Improving VO2 Max Quickly

Many scientists consider VO2 max the most important factor in determining success in an aerobic endurance sport. Here are two methods to improve your V02 max in an 8 week period by 5-7%.
1. 15second running at 90-95% max HR with 15second recovery @ 70% HR (repeat 47x)
2. 4x4 minutes @90-95% max HR with 3 minute recovery @ 70% HR

Either method should increase your V02 significantly over the two month period. Do these workouts 1-2 times per week, with a 10 minute warmup and cooldown.

This study ("Aerobic High-Intensity Intervals Improve V02 max more than moderate training", Medical Sports Exercise Journal, 2007) compared long slow distance (45 minutes @ 70%HR, the two methods above, and Lactate Threshold running-85%HR for 24 minutes). Forty athletes were in the study and ran on treadmills set at 5% incline.

The recommendation is to use the 4minute hard/3 minute easy session, as the 47x 15 seconds is difficult for most of us to count up to while sprinting. 95% effort is 15-30 seconds faster than your 5k pace (8minutes per mile for a 5k=2 minutes per quarter, so for the four minutes you would go through each quarter in 1:52-1:56, meaning you would ideally complete more than 1/2 a mile). 90% effort is closer to 10k race pace. It might be wise to begin the interval just under 10k pace and picking the pace up a bit for the last 1-2minutes if you can. Finishing strong is always good.

A workout I always found useful and similar to the two above and equally tough, was 15x 45 seconds at 1 mile pace with 15 seconds jog recovery. Again, I would do this 1x per week as one of my "fast" days. It's easy to time the minute, which I liked. It always took a couple of weeks to get to the 15 reps, if I was really running as hard as I was supposed to be. I always did this workout by feel, not distance. But if you do the same route, say five miles, with a 1 mile warmup, then the 15 reps, then cooldown, you can check the overall time for the workout and/or see how much further you covered in the fast phase than the week before and see the improvement.