The ability of the heart, lungs, and blood vessels to transport oxygen to muscle cells?

Make your question clearer. 
But I think this is a perfect explanation; the ability of the heart, lungs, and blood vessels to process and transport oxygenrequired by muscle cells so that they can contract over a period of time; cardiorespiratory endurance is produced by exercise that require continuous, repetitive movements.

Hope I helped! :)

-Duolingo