Body __ are imaginary, rectangular surfaces that cut through the body, dividing it into different regions.

Body planes, look at this website for more info

https://www.google.co.uk/url?q=https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/introduction-to-anatomy-and-physiology-1/mapping-the-body-33/body-planes-and-sections-289-1344/&sa=U&ved=0ahUKEwjQs8XR9YrUAhXHKcAKHapnD58QFggUMAI&usg=AFQjCNH0hXmL_w50JNtIeUTU7BDPw10XDg

Maximal strength i believe

Because without physical activity, the body has extra "energy" if you will, and so when it is time for bed you are not tired, so you end up staying up all night. also there is probably an effect on your internal clock, which messes with your melatonin production which goes hand in hand with your sleep cycle