The Q 10 co-enzyme is an important agent modulating the activity of enzymes of the respiratory system, which comprises a series of biochemical reactions that enable the combustion of nutrients by oxygen in the supply of energy. It also reinforces the contractility and efficiency of the muscular system. Co-enzyme Q 10 also has anti-oxidising properties and supports the body's defences. It is therefore recommended for the over-production of free radicals resulting from certain habits of lifestyle. Lack of co-enzyme Q 10 results in a significant diminution of the amount of energy available at the various places it is utilised and thus in a feeling of fatigue and a lack of endurance during exercise.