During a given 24 hour period which better for you in terms of building cariovascular/aerobic fitness and muscle (glycogen storage capacity) endurance.
1) One run of 15 miles
2) 2 runs - 1 of 10 miles and 1 of 7 to 8 miles spaced roughly 8 to 9 hours apart
Please include why in your answer and keep strictly to the question and don't cosnider any period beyond or before that 24 hours.
Thanks