So I plan to focus on endurance races this season, call it 50 miles on average (3-4 hrs). Should I keep VO2 max. interval work in my training schedule? On one hand, even in these endurance events, I'm sure there will be times when I am anaerobic and could benefit from VO2 max. work. However the rule of specificity would say that my training should be closer to what the races are - so hard MTB rides (3-4 hours) with some sweet spot and threshold work. Any advice?