"You cannot run. You may only walk at a normal pace. The Slow effect will last until you rest for five minutes."
It is important to note that you do not have to walk as if you were in slow motion or slogging through molasses. However, despite the wording, you may still walk abnormally slowly while slow - it does not force you to speed up to any "normal" speed. What you may not do is permit both feet to leave the ground at once while perambulating, which is the definition of running.