What denotes a high level of activity?

I think it is important to discuss and consider the concept of level of activity being different to merely the amount of activity someone engages in.
In assessing level of activity, I suggest you must consider all of the following:

• Amount of time spent active.
• Frequency and consistency of attendance and participation in training.
• Quality and efficacy of training strategy.
• Intensity of effort.
• Proficiency and prowess at training.
• Activity levels outside of training.

It stands to reason that a more active person has a higher energy intake requirement than a less active person. A more advanced athlete will have a higher energy intake requirement than a beginner. An athlete who turns up to training regularly and puts in her best effort will have a greater energy requirement than one who turns up less often and drags her feet a little, lacking in enthusiasm.

Activity levels outside of training should be considered as well. It is possible to still have a high level of activity despite working a desk job or being otherwise less active outside of training. Moving around a lot throughout the day will contribute to a higher energy requirement than being inactive, and strenuous activity at a physically demanding job will increase them further still.

A higher level of activity should produce better results in terms of a more lean and athletic physical condition, provided energy requirements are being met. Best results will come when meeting a higher requirement, rather than being further into deficit of it.

It should be noted that while an increase in level of activity should be conducive to improved results, this does not necessarily mean more time spent at exercise or adding extra sessions. First ensure that your training strategy is effective and productive.

It is important to consider quality of activity as important, as well as amount. A high amount of low quality activity will not be conducive to best results, and adding more of the same will not improve the situation, especially if level of energy intake is not appropriate.