Hyperammonemia in athletes: toxic effects and implications for performance

Ammonia (NH4+) is a metabolite produced by the catabolism of proteins and increases proportionally to exercise intensity and due to protein supplementation. Under certain circumstances of sustained exhausting exercise and adequate protein intake, the detoxification capacity may become saturated, therefore blood ammonia may reach a concentration similar to that of liver failure. This condition allows NH4+ to cross the blood-brain barrier inducing a decrease in excitatory and a rise in inhibitory neurotransmitters, as well as altering the rate of energy brain production and subsequent ATP depletion. Some authors have demonstrated high NH4+ levels in central nervous system of healthy athletes induced by exercise intensity affecting cognitive and short term memory processes in addition to loss of motor coordination. Consequently, negative perception of performance may appear together with sensations of fatigue and intellectual task difficulties involving decision-making. Several studies have reported a reduction in NH4+ plasma levels during exercise due to certain amino acids pre-workout supplementation (arginine + glutamate; arginine + citrulline; glutamate + aspartate or ornithine) achieving performance-enhancing effects in different sport disciplines. This is explained as a result of the inhibition of serotonin synthesis through glutamate administration with a resultant better perception of performance. Due to this literature review based evidence we highlight the importance of hyperammonaemia as another determinant factor to consider in terms of performance and endurance optimization, assessing the recommendation of previously cited amino acids supplementation.