Exercise as it relates to Disease/Exercise limitations in athletes with sickle cell disease
Sickle cell disease (SCD) is a serious, genetic disorder that affects the red blood cells and vessels in the body. It is caused when an individual inherits two trait genes for sickle haemoglobin. The haemoglobin mutation causes the haemoglobin A (HbA) to mutate into haemoglobin S (HbS) (). This transmutation is caused by a single nucleotide substitution in the β-globin gene that makes the haemoglobin less soluble than HbA. This form of haemoglobin is an abnormal type that remodifies the shape of the blood cell. The red blood cells become rigid and have a concave shape like a crescent moon. This shape affects the function of the red blood cells by causing blockages and damage in tiny blood vessels, and prevent oxygen from transported to the organs.
Sickle Cell Anaemia Vs Sickle Cell Trait
There are many types of SCD, but the most common types are sickle cell anaemia (SCA) and Sickle Cell Trait (SCT). SCA is only inherited if both the parents have either an SCT gene and/or an SCA gene. SCT is not the same as SCA. Those with SCT carry both HbA and HbS in their blood cells, generally making the individuals as healthy as those with regular HbA, but also having the effects of the symptoms caused by SCA.
- SCA effects about 5% of the world population 
- SCA commonly affects those of an African descent – about 20-40% of the population and only 15% in European metropolises 
- In one particular study on athletes of the National Collegiate Athletic Association (NCAA), there were 72 deaths with 25% of those associated with SCT, with them all occurring in the black division 1 football athletes. The death of the athletes with SCT was 37 times higher than those without SCT.
When an athlete with SCA or SCT is exercising or partaking in physical activity at high intensities, there is a concern of their welfare and the risk of sudden death. Researchers believe that sudden death in athletes in linked to SCT, however there is not a lot of evidence for this to be true. A particular study looked at black African American males that participated in combat training at a high altitude, showed that on arrival, four of them had died, with all of them being SCT carriers. Death occurred from collapsing by muscle exertion, which is a trait of SCD. Athletes that have SCD are generally more vulnerable to rhabdomyolsis  – the breakdown of muscles and because of this they are more likely to experience fatigue.
What Happens During Exercise
Researches do not know why and understand how sudden death occurs with exercise in patients with SCD, but have confidence in arguing that it is related to extreme exercise that causes exhaustion and dehydration. When an athlete exercises at high intensities, there is a change in their pH and temperature levels. In order to facilitate oxygen delivery, the pH levels decrease and their temperature increases. This change in pH and temperature causes the HbS to polymerise, causing the red blood cells to distort. This also increases the concentration of deoxygenated haemoglobin in the body. Therefore there is less oxygen supply, causing the cardiac output to increase significantly to overcome low tissue hypoxia. Cardiovascular function collapses under these conditions as well under the conditions of increase sickling of the red blood cells, heat stress, dehydration and altitude.
The relationship between SCD and athletes, and the effects of exercise has been thoroughly studied with yet a link to be establish. Many researchers have found that the central association between SCT and sudden death in athletes were found in black African American footballers and in military recruits. They believe this may be the case as they are constantly exposed to vigorous exercise that can assist in fatal collapsing. In NCAA division 1 football, SCD has been the main killer of athletes over the past decade. The deaths had occurred from the conditioning of the game that included short sprints, agility tests and weight lifting. Research has not been able to find a way to reverse the condition or possible solutions when partaking exercise. Because of the absence of data, it is hard for researchers to strongly say there is a connection between SCT and athletes, as some of their findings we also found in normal patients. Therefore, some believe the lack of information makes research futile. Researchers have also mentioned that SCT screening in athlete population has now became compulsory in all student athletes. This is to help them diagnosed any problems and prevent death occurring while training.
Limitations and Precautions
When an athlete is training, or any other patient participating in high intensity exercise, they will need to take a few precautions in order to lower the risk of any SCD symptoms occurring. Environmental and physical conditions may trigger changes in the red blood cells to become the sickle shape, therefore athletes should:
- Drink plenty of water and avoid dehydration 
- Exercise slowly and at your own pace. Allow more time for rest 
- Encourage participation in preseason strength and conditioning to prepare the body 
- Avoid exercise if ill 
- Stop exercising if you experience symptoms 
- Avoid extreme hot or cold conditions 
- Physical exertion should be avoided 
The present data suggest that patients with SCA may undertake mild-moderate physical activities without any acute clinical complications. Nevertheless because of these precautions, athletes need to ensure they are careful when they are engaging in exercise at maximal effort so they do not cause any harm to their body.
- Connes, P. et al. (2011) 'Exercise limitation, exercise testing and exercise recommendations in sickle cell anemia'. Clinical Hemorheology and Microcirculation. Vol 49(1-4): pp 151-63
- Monchanin, G. et al. (2005). 'Hemorheology, sickle cell trait, and alpha-thalassemia in athletes: effects in exercise'. Official Journal of the American College of Sports Medicine: pp 1086-1092
- Mitchell, B L. (2007) 'Sickle cell trait and sudden death - bringing it home'. Journal of the National Medical Association. Vol 99 (3): pp 300-305
- SCDAA. (2014). 'Sickle cell trait and athletics'. Sickle Cell Disease American Association. Viewed 29 Sep 2014. Retrieved from: http://www.sicklecelldisease.org/index.cfm?page=sickle-cell-trait-athletics
- World Health Organisation. (2011). 'Sickle-cell disease and other haemoglobin disorders'. World Health Organisation. Viewed 29 Sep 2014. Retrieved from: http://www.who.int/mediacentre/factsheets/fs308/en/
- Harris, K M. et al. (2012). 'Sickle cell trait associated with sudden death in competitive athletes'. The American Journal of Cardiology. Vol 110: pp 1185-1188
- Kark, J A. et al. (1987). 'Sickle cell trait as a risk factor for sudden death in physical training'. The New England Journal of Medicine. Vol 317: pp 781-787
- Eichner, R E. (2010). 'Sickle cell trait in sports'. Current Sports Medicines Reports. Vol 9(6): pp 347-351
- Pearson, H A. (1989). 'Sickle cell trait and competitive athletics. Is there a risk?'. American Academy of Pediatrics. Vol 83(4): pp 613-614
- Loosemore, M. et al. (2012). 'Sudden exertional death in sickle cell trait'. British Journal of Sports Medicine. Vol 46: pp 312-314
- Jones S. et al. (1970). 'Sudden death in sickle cell trait'. New England Journal of Medicine. Vol 282(6): pp 323-5
- Brian, J. et al. (1959). 'Cardiopulmonary physiological responses to heavy exercise in patients with anemia'. The University of Texas Southwestern Medical School: pp 378-388
- Faes, C. et al. (2013). 'Moderate endurance exercise in patients with sickle cell anaemia: effects on oxidative stress and endothelial activation'. British Journal of Haematology. Vol 164(1): pp 124-130