The ability to perform extended training sessions and long runs is a result of

lower body strength
lower body endurance
lower body flexibility
lower body tone

The correct answer is option - b.

Explanation:

The lower body endurance is important for developing the ability of long runs like marathons and extended training.

Endurance is the ability to produce energy and sustain it for a longer period of time by the body of an individual that helps in the extended exercise and long runs.

Thus, the correct answer is option - b. The lower body endurance.