
Energy
Physical Exertion
 Used to describe someone's stamina or strength during physical activities. 
After the marathon, he had no energy left.
 Activity Level
 Reference to how active or lively a person or environment feels. 
The festival was full of energy.
 Mental Sharpness
 Talks about the ability to think or concentrate, not just physical activity. 
I need more energy to focus on this exam.