**2. Is it physical activity, exercise, or fitness?**

Physical activity is associated with changes in brain structure. Regular exercise improves brain function. High aerobic fitness mediates cerebral white matter integrity. Do all these statements mean the same thing, or are there subtle differences in interpretation rendering the results difficult to compare?

#### **2.1 Defining "exercise"**

The terms "physical activity", "exercise", and "fitness" are often used interchangeably. But as with any discipline, these terms have distinct connotations and therefore should not be use as mere synonyms. To add to the terminology confusion, a myriad of additional phrases are incorporated in an attempt to better clarify the exercise paradigm. Typical terms include, but are not limited to: aerobic fitness, health fitness, physical fitness, calisthenics, circuit training, core training, resistance training, stretching and toning, strength training, and weight lifting. Thus, physical activity or exercise could mean participating in a marathon or dance class, lifting a 10 kg medicine ball, raking leaves, meditating while performing yoga, or simply walking around a shopping mall.
