immerse the athlete in an ice bath, use ice towels, or place ice packs over major blood vessels in the groin, neck, and armpits to quickly lower core temperature.
  • If vital signs worsen, call 911, attach and Automated External Defibrillator, start intravenous fluids if available, and get the athlete to the hospital as quickly as possible.
  • Tell the doctors to expect explosive rhabdomyolysis and grave metabolic complications of SCT.
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Clearance for return to activity after a sickling injury will have to be made by a physician and depends on the amount of damage caused. The sooner sickling is stopped and treated with rest, oxygen, cooling, and hydration, the better the outcome will be. When treated quickly, sickle cells can change back to normal and the athletes will feel better in around 15–30 minutes. These athletes have been known to return to the field the next day (8). Although these athletes will feel better within 30 minutes, studies show that vascular adhesion molecule levels remain elevated for hours after exertion, which put these athletes at risk during this time (15). Athletes who experience moderate rhabdomyolysis may have some muscle necrosis and a rise in creatine kinase levels but no renal problems. These athletes will most likely be out for a couple weeks and require a gradual return to play. Those who experience severe rhabdomyolysis, including renal failure, will not return to play and may have permanent loss of function (8). Anyone with SCT who experiences symptoms or complications of rhabdomyolysis should be evaluated and cleared by a physician.

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sickle cell trait; exertional rhabdomyolysis; vascular adhesion; sickling; muscle weakness; hemoglobin

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