We read with interest the recent article by Nguyen et al1 in CHEST (July 2013), which demonstrated novel findings. However, we would like to draw attention to certain conceptual issues that could effectively question the crux of those findings. As the authors mentioned, objectively measured physical activity is an excellent predictor of prognosis for patients with COPD. However, physical activity is distinct from psychomotor activity. Psychomotor activity is defined as motor/physical activity that is secondary to or dependent on a psychic component and is mostly non-goal-directed.2 For example, manic, psychotic, and anxious patients would demonstrate increased psychomotor activity. This is generally state-dependent, that is, it lasts during the course of psychiatric symptoms and normalizes on effective treatment.