Select all of the following ways that you can achieve good and inexpensive muscle strengthening. deep knee bends

light, free weights

sit ups (crunches)

pull ups

200 pound barbells

push ups

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