I think VO2 is a piece of a bigger fitness puzzle. With runners you also need to factor in lactate threshold. Not to mention running efficiency/economy. At the

I think VO2 is a piece of a bigger fitness puzzle. With runners you also need to factor in lactate threshold. Not to mention running efficiency/economy. At the high level I think of fitness as the combination of: Speed, Strength, Power, Endurance, Flexibility, and Balance. Then athleticism would include all of the fitness indicators plus some sport-specific technique and skill (or proprioception).