This illustration shows some simple exercises you can do by your desk. Doing physical exercise every few hours can help release tension, reduce inactivity, avoid bad postures and sedentary lifestyle. Sitting for more than 6 hours a day or for long periods of time can contribute to developing serious illnesses. Take breaks every 2 or 3 hours, and if you can, do some of your daily tasks while standing. Image source: https://www.washingtonpost.com/graphics/health/workout-at-work/

This illustration explains how to properly sit, stand and reach for things while working or studying at a desk.  Image source: http://www.saramulvanny.com/portfolio/office-stretches/