I really notice when I wear the APEX shirt that I'm much more focused and calm. I recently joined a gym that does group sessions with workouts and I purposely did not wear the shirt at times and then, at other times, wore the APEX shirt. The difference was extremely noticeable. I had a lot more endurance and was able to accomplish more without getting as tired. When I wear this shirt to work (under my dress shirt) I have a lot more endurance and focus with my work throughout the day with no lows and less frustration.