Pretty sure it could be head circles because your neck is really delicate and if something happens, you could get seriously hurt or disabled from moving. (Sorry if I’m wrong, I’m no doctor)
        
             
        
        
        
Answer:  He should  Increase the intensity of his exercise program
Explanation:
 
        
             
        
        
        
What device can be used to measure fitness level during a cardio workout? 
Heart rate monitor