The best supporting statement for the assumption that the author has conducted research on this topic is:
"Yet according to the Center for Disease Control (CDC), physical activity in adolescents improves strength and endurance, helps build strong bones, reduces stress, increases self-esteem, and it is also known to increase brain function."
This sentence directly cites a reputable source (the CDC) and provides specific benefits of physical activity based on research, which supports the idea that the author has conducted or referenced research on the topic of physical activity and its benefits for adolescents.