Since the Napa Valley Marathon I've been running some nice 7 mile, sub 7 minute per mile tempo workouts and feeling very strong. Tonight I switched gears a bit and went back to the 800 meter repeats at sub 3 min pace, and wow, what a difference! I immediately felt my legs getting heavy and early onset oxygen debt. At first I blamed yesterday's bike ride and figured I was in for a bad day, however my average times ended up 3-4 seconds faster than I was hitting at my peak prior to Napa.
While I attribute the improvement to the tempo runs, research that has been done on this topic clearly favors the intervals.
The Best Training Stimulus to Increase VO2 Max
Don't Stray Too Far From Intervals
Intervals VS Tempo Running
Intuition tells me that if my tempo workouts have improved my interval workouts, and intervals are superior for boosting VO2, it makes perfect sense to figure out a way to integrate both strategies into your race preparation.