[Influence of the sickle cell trait heterozygote on energy abilities]

The sickle cell trait (SCT) is a genetic abnormality of the red blood cell which mainly affects people of African descent. It is due to the mutation of only one parental gene (one glutamic acid of the chain beta of the globin is substituted by one valin). The prevalence of SCT in the black US population is within the range of 8-9%. It is increasing in Europe and in Africa where it may reach up to 40% in some regions. The rate of prevalence of SCT in athletic populations was found to be similar to that of the general sedentary population in west African countries. SCT is usually asymptomatic. However, SCT has been associated with a higher risk of sudden death during exercise. In fact, the substitution of one amino-acid modifies the properties of haemoglobin and produces physiological disorders such as sickling, less solubility of the deoxidized form and the reduction of affinity for oxygen. The sickling phenomenon (formation of sickle cells) mainly occurs in some conditions related to the practise of sport (intense and/or prolonged exercise, exercise in hypoxic conditions, exercise in heat conditions). These sickled red blood cells reduce the speed of capillary flow or obstruct the blood vessels which, because of the lack of oxygen, become altered. The physical ability of sickle cell trait carriers (HbAS) who practise sport should be different from the physical ability of subjects with normal haemoglobin (HbAA) because of: 1) potential risks due to their haemoglobinopathy and 2) the eventual modification of their performance ability. These two aspects have caused controversies among many researchers particularly in line with their investigation methods. Nevertheless, the following results seem to be established: 1) the ability to perform sprint exercises is not altered in the HbAS subjects. Their performances in these events are similar to those of HbAA subjects; 2) The ability of HbAS subjects to perform intense and prolonged exercise is decreased. Our former results have shown that prolonged aerobic efforts in hypobaric hypoxic conditions may be associated with a deleterious effect on the performance of HbAS subjects. The damaging consequences on their performance in these conditions could be due to tissue oxygen delivery limitations.