I am a keen user of a power meter in my training and have found great results - The Power Post ? What it takes to be a fast cyclist | Deca Ironman Training
Would there be other measurements I should be taking? Always keen to learn more. My understanding is currently power training is considered the most effective method since power meters measure your present output. Heart rate was previously used, but it's only a decent approximation. When you become fatigued and/or dehydrated, your heart rate isn't an accurate reflection of the work you're doing. As for VO2 max, that is your aerobic capacity, and that is a reflection of the length and intensity of training you've performed over X amount of time.