If endurance represents the body's capacity to resist tiredness during a long period of effort, the capacity of performance is defined by an energy potential, in other words, by your fuel reserves. During exertion, in relation to its intensity, you burn either lipids (fat), or glycogene (sugar). As your intramuscular and liver glycogene reserves do not exceed 500 grammes, it is essential that you increase your capacity at burning fat to become more economical and ,therefore, enhance your performance.
This basically means training your basic endurance regularly, with long-duration effort (1h and more) and weak intensity. Only a quarter of your training time should include intensity and that mainly in small intervals. Often people train too long on a regular intense rhythm, which leads to exhaustion and very little progress. It is not rare to see 'patrouilleurs' (competitors) « burnt out » at the end of March simply because they ignored these principals.
Participating in an effort test to define your own capacity as regards to your heart beat frequency allows you to train in a much more effective manner. Alternating basic endurance and interval training permits you to progress over the long-term, in other words, with focused training it is BETTER AND lasts longer.