During study and work breaks this week, which you should take every 20-60 minutes, depending on the task and your level of focus that day, do:
hold the squat position, 2o seconds
throw a tennis ball over head and behind you, then turn and catch it (or throw it up and catch it, if you need to start at a less advanced level), 20 times
roll your arms 10 times, 5 in each direction
roll your wrists 10 times, 5 in each direction
look away at something in the distance while you roll your arms and wrists
dive bomber pushups, 10 (or hold plank position, if you cannot do pushups)
lie on ground, and lift feet over your head to touch the floor behind you, 10 times.
Back to work!