This is interesting ... I never thought anyone would advocate hands on/over head without knowing why. Hands over your head increases your blood pressure as your heart works harder to supply blood to the elevated extremity. This has the “bonus” of providing more oxygen to your brain. The point of sticking your hands on your head is to keep from passing out when you stop if you’ve used pure hate to run yourself into the ground during a maximal effort, not to help you recover faster from reps during a workout.