Repeat 4-minute all-out intervals on a 1.6-mile, 4% incline, performed twice weekly for three weeks, can significantly increase VO2 max.

“there was a workout i would do you know in carmel valley you've got the 56 that goes out and it's got a bike path next to it there's a section of that bike path that is 1 .6 miles long and it goes up at about four percent and just doing repeat intervals of that which takes about four minutes all out to go one direction and then about six minutes to cruise back four of those that was it twice a week for like three weeks and your vo2 max exploded”